Synthesis and characterization of poly(methyl methacrylate) nanoparticles by emulsifier-free emulsion polymerization with a redox-initiated system

Abstract

In this study, the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) was initiated directly by a Cu2+/HSO 3- redox system. Latex particles with negative charge due to the bonded anionic sulfite ion were successfully synthesized after 2 h of reaction at 40-60°C. Scanning electron microscopy pictures showed a uniform particle size distribution, and the average size decreased from 223 to 165 nm wit increasing reaction temperature from 40 to 60°C. The initiation step in the polymerization mechanism was proven to be a redox reaction, in which Cu 2+ oxidized the bisulfite ion to produce an anionic sulfite radical and proton. The produced anionic sulfite radical then initiated the polymerization of MMA. Moreover, Cu2+ not only served as one component in the redox initiator system but also as a chain-transfer agent that terminated growing polymer chains to produce chains with unsaturated end groups [poly(methyl methacrylate) (PMMA) - CH=CH2]. For this system, about 17% PMMA - CH=CH2 was produced. The tacticities of the PMMA latex prepared at 40-60°C were almost the same, about 62-64% syndiotactic, 33-35% heterotactic, and 3% isotactic. These PMMA latexes had almost the same glasstransition temperature, 125-127°C, regardless of the reaction temperatures, and their weight-average molecular weights were in the range between 254,000 and 315.000. © 2008 Wiley Periodicals, Inc.