Radical Photopolymerization of Vinyl Monomers

Abstract

Photopolymerization is the initiation by light of a chain polymerization process. In the more general sense, photopolymerization implies the increase of molecular weight caused by light. Photopolymerization is not only useful for the detection and identification of photochemically produced free radicals; since photopolymerization reactions can be started or stopped at will by the simple expedient of turning on or off light, a means is provided for studying the nonsteady-state kinetics of polymerization [1]. Photopolymerization also allows for the subtle control of molecular weight and molecular weight distribution by varying the intensity of light. Photopolymerization can be confined to local regions since the light can be spatially controlled. Photopolymerization can be carried out at very low temperatures. Hence, chain-transfer processes leading to branched macromolecules will be absent. Photopolymerization at low temperature yields the low-energy stereospecific polymeric species, namely the syndiotactic configuration of the polymer [2]. Certain monomers can only be polymerized at low temperature, i.e., they have low ceiling temperatures; the photopolymerization offers this possibility [3]. Because photopolymerization need not be carried out at elevated temperatures, it has applications to biochemistry. One important application of the method is in disk electrophoresis [4]. Photopolymerization played an important role in the early development of polymer chemistry. One of the first procedures for polymerizing vinyl monomers was to expose the monomer to sunlight. Blyth and Hoffman [5] reported the polymerization of styrene by this method in 1845.