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SynopsisDetails of the thermal behavior, including transition temperatures, transition heats and transition entropies, are reported for three series of nematic liquid-crystalline "backbone" polyesters having the general structure x = 2-10,12 y = 6, 8, 10All polyesters described above were examined by differential scanning calorimetry and were found to have reproducible thermal behavior once the polymer had been annealed by heating to the isotropic phase and then subsequently cooled. Enantiotropic nematic phases were found for all 30 polyesters studied. Many polymers showed multiple endotherms on melting to the nematic phase. Plots of solid-nematic and nematic-isotropic transition temperatures versus number of carbon atoms in the diacid segment ( x ) for each (y) reveal an even-odd alternation reminiscent of trends in homologous series of small-molecule liquid crystals. Entbalpies for the solidnematic and nematicisotropic transitions do not show such a precise alternation.

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SYNOPSISTwo new phenylethynyl endcapping compounds, 3-and 4-amino-4'-phenylethynylbenzophenone, were synthesized and used to terminate imide oligomers from 3,4'-oxydianiline and 4,4'-oxydiphthalic anhydride at a calculated molecular weight of 9000 g/mol and from 3,4'-oxydianiline (0.85 mol) , 1,3-bis (3-aminophenoxy) benzene (0.15 mol) , and 3,3',4,4'biphenyltetracarboxylic dianhydride at a calculated molecular weight of 5000 g/mol. Glass transition temperatures for the cured oligomers were -249°C for the former and -272°C for the latter. Films cured at 350°C for 1 h were tough and flexible and provided high tensile properties. The uncured oligomers were readily compression molded to provide tough, solvent-resistant moldings.

Geveral new polyimides were prepared from the reaction of four aromatic dianhydrides with four new diamines containing carbonyl and ether connecting groups between the aromatic rings. The diamines were prepared from the reaction of 4‐aminophenol with activated aromatic difluoro compounds in the presence of potassium carbonate. Several of these polyimides were shown to be semicrystalline as evidenced by wide angle x‐ray diffraction and differential scanning calorimetry. Glass transition temperatures ranged between 192 and 247°C and crystalline melt temperatures were observed between 350 and 442°C. The polyimide from the reaction of 3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride and 1,3‐bis(4‐aminophenoxy‐4′‐benzoyl)benzene provided a semicrystalline solvent resistant transparent film with high tensile properties and compression molded compact tension specimens with high fracture toughness.