LIQUID-CRYSTALLINE MAIN-CHAIN POLYMERS WITH A POLY(P-PHENYLENE-TEREPHTHALATE) BACKBONE .7. THERMAL-EXPANSION OF ORIENTED FILMS OF THE POLYESTER WITH DODECYLOXY SIDE-CHAINS

The linear thermal expansion coefficients of oriented films of poly(p- phenylene-2,5-didodecyloxy-terephthalate) in the three structures B, A , and L(f) are reported. The results are interpreted in terms of a mol ecular laminate model in which the rigid main-chain layers are separat ed by the aliphatic side chains. In a film oriented unidirectionally t he rigid main-chain layers provide a negative contribution to the ther mal expansion coefficient, while the side chains supply a positive con tribution. Therefore, the resulting expansion coefficient alpha depend s on the details of the main- and side-chain packing and low-temperatu re values between alpha = +0.3 X 10(-5) K-1 (A and L(f)) and alpha = - 1.2 X 10(-5) K-1 (B) are found in highly oriented films. Measurements on undrawn films are in accordance with the molecular laminate model. (C) 1994 John Wiley & Sons, Inc.