PHOTO-CROSS-LINKING OF SILICONES .7. THE INFLUENCE OF THE SILICONE BACKBONE - A KINETIC-STUDY

The photo-induced radical crosslinking of silicone containing pendant acrylate groups was investigated by nanosecond flash photolysis and photocalorimetry. From the results of the flash photolysis is inferred that the photochemically formed benzoyl radicals react with the acrylate groups of the system. A possible H-abstraction from the methyl groups of the silicone backbone was not observed. The silicone backbone functions only as an internal solvent. Calorimetric measurements with model systems support these results. The polymerization process is inhibited by oxygen. From calorimetric results is inferred that oxygen both inhibits and terminates the polymerization process. Due to their high oxygen solubility the silicone units increase the oxygen influence on the crosslinking. The calorimetric measurements shows also that a direct bond between silicone backbone and the acrylate group reduces the oxygen influence. Also, in absence of oxygen a direct bonded acrylate group accelerates the polymerization rate.