UV Curable Silicones from Acryloxymethyldimethylacryloxysilane

Abstract

A facile preparation of acrylate terminated silicones by the condensation reaction between the readily available silanol terminated silicone fluids and acryloxymethyldimethylacryloxysilane is described. The simplicity of the reaction provides a practical route for the preparation of UV curable silicones. The surprising ease of the reaction between the silane and silanol is attributed to the possible hypervalent silicon transition state even though 29 Si-NMR evidence suggests the silane is tetracovalent.The constant quest for faster curing silicones for various industrial applications has led to many important developments for radiation curable silicones in recent years (1,2). Notable examples among these developments include cationic curing silicones (5-7), free-radical curing thiol-ene (8-10% acrylate or acrylamide (11-14) functional silicones, and photohydrosilylation curing silicones (15)(16)(17). Each of these developments offers certain advantages but at the same time imposes limitations in their applications. Cationic curing silicones using iodonium or sulfonium salts as the photoinitiators for the curing of epoxy and vinyl ether functional silicones allows fast cure without the tacky surface that is often associated with the oxygen inhibition of the acrylate cure. However, the high cost of the photoinitiators and the compatibility of the photoinitiator with silicones are problems. Also, acid generated from the decomposition of the onium salt during UV irradiation is responsible for the cationic cure. However, the acid thus generated remains in the cured silicone network. The presence of the strong acid in a siloxane network clearly begs the question of whether the cured silicone will be durable enough for the intended applications. Thiol-ene crosslingking of mercaptosiloxanes and vinylsiloxanes in the presence of free radical initiator is also well known. The curing is fast and also free of oxygen inhibition. However, the shelf stability of the uncured silicones and the thermal stability of the 170