Miscibility of ethylene-styrene copolymer blends

Binary blends of ethylene-styrene copolymers were studied over the full ran ge of copolymer styrene content. A miscibility and cocrystallization map wa s determined from morphology as imaged with atomic force microscopy (AFM), glass transition behavior primarily from dynamic mechanical thermal analysi s (DMTA), and melting behavior from differential scanning calorimetry (DSC) . A difference in styrene content of about 9 wt% marked a transition from m iscible to immiscible amorphous copolymer blends. The miscibility-immiscibi lity boundary encompassed a very small region, estimated as 9-10 wt% differ ence in styrene content, where partial miscibility was clearly evident. Ble nds in this region were characterized by an upper critical solution tempera ture (UCST). The phase behavior in the partial miscibility region was stron gly dependent on temperature and molecular weight. The critical composition difference for blends of amorphous copolymers of about 9 wt% also applied to blends of semicrystalline copolymers. Cocrystallization of miscible, sem icrystalline copolymers occurred if the styrene content difference was less than about 4 wt%. If the styrene content difference was between 4 and 9 wt %, partial cocrystallization was possible depending on the composition of t he blend (wt/wt) and the thermal history of the blend. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.