Introduction. Nonaqueous dispersion polymerization 1-4 is a very versatile method to afford polymer dispersions of controlled morphology. It is initiated in a homogenous medium where all components are miscible. When polymer molar mass exceeds a critical limit, polymers phase separate and aggregate. Steric stabilization of polymer particles is achieved when dispersing agents, usually block copolymers, are added. After formation of particles, further polymerization occurs in bulk of the monomer-swollen particles. Provided that no new particle nucleation takes place, it is possible to obtain narrow particle size distributions. Particle sizes depend mainly upon the solubility of the formed polymer in the medium. In case of better solubility, aggregation of polymer chains is delayed, resulting in larger diameters of the formed particles. Low solubility causes quick aggregation and therefore smaller particle sizes.Advanced methods like living anionic polymerization 5,6 and group transfer polymerization 7,8 (GTP) have been performed in nonaqueous dispersions although most research is concerned with free radical polymerization. Living dispersion polymerization gives both control of molar mass and particle morphology.Controlled radical polymerization [9][10][11][12] is a new living polymerization technique using for example 2,2,6,6tetramethyl-1-piperidyloxy radical (TEMPO) combined with azoisobutyronitrile or benzoyl peroxide (BPO) as initiating system. 13,14,15 Preferably controlled radical styrene polymerization is performed in bulk at temperatures of 100-140 °C. This leads to high viscosities and therefore experimental problems related to stirring at high conversions.Combining controlled radical polymerization and nonaqueous dispersion polymerization should provide the above-mentioned advantages of a living polymerization method and lead to a low viscosity product even at high conversions. In this study living radical polymerization in bulk and nonaqueous dispersion are compared with respect to reaction kinetics and control of polystyrene molar mass. Moreover particle formation during controlled radical styrene dispersion polymerization is investigated.Experimental Section. (a) Materials. Styrene obtained from Fluka was stirred over lithium aluminium hydride for one night and distilled under reduced pressure. TEMPO, BPO (Aldrich), and decane (Fluka) were used as received. The dispersant Kraton G1701, supplied by Shell Chemical Co., is a polystyrene-blockpoly(ethene-alt-propene) with a polystyrene content of 34 wt %. The number average molar mass of the PS block is 35 700 g/mol and of the poly(ethene/-alt-propene) is 68 300 g/mol. Prior to use it was dissolved in

Thermal and microwave-induced free-radical non-aqueous dispersion polymerization of methyl methacrylate (MMA) in the presence of poly(styrene)-block-poly(ethene-alt-propene) dispersing agent were compared. For controlled polymerization in the microwave field, a new microwave polymerization reactor was built to afford uniform heating and to control temperature via microwave power variation. At identical MMA concentration and polymerization temperature of70 "C no special effect of the microwave field on conversions, molecular weights and particle sizes of PMMA was detected with respect to conventional thermal free radical dispersion polymerization.

Non-aqueous dispersions of colloidal PMMA microparticles with average sizes ranging from 70 to 330 nm were prepared by living polymerization of methylmethacrylate (MMA) and methylmethacrylate/ethyleneglycoldimethacrylate (EDMA) in n-heptane diluent using 2-methyl-l-methoxy-l-trimethylsilyloxy-prop-l-ene (MTS) as initiator in the presence of tetrabutylammonium fluoride (TBAF) or tetrabutylammonium cyanide (TBAC) as catalyst, and polystyrene-block-poly-(ethene-alt-propene) (SEP) as dispersing agent. The influence of process parameters such as concentrations of MMA, EDMA crosslinking agent, TBAF, and SEP on conversion, molecular weight, particle size, and molecular weight and particle size distributions has been investigated. In contrast to GTP in solution, group transfer dispersion polymerization (GTDP) was markedly slower and accompanied by agglomeration and drastic broadening of both molecular weight and particle size distributions with increasing MMA conversion. In a new GTDP process colloidal PMMA microparticles, obtained by free radical dispersion polymerization, were added as seeds, thus affording much narrower particle size distribution and high MMA conversion. Experimental 2.1.Materials All compounds were handled and stored under dry argon, obtained from Messer GrieBheim in 99.999% purity, and 226 Acta Polymer., 46, 226-232 (1995) 0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1995 0323-7648/95/0306-0226$5.00 + .25/0 Acta Polymer., 46, 226-232 (1995) Formation of colloidal PMMA 229

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