Photocuring of functionalized rubbers .5. Radical polymerization of rubbers with acrylate groups

The photoinitiated polymerisation of rubbers bearing pendant acrylate groups has been studied by infrared spectroscopy. In the presence of a radical photoinitiator, the polymerisation develops within a few seconds of UV exposure to give a totally insoluble crosslinked polymer. The degree of acrylation of the functionalised rubber, ranging from 10 to 70%, plays an important role on the rate of polymerisation, the gel fraction and the crosslink density. The presence of cyclic structures in the polymer chain decreases the molecular mobility, and is thus slowing down the reaction. The addition of a diacrylate or triacrylate monomer, which acts as a reactive plasticiser, leads to a marked increase of the crosslinking rate. A 0.1 sec exposure proved to be sufficient to polymerise more than half of the acrylate functions and transform the plasticised elastomer into a hard and insoluble material. The great photosensitivity of these systems allows crosslinking of the rubber to be achieved by a simple exposure to sunlight for a few minutes.