Electrochemical transformations of polymeric acid solutions. I. Crossed Koble synthesis

Abstract

Poly(methacrylic acid) was electrolyzed at 20°C. in 0.2 M dry methanol solution in a glass apparatus provided with two polished platinum disk electrodes; the current density was kept constant (300, 800, or 1000 ma.). Before electrolysis the acid was partially neutralized in order to increase the electrical conductivity. The electrolysis was characterized by evolution of carbon dioxide at the anode, while the acid content of the polymer decreased. When the degree of decarboxylation was about 30%, intramolecular lactonization occurred by interaction of unsaturated groups with neighboring acid groups. The changes of chemical composition of the polymer in function of the time were followed by determination of free carboxylic acid groups, of γ‐lactones, and unsaturated groups (bromine addition). The amount of methyl ester formed by methanolysis of the lactones was calculated from methoxyl determinations. At the end of electrolysis only 5–6% free carboxylic groups were present, 35–40% lactones, 30% ester groups; the residue was mainly a hydrocarbon fraction (partially unsaturated). The electrolysis was also carried out in the presence of low molecular weight carboxylic acids, acetic, ϵ‐acetaminocarproic, and cyanoacetic acids, the ratio of the concentration of these acids to that of polymeric acid being varied over a wide range. With acetic acid the chemical composition of the polymer was only slightly affected through grafting of side methyl groups, as was shown by the use of C14 acetic acid. With ϵ‐acetaminocaproic and cyanoacetic acids the crossed Kolbe synthesis reactions are much more important, 20–24% side alkyl acetamino groups and 15% cyanomethylene groups being grafted to the main chain by this method. Chain degradation during these experiments can be practically avoided.