Evaluation of miscibility of 4-substituted polystyrene / polydiene blends

Phase behavior of polystyrene (PS) derivatives with bulky 4-substituent / polydienes blends was investigated by optical microscopy and differential scanning calorimetry (DSC). Firstly, we prepared blend films of polyisoprene with 1,2- and 3,4- microstructures (vinyl-PI) and various PS derivatives, i.e., poly(4-trimethylsilylstyrene) (PTMSS), poly(4-tert-butylstyrene) (PtBS) and poly(4-tert-butoxystyrene) (P/BOS), and then, evaluated miscibility of those blends. All these PS derivatives were miscible with vinyl-PI, but the relative magnitude of miscibility is shown as PffiS>PTMSS>P/BOS. This corresponds to the degree of dipole moment of the elements directly connected with benzene ring of the polystyrenes. Secondly, we examined miscibility of the blends of PTMSS and various polydienes, i.e., vinyl-PI, 1,4-PI, poly(2-tert- butylbutadiene) (PtBB) and poly(2,3-dimethylbutadiene) (PDMB). These polydienes were also compatible with PTMSS. Based on the calculation of the cohesive energy densities, (AE/V), the estimated values for the PS derivatives are different from those for the polydienes. This result indicates that the other factor such as volume change upon mixing must be dominant for miscibility.