Heterophase polymerization of different methacrylates: Effect of alkyl ester group on kinetics and colloidal behavior



In this article, methyl- (MMA), ethyl- (EMA), n-butyl- (BMA), n-hexyl (HMA), and 2-ethyl hexyl (2-EHMA) methacrylates were homopolymerized in heterophase at 60°C using sodium dodecyl sulfate as surfactant and potassium persulfate as initiator. The effects of monomer content in the reaction mixture (2.5 and 3.5 wt %) and the alkyl ester groups of the methacrylates on the kinetics, average particle diameter (Dp), molar masses, tacticity, and glass transition temperature (Tg) were studied. The final weight average molecular weights were in the range of 4.53 × 105 to 2.78 × 106 g/mol with polydispersities between 1.7 and 3.1 for different methacrylates. For 2.5 wt % of monomer concentration, the order of increase in polymerization rate was RpHMA > RpBMA > Rp2-EHMA > RpEMA > RpMMA, whereas for 3.5 wt % of monomer concentration was RpBMA > RpHMA > Rp2-EHMA > RpEMA > RpMMA. This behavior was ascribed to the differences in the water solubility, monomer partitioning between the different phases, and monomers reactivity. The Dp values varied between 42 and 65 nm, increasing according to the hydrophobicity of each monomer. 13C-NMR (nuclear magnetic resonance) and differential scanning calorimetry analysis demonstrated that 79–87% of syndiotactic configuration was obtained for the different polymers. The steric effect of the alkyl ester length in the methacrylates contributed directly to promote the syndiotactic configuration. Nevertheless, Tg values (between −7 and 120°C) for these polymers decreased when the alkyl ester length increased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40191.