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In free radical photopolymerization (FRP) or in radical sensitized cationic photopolymerization such as in free radical promoted cationic photopolymerization (FRPCP) [1,2], one usually observes, under air experimental conditions, the presence of an induction period and the decrease of both the polymerization rate and the final conversion. These effects lead to the reduction of the polymer chain length and to the formation of a “tacky” surface for the coating. Up to now, in FRP, several methods have been proposed to overcome the inhibition effects of oxygen [3]. In cationic polymerization reactions under a visible light exposure, a serious problem is concerned with the lack of efficient photosensitizing routes [4-7]. FRPCP was recognized as an interesting alternative way through the production of a radical R• which is further oxidized by the onium salt [8-10]. The main drawback is, however, the oxygen sensitivity of the system introduced by the radical way. The development of photoinitiating systems for FRP and FRPCP less sensitive to oxygen is therefore of wide interest. The goal of this paper is to review the capability of newly explored radical families in photopolymerization reactions under air. Special attention will be paid on the use of a representative silane in Free Radical Promoted Cationic Photopolymerization FRPCP.
