POLYSILOXANES WITH BENZOPHENONE SIDE-GROUPS - FACTORS AFFECTING THEIREFFICIENCY AS FREE-RADICAL POLYMERIZATION PHOTOINITIATORS

Functionalized silicone copolymers containing 2-benzoylbenzoic acid (2 -BBA) ester side groups were evaluated as radical polymerization photo initiators in the presence of an amine co-reactant. Following up previ ous reports, the study of their efficiency conducted at various concen trations of the photoinitiating system in a model acrylate formulation was compared to that of the low molecular weight 2-BBA ester. The pho tosensitive polysiloxanes were confirmed to exhibit a clear polymer ef fect, the type II photoinitiating efficiency being enhanced when the c hromophores are present as pendant groups on polymer chains and when t he tertiary amine (ethyl 4-dimethylaminobenzoate) is free in the mediu m and with r = [amine](0)/[2-BBA](0) = 1. The influence of the increas e of r in the range 0.5-2 on the initial polymerization rate at consta nt concentration of BBA was shown to improve the initial rate of polym erization as well as the limiting conversion. N,N-Dimethyl and N,N-die thyl aliphatic or aromatic low moleular weight aminoesters were studie d as co-initiators to gain a deeper insight into the process. The effe ct of the incident UV beam wavelength was also examined and showed the complex influence of the amine structure on reactivity. Light absorpt ion characteristics, reducing power and aptitude to charge transfer in itiation of acrylate polymerization seem to contribute to various exte nts to overall efficiency.