1. Field of the Invention
The field of the invention relates to the preparation of random linear injection moldable amide-imide copolymers which process comprises reacting fully or partially acylated aromatic diamines with aromatic tricarboxylic acid anhydrides or mixtures of aromatic tricarboxylic acid anhydrides and aromatic dicarboxylic acids and to novel polytrimellitic amide-imide copolymers and to molded objects and fibers prepared from these copolymers.
2. Background
Amide-imide and polyamide polymers and copolymers are a relatively new class of organic compounds known for their solubility in nitrogen containing solvents when in the polyamic acid form. The major application of these amide-imides has been as wire enamels and film formers. This is illustrated in U.S. Pat. Nos. 3,852,106 (1974), 3,817,942 (1974), 3,661,832 (1972), 3,454,890 (1970) and 3,347,942 (1967).
Polyimide and polyamide-imide polymers have also been found useful for molding applications as shown in U.S. Pat. Nos. 4,016,140 (1977), 3,654,227 (1972) and 3,573,260 (1971).
The general object of this invention is to provide injection moldable amorphous linear amide-imide copolymers. A more specific object of this invention is to provide a novel process for the manufacture of injection moldable amide-imide and amide copolymers by reacting fully or partially acylated aromatic diamines with aromatic tricarboxylic acid anhydrides or mixtures of aromatic dicarboxylic acids and aromatic tricarboxylic acid anhydrides. Another object is to provide novel polyamide-imide copolymers suitable for use as an engineering plastic particularly for and in injection molding. Other objects appear hereinafter.
We have discovered a novel melt condensation process in which fully or partially acylated aromatic diamines are reacted with aromatic tricarboxylic anhydrides or mixtures of aromatic tricarboxylic anhydrides with aromatic dicarboxylic acids to yield engineering plastics suitable for injection molding which feature very high tensile strength and heat distortion temperatures. Our novel process for the preparation of random linear injection moldable amide-imide and amide copolymers comprises reacting fully or partially acylated aromatic diamines with aromatic tricarboxylic acid anhydrides or mixtures of aromatic tricarboxylic acid anhydrides with aromatic dicarboxylic acids in a molar ratio of about 9:1 to about 1:9 at a temperature of about 450.degree. to 750.degree. F.
In the prior art, melt reaction of tricarboxylic acid anhydride compounds with aromatic diamines have produced products which are not suitable for injection molding application. The reason for this is not known, but it is specified that various side reactions occur. It has now been discovered that when fully or partially acylated diamines are reacted, injection molding grade polyamide-imide copolymers are produced. In our process we usually acylate more than half of the diamines utilized in the reaction. The preferred acylation is about 70 to 100 percent.
Evidence for linearity for our novel copolymer is demonstrated by the solubility of the polymer. Polymers produced from tricarboxylic acid anhydride compounds such as trimellitic acid anhydride and aromatic diamines via various melt polymerization methods show no solubility for products having inherent viscosity in excess of 0.5. The copolymer produced according to the novel process utilizing partially or fully acylated diamines is essentially soluble after curing with inherent viscosities in the range of 0.6 to 3.0. For the purpose of this invention, inherent viscosity is measured at 25.degree. C. and 0.5% w/v in 100% sulfuric acid or N-methylpyrrolidone.
The novel injection moldable amorphous random linear polyamide-imide copolymers of this invention comprise units of ##STR1## R comprises R.sub.1 and R.sub.2, R.sub.1 and R.sub.2 are divalent aromatic hydrocarbon radicals of from 6 to about 20 carbon atoms or two divalent hydrocarbon radicals of from 6 to 20 carbon atoms joined directly or by stable linkages selected from the group consisting of --O--, methylene, --CO--, --SO.sub.2 --, and --S-- radicals and wherein said R.sub.1 and R.sub.2 containing units run from about 10 mole percent R.sub.1 containing unit and about 90 mole percent R.sub.2 containing unit to about 90 mole percent R.sub.1 containing unit and about 10 mole percent R.sub.2 containing unit.
The novel injection moldable random linear copolymer may comprise structural Units A and B and also include Unit C of the following formula: ##STR2## wherein X is a divalent aromatic radical usually a divalent benzene radical and R.sub.3 comprises both R.sub.1 and R.sub.2 as defined above or is equal to R.sub.1. Furthermore, if structure C is present R of structural Units A and B can be equal to R.sub.1 or comprise both R.sub.1 and R.sub.2 as set forth above.
In the foregoing structural units Z is a trivalent aromatic radical. Z may be a trivalent radical of benzene, naphthalene, biphenyl, diphenyl ether, diphenyl sulfide, diphenyl sulfone, ditolyl ether, and the like.
Useful aromatic tricarboxylic acid anhydrides which contribute the trivalent radical moiety of Z include those compounds containing at least one pair of carboxyl groups in the ortho position with respect to each other or otherwise situated in a fashion which permits the formation of an anhydride structure, one other carboxyl group and from 9 to 21 carbon atoms. Within these limits, these compounds may contain one or more benzenoid rings such as, for instance, trimellitic anhydride and its isomers and multi-ring compounds such as the 1,8-anhydride of 1,3,8-tricarboxylnaphthalene. Usually these compounds contain up to three benzenoid rings.
The aromatic tricarboxylic acid anhydride used in the novel process to form the polyamide-imide polymers of this invention is of the formula: ##STR3## where Z is a trivalent aromatic radical defined as set forth hereinabove. The following aromatic tricarboxylic anhydrides are preferred: trimellitic acid anhydride; 2,3,6-naphthalene tricarboxylic anhydride; 1,5,6-naphthalene tricarboxylic anhydride, and the like; 2,6-dichloronaphthalene-4,5,7-tricarboxylic anhydride, and the like. One of the preferred aromatic tricarboxylic anhydrides is trimellitic anhydride since this compound is readily available and forms polymers having excellent physical properties of tensile strength and elongation and is resistant to high temperatures.
Suitable fully or partially acylated aromatic diamines useful in applicant's process include para- and meta-phenylenediamine, oxybis (aniline), thiobis (aniline), sulfonylbis (aniline), diaminobenzophenone, methylenebis (aniline), benzidine, 1,5-diaminonaphthalene, oxybis (2-methylaniline), thiobis (2-methylaniline), and the like. Examples of other useful aromatic primary diamines are set out in U.S. Pat. No. 3,494,890 (1970) and U.S. Pat. No. 4,016,140 (1977) both incorporated herein by reference.
Useful aromatic dicarboxylic acids include isophthalic acid and terephthalic acid. In applicant's process further preparation of injection moldable amide-imide and amide copolymers process can be conducted without utilizing a solvent or fluidizing agent though it is preferred to use agents such as N-methylpyrrolidone, dimethyl-acetamide, or acetic acid for the initial mixing of reactants. In general, since these polymers are linear, they may be easily cured in the melt using a twin screw extruder as the finishing reactor instead of a solid state polymerization. However, in some instances, it may be helpful to solid state polymerize the copolymers. The term "solid state polymerization" refers to chain extension of polymer particles under conditions where the polymer particles contain their solid form and do not become a fluid mass.
The solid state polymerizing can be carried out below the melting point of the copolymer and can be conducted in several ways. However, all the techniques require heating the ground or pelletized copolymer below the copolymer melting point, generally of about 400.degree. to 600.degree. F. while either sparging with an inert gas such as nitrogen or air or operating under vacuum.
Injection molding of the novel copolymer is accomplished by injecting the copolymer into a mold maintained at a temperature of about 350.degree.-500.degree. F. In this process a 0.1-2.0 minutes cycle is used with a barrel temperature of about 500.degree. F. to 700.degree. F. The injection molding conditions are given in Table I.
TABLE I ______________________________________ Mold Temperature 350-500.degree. F. Injection Pressure 2,000-40,000 psi and held for 0.5-20 seconds Back Pressure 0-400 psi Cycle Time 6-120 seconds Extruder: Nozzle Temperature 500.degree. F. to 700.degree. F. Barrels: Front heated to 500.degree. F. to 700.degree. F. Screw: 10-200 revolutions/minute ______________________________________
The mechanical properties of the polymers prepared in the Examples are given in Tables II, III, IV, V, VI and VII.
In applicant's process the acylated aromatic diamines need not be isolated or purified prior to their further reaction with the tricarboxylic acid anhydride compound or mixture of the tricarboxylic acid anhydride with dicarboxylic acid. Therefore, one can react one to two moles of acetic anhydride or acid or propionic anhydride or acid or any other C.sub.2 through C.sub.8 containing aliphatic anhydride or acid and one mole of the appropriate aromatic diamine or diamine mixture and use the resulting diacylated diamine solution in acetic acid or propionic acid to react with the tricarboxylic anhydride compound, or mixtures of the tricarboxylic anhydride compound with dicarboxylic acid.
In most cases, linear high molecular weight polyamide-imide polymers result after melt and/or solid state polymerization.