Some Fundamental Aspects of the Polymerization of Vinyl Monomers with Electron Beams

Abstract

The radiation induced polymerization of vinyl monomers has been intensively studied during the past twenty-five years. In general the polymerization has been found to proceed via free radical mechanisms although more recent work shows that ionic mechanisms are also operative under certain conditions^l. Most of the research has been conducted at moderate dose rates, up to one megarad per hour, for example, using cobalt 60 or other convenient radioisotopes. The high penetrating power and low dose rates minimized the experimental difficulties involved in such research. The development of high power electron accelerators in the 200–500 Kv range for high speed industrial radiation processing has led to enormous interest in their use including the polymerization and crosslinking of solvent free organic coatings. Fundamental research, on the other hand, using accelerators for polymerization studies has been rare. This has been due to the experimental difficulties caused by (a) the low penetrating power and (b) the heat effects arising from the rapid deposition of energy and the exotherms arising from the rapid polymerization reactions. The penetration pattern leads to difficulties with uniform fields, accurate dosimetry and to difficulties of conducting experiments in an oxygen free atmosphere together with other control problems. The kinetics of polymerization themselves are further complicated by the use of rapidly scanned electron beams rather than a steady uniform field.