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 molecular weight polystyrenes dissolved in linear alkanes (oligoethylenes) were measured over the range 0.1 to 100 MPa. While (dT/dP)(crit) along the upper critical solution (UCS) locus for a "typical blend'' is positive, and for the "typical solution'' can be either positive or negative (but is usually negative), there is no essential difference between blend and solution. Rather, the difference in sign is a consequence of the location of the hypercritical point (that point in (T,P)(crit) space where (dT/dP)(crit) changes sign, [(dT/dP)(crit)=0 and (T/dP(2))(crit)>0], also called the double critical point, DCP), which is normally found at P >0 for solutions but is shifted to P <0 for blends.