SILICONE ELASTOMER

This invention provides compositions which are curable to hydrophilic, water-absorbing silicone-organic copolymer elastomers via free radical polymerization such as by the use of free radical precursors, ultraviolet light or electron beam radiation. The compositions are mixtures of (A) from 50 to 95 parts by weight of block copolymers containing polydiorganosiloxane segments and polyalkyleneoxy segments which block copolymers contain terminal aliphatically unsaturated groups such as those derived from the reaction of isocyanoethyl methacrylate with terminal free hydroxyl groups present on the polyalkyleneoxy segments and the polyalkyleneoxy segments are ultimately attached to the silicon atoms by means of a linkage formed by reaction with a diisocyanate compound and (B) from 5 to 50 parts by weight of at least one substantially water insoluble aliphatically unsaturated organic monomer which is compatible with (A) such as methyl methacrylate. The cured elastomers, some of which are optically clear, are useful as membranes for gas or fluid separations or for the controlled release of bioactive agents such as insecticides, herbicides, or drugs.