Silicone foams stabilized by surfactants generated in situ from allyl-functionalized PEG

Silicone foams normally require the use of agents or chemical reactions that blow gases, and a surfactant for bubble stabilization. We have discovered that the presence of monoallyl-functionalized poly(ethylene glycol) (PEG) leads to large increases in the viscosity of silicone pre-elastomers such that stable foams form with bubbles mostly being generated by coalescence of dissolved gases during the normal degassing process. Although silicone elastomer cure may take up to 24 h for completion, the foams remain stable during this time when appropriate concentrations of allyl-PEG and curing catalyst are used. No traditional surfactant is required, but PEG-modified silicone surfactants are formed in situ by covalent grafting of the PEG to the silicone matrix, leading to the increase in viscosity. The presence of allyl-PEG decreases elastomer cure efficiency, but this is readily overcome, if necessary, to generate more rigid foams by the use of additional platinum catalyst, in which case foaming occurs both due to loss of dissolved gases and to hydrogen evolution. Foam stabilization with appropriate allyl-PEG compounds is a consequence of an initial viscosity increase.