Layer Structures. 5. Influence of the Spacer Length on the Smectic Phases of Poly(ester imide)s Derived from α,ω-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 α,ω-diaminoalkanes with 6−12 CH 2 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 α,ω-diaminoalkanes. As indicated by well-developed bâttonet textures all homopolyesters form a smectic-A phase before the isotropization. However, wide angle X-ray scattering measurements with synchrotron radiation up to 400 °C suggest that all PEIs also form a smectic-C phase above the melting temperature ( T m ). The homopolyesters with an even number of CH 2 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 CH 2 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.