THERMOTROPIC LIQUID-CRYSTALLINE AROMATIC-ALIPHATIC POLYIMIDES .4. POLY(IMIDE-URETHANE-CARBONATE)S BASED ON PYROMELLITDIIMIDE AND 3,4-3',4'-BIPHENYLDICARBOXIMIDE

Main-chain types of thermotropic liquid-crystalline (LC) poly(imide-ur ethane-carbonate)s were synthesized by melt polycondensation of N,N'-b is(6-hydroxyhexyl)pyromellitdiimide or is(6-hydroxyhexyl)-3,4:3',4'-bi phenyldicarboximide with diphenyl hexamethylenedicarbamate and/or diph enyl hexamethylenedicarbonate. The poly(imide-urethane)s were also obt ained from the dihydroxyalkylene diimide derivatives and hexamethylene diisocyanate by polyaddition. Yields and molecular weights of the res ulting polymers tended to decrease with increasing urethane units. Dif ferential scanning calorimetry (DSC) measurements, polarizing microsco pic observations and powder X-ray analyses at various temperatures dem onstrated that the carbonate-rich copolymers comprising the 3,4:3',4'- biphenyldicarboximide derivative formed a nematic mesophase. Temperatu re-dependent Fourier-Transform infrared measurements suggest that hydr ogen bonding of urethane linkages affects the formation of LC mesophas es.