Functional polysiloxanes with benzophenone side-groups : a photochemical application as radical polymerization macroinitiators

Functional siloxane copolymers containing one or more ester groups derived from 2-benzoyl-benzoic acid (2-BBA), 4-dimethylaminobenzoic acid (4-DMABA) or acrylic acid, were synthetized. These polymers were employed to prepare novel photo-initiating systems based on the phenone/tertiary amine photogeneration of radicals. The influence of nature and relative amount of functional pendant units on the overall efficiency of the system mixed with an acrylate-based composition was examined by quantitative IR spectroscopy. By comparing the different polymeric systems to the low-molecular-weight analogues, one observes a neat polymer effect inducing a greater initiation efficiency, especially when a polysiloxane containing only 2-BBA ester groups is associated to free 4-DMABA esters in the photosensitive composition.