STRUCTURE AND PROPERTIES OF POLY(2,5-DI-N-DODECYL-1,4-PHENYLENE) DEPENDING ON CHAIN-LENGTH

An investigation of the morphologies of solution-cast/melt-pressed fil ms of poly(2,5-di-n-dodecyl-1,4-phenylene) by X-ray diffraction reveal ed a sandwich type structure, with layers of aliphatic side chains per pendicular to the substrate surface separating layers of main chains e xtended parallel to the substrate surface. The physical properties wer e highly influenced by the local conformational mobility of the side c hains. With increasing temperature, the concentration of gauche confor mations in the side chains increases strongly over a temperature range from -50 to 190 degrees C and was reflected in a large negative coeff icient of thermal expansion for the direction normal to the main chain layers, alpha(a) = -9.72 x 10(-4)/K. The linear decrease in the layer spacing of the side chains can be correlated to the linear temperatur e dependence of the tensile properties of solution cast films (E, sigm a(b) approximate to T-1). The M(w) dependence of LC phase formation wa s investigated by DSC, polarizing microscopy, and theological measurem ents. In the molten phase, polymers of M(w) < 30 000 showed only an is otropic phase, polymers of 44 000 less than or equal to M(w) less than or equal to 73 000 gave coexisting isotropic/anisotropic phases, and polymers having M(w) less than or equal to 94 000 showed only a single anisotropic phase. Polymers that formed anisotropic melts behaved as shear thinning non-Newtonian fluids, and the zero-shear viscosity scal ed as eta(0) similar to M(w) (3.2). The viscosity of polymers that for med isotropic melts was independent of deformation frequency, and a sc aling law eta(0) similar to M(w)(2.9) seems to hold.