Miscibility of poly(styrene-co-butyl acrylate) with poly(ethyl methacrylate):: Existence of both UCST and LCST

A miscible homopolymer-copolymer pair viz., poly(ethyl methacrylate) (PEMA)-poly(styrene-co-butyl acrylate) (SBA) is reported. The miscibility has been studied using differential scanning calorimetry. While 1 : 1 (w/w) blends with SEA containing 23 and 34 wt % styrene (ST) become miscible only above 225 and 185 degrees C respectively indicating existence of UCST, those with SEA containing 63 wt % ST is miscible at the lowest mixing temperature (i.e., T-g's) but become immiscible when heated at ca 250 degrees C indicating the existence of LCST. Miscibility for blends with SEA of still higher ST content could not be determined by this method because of the closeness of the T-g's of the components. The miscibility window at 230 degrees C refers to the two copolymer compositions of which one with the lower ST content is near the UCST, while the other with the higher ST content is near the LCST. Using these compositions and the mean field theory binary interaction parameters between the monomer residues have been calculated. The values are XST-BA = 0.087 and XEMA-BA = 0.013 at 230 degrees C. (C) 2000 John Wiley & Sons, Inc.