EMULSION POLYMERIZATION OF METHYL METHACRYLATE WITH ISO-OCTYL-3-MERCAPTOPROPIONATE AS CHAIN TRANSFER AGENT

RONCO, LUDMILA I.; MINARI, ROQUE J.; CIAN, LORENA; VEGA, JORGE R.; GUGLIOTTA, LUIS M.

Bahia Blanca

Simposio; Simposio Argentino de Polímeros; 2011

Comisión Organizadora del Simposio

Some properties of homopolymers are determined by its molecular weight distribution (MWD). In emulsion polymerizations, chain transfer agents (CTA) are normally used for reducing the high molecular weights that would otherwise be produced due to the “compartmentalization” of the free-radicals in the polymer particles. Relevant characteristics of a CTA employed in an emulsion polymerization are its water solubility, its mass transfer resistance to diffusion between phases, and its “effective” reactivity ratios in the polymer phase CX = kfX/kp, where kfX is the global rate constant of chain transfer to the CTA, and kp is the global rate constant of propagation. Iso-octyl 3-mercaptopropionate (iOMP) is normally commercialized as a mixture of several isomers. It is less odorous and toxic (hazard code GHS02) than others more common mercaptane-based CTAs (as e.g., dodecyl nercaptane). The iOMP was not extensively study yet with respect to its ability for controlling MWD in emulsion polymerizations. For example, Minari et al. (2008) investigated the emulsion polymerization of styrene (St) using iOMP as CTA. The characterization of the iOMP (provided by Aldrich Chemical) suggested that it was a mixture of more than 10 isomers, where 5 of them constituted more than 95% of the total mass; and 4 out of such 5 exhibited similar chain transfer characteristics. Therefore, they considered the iOMP as a binary mixture with 2 different CX’s (both higher than 1). Also, the different (and high) reactivity of the CTA-isomers generated polystyrene (PSt) with broad and bimodal MWDs at the end of a batch process. On the other hand, the inclusion of iOMP as CTA does not significantly change the polymerization rate of St. In this work, the isothermal batch emulsion polymerization of methyl methacrylate (MMA) using iOMP as a CTA was investigated with the aim of determining the CTA effect on the kinetics and the MWD. The experimental results were interpreted in the light of a representative mathematical model.