Phase separation behavior of the polyurethane(PU)-polystyrene(PS) interpenetrating polymer networks(IPN's) was investigated by measuring the turbidity during simultaneous polymerization. Decrease in transmitted light intensity through the reacting mixture was recorded with elapsed time.
To compare with the rate of polymerization, the reaction kinetics of the PU and PS were obtained for the 50/50 composition mixture. The PU polymerization rate was much higher than that of PS, thus it was thought that phase separation process was mainly controlled by the PU polymerization rate.
The change in transmitted light intensity during the IPN formation was studied as a function of composition, synthesis temperature, crosslink density and the catalyst concentration.
The process of the phase separation was developed as the result of the increase in molecular weight from an initial homogeneous mixture of PU prepolymer and styrene monomer. However, it was observed that in spite of the thermodynamic incompatibility of the two polymers, the high degree of interlocking between the constituent networks in IPN hindered phase separation.
The onset of phase separation was occurred at around similar molecular weight range of the PU regardless of experimental variables, and the phase separation rate was increased as the polymerization rate was increased.
It was also observed that the rate of phase separation was a function of the rate of the increase in molecular weight and the diffusion rate controlled by the viscosity.
