One of the problems with the polystyrene reaction injection molding systems is shrinkage of the foam before polymerization completes to the degree necessary for the polymer to retain its shape. Commercially available surfactants such as polymethylphenylsiloxane and block copolymer styrene-dimethylsiloxane enable the foam to retain the mold's shape. However, these surfactants react with commonly used initiators requiring more initiator and reducing the product's molecular weight.