WO2019060657A1 - Method of producing semicrystalline polycarbonate powder with added flame retardant for powder be fusing and composites applications - Google Patents

Abstract

Disclosed is a method of preparing a partially crystalline polycarbonate powder containing a phosphorous-containing flame retardant, the method comprising: dissolving an amorphous polycarbonate and a phosphorous-containing flame retardant in a halogenated alkane solvent to form a solution; combining the solution with a crystallizing non-solvent that is miscible with the halogenated alkane solvent; and mixing the combined solution and crystallizing non-solvent under high shear mixing conditions effective to form a partially crystalline polycarbonate precipitate. Also three-dimensional article obtained by powder bed fusing a powder composition comprising it and method for making a unidirectional fiber reinforced polycarbonte composite comprising impregnating a continuous fiber tape with an aqueous dispersion of this powder.

Description

METHOD OF PRODUCING SEMICRYSTALLINE POLYCARBONATE POWDER WITH ADDED FLAME RETARDANT FOR POWDER BE FUSING AND COMPOSITES APPLICATIONS

BACKGROUND

[0001] This application relates to methods for producing a crystalline polycarbonate powder incorporating a phosphorous-containing flame retardant, and the crystalline

polycarbonate powders made by the method. This application also relates to methods of using the crystalline polycarbonate powder in additive manufacturing and in manufacturing fiber reinforced polycarbonate composites, and the additive manufacturing products and fiber reinforced polycarbonate composite products made using the powders.

[0002] Additive manufacturing (AM), also known in the art as "three-dimensional" or "3D" printing, is a process for the manufacture of three-dimensional objects by formation of multiple fused layers. AM methods that can be conducted using thermoplastic polymers such as polycarbonate include material extrusion (ME), for example fused deposition modelling, and powder bed fusing. In powder bed fusing, thermal energy selectively fuses regions of a powder bed. In particular, selective laser sintering (SLS) is a powder bed fusion process using one or more lasers to fuse powdered thermoplastic polymers into the desired three-dimensional shape. Preferred powders for these processes have of a uniform shape, and size and composition.

However, the preparation of such powders from thermoplastic polymers economically on a large scale is not straightforward. In addition, it can be difficult to use amorphous polycarbonates, particularly in powder bed fusing processes such as SLS because they do not have a sharp melting point. This property causes the applied thermal energy source (e.g., a laser beam) to be dissipated into the regions surrounding where the energy beam strikes the bed. This undesired dissipation of thermal energy can cause unstable processing as well as poor feature resolution in the intended three-dimensional articles being produced. Thus, preparation of crystalline polycarbonate having the desired particle sizes, particularly for powder bed fusion, is particularly difficult.

[0003] Separately, fiber reinforced composites can be produced using fibers (such as carbon fibers that are in milled, chopped, woven, or continuous form) combined with a polymer matrix of choice. The fibers primarily serve as the load bearing structural components, with the surrounding polymer matrix holding the fibers together and transferring load between the fibers. There are various ways to produce continuous unidirectional fiber reinforced thermoplastic polymer tapes (UD tapes). One such method, referred to as the "aqueous process," uses a thermoplastic polymer in fine powder form dispersed in water using a suitable surfactant. Continuous fibers are pulled through the aqueous dispersion and combined with the polymer particles followed by evaporation of water, melting of the polymer that is captured within the continuous fibers, and consolidation of the fiber-polymer combination by pulling through a heated die to provide a composite product with the desired fiber content, width, and thickness. This aqueous process relies on using the powder form of the thermoplastic polymer to produce high fiber volume fraction UD tapes. A key to producing high quality UD tapes with the aqueous process is use of a fine polymer particle size, for example particles sizes having a D50 of 20 to 45 micrometers or a D 100 of below 80 micrometers. Polymer particle size and distribution outside the desired range can have detrimental effects on the UD tape process, including lower throughputs and yields, and reduced process continuity, as well as the UD tape products, including less homogenous composition, non-uniform appearance/finish, splits, or tears in the fiber direction, and high void content. These can require additional processing efforts during production of the composite structure, as well as lower part performance.

[0004] Thus a need remains in the art for polycarbonate powders having good crystallinity and good particle size distribution. There further remains a need for a method of making partially crystalline polycarbonate powders having a flame retardant included therein, to provide powders having flame retardancy for use in additive manufacturing and in

manufacturing UD tapes.

BRIEF DESCRIPTION

[0005] A method of preparing a partially crystalline polycarbonate powder containing a phosphorous-containing flame retardant includes: dissolving an amorphous polycarbonate and a phosphorous-containing flame retardant in a halogenated alkane solvent to form a solution; combining the solution with a crystallizing non-solvent that is miscible with the halogenated alkane solvent; and mixing the combined solution and crystallizing non- solvent under high shear mixing conditions effective to form a partially crystalline polycarbonate precipitate.

[0006] Other aspects are a partially crystalline polycarbonate powder comprising a phosphorous-containing flame retardant prepared by the above method as well as a method of preparing a three-dimensional article by powder bed fusing the powder and a method of preparing a unidirectional fiber reinforced polycarbonate composite from the powder.

[0007] The above described and other features are exemplified by the following figures, detailed description, examples, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The figures are exemplary, wherein like elements are numbered alike: [0009] FIG. 1 is a schematic of a process to produce polycarbonate/flame retardant powder using a solvent, a non-solvent, and filtration as the means for removing the precipitate.

[0010] FIG. 2 is a schematic of another process to produce polycarbonate/flame retardant powder using a solvent, a non-solvent, and evaporation as the means for removing the precipitate.

[0011] FIG. 3 is a graph of initial versus final RDP content in FR-PC powder is using the filtration removal technique of FIG. 1.

[0012] FIG. 4 is a graph showing reduction in Tg as function of phosphorous content.

[0013] FIG. 5 is a graph of initial versus final RDP content in FR-PC powder is using the evaporation removal technique of FIG. 2.

DETAILED DESCRIPTION

[0014] Disclosed herein are methods of converting an amorphous polycarbonate to a partially crystalline polycarbonate (PC) powder, while at the same time incorporating a phosphorous-containing flame retardant (FR) into the powders. It was further unexpectedly found that the type of flame retardant can influence the powder product particle size, particle size distribution, and modality. The method includes dissolving the amorphous polycarbonate and the phosphorous-containing polycarbonate in a solvent, and subsequently combining the solution with a crystallizing non-solvent while applying high speed mixing to form a precipitate. Advantageously, the precipitate can be used as the powder directly after isolation. In addition, the flame retardant is incorporated primarily within the powder particles, which can provide greater stability and more consistent processability.

[0015] The method can further have one or more of the following advantages. For example, a partially crystalline polycarbonate powder can be precipitated having good crystallinity, particle size distribution, and flowability. All or most of the particles of the partially crystalline polycarbonate powder can have an average or absolute particle size of less than 150 micrometers (μιη). The partially crystalline polycarbonate powder can therefore be effectively used in powder bed fusion processes, e.g., selective laser sintering processes, to produce layers having a thickness of 100 μιη to 150 μιη. The presence of the FR additive in the partially crystalline polycarbonate powder is especially useful in the manufacture of articles where flame retardancy meets an additional critical need, for example in UD tapes produced for the consumer electronics industry market.

[0016] The terms "amorphous" and "crystalline" as used herein are generally in accordance with their usual meanings in the polymer art. In an amorphous polycarbonate, the molecules can be oriented randomly and can be intertwined, and the polymer can have a glasslike, transparent appearance. In crystalline polycarbonates, the polymer molecules are aligned together in ordered regions. It is to be understood, however, that the process described herein can be used with a polycarbonate composition that is either fully amorphous, or that contains both amorphous and crystalline polycarbonate; and that the process is useful even when only a portion of the amorphous polycarbonate is converted to crystalline polycarbonate.

Therefore, for convenience, the term "amorphous polycarbonate" is used herein to denote a starting polycarbonate wherein at least a portion of the polycarbonate is in an amorphous form. One preferred embodiment is to start with fully amorphous (i.e., 100% amorphous)

polycarbonate; and the term "partially crystalline" is used herein to denote a product polycarbonate wherein at least a portion of the amorphous form in the starting material has been converted to the crystalline form in the product. For some embodiments, the portion of the amorphous form in the starting material has been converted to the crystalline form is not more than 45%

[0017] In some embodiments, the method of preparing a partially crystalline

polycarbonate powder that contains a flame retardant includes dissolving an amorphous polycarbonate and a phosphorus-containing flame retardant in a halogenated alkane solvent to provide a solution. The amorphous polycarbonate and the phosphorus-containing flame retardant components are described in detail further below.

[0018] Suitable halogenated alkanes include, for example, C_1-6 alkanes comprising at least one halogen (preferably chlorine, fluorine, or a combination comprising at least one of the foregoing), preferably at least two halogens (preferably chlorine, fluorine, or a combination comprising at least one of the foregoing). Preferred solvents include dichloromethane, chloroform, methylene chloride or a combination comprising at least one of the foregoing solvents. The amount of halogenated alkane solvent can be sufficient to form both a solution of the amorphous polycarbonate and the flame retardant as well as a precipitated mixture after the crystallizing non- solvent is added as described below. The amount with the type and amount of polycarbonate, type and amount of flame retardant and type and amount of halogenated alkane solvent and crystallizing non-solvent used, as well as the particular manufacturing process conditions used is also described below. In an embodiment, the amount of a halogenated alkane solvent can be 100 to 1000 wt%, based on the weight of amorphous polycarbonate, or 200 to 500 wt%, based on the weight of amorphous polycarbonate.

[0019] The phosphorus-containing flame retardant can be dissolved in the halogenated solvent before the amorphous polycarbonate, or added to the solvent simultaneously with the polycarbonate (individually or already incorporated in the polycarbonate), or added to the solvent in a next sequential step after the polycarbonate or after the polycarbonate is dissolved. Dissolution can be conducted at ambient temperature or slightly elevated temperature.

[0020] The solution of amorphous polycarbonate and flame retardant is then combined with a crystallizing non-solvent under high shear mixing, to form a solid precipitate comprising the partially crystallized polycarbonate and the flame retardant.

[0021] The crystallizing non-solvent is selected to be miscible with the halogenated alkane solvent, and to provide a partially crystalline product under high shear conditions. The crystallizing non- solvent can be a ketone such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPK), or the like. The amount of crystallizing non- solvent can be an amount sufficient to form the partially crystallized polycarbonate/ flame retardant precipitate, and can vary with the type and amount of

polycarbonate, type and amount of flame retardant and type and amount of halogenated alkane solvent used, as well as the particular manufacturing process conditions used. In some embodiments, the amount of crystallizing non-solvent is from 100 to 1000 wt%, based on the weight of amorphous polycarbonate, or from 200 to 500 wt%, based on the weight of amorphous polycarbonate.

[0022] In an embodiment, the solution of amorphous polycarbonate and flame retardant is added dropwise or as a slow stream over a period of time to the crystallizing non- solvent while agitating under high shear mixing conditions to form the precipitate. In another embodiment, the crystallizing non-solvent is added quickly to the solution of amorphous polycarbonate and flame retardant. The duration of the addition can be, for example, 1 minute to ten hours or 5 minutes to 1 hour, and can depend on the total volumes being combined.

[0023] The term "high shear mixing" refers to methods of agitating the components in a mixture (e.g. liquid mixture) under conditions in which high shear forces are generated. As is known in the art, a high shear mixer creates patterns of flow and turbulence, generally using an impellor that rotates inside a stator. Once the impellor has drawn mixture in, it subjects the mixture sudden changes of direction and acceleration, often approaching 90 degrees, such that the mixture contacts the wall of the stator with centrifugal force, or is forced through the holes in the stator at great pressure and speed, in a final disintegrating change of direction and acceleration. In some embodiments of high shear mixing conditions, the high shear mixing comprises mixing at speeds of 2,000 rotations per minute (rpm) to 50,000 rpm, specifically, 10,000 rpm to 30,000 rpm, more specifically 15,000 rpm to 25,000 rpm. High shear mixing can be achieved with any commercially available high shear mixers. For example, a high shear mixer such as a Silverson L5M homogenizer or an IKA T-25 Ultraturrax can be used.

[0024] The duration of the high shear mixing can depend upon the properties desired in the partially crystalline polycarbonate/flame retardant powder composition. In some embodiments, the mixing is from 1 minute to 10 hours, or from 10 minutes to 5 hours, or from 10 minutes to 1 hour. The mixing can be carried out in-line or batch. The process can readily be carried out at manufacturing scale. The flame retardant is incorporated into the partially crystallized polycarbonate structure.

[0025] Without being bound by theory, it is believed that combining the solution of amorphous polycarbonate and flame retardant with the crystallizing non-solvent under high shear mixing causes the crystallization of the polymer chains and results in the precipitation of a partially crystalline polymer powder having the flame retardant incorporated therein. It is further believed that when the precipitation occurs under high shear mixing conditions, the formation of an increased percentage of crystalline polycarbonate particles occurs while simultaneously lowering the chance of firmly agglomerated polycarbonate particles of being formed. It has been found, for example, that even if agglomerates are formed after the removal of solvents, those agglomerates can be readily broken by crushing, high speed mixing, milling, or other low- or high-force shearing processes.

[0026] Following precipitation, the halogenated alkane and crystallizing non- solvent are removed from the solid polycarbonate/ flame retardant precipitate to provide an isolated polycarbonate/ flame retardant precipitate. In some embodiments, the removing of the halogenated alkane solvent and the crystallizing non-solvent from the precipitate comprises filtering the precipitate. Any suitable filtration technique can be used. In other embodiments, the removing the halogenated alkane solvent and the crystallizing non-solvent from the precipitate comprises at least partially evaporating the solvents from the precipitate. Any suitable evaporation technique can be used. A rotary evaporator such as a Rotavapor™ evaporator is one type of suitable evaporation apparatus. It has unexpectedly been found that use of evaporation improves the incorporation of the flame retardant into the polycarbonate particles. In an embodiment, the halogenated alkane solvent is dichloromethane, the

crystallizing non- solvent is methyl ethyl ketone, and the removing the halogenated alkane solvent and the crystallizing non- solvent from the precipitate comprises at least partially evaporating the solvents from the precipitate.

[0027] The isolated polycarbonate/ flame retardant precipitate can be optionally dried at ambient temperature or by heating, either being with or without vacuum. As described above, the isolated and optionally dried precipitate can be used directly as the partially crystalline polycarbonate powder. Alternatively, the isolated and optionally dried precipitate can be further processed to provide the partially crystalline polycarbonate powder. For example, if

agglomerates are formed, the agglomerates can be broken by crushing, high speed mixing, milling, or other low- to high-force shearing processes to form the partially crystalline polycarbonate powder.

[0028] The above process can be used with a wide variety of polycarbonates.

"Polycarbonate" as used herein means a homopolymer or copolymer having repeating structural carbonate units of formula (1)

O

R— O C II O (1)

wherein at least 60 percent of the total number of R¹ groups are aromatic, or each R¹ contains at least one C₆-30 aromatic group. Specifically, each R¹ can be derived from a dihydroxy compound such as an aromatic dihydroxy compound of formula (2) or a bisphenol of formula (3).

In formula (2), each R is independently a halogen atom, for example bromine, a Ci-io hydrocarbyl group such as a Ci-io alkyl, a halogen-substituted Ci-io alkyl, a C₆-io aryl, or a halogen-substituted C6-io aryl, and n is 0 to 4. In formula (3), R^a and R^b are each independently a halogen, Ci-12 alkoxy, or Ci-12 alkyl, and p and q are each independently integers of 0 to 4, such that when p or q is less than 4, the valence of each carbon of the ring is filled by hydrogen. In an embodiment, p and q is each 0, or p and q is each 1, and R^a and R^b are each a C1-3 alkyl group, specifically methyl, disposed meta to the hydroxy group on each arylene group. X^a is a bridging group connecting the two hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each C₆ arylene group are disposed ortho, meta, or para (specifically para) to each other on the C₆ arylene group, for example, a single bond, -0-, -S-, -S(O)-, -S(0)₂-, -C(O)-, or a Ci-18 organic group, which can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. For example, Xa can be a substituted or unsubstituted C3-18 cycloalkylidene; a Ci- 25 alkylidene of the formula -C(R^c)(R^d) - wherein R^c and R^d are each independently hydrogen, Ci-12 alkyl, Ci-i2 cycloalkyl, C7-12 arylalkyl, Ci-i2 heteroalkyl, or cyclic C7-i2 heteroarylalkyl; or a group of the formula -C(=R^e)- wherein R^e is a divalent Ci-12 hydrocarbon group. Some illustrative examples of dihydroxy compounds that can be used are described, for example, in WO 2013/175448 Al, US 2014/0295363 and WO 2014/072923. Specific dihydroxy

compounds that can be used include resorcinol, 2,2-bis(4-hydroxyphenyl) propane ("bisphenol A" or "BPA"), 3,3-bis(4-hydroxyphenyl) phthalimidine, 2-phenyl-3,3'-bis(4-hydroxyphenyl) phthalimidine (also known as N-phenyl phenolphthalein bisphenol, "PPPBP", or 3,3-bis(4- hydroxyphenyl)-2-phenylisoindolin- 1 -one) , 1,1 -bis(4-hydroxy-3 -methylphenyl)cyclohexane, and l,l-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane (isophorone bisphenol).

[0029] Polycarbonate copolymers can include different types of carbonate units or repeat units different from the carbonate units, for example ester units, siloxane units, or the like. For example, poly(ester-carbonate)s further contain, in addition to repeat carbonate chain units of formula (1), repeat ester units of formula (4)

O O

C— T— C— O— J O

wherein J is a divalent group derived from a dihydroxy compound (which includes a reactive derivative thereof), and can be, for example, a C2-10 alkylene, a C₆-20 cycloalkylene, a C₆-20 arylene, or a polyoxy(C2-6alkyl)ene; and T is a divalent group derived from a dicarboxylic acid (which includes a reactive derivative thereof), and can be, for example, a C2-20 alkylene, a C₆-20 cycloalkylene, or a C₆-20 arylene. Copolyesters containing a combination of different T or J groups can be used. The polyester units can be branched or linear. Specific dihydroxy compounds include aromatic dihydroxy compounds of formula (2) (e.g., resorcinol), bisphenols of formula (3) (e.g., bisphenol A), a C_1-8 aliphatic diol such as ethane diol, n-propane diol, i- propane diol, 1,4-butane diol, 1,6-cyclohexane diol, 1,6-hydroxymethylcyclohexane, or a combination comprising at least one of the foregoing dihydroxy compounds. Aliphatic dicarboxylic acids that can be used include C₆-20 aliphatic dicarboxylic acids (which includes the terminal carboxyl groups), specifically linear Cs-i2 aliphatic dicarboxylic acid such as decanedioic acid (sebacic acid); and alpha, omega-Ci2 dicarboxylic acids such as dodecanedioic acid (DDDA). Aromatic dicarboxylic acids that can be used include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, 1,6-cyclohexane dicarboxylic acid, or a combination comprising at least one of the foregoing acids. A combination of isophthalic acid and terephthalic acid wherein the weight ratio of isophthalic acid to terephthalic acid is 91:9 to 2:98 can be used. Specific ester units include ethylene terephthalate units, n-propylene terephthalate units, n-butylene terephthalate units, ester units derived from isophthalic acid, terephthalic acid, and resorcinol (ITR ester units), and ester units derived from sebacic acid and bisphenol A. The molar ratio of ester units to carbonate units in the poly(ester-carbonate)s can vary broadly, for example 1:99 to 99: 1, specifically, 10:90 to 90: 10, more specifically, 25:75 to 75:25, or from 2:98 to 15:85.

[0030] Similarly, poly(siloxane-carbonate)s include repeat carbonate units of formula (1) and repeat siloxane units as are known in the art and described, for example, in U.S. Pat. No. 9,598,578 and U.S. Pat. No. 8,466,249. Poly(siloxane-ester-carbonate)s can also be used, for example poly(ITR-dimethyl siloxane-bisphenol A carbonate)s as described in U. S. Pat. No. 9,266,541.

[0031] The polycarbonates can have an intrinsic viscosity, as determined in chloroform at 25°C, of 0.3 to 1.5 deciliters per gram (dl/gm), specifically 0.45 to 1.0 dl/gm. The

polycarbonates can have a weight average molecular weight of 5,000 to 200,000 Daltons, specifically 15,000 to 100,000 Daltons, as measured by gel permeation chromatography (GPC), using a crosslinked styrene-divinylbenzene column and calibrated to Bisphenol A

homopolycarbonate references. GPC samples are prepared at a concentration of 1 mg per ml (mg/ml), and are eluted at a flow rate of 1.5 ml per minute.

[0032] The types of phosphorus-containing compounds useful as flame retardants can vary greatly. The phosphorus-containing flame retardant is an organic compound that includes an aromatic group, a phosphorus -nitrogen bond, or a combination comprising at least one of the foregoing. Non-brominated and non-chlorinated phosphorus-containing flame retardants can be preferred in certain applications for regulatory reasons. In some embodiments, the phosphorus- containing flame retardant includes an phosphate, phosphite, phosphonate, phosphinate, phosphine oxide, or phosphine, each containing a C3-30 aromatic group optionally comprising up to three heteroatoms in an aromatic ring, a phosphazene, phosphorus ester amide, phosphoric acid amide, phosphonic acid amide, phosphinic acid amide, tris(aziridinyl) phosphine oxide, or a combination comprising at least one of the foregoing. Any of the foregoing compounds can be monomeric or polymeric.

[0033] An exemplary organic compound including an aromatic group is an aromatic phosphate of the formula (GO)₃P=0 wherein each G is independently an alkyl, cycloalkyl, aryl, alkaryl, or aralkyl group, provided that at least one G is an aromatic group. Two of the G groups may be joined together to provide a cyclic group, for example, diphenyl pentaerythritol diphosphate, which is described by Axelrod in U.S. Pat. No. 4,154,775. In an embodiment a suitable aromatic phosphate can be phenyl bis(dodecyl)phosphate, phenyl

bis(neopentyl)phosphate, phenyl bis(3,5,5'-trimethylhexyl)phosphate, ethyl diphenyl phosphate, 2-ethylhexyl di(p- tolyl)phosphate, bis(2-ethylhexyl)p-tolyl phosphate, tritolyl phosphate, bis(2- ethylhexyl)phenyl phosphate, tri(nonylphenyl)phosphate, bis(dodecyl)p-tolyl phosphate, dibutyl phenyl phosphate, p-tolyl bis(2,5,5'-trimethylhexyl)phosphate, 2-ethylhexyl diphenyl phosphate, and the like. In an embodiment a specific aromatic phosphate is one in which each G is aromatic, for example, triphenyl phosphate, tricresyl phosphate, isopropylated triphenyl phosphate, and the like.

[0034] In some embodiments di- or polyfunctional aromatic phosphorus -containing compounds are also useful, for example, compounds of the formulas below:

wherein each G¹ is independently a Ci-30 hydrocarbyl; each G² is independently a Ci-30 hydrocarbyl or hydrocarbyloxy; X^a is as defined in formula (3); each X is independently a bromine or chlorine; m is 0 to 4, and n is 1 to 30. Di- or polyfunctional aromatic phosphorus- containing compounds of this type include resorcinol tetraphenyl diphosphate (RDP), the bis(diphenyl) phosphate of hydroquinone and the bis(diphenyl) phosphate of bisphenol A, their oligomeric and polymeric counterparts, and the like.

[0035] For example, in some embodiments, the phosphorus-containing flame retardant can be a linear or cyclic polyphosphonate homopolymer or copolymer, such as those described in U.S. Patent No. 6,861,499 and 7,816,486. Polyphosphonates can exhibit at least one of a broad molecular weight distribution with polydispersity of 3.2 or greater, 2.5 or greater, and 2.3 or greater, an Mw of greater than 10,000 grams per mole (as measured using polystyrene standards), and a Tg of at least 100°C. In some embodiments, the polyphosphonates can have a Tg of 25 to 140°C, or 50 to 135°C, or 75 to 130°C. The polyphosphonates can be prepared from an aryl phosphonic acid ester and either bisphenol A or a mixture of bisphenol A and another bisphenol in the presence of a phosphonium catalyst or an alkaline metal catalyst such as a sodium catalyst. The polyphosphonates can have a relative viscosity of at least 1.1,

transparency, and improved hydrolytic stability. Exemplary polyphosphonate copolymers include poly(phosphonate-carbonate)s, which can be block or random copolymers. In some embodiments, the polyphosphonate copolymers can have a phosphorus content of 1 to 15 weight percent (wt%) of the total copolyphosphonate, for example 1 to 12 wt%, or 2 to 10 wt%.

[0036] The organic compound containing a phosphorus -nitrogen bond can be a phosphazene, phosphonitrilic chloride, phosphorus ester amide, phosphoric acid amide, phosphonic acid amide, phosphinic acid amide, or tris(aziridinyl) phosphine oxide. These flame-retardant additives are commercially available. In an embodiment, the organic compound containing a phosphorus-nitrogen bond is a phosphazene. A number of phosphazenes and their synthesis are described in H. R. Allcook, "Phosphorus-Nitrogen Compounds" Academic Press (1972), and J. E. Mark et al., "Inorganic Polymers" Prentice-Hall International, Inc. (1992).

[0037] In some embodiments the phosphorus -containing flame retardant comprises a poly(phosphonate) homopolymer, a poly(phosphonate-carbonate), resorcinol diphosphate, bisphenol A bis(diphenyl phosphate), triphenyl phosphate, resorcinol bis(diphenyl phosphate), tricresyl phosphate, phenoxyphosphazene, or a combination comprising at least one of the foregoing. In some embodiments, the phosphorus-containing flame retardant is an aryl phosphate having a molecular weight of about 350 to 1000 Daltons.

[0038] The amount of phosphorous-containing flame retardant present in the solution is an amount at least sufficient to provide a powder that can be used to manufacture an article having a UL94 V-2 rating, more preferable a V-l rating and most preferably aV-0 rating. The amount can vary with the type of polycarbonate and with the efficiency of the particular flame retardant. In some embodiments, the amount of the phosphorous -containing flame retardant in the solution can be from 0.1 to 50 wt%, or from 5 to 15 wt%, each based on the total weight of the polycarbonate. In other embodiments, the amount of the phosphorous-containing flame retardant in the partially crystalline polycarbonate powder product can be from 0.1 to 40 wt%, or from 5 to 20 wt%, each based on the total weight of the partially crystalline polycarbonate powder/phosphorous-containing flame retardant product.

[0039] Various additives can be included in the solution (and the partially crystalline polycarbonate powder), for example those ordinarily incorporated into polycarbonate compositions, with the proviso that the additives are selected so as to not significantly adversely affect the desired properties of the powder or the articles formed from the powder, such as flame retardancy. Such additives can be mixed into the solution before, during, or after the addition of the polycarbonate and the flame retardant. Possible additives include impact modifiers, fillers, non-oxidants, heat stabilizers, light stabilizers, ultraviolet light (UV) absorbers (such as benzotriazoles), plasticizers, lubricants, mold release agents, antistatic agents, colorants, blowing agents, and radiation stabilizers. A combination of additives can be used, for example, an antioxidant, a UV absorber, and a mold release agent. The total amount of additives (other than any impact modifier, filler, or reinforcing agents) can be from 0.1 to 5.0 wt%, based on the total weight of the polycarbonate.

[0040] The product partially crystalline polycarbonate powder containing the

phosphorous-containing flame retardant can have a high percentage of particles having a particle size of less than 150 micrometers, as well as a relatively narrow particle size distribution. In some embodiments, the partially crystalline polycarbonate powder has a D50 of less than 150 μηι, or a D85 particle size of less than 150 micrometers, or a D90 particle size of less than 150 micrometers. A partially crystalline polycarbonate powder in which 100% of the particles (D100) have a size of less than 150 micrometers can also be produced by this method. As used herein, D50 refers to the particle diameter of the powder where 50 volume percent (vol%) of the particles in the total distribution of the referenced sample have the noted particle diameter or smaller. Similarly, a D85 refers to the particle diameter of the powder where 85 vol% of the particles in the total distribution of the referenced sample have the noted particle diameter or smaller; D90 refers to the particle diameter of the powder where 95 vol% of the particles in the total distribution of the referenced sample have the noted particle diameter or smaller; and DlOO refers to the particle diameter of the powder where 100 vol% of the particles in the total distribution of the referenced sample have the noted particle diameter or smaller. Particle sizes can be measured by any suitable methods known in the art to measure particle size by diameter. In some embodiments, the particle size is determined by laser diffraction as is known in the art. For example, particle size can be determined using a diffractometer such as the Mastersizer 3000 from Malvern.

[0041] In some embodiments, the product partially crystalline polycarbonate powder can have an average particle diameter of less than or equal to 100 μιη. Specifically, the partially crystalline polycarbonate powder can have an average particle diameter of 10 μιη to 100 μιη. The term "average particle diameter" refers to the average (mean) size of the particles as measured by diameter.

[0042] The product partially crystalline polycarbonate powder has a percent crystallinity greater than that of the starting amorphous polycarbonate. The term "percent crystallinity" or as used herein, refers to the portion of the amorphous polymer that has been converted to the crystalline form. For some embodiments, the starting crystallinity is of the polycarbonate polymer is 0% (i.e., the polymer is 100% amorphous). The percentage is based upon the total weight of the partially crystalline polycarbonate powder. In some embodiments, the partially crystalline polycarbonate powder can have a percent crystallinity of at least 3%, for example 10% to 45%, or at least 20%, for example 20% to 40%, or at least 25%, for example 25% to 35%. In some embodiments the partially crystalline polycarbonate powder can have 20% to 30% crystallinity.

[0043] Also disclosed herein are methods for powder bed fusing a powder composition including the partially crystalline polycarbonate powder, to form a three-dimensional article. Due to the good flowability of the partially crystalline polycarbonate powder, a smooth and dense powder bed can be formed allowing for optimum precision and density of the sintered part. Also, the partially crystalline nature of the polycarbonate powder allows for ease of processing. Moreover, the use of these partially crystalline polycarbonate powders results in lower required melting energy versus the melting of corresponding amorphous polycarbonates. The particle size of the partially crystalline polycarbonate can affect the ability to use the polymer in powder bed fusion processes. In some embodiments, the partially crystalline polycarbonate powder has a D50 of less than 150 μιη.

[0044] The term "powder bed fusing" or "powder bed fusion" is used herein to mean processes wherein the polycarbonate is selectively sintered or melted and fused, layer-by-layer to provide a 3-D object. Sintering can result in objects having a density of less than about 90% of the density of the solid powder composition, whereas melting can provide objects having a density of 90% to 100% of the solid powder composition. Use of crystalline polycarbonate as herein disclosed can facilitate melting such that densities close to achieved by injection molded can be attained.

[0045] Powder bed fusing or powder bed fusion further includes all laser sintering and all selective laser sintering processes as well as other powder bed fusing technologies as defined by ASTM F2792-12a. For example, sintering of the powder composition can be accomplished via application of electromagnetic radiation other than that produced by a laser, with the selectivity of the sintering achieved, for example, through selective application of inhibitors, absorbers, susceptors, or the electromagnetic radiation (e.g., through use of masks or directed laser beams). Any other suitable source of electromagnetic radiation can be used, including, for example, infrared radiation sources, microwave generators, lasers, radiative heaters, lamps, or a combination thereof. In some embodiments, selective mask sintering ("SMS") techniques can be used to produce three-dimensional articles of the invention. For further discussion of SMS processes, see for example U.S. Pat. No. 6,531,086 which describes an SMS machine in which a shielding mask is used to selectively block infrared radiation, resulting in the selective irradiation of a portion of a powder layer. If using an SMS process to produce articles from powder compositions of the invention, it can be desirable to include one or more materials in the powder composition that enhance the infrared absorption properties of the powder composition. For example, the powder composition can include one or more heat absorbers or dark-colored materials (e.g., carbon black, carbon nanotubes, or carbon fibers).

[0046] In some embodiments, the partially crystalline polycarbonate powder containing a phosphorous -containing flame retardant can be used as the sole component in the powder composition and applied directly in a powder bed fusing step. In other embodiments, the powder can also be combined with other optional components, as described below, such as a flow agent. Any optional component is present in a sufficient amount to perform its intended function without significantly adversely affecting the powder composition or an article prepared therefrom. Any optional components can have an average particle diameter which falls within the range of the average particle diameters of the crystalline polycarbonate powder or flow agent. If needed, an optional component can be milled to the desired particle size and/or particle size distribution. It is not necessary for each optional component to melt during the laser sintering process, but use of optional components compatible with the partially crystalline polycarbonate can provide a strong and durable article of manufacture by the powder bed fusing process.

[0047] The optional components can be particulate materials and include organic and inorganic materials such as fillers, flow agents, coloring agents (dyes or pigments, such as carbon black), reinforcing agents, toners, extenders, fillers, lubricants, anticorrosion agents, thixotropic agents, dispersing agents, antioxidants, adhesion promoters, light stabilizers, organic solvents, surfactants, additional flame retardants, non-static agents, plasticizers, or a

combination comprising at least one of the foregoing. Yet another optional component can be a second polymer that modifies the properties of the partially crystalline polycarbonate. In some embodiments, however, the polymer content in the powder composition used in the powder bed fusing comprises from 50 to 100 wt% of the crystalline polycarbonate, based on the total weight of all polymeric materials in the powder composition. Combinations of the optional components can be used, for example a flow agent, and a second polymer. Each individual optional component can be present in the powder composition in an amount of 0.01 to 30 wt%, based on the total weight of the powder composition. The total amount of all optional components in the powder composition can be from 0 up to 30 wt%, based on the total weight of the powder composition.

[0048] The optional component can be a reinforcing agent that imparts additional strength to the article of manufacture. Examples of the reinforcing agent include glass fibers, carbon fibers, talc, clay, wollastonite, glass beads, or a combination comprising at least one of the foregoing reinforcing agents.

[0049] The optional component can be a flow agent. The optional flow agent can be a particulate inorganic material having a median particle size of 10 μιη or less, or 100 nm or less. The flow agent can be a hydrated silica, amorphous alumina, a glassy silica, a glassy phosphate, a glassy borate, a glassy oxide, titania, talc, mica, a fumed silica, kaolin, attapulgite, calcium silicate, alumina, or magnesium silicate. A particularly useful flow agent is fumed silica. The flow agent can be present in an amount sufficient to allow the polycarbonate to flow and level on the build surface of the laser sintering device. In particular, the powder composition can include a particulate flow agent in an amount of 0.01 to 5 wt%, or 0.05 to 1 wt%, or 0.1 to 0.25 wt%, each based on the total weight of the powder composition.

[0050] Also included herein are all three-dimensional products made by powder bed fusing these powder compositions. After a layer-by-layer manufacture of an article of manufacture, the article can exhibit excellent resolution, durability, and strength. These articles of manufacture can have a wide variety of uses, including as prototypes and as end products as well as molds for end products.

[0051] In particular, powder bed fused (e.g., laser sintered) articles can be produced from the powder compositions using any suitable powder bed fusing processes including laser sintering processes. These articles can include a plurality of overlying and adherent sintered layers that include a polymeric matrix which, in some embodiments, have reinforcement particles dispersed throughout the polymeric matrix. Laser sintering processes are sufficiently well known, and are based on the selective sintering of polymer particles, where layers of polymer particles are briefly exposed to laser light and the polymer particles exposed to the laser light are thus bonded to one another. Successive sintering of layers of polymer particles produces three-dimensional objects. Details concerning the selective laser sintering process are found, by way of example, in the specifications U.S. Pat. No. 6,136,948 and WO 96/06881. However, the powder described herein can also be used in other rapid prototyping or rapid manufacturing processing of the prior art, in particular in those described above. For example, the powder can in particular be used for producing moldings from powders via the SLS

(selective laser sintering) process, as described in U.S. Pat. No. 6,136,948 or WO 96/06881, via the SIB process (selective inhibition of bonding of powder), as described in WO 01/38061, via 3D printing, as described in EP 0 431 924.

[0052] In some embodiments of the methods, a plurality of layers is formed in a preset pattern by an additive manufacturing process. "Plurality" as used in the context of additive manufacturing includes 5 or more layers, or 20 or more layers. The maximum number of layers can vary greatly, determined, for example, by considerations such as the size of the article being manufactured, the technique used, the capabilities of the equipment used, and the level of detail desired in the final article. For example, 5 to 100,000 layers can be formed, or 20 to 50,000 layers can be formed, or 50 to 50,000 layers can be formed.

[0053] As used herein, "layer" is a term of convenience that includes any shape, regular or irregular, having at least a predetermined thickness. In some embodiments, the size and configuration two dimensions are predetermined, and on some embodiments, the size and shape of all three-dimensions of the layer is predetermined. The thickness of each layer can vary widely depending on the additive manufacturing method. In some embodiments the thickness of each layer as formed differs from a previous or subsequent layer. In some embodiments, the thickness of each layer is the same. In some embodiments the thickness of each layer as formed is 0.1 millimeters (mm) to 1 mm.

[0054] The preset pattern can be determined from a three-dimensional digital representation of the desired article as is known in the art and described in further detail below.

[0055] The fused layers of powder bed fused articles can be of any thickness suitable for selective laser sintered processing. The individual layers can be each, on average, preferably at least 50 micrometers (μιη) thick, more preferably at least 80 μιη thick, and even more preferably at least 100 μηι thick. In a preferred embodiment, the plurality of sintered layers are each, on average, preferably less than 500 μιη thick, more preferably less than 300 μιη thick, and even more preferably less than 200 μιη thick. Thus, the individual layers for some embodiments can be 50 to 500 μιη, 80 to 300 μιη, or 100 to 200 μιη thick. Three-dimensional articles produced from the powder compositions using a layer-by-layer powder bed fusing processes other than selective laser sintering can have layer thicknesses that are the same or different from those described above.

[0056] In still other embodiments, the partially crystalline polycarbonate powder with phosphorous-containing flame retardant is used to manufacture a unidirectional fiber reinforced polycarbonate composite. The partially crystalline nature of the polycarbonate powder allows ease of processing, and results in lower required melting energy versus the melting of corresponding amorphous polycarbonates. This method can include providing an aqueous dispersion of a powder composition comprising the partially crystalline polycarbonate powder containing the phosphorous-containing flame retardant composition; passing a continuous fiber tape through said aqueous dispersion to form an unidirectional fiber reinforced polycarbonate composite; drying the unidirectional fiber reinforced polycarbonate composite; and optionally further processing the dried composite form under high temperature and pressure conditions to melt the polymer to achieve better impregnation of unidirectional fiber by the polymer. In an embodiment, the continuous fiber tape is a continuous carbon tape. PCT Publication No. WO 2017/004112 Al discusses making this type of tape with polyimide particles (ULTEM from

SABIC).

[0057] This disclosure is further illustrated by the following examples, which are non- limiting.

EXAMPLES

[0058] Three different phosphorous-containing flame retardant additives were used for initial proof of concept investigation as shown below.

Resorcinol diphenyl phosphate (RDP) Bisphenol A diphenyl phosphate (BPADP) (P content: 10.8%) P content: 9% FRX Homopolymer

P content: 10.8%

Example 1 - Isolation by filtration

[0059] Four formulations of polycarbonate (PC) with and without these three different phosphorous-containing flame retardant additives were prepared using acetone as the crystallizing anti-solvent using the following process. In a glass beaker 20 wt% PC, with a molecular weight of 21,800 g/mol, along with phosphorus containing flame retardant additive was dissolved in dichloromethane at room temperature. 100 gram of the dissolved PC/flame retardant mixture was gradually poured in about 10 minutes into a glass beaker filled with 100 g of acetone as non-solvent. During this addition process, the beaker with acetone was stirred at 20,000 rpm using a IKA T-25 Ultraturrax homogenizer and a fine powder precipitate was formed. Once the addition process is complete, the final mixture is stirred for another minute and then the powder/solvent mixture was left for 30 minutes to settle down. The acetone and dichloromethane mixture was then decanted. The resulting wet cake was dried in vacuum oven at 105°C for 2 hours to get dry micronized FR containing PC powder. The formulations used with the process are shown in Table 1 below, with the goal being to target 2 wt% phosphorous based on the amount of PC used in the formulation before precipitating the PC powder.

Table 1: Formulations evaluated

[0060] Phosphorous can be incorporated within the PC particles following the process flow diagram shown in FIG. 1. However, in the case of FRX-PC, all phosphorous appeared to be lost during the step of isolating the precipitated by decanting the acetone/DCM solvent/non- solvent combination. Hence, the process was modified to evaporate this acetone/DCM combination instead, which then successfully demonstrated retention of phosphorous on the PC particles. See additional experiments below.

[0061] In summary, the proposed method allows successful incorporation of non- halogenated flame retardant additives (fluid/pellet form) within polycarbonate powders, without affecting its percent crystallinity or free flowing characteristics.

[0062] Control PC (no FR) and PC with RDP and BPADP show resulting powders to have a mono-modal distribution. However, the particle size increases as a function of the viscosity of the medium. In contrast, PC with FRX-PC showed a bi-modal distribution, as can be seen from the particle size distribution figures below. Table 2 shows the different levels of particle sizes measured from the experimental samples.

Table 2: Particle size measurements for PC and FR-PC powders

Phosphorous Detection in PC Powders:

[0063] Energy dispersive X-ray spectroscopy (EDX) coupled with SEM was conducted on PC powder samples to obtain estimated quantitative elemental information, specifically the presence of phosphorous in the powders. Table 3 below shows the elemental breakdown of the various PC powders produced based on analysis of a small sample surface area. The percent phosphorous detected is slightly higher than the theoretical level of 2 wt%, possibly indicating non-even distribution of the phosphorous in the FR-PC powder surface and thus also within the overall FR-PC powder particles.

Table 3: Elemental breakdown of various PC partic es as estimated from EDX measurements.

[0064] The presence of phosphorus in the bulk particles was detected by ³¹P NMR spectroscopy of all FR incorporated PC powder samples. However, the chemical shift depends on the electronic environment of the phosphorus atom present in the impregnated additive. With RDP and BPADP, phosphorus is surrounded by three phenyl groups, causing a downfield (deshielded) shift in its ³¹P NMR signal (approx. -17 ppm) in comparison to the FRX polymer (+24 ppm), where phosphorus is in relatively constraint free zone (2 phenyl groups). An additional observation is that the FR additive, when analyzed alone or as the PC powders exhibit similar chemical shift in all the cases. This indicates that degradation of the FR agents did not occur during or after powder formation.

Thermal Properties of PC Powders

[0065] Differential Scanning Calorimetry (DSC) conducted on the PC powders shows that the crystallinity of PC powders produced through the solvent/non- solvent process is maintained (although a small drop is detected) upon addition of FR additives. A drop in the glass transition temperature (T_g) of PC resin was also observed, which confirms and is expected due to the presence of the FR additive in the PC powders. This plasticizing effect from the FR additives improves processability of the composite.

[0066] DSC was conducted using ASTM El 131 (2014) protocol with TA Instruments Q1000 instrument. Temperature range was -70°C to 300°C with a ramp rate of 10°C/min. Table 4: Thermal properties data for various PC powders

[0067] The method enables production of flame retardant PC powders through a single process approach based on solvent/non- solvent process. This invention, as a result, addresses a critical need to have fine PC powder particles (compared to current state of the art) to produce high quality continuous fiber reinforced PC tapes with flame retardant properties.

Example 2 - Isolation by Evaporation vs. Filtration

[0068] First, additional experiments were conducted using methyl ethyl ketone as the crystallizing non-solvent instead of acetone. This process starts with dissolving the desired amounts of polycarbonate resin and the FR additive in dichloromethane (DCM) solvent. In the present case, a polycarbonate with a molecular weight of 21,800 g/mol and resorcinol-diphenyl phosphate (RDP) flame retardant were used. Following solution formation, MEK was added as the non- solvent under high shear mixing over a defined period of time. During the addition of the non-solvent combined with high shear mixing, the FR-PC powder precipitated. The resulting suspension was then filtered using a suitable filtering medium and the wet cake of the polymer powder was finally dried in an oven. This process is the same as shown in FIG. 1.

[0069] In another set of experiments, instead of filtering the DCM/MEK suspension to isolate the precipitated FR-PC powder, a rotary evaporator was used to remove the solvents by evaporation. The approach is shown in FIG. 2.

[0070] To evaluate the solubility of RDP in various (non-) solvents 1.5 g of RDP (Fyrolflex™ RDP, CAS 57583-54-7) was mixed with 98.5g of acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPK), isopropanol, or dichloromethane (DCM). Each resulting mixture contained 1.5 wt% RDP, which equals the RDP concentration for a 15 wt% FR-PC solution containing 10 wt% RDP relative to the PC.

[0071] The results are shown in Table 5. Table 5.Solubility of RDP

NT = not tested

[0072] The data in Table 5 shows that RDP is soluble in all of the solvents at the given concentration, including non-solvent and DCM. Also when adding 50 g (1:0.5), 100 g (1: 1) or 200g (1:2) acetone, the standard non-solvent used to precipitate PC powder in Example 1, to a 1.5 wt% solution of RDP in DCM, the RDP stays in solution. This likely accounts for loss of some of the RDP, which is dissolved in the filtrate during the filtration step.

[0073] The amounts of polycarbonate and RDP shown in Table 6 were combined in a 500-ml glass bottle to provide FR-PC mixtures containing 1, 3, 5, 10, 20, and 30 wt% RDP. The same polycarbonate with a molecular weight of 21,800 g/mol was used in these experiments as used above in the previous Examples. Each FR-PC mixture was dissolved in 212.5g DCM on a shaker overnight at room temperature to provide a 15 wt% FR-PC solution. Subsequently, 250 g MEK was rapidly added to each solution in one portion while mixing with an IKA T25 Ultra Turrax homogenizer at 20000 rpm for 10 minutes. The precipitated FR-PC powders were isolated by vacuum filtration using Whatman™ paper filter (ashless) with 8 μιη pore size. The residue was washed with DCM and dried in the vacuum oven (50 mbar) overnight at 100°C.

Table 6: Formulations of FR-PC solutions

[0074] The following techniques were used to analyze the isolated, dried FR-PC powder.

[0075] Particle Size Distribution (PSD). The volume based particle size distribution was measured in methanol (shown in Table 7) using laser diffraction technology (Mastersizer 20000 from Malvern) and reported as D10, D50, and D90 values. A small amount of the DCM/MEK suspension was taken and diluted with acetone. The resulting slurry was added to the Malvern reservoir filled with methanol to study the particle size distribution.

[0076] Differential Scanning Calorimetry (DSC). DSC analysis of the dried FR-PC powders was conducted with a TA Instruments Q2000 instrument, using a heating/cooling/heating scan (20-300°C/300-20°C/20-300°C, 20°C/min) under N₂ atmosphere. The melting temperature (T_m) and percent crystallinity were determined from the first heating curve. The percent crystallinity was calculated based on a heat of melting of 109.8J/g for a 100% crystalline material. The T_g was determined from the second heating curve.

[0077] Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Approximately 200 mg of the dried FR-PC powder was digested in 6 ml concentrated nitric acid (trace metal grade) by microwave assisted acid digestion using an Anton Paar Multiwave 3000 equipped with closed high pressure Quartz digestion vessels. After the microwave digestion run, the acid was analytically transferred into a pre-cleaned plastic centrifuge tube containing 1ml of internal standard solution and was diluted with Milli-Q water up to the 50ml mark. Each sample is diluted another 20, 50, or 100 times in order to maintain the measured concentration of phosphorus within the calibration range. The phosphorus concentration (%P) in the diluted sample solutions was quantified using a multi-element calibration standard set from Inorganic Ventures using an Agilent 7500cx ICP-MS system and converted to RDP concentration (%RDP) based on a 10.9 wt% phosphorus content of RDP. The same polycarbonate with a molecular weight of 21,800 g/mol was used in these experiments as used above in the previous Examples.

[0078] The measured data for FR-PC powders produced from the process involving use of filtration technique to remove the solvent/non-solvent mixture is shown in Table 7.

Table 7: Property data for FR-PC powders produced from varying initial RDP content, using filtration to isolate the powders.

[0079] From the data in Table 7, it is seen that the particle size of the precipitated FR-PC powders is not affected by the initial amount of RDP used in the process. The resulting final particle size might be expected to have stronger dependency on the rate of shear mixing and the time of mixing.

[0080] The initial amount of RDP, however, clearly plays a role in the final FR-PC powders as seen from the general trend of reducing Tg with increasing amount of retained RDP in the final product. It is also seen that about 60% of the RDP is lost in the process of filtration regardless of the starting amount of RDP used in the process. FIG. 3 shows a graph comparing the starting and final amounts of RDP measured along with a representative 'ideal' situation assuming how the data plot might look like if 100% of the RDP was retained in the final FR-PC powder.

[0081] A decreasing trend in Tg as a function of increasing RDP content, and hence phosphorus content, in the FR-PC powders is shown in FIG. 4. This relationship would be expected to be seen regardless of the process used to produce the FR-PC powders.

[0082] Besides being a FR additive, RDP is also desirable due to its ability to reduce the Tg of polycarbonates. In certain applications, such as those in the consumer electronics, it is highly desirable to have a polycarbonate with suppressed Tg to enable low temperature processing and fast throughput rates for manufacturing operations. In some embodiments involving unidirectional fiber reinforced polycarbonate composite, it is desirable to suppress the Tg of the particular polycarbonate employed by 3 to 50 degrees C by the addition of sufficient amount of the phosphorous -containing flame retardant to improve such manufacturing operations.

[0083] The greatest limitation of the filtration process is the excess loss of RDP through the solvent/non-solvent filtrate. This not only makes it necessary to use extra RDP, an expensive additive, in the process to produce FR-PC powders to compensate for the lost amount, but also brings in further processing needs to recover or bear the loss of RDP. These limitations are highly undesirable due to additional prohibitive costs to the overall process.

[0084] A more effective embodiment is shown in FIG. 2, replacing the filtration step for an evaporation step, which forces a much higher amount of RDP to be retained in the remaining FR-PC powder. Table 8 shows the results for formulations with 5wt%, 10 wt% and 20 wt% RDP in the starting FR-PC mixture (see Table 6), where the DCM/MEK suspensions were transferred to a round-bottom flask and put on a rotary evaporator with the temperature of the water bath set at 40°C. The pressure was stepwise reduced to 500 mbar and kept at this pressure for an additional 60 minutes, to remove the solvent (DCM) and non- solvent (MEK). The remaining FR-PC powder was dried in a vacuum oven (50 mbar) overnight at 100°C. The same polycarbonate with a molecular weight of 21,800 g/mol was used in these experiments as used above in the previous Examples.

Table 8: Property data for FR-PC powders produced from varying initial RDP content, using evaporation to isolate the powders.

[0085] From the data in Table 8, is seen that the change in approach results in the much desired and successful result of the majority of the RDP, and hence phosphorous, being retained in the final product. This is clearly demonstrated by much lower Tg values for the evaporation based samples as a result of higher %P and %RDP, compared to the corresponding filtration based samples in Table 7.

[0086] The benefit of using evaporation instead of filtration to produce crystalline FR- PC powders with better RDP retention is show in FIG. 5. Where using filtration to isolate the FR-PC powders, as shown in Fig. 3, only about 40% of the RDP is retained regardless the amount of RDP at the start of the process. With the evaporation approach retention of the RDP additive is much better and yields of around 85-90% were found for 5wt% and 10wt% RDP at the start of the process. Also when using higher amounts of RDP (20wt%) at the start of the process, the RDP retention is improved when using the evaporation approach, but the effects appears to be less beneficial. The latter might be assigned to partial loss of the RDP due the higher partial vapor pressure of RDP at these high RDP concentrations.

[0087] The present invention is further illustrated by the following aspects.

[0088] Aspect 1. A method of preparing a partially crystalline polycarbonate powder containing a phosphorous -containing flame retardant, the method comprising: dissolving an amorphous polycarbonate and a phosphorous -containing flame retardant in a halogenated alkane solvent to form a solution; combining the solution with a crystallizing non-solvent that is miscible with the halogenated alkane solvent; and mixing the combined solution and

crystallizing non- solvent under high shear mixing conditions effective to form a partially crystalline polycarbonate precipitate.

[0089] Aspect 2. The method of Aspect 1 wherein the phosphorous -containing flame retardant is added to the solvent before the polycarbonate is dissolved, or together with the polycarbonate, before the addition of the crystallizing non-solvent.

[0090] Aspect 3. The method of Aspect 1 wherein the phosphorous-containing flame retardant is added after dissolving the amorphous polycarbonate solution and before the addition of the crystallizing non-solvent.

[0091] Aspect 4. The method of any of Aspects 1-3, further comprising: removing the halogenated alkane solvent and the crystallizing non-solvent from the precipitate; and optionally, drying the precipitate.

[0092] Aspect 5. The method of Embodiment 4, wherein the removing the halogenated alkane solvent and the crystallizing non- solvent from the precipitate comprises filtering the precipitate. [0093] Aspect 6. The method of Aspect 4, wherein the removing the halogenated alkane solvent and the crystallizing non- solvent from the precipitate comprises at least partially evaporating the solvents from the precipitate.

[0094] Aspect 7. The method of any of Aspects 1-6, wherein the halogenated alkane solvent comprises dichloromethane, chloroform, methylene chloride, or a combination comprising at least one of the foregoing.

[0095] Aspect 8. The method of any of Aspects 1-7, wherein the crystallizing non- solvent comprises acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, or a combination comprising at least one of the foregoing.

[0096] Aspect 9. The method of any of Aspects 1-8, wherein the high shear mixing comprises mixing at a speed of 2,000 to 50,000 rpm.

[0097] Aspect 10. The method of any of Aspects 1-9, wherein the amorphous polycarbonate is a polycarbonate homopolymer, a poly(ester-carbonate), a poly(siloxane- carbonate), a poly(ester-siloxane-carbonate), or a combination comprising at least one of the foregoing.

[0098] Aspect 11. The method of any of Aspectsl-10, wherein the phosphorus- containing flame retardant comprises a poly(phosphonate) homopolymer, a poly(phosphonate- carbonate), resorcinol diphosphate, bisphenol A bis(diphenyl phosphate), triphenyl phosphate, resorcinol bis(diphenyl phosphate), tricresyl phosphate, phenoxyphosphazene, or a combination comprising at least one of the foregoing.

[0099] Aspect 12. The method of any of Aspects 1-11, wherein the halogenated alkane solvent is dichloromethane, wherein the crystallizing non-solvent is methyl ethyl ketone, and the removing the halogenated alkane solvent and the crystallizing non-solvent from the precipitate comprises at least partially evaporating the solvents from the precipitate.

[0100] Aspect 13. A partially crystalline polycarbonate powder comprising a phosphorous-containing flame retardant prepared by the method of any of Aspect s 1-12.

[0101] Aspect 14. The partially crystalline polycarbonate powder of claim 13, wherein the polycarbonate is a polycarbonate homopolymer, a poly(carbonate-siloxane), or a

combination comprising at least one of the foregoing; wherein the phosphorus-containing flame retardant is a poly(phosphonate) homopolymer, a poly(phosphonate-carbonate), resorcinol diphosphate, bisphenol A bis(diphenyl phosphate), triphenyl phosphate, resorcinol bis(diphenyl phosphate), tricresyl phosphate, phenoxyphosphazene, or a combination comprising at least one of the foregoing; and wherein the amount of the phosphorous-containing flame retardant in the partially crystalline polycarbonate powder product is from 0.1 to 40 wt%, based on the total weight of the partially crystalline polycarbonate powder/phosphorous-containing flame retardant product.

[0102] Aspect 15. A method of preparing a three-dimensional article, the method comprising: providing a powder composition comprising the partially crystalline polycarbonate powder containing phosphorous-containing flame retardant of any of Aspects 13-14; and powder bed fusing the powder composition to form a three-dimensional article.

[0103] Aspect 16. The method of Aspect 15, wherein the powder bed fusing comprises selective laser sintering.

[0104] Aspect 17. A three-dimensional article made by the method of any of Aspects 15-16, comprising a plurality of fused layers, preferably comprising at least five fused layers.

[0105] Aspect 18. A method of preparing a unidirectional fiber reinforced polycarbonate composite, the method comprising: providing an aqueous dispersion of a powder composition comprising a partially crystalline polycarbonate powder containing a phosphorous-containing flame retardant of any of Aspects 13-14; passing a continuous fiber tape through said aqueous dispersion to form an unidirectional fiber reinforced polycarbonate composite; and drying the unidirectional fiber reinforced polycarbonate composite.

[0106] Aspect 19. The method of Aspect 19, wherein the continuous fiber tape is a continuous carbon tape.

[0107] Aspect 20. The method of Aspect 19, wherein the Tg of the polycarbonate in the unidirectional fiber reinforced polycarbonate composite is suppressed 3 to 50 degrees C by the presence of the phosphorous -containing flame retardant.

[0108] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0109] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. "Combinations" is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms "a" and "an" and "the" do not denote a limitation of quantity, and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. "Or" means "and/or" unless clearly stated otherwise. Reference throughout the specification to "an embodiment" or aspect" and so forth, means that a particular element described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. Also, the described elements may be combined in any suitable manner in the various embodiments.

[0110] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

[0111] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this application belongs. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0112] Compounds are described using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash ("-") that is not between two letters or symbols is used to indicate a point of attachment for a substituent, unless indicated otherwise by context. For example, -CHO is attached through carbon of the carbonyl group.

[0113] The term "alkyl" means a branched or straight chain, unsaturated aliphatic hydrocarbon group, e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, s- pentyl, and n- and s-hexyl. "Alkenyl" means a straight or branched chain, monovalent hydrocarbon group having at least one carbon-carbon double bond (e.g., ethenyl (-HC=CH₂)). "Alkoxy" means an alkyl group that is linked via an oxygen (i.e., alkyl-O-), for example methoxy, ethoxy, and sec-butyloxy groups. "Alkylene" means a straight or branched chain, saturated, divalent aliphatic hydrocarbon group (e.g., methylene (-CH₂-) or, propylene (-(CH₂)₃- )). "Cycloalkylene" means a divalent cyclic alkylene group, -C_nH_2n-_x, wherein x is the number of hydrogens replaced by cyclization(s). "Aryl" means an aromatic hydrocarbon group containing the specified number of carbon atoms, such as phenyl, tropone, indanyl, or naphthyl. "Arylene" means a divalent aryl group. "Alkylarylene" means an arylene group substituted with an alkyl group. "Arylalkylene" means an alkylene group substituted with an aryl group (e.g., benzyl). The prefix "halo" means a group or compound including one more of a fluoro, chloro, bromo, or iodo substituent. A combination of different halo groups (e.g., bromo and fluoro), or only chloro groups can be present. The prefix "hetero" means that the compound or group includes at least one ring member that is a heteroatom (e.g., 1, 2, or 3 heteroatom(s)), wherein the heteroatom(s) is each independently N, O, S, Si, or P. "Substituted" means that the compound or group is substituted with at least one (e.g., 1, 2, 3, or 4) substituents that can each independently be a C1-9 alkoxy, a C1-9 haloalkoxy, a nitro (-N0₂), a cyano (-CN), a Ci-6 alkyl sulfonyl (-S(=0)₂-alkyl), a C₆-i2 aryl sulfonyl (-S(=0)₂-aryl)a thiol (-SH), a thiocyano (-SCN), a tosyl (CH3C6H₄S0₂-), a C3-12 cycloalkyl, a C2-12 alkenyl, a C5-12 cycloalkenyl, a C₆-i2 aryl, a C7-13 arylalkylene, a C_4-12 heterocycloalkyl, and a C3-12 heteroaryl instead of hydrogen, provided that the substituted atom's normal valence is not exceeded. The number of carbon atoms indicated in a group is exclusive of any substituents. For example -CH2CH2CN is a C2 alkyl group substituted with a nitrile.

[0114] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

Claims

CLAIMS What is claimed is:

1. A method of preparing a partially crystalline polycarbonate powder containing a phosphorous-containing flame retardant, the method comprising:

dissolving an amorphous polycarbonate and a phosphorous -containing flame retardant in a halogenated alkane solvent to form a solution;

combining the solution with a crystallizing non-solvent that is miscible with the halogenated alkane solvent; and

mixing the combined solution and crystallizing non- solvent under high shear mixing conditions effective to form a partially crystalline polycarbonate precipitate.

2. The method of claim 1 wherein the phosphorous -containing flame retardant is added to the solvent before the polycarbonate is dissolved, or together with the polycarbonate, before the addition of the crystallizing non-solvent.

3. The method of claim 1 wherein the phosphorous-containing flame retardant is added after dissolving the amorphous polycarbonate solution and before the addition of the crystallizing non- solvent.

4. The method of any of claims 1-3, further comprising:

removing the halogenated alkane solvent and the crystallizing non- solvent from the precipitate; and

optionally, drying the precipitate.

5. The method of claim 4, wherein the removing the halogenated alkane solvent and the crystallizing non-solvent from the precipitate comprises filtering the precipitate.

6. The method of claim 4, wherein the removing the halogenated alkane solvent and the crystallizing non-solvent from the precipitate comprises at least partially evaporating the solvents from the precipitate.

7. The method of any of claims 1-6, wherein the halogenated alkane solvent comprises dichloromethane, chloroform, methylene chloride, or a combination comprising at least one of the foregoing.

8. The method of any of claims 1-7, wherein the crystallizing non- solvent comprises acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, or a combination comprising at least one of the foregoing.

9. The method of any of claims 1-8, wherein the high shear mixing comprises mixing at a speed of 2,000 to 50,000 rpm.

10. The method of any of claims 1-9, wherein the amorphous polycarbonate is a polycarbonate homopolymer, a poly(ester-carbonate), a poly(siloxane-carbonate), a poly(ester- siloxane-carbonate), or a combination comprising at least one of the foregoing.

11. The method of any of claims 1-10, wherein the phosphorus-containing flame retardant comprises a poly(phosphonate) homopolymer, a poly(phosphonate-carbonate), resorcinol diphosphate, bisphenol A bis(diphenyl phosphate), triphenyl phosphate, resorcinol bis(diphenyl phosphate), tricresyl phosphate, phenoxyphosphazene, or a combination

comprising at least one of the foregoing.

12. The method of any of claims 1-11, wherein the halogenated alkane solvent is dichloromethane, wherein the crystallizing non- solvent is methyl ethyl ketone, and the removing the halogenated alkane solvent and the crystallizing non-solvent from the precipitate comprises at least partially evaporating the solvents from the precipitate.

13. A partially crystalline polycarbonate powder comprising a phosphorous- containing flame retardant prepared by the method of any of claims 1-12.

14. The partially crystalline polycarbonate powder of claim 13, wherein the polycarbonate is a polycarbonate homopolymer, a poly(carbonate-siloxane), or a combination comprising at least one of the foregoing; wherein the phosphorus -containing flame retardant is a poly(phosphonate) homopolymer, a poly(phosphonate-carbonate), resorcinol diphosphate, bisphenol A bis(diphenyl phosphate), triphenyl phosphate, resorcinol bis(diphenyl phosphate), tricresyl phosphate, phenoxyphosphazene, or a combination comprising at least one of the foregoing; and wherein the amount of the phosphorous-containing flame retardant in the partially crystalline polycarbonate powder product is from 0.1 to 40 wt%, based on the total weight of the partially crystalline polycarbonate powder/phosphorous-containing flame retardant product.

15. A method of preparing a three-dimensional article, the method comprising:

providing a powder composition comprising the partially crystalline polycarbonate powder containing phosphorous-containing flame retardant of any of claims 13-14; and

powder bed fusing the powder composition to form a three-dimensional article.

16. The method of claim 15, wherein the powder bed fusing comprises selective laser sintering.

17. A three-dimensional article made by the method of any of claims 15-16, comprising a plurality of fused layers, preferably comprising at least five fused layers.

18. A method of preparing a unidirectional fiber reinforced polycarbonate composite, the method comprising:

providing an aqueous dispersion of a powder composition comprising a partially crystalline polycarbonate powder containing a phosphorous-containing flame retardant of any of claims 13-14;

passing a continuous fiber tape through said aqueous dispersion to form an unidirectional fiber reinforced polycarbonate composite; and

drying the unidirectional fiber reinforced polycarbonate composite.

19 The method of claim 19, wherein the continuous fiber tape is a continuous carbon tape.

20. The method of claim 18, wherein the Tg of the polycarbonate in the

unidirectional fiber reinforced polycarbonate composite is suppressed 3 to 50 degrees C by the presence of the phosphorous -containing flame retardant.