Factors Affecting the Ultraviolet-Initiated Polymerization of Vinyl Monomers

Measurements of the extent of polymerization have been made for photoinitiated polymerization reactions using consistent conditions and a common monomer, butyl acrylate. Three radiation wavelengths were used and it was found that in most cases polymerization proceeded in the order 350 > 300 > 254 nm. From the range of photoinitiators studied it was found that those of the benzoin type, undergoing cleavage, promoted reaction faster than the benzophenone type, requiring a hydrogen abstraction mechanism. At 350 nm, those undergoing a cleavage mechanism showed reaction rates following the order of their ultraviolet absorption. A hydrogen donor such as a tertiary amine was necessary for the benzophenone-type initiators. Hydrogen donors tended to have mixed effects on polymerization produced by benzoin-type initiators. From a broad range of hydrogen donors used with benzophenone it was found that aliphatic tertiary amines were the most effective.