PRESSURE AND TEMPERATURE EFFECTS IN HOMOPOLYMER BLENDS AND DIBLOCK COPOLYMERS

Thermal composition fluctuations in homopolymer mer blends and diblock copolymers were studied with SANS in varying pressure and temperature fields. For homopolymers we find a quite consistent behavior: The dom inating effect of compressibility or packing leads to a reduction of t he entropic contribution of the Flory-Huggins parameter at larger pres sure fields. This gives rise to a shift of the phase boundaries to hig her temperatures and to a strong reduction of the Ginzburg parameter. Diblock copolymers show a different behavior. Neither the entropic ter m of the Flory-Huggins parameter nor the Ginzburg number seems to be r elated to the compressibility.