Some representative examples of additional ethylenically unsaturated monomers that can potentially be synthesized into the rubbery polymer include alkyl acrylates, such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, and the like; vinylidene monomers having one or more terminal CH2???CH??? groups; vinyl aromatics, such as styrene, ??-methylstyrene, t-butylstyrene, bromosty