Synthesis and Characterization of Organo-Soluble, Thermally-Curable, Phenylated Aromatic Polyimides

Phenylated aromatic polyimides have been prepared in two steps by the Diels-Alder polymerization of biscyclopentadienones with dimaleimides followed by dehydrogenation and in one step by the polymerization of phenylated bis(phthalic anhydrides) with diamines. Although the polymers prepared by both routes were soluble in chlorinated-hydrocarbon solvents, the latter afforded considerably higher molecular weight materials. Polyimides obtained in this manner had intrinsic viscosities as high as 4.0 dl/g and glass transition temperatures that ranged from 238 to 466°C. Thermogravimetric analysis thermograms of the polymers in air and nitrogen atmospheres showed no weight loss until near 530°C. Two new ethynyl-substituted diamines, 4(2,4-diaminophenoxy)phenylacetylene (1) and 3,5-diaminodiphenylacetylene (2), have been synthesized and polymerized with a phenylated bis(phthalic anhydride). The polymer prepared with diamine 1 underwent cross-linking at 250°C without the evolution of volatile byproducts, while the polymer prepared with diamine 2 underwent an analogous cure at 350°C. A phenylated bis(phthalic anhydride) has also been copolymerized with pyromellitic dianhydride (PMDA) and 4,4’-diaminodiphenyl ether to afford soluble copolymers that contain as high as 50 mole % PMDA.