Phase separation during the chemical blending of PBD / PS system

Abstract

Phase separation behavior of the polybutadiene (PBD) - polystyrene(PS) linear blend and semi-IPNs(interpenetrating polymer networks) was investigated by the light scattering technique during the polymerization of styrene in PBD-styrene mixture. Transmitted light intensity and scattered light intensity during the reaction were recorded with time. It was observed that the phase separation behavior of PS/PBD semi-IPN formation depeneded strongly on the reaction conditions such as the composition, reaction temperature, catalyst concentration, and crosslink density. As the polymerization proceeds, the styrene solution, which is a ternary system of the solvent(styrene monomer) and PS and PBD polymers, separated into two phases. One phase is the PS-styrene monomer solution and the other is the PBD-styrene monomer solution. The phase separation resulted from the decrease of compatibility between the PBD and PS by the conversion of styrene monomer into polystyrene during the polymerization. However, it was observed that in spite of the thermodynamic incompatibility of the two polymers, the high degree of interlocking in semi-IPNs hindered the phase separation. It was also observed that the rate of phase separation was a function of the diffusion rate controlled by the viscosity. An obvious feature in the light scattering experiment was that phase separation proceeded nucleation/growth followed by spinodal decomposition which was mainly cintributed to the early stage phase separation. When the PBD or Divinylbenzene content was increased, the average domain correlation length, $A_m$ decreased due to the viscosity effects. The high reaction rate at elevated reaction temperature or high catalyst concentration led to earlier gelation which restricted the to phase separation. The transmission electron micrographs for various process conditions showed similar results as the light scattering experiment. The morphology revealed that the large PS domains dispersed in the PBD matr...