DIELECTRIC INVESTIGATION OF MOLECULAR-DYNAMICS OF BLENDS .3. EFFECT OF MOLECULAR-WEIGHT IN TMPC PS BLENDS/

Dielectric and calorimetric measurements have been carried out for tet ramethyl polycarbonate/polystyrene (TMPC/PS) blends with different com positions. The effect of varying the molecular weight of the weakly po lar component (PS) on the molecular dynamics of the polar segments of TMPC has been thoroughly studied over wide ranges of frequency (10(-2) -10(5) Hz), temperature (50-220 degrees C) and number average molecula r weight, <(m)over bar (n)>, (6500-560 000 g mol(-1)). All blends were found to be compatible regardless of the composition ratio and the mo lecular weight of PS. Some new and interesting experimental findings h ave been observed concerning the effect of molecular weight on the gla ss temperature and on the broadness of the glass transition and relaxa tion. Neither the kinetics nor the distribution of relaxation times of the local process observed in pure TMPC was affected by blending with PS, regardless of the composition ratio or the molecular weight of PS . It has been concluded that the mixing of the polymeric components to form a homogeneous single phase (compatible blend) does not take plac e on a segmental level but on a structural one. The size of this struc tural level has been suggested to have the same volume as the cooperat ive dipoles, which is assumed to be the minimum volume responsible for a uniform glass transition (10-15 nm). The molecular weight dependenc e of the relaxation characteristics of the glass process and temperatu re could be attributed to the variation in the size and packing of the structural units.