Multiple glass transitions in block copolymer films cast from cyclohexane solutions at two temperatures

Films of block copolymers of polystyrene + isoprene, cast from cyclohexane at temperatures above and below a conformational transition temperature (T_p) derived from the plot of η] vs. T, have been examined for glass transition temperatures. In every case, two glass transitions were found, T_g1 (polyisoprene) and T_g2 (polystyrene) or T_g1 and T_g (an intermediate species). T_g is assumed to be characteristic of a mixed phase thus providing further evidence that T_p marks a conformational transition from a phase-separated to a phase-mixed form.