PHOTO-CROSS-LINKING OF EPDM ELASTOMERS - EFFECTS OF THE FUNCTIONALITY OF PHOTOINITIATORS AND CROSS-LINKING AGENTS

Compositions consisting of an EPDM elastomer with ethylidenenorbornene units, photoinitiators and multifunctional crosslinkers were exposed to mercury radiation and their state of crosslinking was characterized by gel content, swelling ratio and stress - elongation curves. It was concluded that the irradiated compositions containing easily polymerizable crosslinkers can be roughly classified in the following two types of bimodal networks : - crosslinked interpenetrating networks or crosslinked elastomers when the photoinitiator is a hydrogen photo-extracting one, and - independent interpenetrated networks or reinforced elastomers when the photoinitiator is a photofragmenting one. When the crosslinker is an allylmercaptan thiol-ene system, the irradiated compositions are branched elastomers, mainly. Also, an abnormal dependence between the swelling ratio and the gel content was observed and an explanation based on an unhomogeneous crosslinking distribution is proposed for it.