THERMAL-CONDUCTIVITY AND THERMAL EXPANSIVITY OF THERMOTROPIC LIQUID-CRYSTALLINE POLYMERS

The thermal conductivity and thermal expansivity of a thermotropic liq uid crystalline copolyesteramide with draw ratio lambda from 1.3 to 15 have been measured parallel and perpendicular to the draw direction f rom 120 to 430 K. The sharp rise in the axial thermal conductivity K-p arallel to and the drastic drop in the axial expansivity alpha(paralle l to) at low lambda, and the saturation of these two quantities at lam bda > 4 arise from the corresponding increase in the degree of chain o rientation revealed by wide-angle x-ray diffraction. In the transverse direction, the thermal conductivity and expansivity exhibit the oppos ite trends but the changes are relatively small. The draw ratio depend ences of the thermal conductivity and expansivity agree reasonably wit h the predictions of the aggregate model. At high orientation, K-paral lel to of the copolyesteramide is slightly higher than that of polypro pylene but one order of magnitude lower than that of polyethylene. In common with other highly oriented polymers such as the lyotropic liqui d crystalline polymer, Kevlar 49, and flexible chain polymer, polyethy lene, alpha(p)arallel to of the copolyesteramide is negative, with a r oom temperature value differing from those of Kevlar 49 and polyethyle ne by less than 50%. Both the axial and transverse expansivity show tr ansitions at about 390 and 270 K, which are associated with large-scal e segmental motions of the chains and local motions of the naphthalene units, respectively. (C) 1995 John Wiley & Sons, Inc.