Network formation in nitroxide-mediated radical copolymerization of styrene and divinylbenzene in miniemulsion

Polymer network formation in controlled/living radical crosslinking copolymerization of S/DVB initiated by a poly(S)-TEMPO macroinitiator in aqueous miniemulsion at 125 degrees C is investigated. The crosslinking proceeded differently in miniemulsion (heterogeneous systems) and in bulk/ solution (homogeneous systems), with markedly lower apparent pendant reactivity in miniemulsion. The relative rate of DVB consumption was lower in miniemulsion than in bulk/solution. It is proposed that the interface between the particle (monomer droplet at time = 0) and the aqueous phase may play an important role during the crosslinking process. The presence of tetradecane as a hydrophobe in the monomer droplets strongly influenced both the pendant reactivity and the molecular weight distributions in miniemulsion, whereas only small effects were observed in the corresponding bulk/ solution polymerizations. It is believed that this is related to previous results of the hydrophobe promoting migration of poly(DVB) to the interface of toluene droplets in aqueous emulsion. The results suggest novel approaches towards control of polymer network development in crosslinking radical polymerizations.