Polysiloxanes with benzophenone side groups: factors affecting their efficiency as free radical polymerization photoinitiators

Abstract

AbstractFunctionalized silicone copolymers containing 2‐benzoylbenzoic acid (2‐BBA) ester side groups were evaluated as radical polymerization photoinitiators in the presence of an amine co‐reactant. Following up previous reports, the study of their efficiency conducted at various concentrations of the photoinitiating system in a model acrylate formulation was compared to that of the low molecular weight 2‐BBA ester. The photosensitive polysiloxanes were confirmed to exhibit a clear polymer effect, the type II photoinitiating efficiency being enhanced when the chromophores are present as pendant groups on polymer chains and when the tertiary amine (ethyl 4‐dimethylaminobenzoate) is free in the medium and with r = [amine]0/[2‐BBA]0 = 1. The influence of the increase of r in the range 0.5‐2 on the initial polymerization rate at constant concentration of BBA was shown to improve the initial rate of polymerization as well as the limiting conversion. N,N‐Dimethyl and N,N‐diethyl aliphatic or aromatic low molecular weight aminoesters were studied as co‐initiators to gain a deeper insight into the process. The effect of the incident UV beam wavelength was also examined and showed the complex influence of the amine structure on reactivity. Light absorption characteristics, reducing power and aptitude to charge transfer initiation of acrylate polymerization seem to contribute to various extents to overall efficiency.