Summary: The nitroxide‐mediated controlled/living free radical copolymerization of styrene and divinylbenzene using a polystyrene‐TEMPO macroinitiator in aqueous miniemulsion and in bulk have been investigated. The crosslink densities were estimated based on the content of pendant vinyl groups as determined by 1H NMR. Considerably lower crosslink densities were revealed in the miniemulsion than in the corresponding bulk system. The rate of polymerization in the miniemulsion increased with decreasing particle size, and was significantly higher than in bulk.Crosslink density for the TEMPO‐mediated free radical copolymerization of S(1) and DVB(2) (f = 0.99, f = 0.01) at 125 °C in bulk (□) and in miniemulsions with dn = 585 nm (○) and 53.3 nm (•).magnified imageCrosslink density for the TEMPO‐mediated free radical copolymerization of S(1) and DVB(2) (f = 0.99, f = 0.01) at 125 °C in bulk (□) and in miniemulsions with dn = 585 nm (○) and 53.3 nm (•).

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Part CCXCVI of the series "Studies on Suspension and Emulsion" 2 ABSTRACT: Bimolecular termination in nitroxide-mediated radical polymerization in miniemulsion has been investigated by heating a polystyrene-2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) macroinitiator, and its 4-hydroxy-TEMPO analogue, in an aqueous toluene dispersion using sodium dodecylbenzenesulfonate as surfactant at 125 °C. The level of bimolecular termination by combination, evaluated from the high molecular weight shoulder, was higher in miniemulsion than solution, and increased with decreasing particle size. Quantitative analysis revealed that these results cannot be rationalized solely by nitroxide partitioning to the aqueous phase.The results are explained by an "interface effect", whereby nitroxide is adsorbed at or located at the aqueous-organic interface.

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a b s t r a c tNitroxide-mediated crosslinking radical copolymerizations of styrene and divinylbenzene have been carried out in aqueous miniemulsion with Dowfax 8390 as surfactant at 125 C employing TEMPO-based macroinitiators of various hydrophilicities (random copolymers comprising styrene and methyl acrylate). The pendant conversion (i.e. the degree of crosslinking) increased with increasing macroinitiator hydrophilicity and with decreasing particle size. It is proposed that a concentration gradient is generated within the particle such that the macroinitiator concentration tends to be higher near the oil-water interface than in the particle interior. The macroinitiators are surface active and are thus preferentially adsorbed at/located near the oil-water interface. This in turn leads to an increase in the ratio [pendant unsaturation]/[monomer] in the vicinity of propagating radicals, which are generated from the macroinitiators, and thus an increase in pendant conversion. This effect is enhanced by an increase in macroinitiator hydrophilicity and a decrease in particle size. The present approach offers novel means of controlling network formation in dispersed systems.