Photocrosslinking of Silicones. Part 11. Radical Photopolymerization Under Oxygen-Silicone Acrylates as Model Systems

Abstract

Silicone acrylates were used as model systems for radical photopolymerization under oxygen with commercial photoinitiators of the acleavage type. From calorimetric results, it is inferred that oxygen inhibits and terminates the chain process. The reaction rate, the final conversion, and the inhibition time of polymerization are proportional to the air pressure, to the intensity of the incident light, and to the quantum yield of the initiator photolysis. We show that the reaction starts if all oxygen is consumed in the silicone layer. Only oxygen which diffuses into the system determines the termination reaction. By means of the first Fickian diffusion law, it is demonstrated that the oxygen which diffuses into the silicone layer also determines the final conversion of double bonds in the system. However, in the absence of oxygen, the observed final conversion of double bonds is approximately 1. The high final conversion is combined with a high reaction rate.