WIDE-ANGLE X-RAY-SCATTERING STUDY OF LIQUID-CRYSTALLINE POLYCARBONATES BASED ON ALPHA-METHYL STILBENE MESOGEN AND METHYLENE-CONTAINING FLEXIBLE SPACER

Solid state structure has been studied for a series of recently synthe sized liquid crystalline polycarbonates(1) based on methyl-substituted stilbene mesogen and methylene-containing flexible spacer. These poly mers are referred to as HMS-n, where n is the number of methylenes in the flexible spacer group. The stability of the liquid crystalline pha se and its relationship to the three dimensional crystalline phase wer e studied. X-ray diffraction patterns of raw fibers drawn from the mes ophase revealed that the stability of the mesophase decreases as the m ethylene spacer length gets close to that of mesogen. From X-ray diffr action patterns of annealed fibers and molecular modeling studies, the unit cell parameters of HMS-5 to 8 were determined. HMS-5 and 6 have an orthorhombic structure while HMS-7 and 8 have a monoclinic structur e. More important, an odd-even oscillation is observed in the d-spacin gs of the (0 2 0) and (1 1 0) reflections as a function of n, which re lates to differences in interchain packing in the odd and even members of the series. All HMS-5 to 8 have a stable intermeshed crystal struc ture in which the mesogen and the flexible spacer group on adjacent ch ains are aligned. In this structure the disposition of the carbonate g roup differs from n-even to n-odd, and is responsible for the odd-even effect seen in the two dominant interchain d-spacings. We suggest the higher degree of overlap of the carbonate linkage of HMS-7 and 8 migh t be the reason for their less stable mesophase compared with HMS-5 an d 6.