THERMOTROPIC PROPERTIES AND CONFORMATIONAL STUDIES ON POLY(TRIETHYLENE GLYCOL PARA,PARA'-BIBENZOATE) AND POLY(OCTAMETHYLENE PARA,PARA'-BIBENZOATE)

The influence of oxygen atoms in the spacer on the thermotropic ability of poly(triethylene glycol p,p'-bibenzoate) (PTEB) has been studied by comparing the properties of this polymer with those of poly(octamethylene p,p'-bibenzoate) (P8MB), the analogue polyester with an all-methylene spacer. It has been found that the effect of the oxygen atoms is to lower the transition temperatures and to diminish the ability to develop a three-dimensional crystal. Moreover, a smectic S0 mesophase is formed in the case of PTEB. Both the integrated distributions of the angles between two successive rigid cores and the distribution of chain sequence extensions are calculated by the rotational isomeric state model for PTEB and P8MB, and it is found that these distributions are very sensitive to the presence of oxygen atoms in the spacer. The former polymer offers fewer conformers than the latter which are compatible in both orientation and extension with the requirements of the smectic layer determined from X-ray measurements. The internal energy of the highly extended conformer compatible with the layer thickness in PTEB is higher than the average energy of all the conformers, whereas the opposite occurs in P8MB.