THE USE OF THERMAL-ANALYSIS IN THE STUDY OF LIQUID-LIQUID PHASE-SEPARATION IN BLENDS OF SOME CRYSTALLIZABLE HOMOPOLYMERS WITH THEIR BRANCHED COPOLYMERS

It is difficult to determine the degree of mixing or demixing in blends in which the two components have closely similar physical properties, such as homopolymer-lightly branched copolymer blends. Direct methods of observation of liquid-liquid phase separation are not possible, but in the course of our studies of blends of linear with branched polyethylenes we have developed several indirect techniques. We examine samples after rapid quenching from the melt in order to determine whether the melts were mixed or demixed prior to quenching. One of the most useful techniques is DSC; however, there are limitations to its applicability and it is usually necessary to use a second technique. This paper describes the techniques in detail and pays particular attention to the strengths and weaknesses of DSC in determining phase separation.