Synthesis of graft copolymers

Abstract

AbstractThe two‐step synthesis of graft copolymers was carried out by several methods. In the first method, the initial peroxidized polymer was prepared from a copolymer of methyl acrylate and acroyl chloride by recation with tert‐butyl hydroperoxide; the content of perester could be varied. The rate of decomposition of these perester groups and the degradation velocity of this first‐step polymer were determined in benzene solution at various temperatures. The activation energies were 30.1 kcal./mole, respectively, which values correspond to the scission of the OO linkage. Grafting experiments were carried out in dilute solutions (1%) in order to avoid any grafting by transfer to the polymer. The second‐step polymerization followed the square‐root law dependence with respect to the peroxide polymer concentration. This rate was also of the first order with respect to the monomer, i.e., styrene, concentration. The rate of grafting was also evaluated by quantitative fractionation of the reaction products (precipitation method), taking into account the weight per cent of styrene in these isolated graft copolymers. The rate of grafting was also of the first order with respect to the monomer concentration. A comparison of the total rate, Rp, and the rate of grafting, Rg, indicates that, at low perester‐content, Rg is about one‐half of Rp, while at high perester content, Rg is much lower than Rp as a result of the recombination of redicals. These kinetic result are discussed on the basis of a general reaction scheme. In the second method, first‐step polyners carrying tert‐butyl peroxide endgroups, were prepared on the basis of the decomposition of tert‐butyl hydroperoxide in the presence of cupric octoate. The influence of the concentration of this copper salt on the rate of polymerization has been considered. The first‐step polymers so produced can initiate the polymerization of a second monomer, so that block copolymers are obtained by chain extension, probably on both sides. In a third method, the initial peroxidic polymer was obtained by electrolysis of an aqueous solution of polymethacrylic acid. The experimental conditions are discussed. The hydroperoxide‐containing polymers, prepared and isolated at below 10°C., can be used for a second‐step polymerization with another monomer, e.g., acrylamide. Graft copolymers were thus obtained; these hydroperoxidic polymers are, however, relatively unstable, particularly because of the presence of neighboring acid groups.