WO2015162609A1

WO2015162609A1 - Process for the polymerization of pentabromobenzyl (meth) acrylate, the polymer obtained and uses thereof

Info

Publication number: WO2015162609A1
Application number: PCT/IL2015/050418
Authority: WO
Inventors: Dov Beruben; Bertha Croitoru; Dan Kopel; Michael Peled
Original assignee: Bromine Compounds Ltd.
Priority date: 2014-04-23
Filing date: 2015-04-21
Publication date: 2015-10-29

Abstract

The invention provides a solution polymerization process comprising polymerizing the monomer pentabromobenzyl acrylate or pentabromobenzyl methacrylate in water-immiscible organic solvent(s) in the presence of a chain length modifier. Poly (pentabromobenzyl acrylate) comprising chains terminated with isopropylbenzene moiety is also disclosed.

Description

Process for the polymerization of pentabromobenzyl

(meth) acrylate , the polymer obtained and uses thereof

Pentabromobenzyl acrylate is a monomer useful for the production of poly (pentabromobenzyl acrylate) , a polymer which is used as a flame retardant agent in flammable materials. The monomer and the polymer, abbreviated herein PBBMA and PBBPA, respectively, are represented by the following formulas:

PBBMA PBBPA (n=degree of polymerization)

The polymerization of PBBMA to form PBBPA can be accomplished either in bulk (in an extruder at a temperature in the range from 120°C to 290°C as described in US 4, 996, 276), or in solution .

In solution polymerization, solvents must be chosen carefully. US 4,128,709 describes a solution polymerization of PBBMA in methyl glycol. CN 102167762 describes the synthesis of the monomer PBBMA, following which the monomer undergoes polymerization in ethylene glycol monomethyl ether (i.e., the same solvent as in US 4, 128, 709) in the presence of dicumyl peroxide as a free radical initiator. According to US 6,028,156, aprotic solvents such as methyl ethyl ketone, ethyleneglycol dimethylether and dioxane were used for the solution polymerization, achieving reaction yields of not more than 80%. According to WO 2012/140649, the polymerization of the monomer was carried out in halogenated aromatic solvents and specifically in chlorobenzene . The commercially-used process for preparing the presently sold PBBPA (FR-1025) involves the bulk polymerization of PBBMA in a twin-screw extruder. High temperature gel permeation chromatography analysis of commercial FR-1025 by the method set out below indicates weight average molecular weight (Mw) above 400,000 (e.g., 600,000) and high polydispersity index, e.g., above 20. Poly (pentabromobenzyl acrylate) produced according to WO 2012/140649 is characterized by Mw in the range from 200,000 to 600,000 and polydispersity index of less than 15.

In a co-assigned, recently filed patent application (PCT/IL2013/000078≡WO 2014/061010), we reported that the monomer pentabromobenzyl acrylate undergoes polymerization in a solution consisting of a mixture of water-miscible aprotic solvent and water, in the presence of water-soluble initiator and a chain length regulator (i.e., a polymerization inhibitor) , to afford, after a relatively short reaction period, the polymer product in a good yield. The so-formed polymer is characterized by a relatively low molecular weight: the weight average molecular weight is in the range of 4,000 to 199,000, more specifically from 4,000 to 120,000, displaying narrow molecular weight distribution and good thermal stability. It has also been reported that the novel low molecular weight poly (pentabromobenzyl acrylate) exhibits good activity in reducing the flammability of various polymer formulations and is also useful in textile products due to the fact that its glass transition temperature (T_g) matches well with the softening temperature of polyester sieves and drying temperatures employed in the textile industry.

We have now found that low molecular weight poly (pentabromobenzyl acrylate) and poly (pentabromobenzyl methacrylate ) can be formed from the corresponding monomers when the solution polymerization takes place in a water- immiscible organic solvent in the presence a chain length modifier. The monomer may undergo polymerization on heating in the absence of any added free radical initiator, or in the presence of an initiator.

From the standpoint of industrial production, the use of water-immiscible organic solvent in the polymerization reaction offers several advantages. For instance, the synthesis of the PBBMA monomer typically takes place in this type of solvents, and therefore the polymerization reaction according to the invention may immediately succeed the monomer synthesis reaction, obviating the need for monomer isolation prior to polymerization. Furthermore, certain chain length modifiers which demonstrated insufficient activity in aqueous mixtures of organic solvents turn to be highly effective in controlling the molecular weight of the polymer produced in the water-immiscible solvent of the invention. Likewise, commonly used free radical initiators of the peroxide class, which display poor solubility in aqueous medium, are suitable for use as free radical initiators in the process of the invention .

The invention therefore primarily relates to a solution polymerization process comprising polymerizing a monomer of the formula:

(Formula I) wherein R is H or methyl, indicating the monomers pentabromobenzyl acrylate or pentabromobenzyl methacrylate, respectively, in water-immiscible organic solvent (s) in the presence of a chain length modifier.

The monomers employed in the process of the invention are either commercially available (e.g., FR-1025M from ICL-IP) or can be prepared by methods known in the art (see US 6,028,156, WO 2012/140649 and publications mentioned therein) .

In the case of homopolymerization of pentabromobenzyl acrylate or pentabromobenzyl methacrylate , the products formed are poly (pentabromobenzyl acrylate) and poly (pentabromobenzyl methacrylate) , respectively, which may have an end group depending on the chain terminator chosen. It should be noted, however, that the polymerization according to the invention may take place when two or more different monomers are present in the solution to form copolymers with a first repeating unit, which corresponds to either pentabromobenzyl acrylate or pentabromobenzyl methacrylate, and a second repeating unit, which is either capable of undergoing bromination (e.g., a styrene group) or is derived from a monomer which is a bromine-containing polymerisable compound (e.g., brominated styrene and tribromoneopentyl acrylate ester) , again with an end group as set forth above.

By the term "water-immiscible solvent" is meant a solvent with solubility in water of less than 1 gr. per 100 gr . water at room temperature. The water-immiscible solvent is preferably selected from the group consisting of aromatic hydrocarbons, which may be halogenated or non-halogenated. For example, non- halogenated aromatic hydrocarbons such as alkyl-substituted benzenes, e.g., toluene, xylene and mesitylene can be used. Mixtures of the aforementioned solvents can also be used. In general, the solution polymerization of the monomer is carried out with stirring under heating, preferably at a temperature in the range from 70°C to the reflux temperature. It should be noted that the reaction is generally carried out under atmospheric pressure. The weight concentration of the monomer in the water-immiscible solvent is preferably from 1 to 75 wt%, more preferably from 25 to 50 wt%.

The polymerization reaction can be accomplished in the presence of an initiator, namely, a free radical initiator. Preferred are peroxides or hydroperoxides (e.g., dicumyl peroxide) and azo compounds (e.g. those having cyano groups on the carbons attached to the azo linkage) . The amount of the initiator is preferably between 0.01 and 10% w/w based on the monomer, preferably about 0.5 to 5%, e.g. about 1%. However, the experimental results reported below indicate that the presence of a free radical initiator is not obligatory: on heating PBBMA in an aromatic hydrocarbon in the presence of a chain length modifier, a polymer having molecular weight in the range of 10, 000 to 20, 000 can be produced in the absence of an initiator.

As noted above, a chain length modifier/regulator is present in the reaction vessel during polymerization. The amount of the chain length regulators may vary within a broad range, dependent on the solvent chosen and other variables related to the polymerization. 0.01 to 20 parts by weight of a chain length modifier, e.g., 0.01-10 (per 100 parts of the monomer) can be used. In the presence of an initiator, the weight ratio between the initiator and the chain length modifier can vary within a broad range, for example, from 100:1 to 1:50, preferably from 10:1 to 1:10. Thus, the degree of polymerization and molecular weight distribution of poly (pentabromobenzyl acrylate) are controlled by suitably adjusting the amount of the chain length regulator in the solution .

Suitable chain length modifiers are sulfur containing compounds, in particular thiol compounds ( RiSH , wherein Ri indicates an organic moiety, e.g. Ri is an alkyl group composed of not less than 8 carbon atoms) . For this purpose, mercapto-compounds , especially hydrocarbylmercaptans with 8-20 carbon atoms per molecule are preferred. Suitable examples include n-dodecyl mercaptan, n-octyl mercaptan, tertiary dodecyl mercaptan, tertiary nonyl mercaptan, tertiary hexadecyl mercaptan, tertiary octadecyl mercaptan, tertiary eicosyl mercaptan, secondary octyl mercaptan, secondary tridecyl mercaptan, cyclododecyl mercaptan, cyclododecadienyl mercaptan, aryl mercaptan like 1-naphthalene thiol etc. Mixtures of these compounds may also be used.

Molecular weight control of poly (pentabromobenzyl acrylate) or poly (pentabromobenzyl methacrylate ) can also be achieved in the solution polymerization by the use of a modifier such as -methylstyrene .

The polymerization is carried out by charging a reaction vessel with suitable amounts of the solvent, the monomer and the auxiliaries (the initiator and the chain length regulator) , and maintaining the reaction mixture under heating (e.g., at the reflux temperature) for a sufficient time in order to allow the reaction to reach completion. The progress of the reaction can be monitored by high pressure liquid chromatography (HPLC) for the disappearance of the monomer.

Upon completion of the polymerization, the reaction mixture is cooled whereby the product precipitates. The solid polymer is easily separable from the reaction mixture and can be recovered using conventional techniques, e.g., filtration or solvent evaporation etc. The solid polymer is washed with water and dried to constant weight.

The so-formed poly (pentabromobenzyl acrylate) or metacrylate has weight average molecular weight (Mw) in the range from 10,000 to 199,000, more specifically from 10,000 to 198,000, e.g., from 10,000 to 90,000, and number average molecular weight (Mn) in the range from 7,000 to 70,000, (e.g., 10,000 to 70,000) with polydispersity index (PD) , defined as the ratio Mw/Mn, of less than 15, preferably less than 5 and more preferably less than 3 e.g., from 1.5 to 3, based on high temperature gel permeation chromatography (in 1,2,4- trichlorobenzene at 120°C) reported in detail below. The polydispersity index serves as an indication of the breadth of molecular weight distribution of a polymer product.

The low molecular weight poly (pentabromobenzyl acrylate) produced by a solution polymerization in water-immiscible organic solvent in the presence of a chain length modifier exhibits good thermal stability, as shown by thermogravimetric analysis (TGA) , which measures the weight loss of a sample as sample temperature is increased. Weight losses of 5 wt% and 10 wt% are recorded at temperatures above 320°C and above 330°C, respectively, as sample temperature is increased in air at heating rate of 10°C/minute.

The glass transition temperature (T_g) of the low molecular weight poly (pentabromobenzyl acrylate) identified above was measured by differential scanning calorimetry (DSC) . The T_g, indicated by the midpoint temperature in the DSC plot, is in the range of 125 to 155 °C for polymers having weight average molecular weight in the range of 10, 000 to 70, 000 and PD of less than 3. The poly (pentabromobenzyl acrylate) of the invention may comprise chains terminated by a chemical unit which corresponds to the chain length modifier employed in the polymerization reaction. For example, when thiols of the formula RiSH are used to control the growth of the polymer, then the poly (pentabromobenzyl acrylate) comprises chains where the end group (s) is (are) -SRi, wherein Ri is preferably a linear or branched alkyl group composed of not less than 8 carbon atoms, e.g., a linear alkyl group of the formula -

(CH2)_nCH3 wherein n is from 8 to 20. In one embodiment of the invention, the polymer comprises chains which are terminated by at least one end group of the formula -S (CH2) 11CH3, which corresponds to n-dodecyl thiol. When the modifier used in the polymerization reaction is -methylstyrene, then the invention provides poly (pentabromobenzyl acrylate) or poly

(pentabromobenzyl methacrylate ) comprising chains where the end group (s) is (are) isopropylbenzene moiety. Thus, poly

(pentabromobenzyl acrylate) comprising chains terminated with isopropylbenzene moiety forms another aspect of the invention, especially with molecular weight distribution (Mw and PD) , thermal stability (indicated by TGA) and T_g as set out above.

The polymer obtainable by solution polymerization of the invention is of high purity, containing low level of the residual monomer, i.e., less than 1.0% by weight, and even less than 0.5% by weight

The low molecular weight poly (pentabromobenzyl acrylate) of the invention is useful as a flame retardant agent in a flammable material. Accordingly, another aspect of the present invention is a flame-retarded formulation which comprises a flammable material (e.g., a polymer) and the poly (pentabromobenzyl acrylate) of the invention. The formulation of the invention comprises a flame-retarding effective amount of poly (pentabromobenzyl acrylate) . The precise amount of the poly (pentabromobenzyl acrylate) in the formulation is adjusted in order to achieve the desired level of flame retardancy. The flammability characteristics of plastic materials are quantifiable according to the method specified by Underwriter Laboratories standard UL 94. The UL 94 ratings are V-0, V-l, and V-2. A material assigned with the V-0 rating is considered to be the least flammable. For certain applications the lower V-2 rating is acceptable, whereas for other applications the more strict V-l and V-0 ratings are needed. A formulation according to the invention which contains between 4 and 20 wt% bromine would generally satisfy at least the UL 94 V-2 burning test (assuming that the entire bromine content is supplied by poly (pentabromobenzyl acrylate) ) . Unless otherwise indicated, the concentrations indicated herein are weight concentrations calculated relative to the total weight of the formulation.

Other conventional additives may also be included in the polymeric formulation. For example, an inorganic compound (typically a metal oxide) capable of cooperating with brominated flame retarding agents in reducing the flammability of the polymeric formulation is preferably also present in the formulation. A preferred example of a suitable inorganic compound, which is generally considered as an "inorganic synergist", is antimony trioxide.

In addition to the flammable polymer, poly (pentabromobenzyl acrylate) and antimony trioxide, the formulation of this invention may further contain conventional additives, e.g., lubricants, antioxidants (e.g., of hindered phenol or phosphite type) , pigments, UV stabilizers and heat stabilizers. The concentration of each of the conventional additives listed above is typically in the range of 0.05 to 10 wt%.

The poly (pentabromobenzyl acrylate) of the invention demonstrates especially good activity in reducing the flammability of polypropylene (PP) and polybutylene terephthlate (PBT) .

Polymer formulation of the invention are produced by melt- mixing the components, e.g., in a co-kneader or twin screw extruder, wherein the mixing temperature may be in the range from 200 to 300°C. The resultant compositions, in the form or granules or pellets, are dried and are suitable for feed to an article shaping process, such as injection molding. Articles molded from the polymer compositions form another aspect of the invention.

Examples

Methods

High Temperature Gel Permeation Chromatography:

HT GPC instrument (Malvern Instruments Ltd.) that includes HT- GPC Viscotek module 350A, two VE 1122 solvent delivery systems, HT stirred autosampler 430 model and OmniSec 4.7.0 analysis software was used to determine the molecular weight distributions of the polymer product. The instrument is equipped with refractive index (RI), viscometric (Vise), Low Angle Light Scattering (LALS) and Right Angle Light Scattering (RALS) detectors. Samples were dissolved in 1,2,4- trichlorobenzene (TCB) , stabilized with 2 , 6-Di-tert-butyl-4- methyl-phenol (BHT) , at 120°C. Ca . 8 mg/ml PBBPA solutions were prepared. 200μL of the sample solution were injected into GPC columns. A series of two columns (2xTosoh TSK-GEL GMHhr-H ( S ) HT 7.8mmx30.0cm, 13μπι GPC columns) connected consecutively was used. TCB at 120°C was used as the mobile phase with a flow rate of 1.0 ml/min. Polystyrene Calibration Standards kit TDS 2000 were used for the calibration of the HT GPC. OmniSec software was used for the calculation of the Mn and Mw of the tested samples.

Preparation of the standard solutions:

1) Add 0.5 gram of BHT per 1 liter of TCB and shake well.

2) Filter TCB stabilized solution through GF/F 47mm diameter, 0.7μπι glass microfiber filter Cat No. 1825047.

3) Use Malvern PS standards kit for calibration and verification of system suitability.

4) Add exactly 10 ml of stabilized TCB solution to both (99kDa and 235kDa) polystyrene standard vials. Add magnetic stirrer.

5) Hold standard solution stirred at 120°C at least 30 minutes prior to injection. Preparation of the sample solution:

1) Weigh 80 mg of sample into HT-GPC glass vials.

2) Add magnetic stirrer and stir at 120°C at least 30 minutes prior to injection.

Injection volume was 0.2 ml and run time was 60 minutes. TGA analysis:

The TGA analysis was performed using a Mettler-Toledo instrument model TGA850. 10 mg sample were heated in aluminum oxide crucible from room temperature to about 650°C with a heating rate of 10°C/min in an air atmosphere.

DSC analysis:

The DSC analysis was performed using a Mettler-Toledo instrument model DSC821e. Samples were heated in hermetically sealed aluminum crucibles from room temperature to about 210°C at a heating rate of 20°C/min.

Example 1

Polymerization of pentabromobenzyl acrylate

Reaction solvent: toluene

Initiator: dicumyl peroxide

Chain length regulator: a-methylstyrene

A 250ml reactor equipped with mechanical stirrer, condenser and thermometer was charged with 20g of PBBMA and 40 ml of toluene. The mixture was heated to 100°C, followed after 5 minutes by the successive addition of 2g of a-methylstyrene and 0.2g of dicumylperoxide . The reaction mixture was heated to 110°C. The reaction was monitored by HPLC, to determine the consumption of the PBBMA. After 22 hours the reaction reached completion. The reaction mass was cooled to room temperature. The product was separated from the reaction mass by filtration, washed with water and dried to constant weight in an oven vacuum at 120°C, giving PBBPA in almost quantitative yield .

TGA analysis indicates that under heating rate of 10°C/min in an air atmosphere, the polymer undergoes the following weight losses :

Table 1

DSC analysis indicates that the T_g is at 153°C. The molecular weight was determined by HT GPC as set forth, indicating Mw of 49, 100 and Mn of 22, 000 with PD of 2.2. The bromine content, determinate by parrbomb method, is 64.4%. The residual monomer was less than 0.5%.

Example 2

Polymerization of pentabromobenzyl acrylate

Reaction solvent: toluene

Initiator: dicumyl peroxide

Chain length regulator: dodecanethiol

The procedure of Example 1 was repeated, but this time the chain length regulator employed was dodecanethiol, in an amount of 0.2g. The TGA profile of the polymer obtained, its T_g and molecular weights are set out below.

Table 2

temperature T1=297°C T2=323°C T3=334°C

% weight loss 2.0 5.0 10.0 T_g was estimated at 132°C; Mw=27,400 and Mn=12,900, such that the PD is 2.12. The bromine content, determined by parrbomb, is 70%.

Example 3

Polymerization of pentabromobenzyl methacrylate

Reaction solvent: toluene

Initiator: dicumyl peroxide

Chain length regulator: dodecanethiol

The procedure of Example 2 was repeated, but this time the monomer which underwent polymerization was pentabromobenzyl methacrylate. The TGA profile of the polymer obtained, its T_g and molecular weights are set out below.

Table 3

DSC analysis indicates that the T_g is 193°C. Mw=63,300 and Mn= 28,300, such that the PD is 2.23. The bromine content, determined by parrbomb, is 67.3%.

Example 4 (comparative)

Polymerization of pentabromobenzyl methacrylate

Reaction solvent: toluene

Initiator: dicumyl peroxide

The procedure of Example 3 was repeated, but this time in the absence of a chain length regulator. The TGA profile of the polymer obtained, its T_g and molecular weights are set out below . Table 4

DSC analysis indicates that the T_g is 178°C. Mw=325, 000 and Mn= 70,800, such that the PD is 4.59.

Example 5

Polymerization of pentabromobenzyl acrylate

Reaction solvent: mesitylene

Chain length regulator: a-methylstyrene

A 250ml reactor equipped with mechanical stirrer, condenser and thermometer was charged with 20g of PBBMA and 40 ml of mesitylene. The mixture was heated to 100°C, followed after 5 min by the addition of 2g of a-methylstyrene. The reaction mixture was heated to 160°C. The reaction was monitored by HPLC, to determine the consumption of the PBBMA. After 5 hours, the reaction reached completion. The reaction mass was cooled to room temperature. The product was separated from the reaction mass by filtration, washed with water and dried to constant weight in an oven vacuum at 120°C, giving PBBPA in almost quantitative yield.

Table 5

DSC analysis indicates that the Tg is at 124°C. The molecular weight was determined by HT GPC as set forth, indicating Mw of 15, 500 and Mn of 8, 300 with PD of 1.86. The bromine content, determinated by parrbomb method, is 63.5%. The residual monomer was less than 0.5%.

Claims

1) A solution polymerization process comprising polymerizing a monomer of the formula: ^CH₂

2) A solution polymerization process according to claim 1, wherein the water-immiscible organic solvent is selected from the group consisting of non-halogenated aromatic hydrocarbons.

3) A solution polymerization process according to claim 2, wherein the non-halogenated aromatic hydrocarbon solvent is selected from the group consisting of alkyl-substituted benzene compounds and mixture thereof.

4) A solution polymerization process according to claim 3, wherein the alkyl-substituted benzene is selected from the group consisting of toluene, mesitylene and mixtures thereof.

5) A process according to any one of claims 1 to 4, wherein the monomer undergoes polymerization on heating in the absence of any added free radical initiator. 6) A process according to any one of claims 1 to 4, wherein the monomer undergoes polymerization on heating in the presence of a free radical initiator.

7) A process according to any one of claims 1 to 6, wherein the chain length modifier is selected from the group consisting of thiol of the formula RiSH , wherein Ri indicates an organic moiety.

8) A process according to claim 7, wherein Ri is an alkyl group composed of not less than 8 carbon atoms.

9) A process according to any one of claims 1 to 6, wherein the chain length modifier is -methylstyrene .

10) A process according to any one of the preceding claims, wherein the monomer undergoing polymerization is pentabromobenzyl acrylate.

11) Poly (pentabromobenzyl acrylate) comprising chains terminated with isopropylbenzene moiety, having weight average molecular weight (Mw) in the range from 10,000 to 90,000 and polydispersity index (PD) of less than 5, based on high temperature gel permeation chromatography (in 1,2,4- trichlorobenzene at 120°C) .

12) Poly (pentabromobenzyl acrylate) according to claim 11 showing weight losses of 5 wt% and 10 wt% at temperatures above 320°C and 330°C, respectively, when subjected to thermogravimetric analysis as sample temperature is increased in air at heating rate of 10°C/minute.