NETWORK FORMATION .2. RADICALFORMING PROCESS IN PRESENCE OF SOLVENTS

The formation in solution of networks consisting of polyvinyl trichloracetate crosslinked by methyl methacrylate chains has been studied. Benzene, ethyl acetate and dioxan have been used as diluents, with molybdenum carbonyl as thermal initiator at 80°C and manganese carbonyl as photoinitiator at 25°C. Relations have been developed which allow corrections to be made to the observed gel-times to take account of chain transfer and initiator consumption. With molybdenum carbonyl the corrected gel-times agree with those calculated from the prevailing rates of initiation, showing that all the initiating radicals are attached to the prepolymer (polyvinyl trichloracetate) chains. In ethyl acetate and dioxan solutions the majority (and probably all) of the radicals are similarly attached. Gelation experiments with photoinitiation by manganese carbonyl provide no evidence for the formation of any unattached radicals in solutions containing up to 70% v v benzene. With ethyl acetate as diluent abnormally long gel-times were observed. Tracer investigations with CCl314COOEt as the halide component of the initiating system indicate that only attached radicals are formed, consequently the long gel-times indicate an unexpectedly low rate of photoinitiation under these conditions. This conclusion has been confirmed by direct measurement of the rates of initiation in the presence of ethyl acetate. Deviations from the inverse relation between gel-time and initiator concentration predicted by simple gelation theory are encountered when the carbonyl concentration is relatively high and are discussed briefly. © 1969.