APPLICATION OF A MOLECULAR SIMULATION TECHNIQUE FOR PREDICTION OF PHASE-SEPARATED STRUCTURES OF SEMIRIGID MODEL POLYURETHANES

A combination of a molecular simulation method and the Monte Carlo met hod has been successfully utilized to calculate phase diagrams of mode l polyurethanes. In our model, the entropic contribution of the Flory- Huggins expression has been modified to incorporate the contribution a rising from orientation of hard segments. The constraint associated wi th chain rigidity of hard segments has been explicitly considered. In addition, the interaction term has been modified to include the relati ve packing of hard segments. Phase diagrams of various MDI-PPG model p olyurethanes have thus been predicted utilizing these modifications. T he effects of soft- and hard-segment lengths have been considered and the actual degree of phase separation calculated. Our predictions have been compared to experimental values. Additionally, the contribution of hydrogen bonding to the miscibility behavior of hard and soft segme nts needs to be reevaluated.