Layer structures .5. Influence of the spacer length on the smectic phases of poly(ester imide)s derived from alpha,omega-alkane bis(trimellitimides) and 4,4'-dihydroxybiphenyl

A series of homopoly(ester imide)s, PEIs, was prepared by polycondensation of 4,4'-bis(acetoxybiphenyl) with the bis(trimellitimides) of alpha,omega-diaminoalkanes with 6-12 CH2 groups. Furthermore, a series of copoly(ester imide)s was prepared from equimolar mixtures of 1,12-diaminodocedane bis(trimellitimide) and the bis(trimellitimides) of shorter alpha,omega-diaminoalkanes. As indicated by well-developed battonet textures all homopolyesters form a smectic-A phase before the isotropization. However, wide angle X-ray scattering measurements with synchrotron radiation up to 400 degrees C suggest that all PEIs also form a smectic-C phase above the melting temperature (T-m). The homopolyesters with an even number of CH2 groups have mesogens in upright position in the solid state (smectic-E), whereas the mesogens of the homo PEIs with odd-numbered spacers are tilted relative to the layer plane. WAXS fiber patterns demonstrate that in oriented samples the chain axes may adopt a parallel or perpendicular orientation relative to the draw direction. Also most coPEIs form a smectic-A phase in the melt, but when the difference of the spacer lengths increases (e.q. 6+12 and 5+12 CH2 groups), the layer structure is destabilized and a nematic melt is formed. A fiber drawn from the nematic melt of PEI 6+12 (2g) shows the chain axis parallel to fiber axis, whereas in the case of PEI 5+12 (2h) the chain axis is perpendicular to the fiber axis.