PROCESS FOR PREPARING BLOCK COPOLYMERS
Original Publication Date: 1977-Apr-30
Included in the Prior Art Database: 2004-Mar-29
Xerox Disclosure Journal
There is described a process for the preparation of block co-polymers having photoconductive segments derived from a vinyl monomer, e.g., vinylcarbazole, vinylpyrene, vinylanthracene or the like, and segments derived from a second addition mono-mer (which may also be photoconductive), e.g., acrylates, dienes or certain vinyl polymers such as polystyrene. The process is especially suitable for preparing block copolymers where at least one of the constituent monomers is incapable of polymerization by anion initiated polymerization yet capable of radical initiated polymerization. According to the process a photoconductive vinyl polymer having terminal groups capable of decomposition to free radicals is combined with the second monomer by dissolving them in a liquid reaction medium. The reaction medium must be a solvent for the vinyl polymer and the second monomer but it must be a non-solvent for the homo-polymer of the second monomer and the copolymer of the vinyl polymer and the second monomer The terminal groups, e g., peroxide groups, of the vinyl polymer are decomposed to free radicals whereby some of the second monomer polymerizes and forms a polymer segment attached to the vinyl polymer. There is also formed some homopolymer of the second monomer. Both the copolymer and the homopolymer of the second monomer are insoluble in the reaction medium and there is formed a gel-like mixture comprised of solid phase particles in the liquid reaction medium. The free radical species which remain become trapped or immobiLized within the polymeric solids and thereby termination of the growing polymer by coupling or dispropor-tionation is prevented. Subsequently there is added to the mixture sufficient vinyl monomer to effect termination of the propagating radical by forming a block copolymer with the homopolymer of the second monomer which was previously formed. Hence, substantially all of the product comprises a block co-polymer.