PARTITION-COEFFICIENT FOR SMALL AMOUNTS OF MONOMER, SOLVENT, OR PLASTICIZER IN A 2-PHASED POLYMER BLEND OR IPN

Theoretical calculations based on statistical thermodynamics are prese nted addressing the partitioning behavior of a monomer, solvent, or pl asticizer in a two-phased polymer system. A phase-separated interpenet rating polymer network (IPN) consisting of a polyurethane (PU) and pol y(methyl methacrylate) (PMMA) (50/50 by weight) is chosen as the model . Methyl methacrylate (MMA) is chosen as the partitioning small molecu le, which is added at 20% by weight of the polymers. It is shown that the free energy of mixing this MMA is minimum only when the MMA is par titioned nearly uniformly between the two phases. It is also shown tha t such mixing of a small molecule in a polymer system is controlled by the entropic rather than enthalpic contributions to the free energy c hanges. (C) 1996 John Wiley & Sons, Inc.