Compositional Gradients in Siloxane Copolymers by Photocontrolled Surface Segregation

We demonstrate how to tune the surface chemistry and properties of copolymers obtained by the photopolymerization of polyoxyethylene (meth)acrylic monomers and a low polarity siloxane comonomer which spontaneously migrates to the free surface. By controlling the photopolymerization conditions, such as the light gradient through the thickness of the film and selecting the proper monomer functionality, it is possible to optimize and photoenforce the surface segregation of the siloxane comonomer. Photocured films containing the same amount of siloxane component (1 wt %) can exhibit a surface energy ranging from 42 to 22 mN m(-1) depending on the process conditions. XPS and AFM analyses confirm that polymers with a compositional gradient are obtained and that the surface segregation can be finely photocontrolled. Photopolymerization is thus proven to be a facile, single step method for generating gradient films and for independently and simultaneously tune their surface and bulk properties.