NITROXIDE-MEDIATED FREE-RADICAL POLYMERIZATION OF STYRENE. EVOLUTION OF THE MOLECULAR WEIGHT DISTRIBUTIONS

SPIES, C.; ESTENOZ, D. A.; LUCIANI, C. V.; OLIVA, H. M.; MEIRA, G. R.

Plaza Herradura, Costa Rica

Simposio; XII Simposio Latinoamericano de Polímeros, SLAP2010; 2010

Univ. Nacional, Costa Rica

Nitroxide-mediated free-radical polymerizations (NMRPs) are of great scientific and industrial interest. They represent an economically-feasible alternative to the more expensive and experimentally-demanding anionic polymerizations. Since the pioneering work of Georges et al. [1], many publications have appeared on the polymerization of styrene in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) and other nitroxides. For instance, mathematical models that calculate the evolution of the styrene conversion, average molecular weights, and polydispersity have been developed [2, 3]. However, none of such models are capable of predicting the evolution of the complete MWDs of the dormant, dead, and “living” polystyrene (PS) fractions along a NMRP. Size exclusion chromatography (SEC) measures the MWD of the total polymer, but it cannot distinguish between the different polymer fractions. When block copolymers are produced on the basis of polyalcoxyamine PS-based prepolymers, only the dormant fraction continues the polymerization and the final polymer is a blend of a block copolymer plus dead homopolymer. Thus, the molecular characteristics of the final block copolymer strongly depend on the MWD of the dormant PS produced in the first reaction stage. In this work, a free radical polymerization of styrene in the presence of a nitroxide mediator and a chemical initiator is theoretically and experimentally investigated, with the aim of calculating the MWDs of the living, dormant, and dead polymer fractions.