New silicone hydrogels based on interpenetrating polymer networks comprising polysiloxane and poly(vinyl alcohol) networks

A method for the synthesis of a new silicone hydrogel as a biphase material for soft contact lenses is considered. The method is based on the synthesis of sequential interpenetrating polymer networks (IPN) and includes the following stages: (1) cross‐linked silicone synthesis by the reaction of vinyl‐ and hydride‐containing oligosiloxanes; (2) silicone network saturation with vinyl acetate and cross‐linking monomer followed by UV‐initiated polymerization to form an IPN comprising the silicone and cross‐linked poly(vinyl acetate) (PVAc) network; (3) PVAc network alcoholysis with methanol to obtain silicone hydrogels comprising the silicone and cross‐linked poly(vinyl alcohol) (PVAl). A study of hydrophilic, optical, mechanical, and structural features of the silicone hydrogels showed that optical transparency is achieved for materials with the highest density of silicone network cross‐linking where the size of IPN structural units does not exceed 100 nm. The water content in hydrophilic networks of silicone hydrogel is found to be below the values typical of cross‐linked PVAl, leading to non‐additivity of IPN mechanical properties. Indeed, the elasticity moduli (E) of the hydrophilic and silicone networks are 0.4–0.7 and 0.7–1.8 MPa, respectively, whereas for some IPN this value reaches 3.0 MPa. The optimal parameters of synthesis providing the reduction of E to 0.8–1.6 MPa without deterioration of the required performance characteristics (optical transparency 90–92%, water content 20–39 wt%) are determined. Copyright © 2009 John Wiley & Sons, Ltd.