Aqueous polymerization of ethylenically dicarboxylic acids and multicarboxylic acids studied by mass spectroscopy and nuclear magnetic resonance
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Maleic acid is extremely difficult to homopolymerize due to the severe steric hindrance and polar effects of two carboxylic acid groups. For the reason, poly(maleic acid) (PMA), a versatile industrial polymer, is conventionally prepared by hydrolysis of poly(maleic anhydride). Recently, a new initiation system consisting of hypophosphite and persulfate has been found to initiate the polymerization of maleic acid quickly in water. The mechanism of the polymerization was investigated in the research. The end-groups and molecular weight of PMA were analyzed by MALDI-TOF-MS and LC/MS. The end-groups were confirmed and the products of polymerization were quantified by 31P-NMR. A mechanism of polymerization involving the formation of hypophosphite radical and chain transfer to hypophosphite was postulated. The new initiation system was further explored for polymerization of itaconic acid, fumaric acid, 3-butene-1,2,3-tricarboxylic acid, mesaconic acid, and trans-conic acid, the last four of which had never been reported to homopolymerize before.