On the effect of pressure on the phase transition of polymer blends and polymer solutions: Oligostyrene-n-alkane systems

Critical temperatures of some binary solutions of weakly interacting low mo lecular weight polystyrenes dissolved in linear alkanes (oligoethylenes) we re measured over the range 0.1 to 100 MPa. While (dT/dP)(crit) along the up per critical solution (UCS) locus for a "typical blend'' is positive, and f or the "typical solution'' can be either positive or negative (but is usual ly negative), there is no essential difference between blend and solution. Rather, the difference in sign is a consequence of the location of the hype rcritical point (that point in (T,P)(crit) space where (dT/dP)(crit) change s sign, [(dT/dP)(crit)=0 and (T/dP(2))(crit)>0], also called the double cri tical point, DCP), which is normally found at P >0 for solutions but is shi fted to P <0 for blends.