WO1992017516A1

WO1992017516A1 - Process for curing polyquinoline polymers and compositions thereof

Info

Publication number: WO1992017516A1
Application number: PCT/US1992/002494
Authority: WO
Inventors: Neil Hyer Hendricks; Robert Raymond GAGNÉ; Matthew Louis Morrocco, Iii
Original assignee: Maxdem Incorporated
Priority date: 1991-03-28
Filing date: 1992-03-27
Publication date: 1992-10-15

Abstract

This invention relates to polyquinoline polymers which have improved solvent resistance, and to the process for producing the solvent-resistant polymers. The process includes the initial preparation of the polymer by, in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting en AB monomer alone or with an AA or a BB monomer, to provide a polymer. The polymer is then heated to a temperature of greater than about 150 °C; preferably, from about 200 °C to about 500 °C, for a period of time sufficient to increase the solvent resistance of the polymer.

Description

PROCESS FOR CURING POLYQUINOLINE POLYMERS AND

COMPOSITIONS THEREOF

Field of the Invention:

This invention relates to a process incorporating the use of heat to improve the solvent resistance of polyquinoline polymers, and to the compositions resulting from the process.

Background of the Invention: Many types of thermally stable (heat resistant) polymers are used in the form of films, fibers, coatings, resins, molded parts and composites. Quite often, this wide range of product forms is processed from solution, i.e., from a mixture consisting of the polymer dissolved in a liquid solvent. Upon processing the finished product from solution, residual solvent is normally removed by evaporation, leaving behind the polymer in its final form as a film or fiber or the like. The fabricated polymer is, however, still soluble in the solvent from which it was processed and, most likely, in other solvents as well. This is often a serious drawback to the utility of the finished product polymer, since inadvertent contact with such solvents may degrade the performance (e.g. strength, electrical properties, etc.), appearance, or other aspects of the utility of the polymer. Some thermoplastic polymers which have a high solvent resistance can be formed directly from the melt without using a solvent system. For example, such thermoplastics may be melt extruded, injection or compression molded, blow molded, or processed by thermoforming techniques. Fabrication .from the melt, however, is often not the preferred approach for forming films and coatings because higher quality, more uniform, films and coatings are produced from solution. In addition, many heat resistant polymers do not possess the appropriate melting and/or rheological characteristics needed to be processed from the melt in a practical fashion. Often times, the melting temperature of a heat resistant polymer contemplated for use as a coating is sufficiently high so that damage to the object which is to be coated would occur using the melt process.

Another common method of obtaining fabricated thermally stable, solvent resistant films, coatings, fibers, etc., is to process a prepolymer from solution. The term "prepolymer" as used herein is a polymer entity which can be converted, for example, by chemical, photochemical or thermal treatment, to a chemically different polymer which is inherently more solvent resistant than the prepolymer. An example of such a prepolymer is a polyamic acid, which is chemically or thermally converted into a heat resistant polyimide after it is initially formed into a film, fiber, or coating. Fabrication of thermally stable, solvent resistant polymers by conversion of a prepolymer to its final polymer form has certain drawbacks. For example, the conversion of one distinct polymer structure into another is a relatively complex process, which can often require precisely controlled conditions in order to obtain a consistent result from one attempt to the next. Since, during the course of this conversion, factors such as viscosity, density, and morphology can change dramatically, problems can occur such as incomplete conversion and unacceptable shrinkage. In addition, since conversion of a prepolymer to final polymer usually involves the evolution of significant quantities of small molecules (for example, water or alcohol) , bubbles or other irregularities in the final fabricated polymer forms often occur. Prepolymers are inherently chemically reactive and often change in chemical composition (and, thus, important properties, including solution viscosity) during storage, e.g. , after preparation and prior to fabrication in the final polymer. Once again, this leads to problems in obtaining reproducible results from one fabrication attempt to the next.

A third common method of obtaining fabricated, thermally stable, solvent resistant polymers is by using what are commonly referred to as thermosetting resins. Typically, these are soluble materials which are initially processed from solvents into films, fibers, coatings, or the like, in a non-polymeric (e.g., monomeric or oligomeric) state. Upon addition of, for example, catalysts, radiation, or heat, the monomeric or oligomeric thermoset materials crosslink to form a thermally stable, solvent resistant polymer. An example of a thermosetting system is an oligomeric bis- (epoxide) , which is converted to a highly crosslinked, solvent resistant polymer by a thermally induced chemical reaction with a catalyst, such as an amine or phenol.

Thermosetting polymer systems tend to suffer from some of the same drawbacks that are associated with the polymers produced by the above-described prepolymer process. Thermosetting resins tend to react during storage, and, thus, reproducibility in the crosslinked films, fibers, coatings, and molded products is difficult to achieve. Inhibiting thermoset resins from reaction during storage often requires refrigeration, which is expensive. Additionally, thermosetting resins often exhibit a high degree of shrinkage during the crosslinking process, and, thus, they are not suitable for many applications where dimensions are critical. Although thermoset polymers often exhibit good solvent resistance, they tend to be relatively polar and, thus, absorb significant quantities of moisture, resulting in an increase of the dielectric constant and degradation of other electrical properties, in failure of adhesive bonds and in dimension changes in the finished parts. Finally, highly crosslinked structures typically do not possess the required combinations of properties, for example, the mechanical, optical and electrical properties, required for many applications.

Although polyquinoline polymers are known to be useful as coating materials, films and fibers, and the like, the resistance of such polymers to solvents may not be as high as desired. As used herein, a "polyquinoline" or "polyquinoline polymer" is a polymer which incorporates at least 10% polyquinoline groups or units by weight compared to the total weight of the polymer.

Polyquinolines are typically prepared by condensation polymerization of monomers which are called AA, BB, and AB monomers based on the functionality of their end groups. In general, an A group condenses with a B group to form one or more linking bonds. In one case, two monomers are used; a bisaminoketone and a bisketomethylene. These A and B groups condense to form a quinoline group. The bisaminoketone is called an AA monomer herein and the bisketomethylene is called a BB monomer. In a second case, a single monomer can be used which incorporates an aminoketone group on one end and a ketomethylene group on its other end. This monomer is called an AB monomer herein. For AA/BB-type polymers, the highest molecular weight is obtained when equal molar amounts of the two monomers are reacted together. If one monomer is in excess, the molecular weight will be limited according to relations well known in the art, and the resulting polymer will have chain ends terminated with the functionality of the excess monomer. For example, when the AA monomer is a bisaminoketone and excess AA monomer is used, the polymer ends will be terminated with an aminoketone function. Conversely, when the BB monomer is a bisketomethylene and excess BB monomer is used, the polymer ends will be terminated with a ketomethylene function. For AB type polymers, monomer offset is not possible; however, molecular weight may still be controlled by addition of either an AA- or a BB-type monomer. If an AA-type monomer is added, the resulting polymer chain ends will have A-type end groups or functionality. Conversely, if a type BB monomer is added, the resulting polymer will have B-type end groups or functionality. As is mentioned above, in one synthetic route, the type A functionality is an aminoketone, and the type B functionality is a ketomethylene. However, other routes to polyquinolines are possible where A and B represent other functionalities. For example, A might represent an amine and B an ester, where one of the monomers contains a preformed quinoline group, to give a polyquinoline amide.

We have found that the molecular weight of polyquinolines, like other condensation polymers, may be controlled by adjusting the monomer balance and/or by adding endcappers during_, polymerization. For example, where the monomer balance is adjusted in an AA/BB-type polymer system, preferably the endcapper will be added in such an amount sufficient to compensate for the monomer imbalance. For AA/BB- and AB-type polymers, endcappers may be of a type AE or BE, where E is the end group and may be either active or inactive. E is not reactive with A- or B-type groups. For example, 3- aminoacetophenone is considered an AE-type endcapper and 3-benzoylbenzidine is considered a BE-type endcapper. When one reactive group of a difunctional monomer adds to a growing chain, the second reactive group is still available for continued growth. When an endcapper reacts with a growing chain end, growth stops because the endcapper has only one group that is reactive with the A- or B-type groups on the chain. Ideally, at the end of the polymerization reaction when endcappers are used, the ends of all chains are terminated with endcappers. In practice, impurities or inadvertent monomer imbalance also limit molecular weight, and some chains may be terminated with the monomer which was in excess or by unknown groups from impurities.

Attempts have been made to improve the solvent resistance of polyquinolines. For example, polyquinolines endcapped with biphenylene groups and heated in the presence of a catalyst to enhance solvent resistance are described in U.S. Patent No. 4,507,462, which issued to J. . Stille on March 26, 1985. As further described in U.S. Patent No. 4,507,462 and in J. P. Droske and J. K. Stille, Macromolecules, 17, 1-10 (1984) , polyquinoline polymers with chemically unreactive end groups, such as phenyl, are not expected to cure, i.e., are not expected to improve in solvent resistance in response to heating. Preparation of polyquinoline polymers with reactive bisphenylene end groups can be complex and costly. The biphenylene endcappers, for example, are prepared from explosive intermediates and in low yield.

In another example of an attempt to improve the solvent resistance of polyquinoline polymers, hexaarylbenzene units were incorporated into a polyquinoline backbone structure in order to provide a site which could enter into a thermal crosslinking reaction. Using such hexaarylbenzene units for crosslinking polyquinoline polymers is described in G. Baker and J. Stille et al, "Hexaarylbenzene Units as Crosslinking Sites for Polyquinolines," Macromolecules. 12., 369-373 (1979) . An aromatic nucleus substituted in at least four adjacent positions with phenyl groups, for example, 1,2,3,4-tetra-phenylphenyl but not 1,2,3,5- tetra-phenylphenyl, is called a "polyphenylated group" herein. Thus, the monomer units disclosed in the article incorporate such polyphenylated groups. In yet another example of crosslinked polyquinoline polymers, the polymers are formed from oligomers prepared with cyanate endcaps. J. Stille et al, "The Cross-linking of Thermally Stable Aromatic Polymers by Aryl Cyanate Cyclotrimerization," Macromolecules. 9. 516-523 (1976). Although the polymers produced by the methods disclosed in the two above-referenced articles may have enhanced solvent resistance, they are highly crosslinked and, thus, suffer from the deficiencies noted above for other crosslinked polymers; namely, a high degree of shrinkage during the crosslinking process, and, thus, may not be suitable for application where dimensions are critical and may not possess the desired optical, mechanical and electrical properties.

One significant disadvantage of using monomers comprising polyphenylated groups and biphenylene endcapped polymers is the undesirably high expense of adding these exotic crosslinking groups. Use of monomers or endcappers bearing functional groups, such as biphenylene, aryl cyanates, polyphenylated groups, and the like, also require extra synthetic steps which further adds to the cost of the polymer.

There is, therefore, a need in the art for a process for producing stable polyquinoline polymers which can be fabricated from common polymer solvents into useful forms such as films, coatings, fibers, molded parts and composites, and which can then be further processed inexpensively and efficiently to render the polymer resistant to the processing solvent, as well as to a wide range of additional solvents. The polyquinoline polymers desirably have mechanical, optical and electrical properties which are more uniform and more desirable than similar properties of thermoset polymers, polymers produced from the conversion of prepolymers into final polymers, or highly crosslinked polyquinolines.

summary of the Invention:

In one exemplary embodiment of practice of this invention, a process for producing a polyquinoline polymer having enhanced solvent resistance is provided. The process comprises, in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer, to thereby provide a polyquinoline polymer, wherein said monomers do not incorporate a polyphenylated group. The polyquinoline polymer is heated, preferably, to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the polymer. More preferably, the temperature is from about 200°C to about 500^βC. If desired, heating the polyquinoline polymer is conducted after the polymer has been formed into a film, a coating, a fiber, a molded article, or a composite. Also contemplated by the invention is the solvent resistant polymer produced by the aforementioned process.

In another embodiment of practice of the present invention, a process for producing a composite comprising a polyquinoline polymer of enhanced solvent resistance is provided. The process includes the steps of, in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer to provide a polyquinoline polymer, wherein the monomers do not incorporate a polyphenylated group. A composite of the polyquinoline polymer is formed with a material selected from the group consisting of reinforcing fibers and particulate fillers and mixtures thereof. The composite is heated, preferably, to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the composite. More preferably, the temperature is from about 200°C to about 500°C. In yet another embodiment of practice of the present invention, a process for producing a polyquinoline polymer having enhanced solvent resistance comprises the steps of preparing an amine-endcapped polyquinoline polymer and heating the amine-endcapped polyquinoline polymer, preferably, to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the polymer. More preferably, the temperature is from about 200"C to about 500"C.

In another embodiment of practice of the present invention, a process for preparing a solvent resistant dielectric coating on a substrate is provided. The process includes the steps of, in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer, to thereby provide a polyquinoline polymer, wherein the monomers do not incorporate a polyphenylated group. A solution comprising the polyquinoline polymer and an organic or acidic solvent is coated onto the electronic substrate. The polyquinoline-coated substrate is then heated, preferably, to a temperature of greater than about 150^βC for a period of time sufficient to increase the solvent resistance of the polyquinoline polymer. More preferably, the temperature is from about 200°C to about 500^βC.

In yet a further embodiment of practice of the present invention, a multi-chip module comprising multiple layers of polyquinoline dielectric onto which electrical conducting lines are deposited is provided. The multi-chip module is formed by the steps of providing a polyquinoline polymer by reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or in combination with an AA monomer or a BB monomer. Each such polyquinoline dielectric layer is then formed by depositing the polyquinoline polymer onto a surface of the multi-chip module. The polyquinoline dielectric layer is then heated, preferably, to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the polymer. More preferably, the temperature is from about 200°C to about 500°C.

Brief Description of the Drawing:

These and other features, aspects, and advantages of the present invention will be more fully understood when considered in connection with the following detailed description, appended claims and accompanying drawing, wherein the drawing is a fragmentary semi- schematic, cross-sectional side view of a multi-chip module provided in accordance with practice of the present invention.

Detailed Description:

The polyquinoline polymers prepared in accordance with practice of the present invention are thermally stable and relatively insoluble in most common organic solvents. The characteristic of insolubility is imparted to the polymer by curing (heat treating) the polyquinoline at a selected temperature for a selected period of time as is described below in greater detail. The term "curing" as used herein is a process by which a material soluble in certain solvents is rendered insoluble, or at least less soluble, in some or all of those solvents by heating the material to a selected temperature for a selected period of time. Curing may be incomplete or partial, such that some quantitative measure of solubility is changed after curing. Some processes may exploit partial curing or curing in several steps or stages. Note that curing as used herein does not imply polymerization. The material to be cured is typically polymeric but soluble before the cure and less soluble after curing.

Contrary to what is thought in the art, we have found, surprisingly, that functional endcappers such as biphenylene or cyanate groups or polyphenylated groups for crosslinking are not required to be present in order that heat treatment of polyquinoline polymers results in enhanced insolubility, i.e., in enhanced or improved solvent resistance. We have discovered that simple offsetting of monomer balance, with no added endcappers and without incorporating groups into the monomers or polymers which would result in crosslinking reactions, provides sufficient reactivity jto the polyquinoline for effective heat treating.

In addition to our surprising discovery that functional endcappers or added crosslinking groups are not required to be present to provide polyquinoline polymers that can be heat treated to enhance their solvent resistance, we have found that polyquinolines with relatively inert end groups, such as phenyl and quinolinyl, can be made to cure with the appropriate thermal cure cycle.

We have also discovered that, when polyquinolines are prepared by employing equimolar amounts of AA and BB monomers, which produce polyquinolines which contain statistical distributions of A- and B-type end groups, the use of heat treatment in accordance with practice of the present invention increases solvent resistance of the polymer. Even when the polyquinoline polymers which are produced are of high molecular weight (greater than about 80,000), surprisingly, the use of heat treatment in accordance with the present invention increases the solvent resistance of the polymer. In one exemplary embodiment of practice of the present invention, the polyquinoline polymers are produced from AA, BB, and AB monomers as disclosed in J. K. Stille, "Polyquinolines," Macromolecules. 14, 870- 880 (1981), and P. D. Sybert et al, "Synthesis and Properties ofRigid-Rod Polyquinolines," Macromolecules. 14, 493-502 (1981) , and in U.S. Patent Applications Nos. 07/723,555, filed November 18, 1988 by J. K. Stille (now deceased) and 07/568,059, filed August 16, 1990 by Neil H. Hendricks. AA and BB monomers and the production of polyquinoline polymers from such monomers is also disclosed in U.S. Patent No. 4,000,187 issued to J. Stille on December 28, 1976. The two above-mentioned articles, U.S. Patent Applications Nos. 07/273,555 and 07/568,059, and U.S. Patent No. 4,000,187 are incorporated herein in their entirety by this reference.

In accordance with the present invention, new, solvent resistant polymer compositions are obtained by heating relatively soluble polyquinoline polymers, such as those disclosed in the aforementioned articles, patents and patent applications (or useful forms, such as films, fibers, coatings, or the like, fabricated therefrom) , to a temperature of greater than about 150"C for a period of time sufficient to improve solvent resistance. Curing is completed in shorter times when higher temperatures are used, and vice versa. The upper limit of temperature to which the polyquinoline polymers are preferably heated to effect curing is a temperature which will not undesirably degrade the properties of the polymer. Although the upper limit for practical purposes is about 500"C, higher temperatures can be used, if desired. For example, temperatures of up to about 650°C-700°C can be used for relatively short periods of time, so long as the polymer is not degraded to an undesirable extent. Typical, non-limiting time/temperature combinations required to induce (e.g., enhance) solvent resistance in the polyquinolines (or useful forms fabricated therefrom) include, for example: (a) 200°C for 5 to 100 hours; (b) 250"C for 5 to 50 hours; (c) 300°C for from 2 to 25 hours; (d) 350°C for from 1 to 50 hours; (e) 375°C for from 0.5 to 50 hours; (f) 400°C for from 0.5 to 10 hours; (g) 450°C for from 0.1 to 1 hour; (h) 500°C for from 0.1 to 1 hour. It is noted that curing for excessive periods of time at extremely high temperatures, for example above about 500°C for 200 hours or so, tends to thermally degrade the polyquinolines, thus detracting from the utility of the curing process and the compositions resulting therefrom. If heating is at less than about 150"C, the improvement in solvent resistance is slower than desired.

The method of heating polyquinoline polymers to effect curing in accordance with practice of the present invention is not critical. For example, such heating can be done in a standard oven, a vacuum oven, on a hot plate, in an autoclave, by radiant heating, in a heated press, and by laser treatment, or the like. The exact behavior of any given batch of polyquinoline polymer is somewhat history dependent, and the precise time temperature recipe needed for curing to a desired level may vary. We have found that curing several small film samples over a range of temperatures, followed by testing the solubility of each sample is an efficient method of establishing a cure schedule. Solubility may be tested using the method of J. K. Stille, U.S. 4,507,462, where solubility is defined as:

Solvents other than CHC1₃ may be substituted in the solubility test as required by end use. For example, if the end use might place the polyquinoline polymer in contact with toluene, then toluene can replace CHC1₃ in the solubility test, if desired.

We have found it useful to test new or modified polyquinolines by heat treating samples for 2 hr at increasingly higher temperatures (typically 50^βc increments) until a desired degree of solvent resistance is achieved. Polyquinolines which contain thermally labile groups, either in the main chain or in a side chain, may decompose or degrade before the desired degree of solvent resistance is achieved. We have found that, in addition to the quinoline group itself, the following groups possess high enough thermal stability so that, if added to the quinoline moiety, sufficient solvent resistance can be obtained without polymer decomposition: phenyl, phenylene, aryl, keto, phenoxy, sulfone, hexafluoroisopropylidene, diphenylether, diphenylsulfone, diphenylsilyl, and the like. Introduction of amino end groups by endcapping, or introduction of aminoketone end groups by monomer imbalance, will lower the temperature required for the heat treatment process and allow a greater variety of main chain and side chain functional groups to be used.

Polyquinoline films on a support (e.g. spin-coated onto silicon or alumina) may be tested for solubility by placing a drop of solvent on the heat treated film and allowing the solvent drop to evaporate (typically in an oven) . Cured film will show no change; uncured film will be attacked by the solvent. This method is applied in Example 5 below. Several such tests of curing at increasingly higher temperature and/or longer time will quickly establish a curing schedule.

In another embodiment of the present invention, a process for obtaining polyquinolines and useful fabricated forms derived therefrom includes subjecting films, fibers, coatings, molded parts and composites formed from polymers provided in accordance with practice of the invention to typical, non-limiting time/temperature combinations such as those described above.

In an exemplary embodiment of practice of the present invention, the process for producing a polyquinoline polymer comprises, in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer, to thereby provide a polyquinoline polymer. The monomers provided in accordance with practice of the present invention do not incorporate a polyphenylated group. The phrase "in the absence of an added endcapper" as used herein means that no materials are added to the reaction mixtures along with the AA, BB or AB monomers in order to provide endcapping groups. Thus, the polymers formed in accordance with the present invention do not incorporate groups that have been added to enhance crosslinking which might take place upon heating or in the presence of an added catalyst, for example.

In an exemplary embodiment of practice of the present invention, the polyquinoline polymer comprises recurring units of the following structural formula:

wherein X and Y are separately selected from the group consisting of nil, -0-, -CO-, -S0₂-, -OArO-, -0Ar6FAr0-, -6F- and -OArCOArO-, wherein Ar is an arylene group having 6 to 18 carbons and 6F is hexafluoro- isopropylidene.

The polyquinoline polymers provided by the polymerization of the AA, BB and AB monomers in accordance with the present invention are heated, preferably, to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the polymer. More preferably, the polymer is heated to from about 200"C to about 500"C. As is described above, preferred time/temperature profiles useful for heating the polymer to improve its solvent resistance can be developed by data from solubility tests as are described above.

Usually, heating of the polyquinoline polymer of the present invention is conducted after the polymer has been formed into its final shape, i.e., after it has been formed into a film, a coating, a fiber, a molded article, or a composite. 'However, partial curing of the polymer may be accomplished by heating prior to forming it into its final configuration. Final curing is then accomplished in a subsequent heating step.

In another exemplary embodiment of practice of the present invention, a process is provided for producing a finished polyquinoline polymer that has enhanced solvent resistance by initially preparing an a ine- endcapped polyquinoline polymer. In one example of providing such an amine-endcapped polyquinoline polymer, the polymer is- prepared by reacting a mixture of an AA monomer, a BB monomer, or an AB monomer (either alone or in combination with an AA or a BB monomer) , and an endcapper selected from the group consisting of an AE and a BE endcapper, where E is a free or protected a ine group. Examples of AE endcappers which may be used are benzoyl-l,4-phenylenediamine and 3-benzoylbenzidine. Examples of BE endcappers which may be used are 3- aminoacetophenone, 4-succinimidoacetophenone, and 4- aminodeoxybenzoin. The amine-endcapped polyquinoline polymer is then heated to a temperature of greater than about 150°C; preferably, from about 200°C to about 500^βC, for a period of time sufficient to increase its solvent resistance.

In another exemplary embodiment of practice of the present invention, a process is provided for producing a composite comprising a polyquinoline polymer of enhanced solvent resistance. The process includes the steps of, in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer, to provide a polyquinoline polymer, wherein the monomers do not incorporate a polyphenylated group. A composite of the polyquinoline polymer is formed with a material selected from a group consisting of reinforcing fibers and particulate fillers and mixtures thereof. Non-limiting examples of such reinforcing fibers useful in accordance with practice of the practice of the present invention are glass, carbon, boron, silicon carbide, tungsten, and the like. Non-limiting examples of particulate fillers useful for forming the composites of the present invention are carbon black, silica and talc.

In one embodiment, the composite is initially formed and is then heated to a temperature of greater than about 150"C; preferably, from about 200°C to about 500°C, for a period of time sufficient to increase the solvent resistance of the polyquinoline polymer and, hence, the solvent resistance of the composite per se. In another exemplary embodiment of practice of the present invention, a process is provided for preparing a solvent resistant organic dielectric coating on a substrate. Such substrates can include, for example, silicon wafers, silicon-dioxide-coated silicon wafers, aluminum wafers, aluminum-oxide-coated silicon wafers, ceramics, gallium arsenide, silicon nitride, aluminum nitride, copper, aluminum and gold, and the like. The organic dielectric coating comprises a polyquinoline polymer that is formed, in the absence of an added endcapper, by reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer, to thereby provide the polymer. A solution comprising the polyquinoline polymer and an organic or acidic solvent is coated onto the electronic substrate. Preferably, the percent of the polyquinoline polymer in solution is from about 0.1% to about 60% by weight of polyquinoline polymer compared to the total weight of the solution. More preferably, the percent of the polyquinoline polymer is from about 5% to about 50% by weight. If the solution contains less than about 0.1% polyquinoline polymer, the coating will be undesirably thin; whereas, if the solution contains greater than about 60%, its viscosity will be greater than desired. The polyquinoline-coated substrate is then heated to a temperature of greater than about 150"C; preferably, from about 200°C to about 500°c, for a period of time sufficient to increase the solvent resistance of the polyquinoline polymer dielectric coating. Polyquinoline polymers provided in accordance with practice of the present invention are useful, for example, for the fabrication of multi-chip modules. Referring to the drawing, a semi-schematic cross- sectional side view of a multi-chip module 10 is shown. Such multi-chip modules are wiring boards designed to hold several integrated circuit chips (IC's) (not shown) directly without the IC's first being packaged into individual chip carriers. The multi-chip module is typically (but not necessarily) fabricated using photolithographic techniques similar to those used in IC fabrication. The following procedure outlining ulti- chip module fabrication is illustrative and many variations are known in the art and may be used with the present invention.

A substrate 12, typically a four- or six-inch silicon or alumina wafer having a plurality of resistors 13 on its surface, is spin-coated with a layer of polyquinoline 14 provided by the process of the present invention. Solvent from the spin-coating process is removed in an oven, and the polyquinoline layer is cured by heating to a selected temperature for a selected period of time as described above to enhance the solvent resistance of the polyquinoline layer. Vias (not shown) are cut through the polymer by any of several techniques, for example, laser drilling or patterning and etching. A layer of metal 16, typically copper or aluminum, is deposited and patterned using techniques known in the art to form metal lines with a portion of the metal 16a extending through the via and contacting the resistors 13. A second layer of polyquinoline 18 provided by the process of the present invention is spin-coated, dried and cured, completely covering the underlying metal. Vias are cut as above, and a second layer of metal is deposited and patterned. Additional layers of polymer 20 and metal 22 are added by repeating the above procedure. In some processes, it may be desirable to use adhesion promoters to enhance adhesion of the polymer to the silicon substrate or subsequent layers, or to plate the metal lines with chromium or gold before the application of the polymer.

The following examples are illustrative of the present invention, but are not considered limiting thereof in any way. EXAMPLE 1

Polymerization of 2,2'-bis[4-(4-acetγlphenoxy_phenyl~) hexafluoropropane and 3,3'-dibenzoyl-4,4'- diaminobiphenyl in a Mixture of m-cresol and Diphenyl Phosphate

A solution containing 1.9999 grams (3.493 mmol) of 2,2 '-bis[4-(acetylphenoxy)phenyl] hexafluoropropane, 1.3710 grams (3.493 mmol) 3,3'-dibenzoyl-4,4'- diaminobiphenyl, 4.1 milliliters of m-cresol and 21.85 grams of diphenyl phosphate was prepared by combining the reagents in a 100 illiliter three-neck round bottom flask equipped with a reflux condenser, a nitrogen inlet and a mechanical stirrer. The mixture was heated to a constant temperature of approximately 90"C with stirring. After approximately 72 hours, the polymer was precipitated by pouring the solution into a coagulation bath consisting of 90% anhydrous ethanol and 10% triethylamine. The polymer was isolated by filtration, redissolved in chloroform, and further purified by allowing it to reprecipitate by dripping the chloroform solution into a fresh coagulation bath consisting of ethanol/triethylamine. The polymer was collected by filtration, washed with anhydrous ethanol, and dried under vacuum at room temperature.

The polyquinoline polymer produced in accordance with this example has recurring units of the following structural formula:

EXAMPLE 2

Heat Treatment (350'C, of a Polymer Film Produced from the Polyguinoline Polymer of Example 1

The polyquinoline polymer produced in Example 1 was dissolved in l-methyl-2-pyrrolidinone (the common organic solvent NMP) to produce a 10 weight percent solution from which a film was cast using standard film casting techniques. The solvent was removed from the film by evaporation in a vacuum oven at a pressure of 10 torr and a temperature of 200°C over the course of 2 hours. A portion of the dry polyquinoline film which resulted readily redissolved in a matter of several minutes in various common organic solvents, including NMP, m-cresol and toluene. The polyquinoline film was then subjected to a heat treatment in a tubular furnace at 350°C for 2 hours. Upon removing the film and attempting to dissolve a portion of the film in toluene, it was observed that after stirring the film sample in toluene for 2 hours, it remained undissolved. Continuing to stir the film sample in toluene for an additional 8 hours did not cause dissolution of the polymer film. Similarly, where the film sample could be dissolved in NMP or m-cresol in from 5 to 30 minutes prior to the heat treatment, the film, after heat treatment, did not redissolve in NMP or in m-cresol over the course of 2 or more hours of stirring in either of these solvents. After 10 hours of stirring in either NMP or m-cresol, it was observed that a small portion of the cured film sample appeared to have dissolved.

EXAMPLE 3

Heat Treatment of the Film of Example 2 (325"C, 350°C, 450-C-

The polymer film of Example 2 was cured with three temperature/time schedules and the solubility measured in toluene and chloroform.

Table 1 shows that at 325°C for one hour the film is still completely soluble in both toluene and chloroform, whereas after two hours at 350"C it is completely insoluble in toluene and nearly insoluble in chloroform.

EXAMPLE 4

Preparation of Polvf2_2'-(p,p'-θ-gydiphenylene)- 6,6'-oxybis(4-phenγlquinoline. ] A mixture of 3.2993 grams (8.0775 mmol) 4,4'- diamino-3,3'-dibenzoyldiphenyl ether, of 2.0540 grams (8.0775 mmol) 4,4 '-diacetyldiphenyl ether, 50 grams diphenyl phosphate, and of 10 grams distilled m-cresol was loaded into a three-neck flask in an inert atmosphere box. The flask was removed from the inert atmosphere box, equipped with an overhead stirrer, and connected to an argon line, purged with argon and warmed until the diphenyl phosphate began to melt. The temperature was raised slowly to 110"C with an oil bath, and stirring was continued for 24 hours, after which heating was stopped and the mixture poured into ethanol containing 5% v/v triethylamine to precipitate the polymer. The polymer was chopped in a blender with solvent, followed by filtering, alternately with ethanol, water, then ethanol. The solids were washed with ligroin and dried. The polymer was then extracted in a soxhlet extractor with ethanol/10% triethylamine for 24 hours and dried in vacuum. The polymer was then dissolved in chloroform and precipitated by pouring into ethanol/5% triethyl amine. The solids were dried in vacuum. The yield was 91.6%. The polymer produced in accordance with this example has recurring units of the following structural formula:

EXAMPLE 5

Heat Treatment (360"C. of a Polymer Film Produced from the Polyquinoline Polymer of Example 4

The polyquinoline polymer produced in Example 4 was cast into a film from NMP solution using standard film casting techniques. The dry polyquinoline film which resulted was readily redissolved in a matter of several minutes in various common organic solvents. For example, the majority of the film sample dissolved in chloroform within a few minutes. Attempts to dissolve the polyquinoline film in NMP yielded a turbid polymer solution. The polyquinoline film was then subjected to a heat treatment in a tubular furnace at 360°C for 2 hours. Upon removing the film and attempting to dissolve a portion of the film in chloroform, it was observed that after stirring the film sample in chloroform for 2 hours, it remained undissolved. Continuing to stir the film sample in chloroform for an additional 8 hours did not cause any apparent dissolution of the polymer film. Similarly, where the film sample could be dissolved to yield a turbid solution in NMP in a matter of a few minutes prior to the heat treatment, the film did not redissolve in NMP over the course of 2 or more hours. After 10 hours, it was observed that a small portion of the film sample appeared to have dissolved in the NMP. Comparable results were obtained when either xylenes or m-cresol were used as test solvents. For example, prior to the heat treatment process, the polyquinoline film was insoluble in m-cresol if stirred at room temperature. However, the uncured polyquinoline film was observed to dissolve if stirred for approximately 30 minutes in m-cresol at a temperature of 80°C. Subsequent to heat treatment at 360^βC for two hours, the film did not dissolve when stirred in m-cresol at 80"C for a period of several hours.

When the uncured polyquinoline film was stirred in xylenes at room temperature, the film was observed to swell but not dissolve. However, subsequent to the aforementioned heat treatment, the polyquinoline film did not swell (nor dissolve) when stirred in xylenes for several hours.

EXAMPLE 6

Heat Treatment (275'O of the Polyguinoline Polymer of Example 1

The polymer of Example 1 was dissolved as a 3 weight percent solution in toluene, and using standard spin-coating techniques, was spin-coated onto two thin glass slides. Upon removal of toluene by application of mild heat (100°C for one hour), a glass pipette was used to place drops of various common solvents at distinctly different locations on one of the polymer coated slides. Several solvents, including toluene, m-cresol, NMP, xylenes, and chloroform, were observed to either completely dissolve the portion of the film which was exposed to the solvent drops or cause the appearance of roughly concentric circles at the location on the film where the solvent was placed. This latter effect, referred to herein as crazing, is associated with a partial dissolution of the polymer film through contact with (e.g., attack by) the solvent(s). The second glass slide, e.g. , the one which was not exposed to various solvents, was subjected to a tubular furnace at a temperature of 275°C for a period of 12 hours. The slide was removed from the furnace, cooled to room temperature, and tested by the aforementioned procedure for resistance to the solvents listed above. It was observed that where the film was, prior to the heat treatment, dissolved or crazed by the afore¬ mentioned solvents, only NMP and, to a lesser extent, m-cresol were observed to craze the film surface subsequent to the heat treatment.

This second glass slide was then returned to the tubular furnace and baked at a temperature of 340"C for 2 hours. Upon removal from the furnace and cooling to room temperature, it was then observed that exposure to drops of NMP and m-cresol caused no evidence of dissolution nor crazing of the polymer surface.

EXAMPLE 7 Heat Treatment (350"C) of a Coating of the

Polyquinoline Polymer of Example 1

The polymer of Example 1 was dissolved as a 3 weight percent solution in toluene and, using standard spin-coating techniques, was spin-coated onto a silicon wafer measuring four inches in diameter. The resulting polymer coating, after removal of solvent by evaporation, was approximately 3 microns in thickness. A glass pipette was used to dispense droplets of various solvents at distinct locations onto the polymer coating. It was observed that NMP, toluene, chloroform and m-cresol dissolved and/or crazed the polymer coating. The polymer coated silicon wafer was then subjected to a* heat treatment in a tubular furnace at 350°C for a period of 2 hours. Upon removal from the furnace and cooling to room temperature, the application of the test solvents mentioned above was repeated at fresh, previously undisturbed locations on the polymer coating. It was noted that, subsequent to the heat treatment, no indications of dissolution or crazing of the polymer coating were observed even when these solvents were allowed to remain at room temperature on the polymer coating and then boiled off by placing the polymer coated wafer in a tubular furnace that had been preheated to 250°C.

EXAMPLE 8 Heat Treatment of Polymers Produced in Accordance with Example 1 Where (1) the Monomer Balance was Offset by Providing the Bisaminoketone Monomer in Excess and (2) 2-aminobenzophenone Was Added as Endcapper

The polymer of Example 1 was prepared with a controlled molecular weight of 20,000 by offsetting the monomer balance with the bisaminoketone monomer in excess. The resulting polymer, therefore, had 4-amino- 3-benzoylphenyl end groups. This polymer was designated A20. The same polymer was prepared with molecular weight 10,000 and 20,000 using 2-aminobenzophenone as endcapper. The resulting polymers had 2-quinoline end groups. These polymers were designated Q10 and Q20, respectively. Each polymer was spin-coated from toluene onto glass slides and cured using the schedules in Tables 2 and 3. They were tested for NMP resistance as in Example 7.

Table 2

Polymer TemperatureCO /Time(Hr, Attacked by NMP A20 320/12 Yes

350/ 4 No

Q20 320/12 Yes

350/ 4 Yes Table 3

Polymer TemperatureC /Time(Hr. Attacked by NMP

(cumulative)

Q20 300/ 6 Yes 350/ 3 Yes 400/ 3 Yes (slight) 450/ 2 No

Q10 300/ 6 Yes 350/ 3 Yes 400/ 3 Yes 450/ 2 No

It can be seen from Table 2 that A20 with 4-amino-3- benzoylphenyl end groups cures at 350°C for 4 hr; whereas, Q20 with quinoline end groups does not cure under these conditions. Q20 and Q10 do cure at higher temperatures (Table 3) .

EXAMPLE 9

Heat Treatment of a Polyquinoline Polymer Prepared using an Ami o Endcapper

The polymer of Example 1 is prepared with a controlled molecular weight of 50,000, using as endcapper 4-aminoacetophenone. All amounts and conditions are the same for this example as was the case for Example 1 except that the amount of 3,3'-dibenzoyl- 4,4'diaminobiphenyl used is 1.4068 grams (3.5845 mmol), and 0.025 grams (0.182 mmol) 4-aminoacetophenone is added with the monomers. The dried polymer is dissolved in NMP to give a 10 weight percent solution. The solution is then spin-coated^' onto a silicon wafer and dried in a vacuum oven at 100°C for two hours. At this point, the film is still soluble in NMP. The coated wafer is cured for two hours at 400°C in an oven, at which point NMP no longer dissolves the film. We have described a process for dramatically enhancing the utility of polyquinolines, and fabricated parts, including films, fibers, coatings, molded parts and composites derived therefrom. The observation that dramatic increases in the solvent resistance of initially organic solvent-soluble polyquinolines can be achieved by the heat treatment conditions described herein was unexpected, and is extremely useful. Whereas there exists many applications for thermally stable polymers wherein extreme resistance to a wide range of solvents is desirable, and whereas the previously described methods of achieving this result tend to have drawbacks as described herein, and whereas it has been shown, for example, in U.S. Patent Application 07/568,059, that many polyquinolines exhibit a wide range of performance and processing characteristics not readily exhibited by other thermally stable polymers, the ability to enhance the solvent resistance of polyquinolines dramatically increases their utility, and thus the likelihood that these polymers will be widely used in structural, electronic, and electrical applications, among other areas.

Specifically, the chemical compositions resulting from use of the process described herein for curing, and thus increasing solvent resistance in polyquinolines, will have enhanced utility:

(a) as matrix resins in advanced composite applications used in aerospace, where resistance to solvents, lubricants and hydraulic fluids commonly found in aircraft and spacecraft environments is a critical performance characteristic; , it is known that many thermally stable polymer systems which might otherwise be considered for these applications do not possess the required solvent resistance, and that unlike the cured polyquinoline compositions described herein, increased solvent resistance in these other polymer systems cannot be readily achieved; (b) as interlayer, passivating dielectric coatings in high density microelectronics packaging applications, such as multi-chip modules, where resistance to a wide range of solvents commonly employed in various steps of electronic fabrication processes is necessary for a thermally stable polymer to be of practical utility. Thus, by spin-coating layers of soluble polyquinoline onto electronic substrates such as silicon, with the optional use of adhesion promoters, followed by curing under the time/temperature combinations described herein, new polyquinoline-based compositions can be obtained which have been shown to possess the required solvent resistance needed to accommodate additional microelectronics fabrication steps; (c) as wire coatings and cable wraps, particularly in environments where protection against various solvents, greases, lubricants, hydraulic fluids, etc., which can cause short circuits in conducting wires and cables, is important; additionally where protection of wires and cables against corrosion induced by contact with various solvents is important;

(d) as fabricated components, such as gaskets, seals, and related parts which are useful in chemical processing industries; (e) as free standing films. These films may be useful as curable films to be cured in a later application, or as precured, solvent resistant films;

(f) as adhesives. Solutions or films of polyquinoline can be applied between two surfaces and cured. Polyquinolines tailored to have low melting or softening points, by introduction of flexible groups or by decreasing molecular weight will be useful as melt adhesives;

(g) as laminating materials, and barrier coatings and films; (h) as dielectric layers in integrated circuits; for example, as planarizing layers or as passivating layers; and

(i) as dielectrics in capacitors.

Although the description above contains many specifics, these should not be construed as limiting the scope of the invention, but merely providing illustrations of some of the presently preferred embodiments of this invention. For example, heat- induced solvent resistance in polyquinolines is also a highly desirable process (and highly desirable compositions are derived therefrom) for many additional film, electronics packaging, electronics coating, matrix resin and other coating applications, as well as many applications for fibers, etc.

The above description of preferred embodiments of processes for curing polyquinolines provided in accordance with this invention is for illustrative purposes. Because of variations which will be apparent to those skilled in the art, the present invention is not intended to be limited to the particular embodiments described above. The scope of the invention is defined in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A process for producing a polyquinoline polymer having enhanced solvent resistance, the process comprising the steps of:

(a) in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer, to thereby provide a polyquinoline polymer wherein said monomers do not incorporate a polyphenylated group; and

(b) heating the polyquinoline polymer produced in step (a) to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the polymer.

2. The process of claim 1 wherein heating the polyquinoline polymer is conducted after the polymer has been formed into a film, a coating, a fiber, a molded article, or a composite.

3. The process of claim 1 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

4. The process of claim 1 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

5. The process of claim 1 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

6. The process of claim 1 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

7. The process of claim 1 wherein a BB monomer is reacted with an excess of AA monomer.

8. The process of claim 1 wherein stoichiometric amounts of an AA monomer a BB monomer are reacted to provide the polyquinoline polymer.

9. The process of claim 1 wherein a BB monomer is reacted with an excess of AA monomer to provide the polyquinoline polymer with aminoketone endcaps.

10. A solvent resistant polyquinoline polymer produced by a process comprising the steps of:

11. A polyquinoline polymer as claimed in claim 10 wherein the polymer comprises recurring units of the following structural formula:

12. A polyquinoline polymer as claimed in claim 10 wherein the polymer comprises recurring units of the following structural formula:

13. 10 wherein following

14. 10 wherein monomer.

16. A process for producing a composite comprising a polyquinoline polymer of enhanced solvent resistance, the process comprising the steps of:

(a) in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer, to thereby provide a polyquinoline polymer wherein said monomers do not incorporate a polyphenylated group;

(b) forming a composite of the polyquinoline polymer produced in step (a) with a material selected from the group consisting of reinforcing fibers and particulate fillers, and mixtures thereof; and

(c) heating the composite to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the composite.

17. The process of claim 16 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

wherein X and Y are separately selected from the group consisting of nil, -0-, -CO-, -SO-.-, -OArO-, -OAr6FArO-, -6F- and -OArCOArO-, wherein Ar is an arylene group having 6 to 18 carbons and 6F is hexafluoro- isopropylidene.

18. A process for producing a polyquinoline polymer having enhanced solvent resistance, the process comprising the steps of:

(a) preparing an amine-endcapped polyquinoline polymer by adding an AE or a BE endcapper to the monomers which are reacted to form the polymer, wherein E is a free or protected amine group; and

(b) heating the amine-endcapped polyquinoline polymer produced in step (a) to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the polymer.

19. The process of claim 18 wherein a mixture of AA- and BB-type monomers are reacted.

20. The process of claim 18 wherein an AB-type monomer is reacted.

21. A process for increasing the solvent resistance of a polyquinoline polymer which has been formed by a procedure comprising, in the absence of an added endcapper, reacting an AA monomer with a BB monomer, or reacting an AB monomer alone or with an AA or a BB monomer, to thereby provide the polyquinoline polymer, wherein said monomers do not incorporate a polyphenylated group; the solvent resistance of said polyquinoline polymer being increased by heating the polyquinoline polymer to a temperature of greater than about 150°C for a period of time sufficient to effect the increase.

22. The process of claim 21 wherein, prior to heating the polyquinoline polymer, it is formed into a film, a coating, a fiber, a molded article, or a composite.

23. The process of claim 21 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

24. The process of claim 21 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

25. The process of claim 21 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

26. The process of claim 21 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

wherein X an Y are separately from the group consisting of nil, -0-, -CO-, -S0₂-, -OArO-, -0Ar6FAr0-, -6F- and -OArCOArO-, wherein Ar is an arylene group having 6 to 18 carbons and 6F is hexafluoro- isopropylidene.

27. A multi-chip module comprising one or more layers of polyquinoline dielectric onto which electrical conducting lines are deposited, the multi-chip module formed by the steps of:

(a) forming a polyquinoline dielectric layer by depositing a polyquinoline polymer onto a surface of the multi-chip module; and

(b) heating the polyquinoline polymer dielectric layer to a temperature of greater than about 150°C for a period of time sufficient to enhance the solvent resistance of the polymer.

28. The multi-chip module of claim 27 wherein the polyquinoline dielectric layers are deposited by a process selected from the group consisting of spin- coating, dip-coating, spray-coating, electro-depositing, and laminating.

29. The multi-chip module of claim 27 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

30. The process of claim 27 wherein the polyquinoline polymer comprises recurring units of the following structural formula:

wherein X and Y are separately selected from the group consisting of nil, -0-, -CO-, -S0₂-, -OArO-, -OAr6FArO-, -6F- and -OArCOArO-, wherein Ar is an arylene group having 6 to 18 carbons and 6F is hexafluoro- isopropylidene.

31. A process for preparing a solvent resistant organic dielectric coating on a substrate, the process comprising the steps of:

(b) coating onto an electronic substrate a solution comprising the polyquinoline polymer formed in step (a) and an organic or acidic solvent, wherein the weight percent of the polyquinoline polymer in the solution is between 0.1% and 60%; and

(c) heating the polyquinoline-coated substrate to a temperature of greater than about 150°C for a period of time sufficient to increase the solvent resistance of the polyquinoline polymer.

32. The process of claim 31 wherein the polyquinoline polymer comprises recurring units of the following structural formula: