THERMOCHEMICAL STUDIES OF SOME ACRYLATE AND METHACRYLATE POLYMERIZATIONS IN EMULSION SYSTEMS

Abstract

With the use of a Tian–Calvet microcalorimeter, the heats of polymerization of a number of monomers have been measured in aqueous emulsion systems: the emulsifying agent was cetyltrimethylammonium bromide, and initiation was by Fenton's reagent (Fe++ + H2O2). The monomers employed were acrylic acid, methyl, ethyl, and butyl acrylates, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, methacrylic acid, and methyl, ethyl, butyl, and hexyl methacrylates. The heats of polymerization lie in the range from 13 to 19 kcal per mole, the experimental standard deviations being 40 to 110 cal per mole. A steady increase was observed for acrylic acid and its CH3, C2H5, and C4H9 esters, and for methacrylic acid and its CH3, C2H5, C4H9, and C6H13 esters. This change is attributed to a steady increase in the proportion of head-to-head, tail-to-tail polymers, leading to a decrease in steric hindrance. Abnormally low heats observed with hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate are attributed to the solvation of the monomer, less solvation being possible in the polymer as a result of shielding.