Photochemical synthesis of block copolymers

Abstract

AbstractA new photochemical synthesis of block copolymers is described. Polyesters are prepared containing γ‐keto pimelic acid. This provides ketone carbonyl functions along the backbone of the polymer chain. When irradiated with ultraviolet light in the presence of a vinyl monomer such as methyl methacrylate, free radicals are formed by the scission of the main chain of the polyester at the ketone groups. These radicals initiate the polymerization of the vinyl monomer to form a block copolymer. If light is used which is absorbed by the ketone group but not the vinyl monomer, and no transfer occurs, only block polymer is formed. The quantum efficiency for initiation (2.4 × 10−4) is low compared with that for chain breaking (4.0 × 10−3) indicating the possibility that the addition of polymer radicals to the vinyl monomers may be a relatively inefficient process. The activation energy for the block copolymerization of methyl methacrylate is 3.7 kcal./mole which is very similar to that observed in the photopolymerization of this monomer with conventional sensitizers.