Polymérisations à l’état vitreux

Abstract

Numerous vinyl monomers polymerize rapidly when irradiated at low temperature (−78 to −196°) in vitreous mixtures with oils, polymers or certain solvents. The kinetic features of all these reactions are similar: very high conversions can be reached; polymerization rates and molecular weights exhibit a maximum for diluted monomer solutions. The polymerization proceeds by a free radical mechanism in hydrocarbon media; it may be anionic if the solvent used is an amide or an amine, or cationic in a halogenated compound. The structure of the binary glasses was investigated and it was found that phase separation occurs at low temperature, the monomer being dispersed in little droplets embedded in the vitreous medium. The polymerization occurs in these droplets which may remain in a supercooled state, at temperatures as much as 80 °C below the normal melting point of the monomer. When the mixtures are irradiated at temperatures below the glass transition point of the monomer, a polymerization is observed which may still proceed very rapidly. This reaction occurs at a temperature very close to the transition point in a highly viscous medium in which chain termination is strongly reduced.