The synthesis of block copolymers in a flow system

Abstract

A method is described for the synthesis of linear block copolymers. The principle of the method is to start off polymerization of a vinyl compound in a system in which the liquid flows down a capillary tube at a regulated rate. Initiation of the reaction is made at a fixed point in the capillary tube, and the radicals so formed are allowed to grow until a specified size is reached. These radicals are then allowed to flow into a large excess of another monomer in which new environment polymerization is completed so that one half of the molecule is synthesized in the capillary and the other in the receiver attached to that capillary. The systems studied are butylacrylate-styrene and acrylonitrile-styrene. In order to achieve the synthesis of reasonable amounts of material for examination a special apparatus has been designed to initiate polymerization photochemically at extremely high rates. This is done by illuminating a 1 mm capillary tube by means of a specially designed elliptical reflector from a capillary mercury arc lamp. The lamp and the capillary are at the two foci of the ellipse. By using this arrangement radical concentrations 10000 times greater than that normally achieved have been obtained, and methods have been developed to demonstrate that it is possible to arrange matters to have a solution of polymer radicals in monomer issuing from the capillary tube. The kinetics of reaction in a flow system have been worked out, and incidentally the method provides an additional means whereby the absolute velocity coefficients of radical polymerization can be determined.