Properties of Post-Cured Siloxane Networks.

Post-curing of vinyl-addition cured siloxane networks can take place due to the presence of excess silicon hydride. The reaction of these groups, which leads to increased cross-link density especially at elevated temperatures, can be retarded by treatment with ammonia gas or eliminated by exposure to ethylene gas. There is a interesting correspondence between the post-curing behavior and the gelation process. In both cases, two curing regimes are observed. For low extents of reaction, the mobility of chains is high, even though the post-curing experiment is performed on samples which have already gelled, and the cure is controlled by reaction kinetics, not by the diffusion of the reactants.