Thermal degradation behavior of PMMA synthesized by emulsifier‐free emulsion polymerization with a Cu2+/HSO3− redox system

Abstract

AbstractIn this study, poly(methyl methacrylate) (PMMA) latex was synthesized in an emulsifier‐free emulsion polymerization at 60°C using a Cu2+/HSO redox initiator system with different concentrations of Cu2+. The experimental results showed that the monomer conversion reached above 90% for all systems. Zeta potential was all negative due to the bonded bisulfite ion and the magnitude was greater than 30 mV, providing the stability of PMMA emulsion. The morphology of the latex observed by scanning electron microscope revealed a uniform particle size, and the average particle size increased from 181.9 to 234.2 nm as the Cu2+ ion concentration increased from 2.0 to 6.0 mM in 1M of MMA solution. Thermal degradation behavior of synthesized PMMA was studied by thermogravimetric analysis, in which a two‐stage degradation behavior was observed. These two stages were found to be caused by the degradation of unsaturated end group (PMMACRCH2) and saturated end group (PMMAH), respectively. In addition, the higher the concentration of Cu2+ ion, the greater the proportion of PMMACRCH2 in the final product, and in turn rendering more weight loss in the first‐stage degradation. The copper ion not only played a role in the redox initiation, but also acted as a chain transfer agent to terminate growing polymer chains, thus producing PMMACRCH2. The apparent activation energies of the first stage (Ea1) and second stage (Ea2) were calculated by Ozawa's and Boswell's method. The results showed that Ea1, representing the degradation of PMMA‐CRCH2, was lower than Ea2 for the degradation of PMMA‐H. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009