RELAXATIONS IN POLY(TETRAMETHYLENE TEREPHTHALOYL-BIS-4-OXYBENZOATE) -EFFECT OF SUBSTITUTION IN THE MESOGENIC UNIT AND IN THE FLEXIBLE SPACER

The relaxation behaviour of a thermotropic polymer liquid crystal, pol y(tetramethylene terephthaloyl-bis-4-oxybenzoate), and its derivatives with substitution in the mesogen and/or in the spacer, have been anal ysed by dynamic mechanical analysis and differential scanning calorime try (d.s.c.). By comparing the relaxation spectra of the four polymers some conclusions can be drawn. They all show a beta relaxation at low temperature and an alpha relaxation above room temperature. The beta relaxation has been associated with local motions of the mesogenic uni t. The substitution of chlorine in the mesogen increases the temperatu re of this relaxation by 60 degrees C, but it is not affected by subst itution in the spacer. The alpha relaxation has been associated with t he glass transition of the amorphous phase. It increases by approximat ely 15 degrees C with the introduction of lateral methyls in 1,4 posit ion in the spacer, independently of substitution in the mesogen. The p resence of crystalline order, besides the nematic mesophase, broadens this relaxation. (C) 1997 Elsevier Science Ltd.