PHOTO-CROSS-LINKING OF EPDM ELASTOMERS - EFFECTS OF THE FUNCTIONALITYOF 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 polymeri zable crosslinkers can be roughly classified in the following two type s of bimodal networks : - crosslinked interpenetrating networks or cro sslinked elastomers when the photoinitiator is a hydrogen photo-extrac ting one, and - independent interpenetrated networks or reinforced ela stomers when the photoinitiator is a photofragmenting one. When the cr osslinker is an allylmercaptan thiol-ene system, the irradiated compos itions are branched elastomers, mainly. Also, an abnormal dependence b etween the swelling ratio and the gel content was observed and an expl anation based on an unhomogeneous crosslinking distribution is propose d for it.