Layer structures .4. Role of long alkane spacers in poly(ester imide)s derived from N-(4'-hydroxyphenyl)-4-hydroxyphthalimide

Several polyesters were prepared from N-(4'-hydroxyphenyl)-4-hydroxyphthalimide and various alkanedicarboxylic acids. The dicarboxylic acids contained 12, 14, and 20 methylene groups. Optical microscopy, DSC, and X-ray measurements at variable temperatures revealed that the poly(ester imide)s (PETs) containing up to 10 CH2 groups form a enantiotropic nematic phase, whereas those PEIs with 12 or more CH2 groups form only a monotropic LC phase upon rapid cooling. All of these PEIs form a crystalline state with a smectic E-like layer structure, which undergoes a reversible change upon heating and cooling. Another interesting result is the predominance of transconformations of the spacers, as revealed by C-13 NMR CP/MAS spectroscopy. Copolymers were synthesized from 1:1 mixtures of n = 20 and n = 12 spacers or n = 20 and n = 7 spacers. They form an enantiotropic nematic phase, but again smectic layer structures in the solid state. The conformations of the spacers in both copolymers show different behavior. Whereas heating of the 20 + 12 copolymer favors gauche conformations and a rapid exchange with the trans conformation, the exchange between gauche and trans is extremely slow in the case of the 20 + 7 copolymer, because the n = 20 spacers are almost fully extended. Furthermore, the layer model of the 20 + 7 copolymer requires a dispersion of imide mesogens in the spacer layer.