No abstract

Gelation in 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)-mediated cross-linking copolymerization of styrene and divinylbenzene (8.2 mol%) in aqueous miniemulsion at 125 C has been investigated. The rate of gel formation relative to monomer conversion was the same in miniemulsion and the corresponding solution polymerization when the organic phase contained 6 vol% tetradecane (TD; hydrophobe) and 48 vol% toluene. However, at 54 vol% TD and no toluene (the same total monomer concentration), the conversion at the gel-point was lower in miniemulsion than in solution, consistent with our previous results describing enhanced apparent pendant reactivity related to the presence of TD in the present system. The primary chain lengths were higher in miniemulsion with 54 vol% TD than in miniemulsion with 6 vol% TD and in solution (6 and 54 vol% TD). It was deduced via application of Flory-Stockmayer gelation theory that this difference in primary chain lengths, although significant with regards to gelation, was insufficient to explain the rapid gel formation in the miniemulsion containing 54 vol% TD, which is speculated to be related to specific effects of the heterogeneity of the miniemulsion system.

The compressive strengths of micron-sized, cross-linked poly(styrene-divinylbenzene) particles synthesized by conventional radical copolymerization (70 C) and nitroxide (TEMPO)-mediated radical copolymerization (125 C) in aqueous micro-suspension have been measured. In the conventional system, the breaking energies and the compressive strengths of the particles (after removal of unreacted monomer) remained approx. constant from low to high conversion, whereas in the NMP system, both quantities increased close to linearly with conversion. The results suggest that the network formation is more homogeneous in the NMP system than in the conventional system.

Network formation in the nitroxide‐mediated cross‐linking copolymerization of styrene and divinylbenzene (3 or 8.2 mol‐% relative to total monomer) using the nitroxide 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) at 125 °C can proceed markedly differently in aqueous miniemulsion compared to the corresponding solution polymerization depending on the organic‐phase composition. When the organic phase comprises 54 vol‐% of the hydrophobe tetradecane, gelation occurs at much lower conversion in miniemulsion than in solution, and at significantly lower conversion than predicted by Flory–Stockmayer gelation theory. This is proposed to be a result of an effect of the oil–water interface, whereby the concentration of polymer with pendant unsaturations is higher near the interface than in the particle interior.magnified image