The structure of “living” poly(n-butyl acrylate) homopolymers prepared via nitroxide-mediated controlled radical polymerization in bulk and in miniemulsion at 112 °C was examined by SEC, NMR, and MALDI−TOF mass spectrometry in order to study the influence of chain transfer to polymer. The absence of detectable terminal unsaturation was confirmed by proton NMR. The branched structure was observed by 13C NMR. MALDI−TOF MS demonstrated that the majority of chains, even at high conversion, had the ideal structure with one initiator fragment and one nitroxide end group. From these results, we concluded that intramolecular chain transfer occurred (presumably by backbiting) and was the predominant mechanism throughout the polymerization at 112 °C.

Chain transfer to polymer (CTP) in conventional free-radical polymerizations (FRPs) and controlled radical polymerizations (ATRP, RAFT and NMP) of n-butyl acrylate (BA) has been investigated using (13) C NMR measurements of branching in the poly(n-butyl acrylate) produced. The mol-% branches are reduced significantly in the controlled radical polymerizations as compared to conventional FRPs. Several possible explanations for this observation are discussed critically and all except one refuted. The observations are explained in terms of differences in the concentration of highly reactive short-chain radicals which can be expected to undergo both intra- and inter-molecular CTP at much higher rates than long-chain radicals. In conventional FRP, the distribution of radical concentrations is broad and there always is present a significant proportion of short-chain radicals, whereas in controlled radical polymerizations, the distribution is narrow with only a small proportion of short-chain radicals which diminishes as the living chains grow. Hence, irrespective of the type of control, controlled radical polymerizations give rise to lower levels of branching, when performed under otherwise similar conditions to conventional FRP. Similar observations are expected for other acrylates and monomers that undergo chain transfer to polymer during radical polymerization.

The RAFT-mediated nonaqueous dispersion polymerization of methyl acrylate in isododecane, a nonsolvent for poly(methyl acrylate), was carried out using two soluble poly(2-ethylhexyl acrylate) macromolecular RAFT agents, containing either a dithiobenzoate reactive function or a trithiocarbonate one. The method produced stable colloidal particles, with hydrodynamic diameters below 100 nm. Using poly(2-ethylhexyl acrylate) with a dithiobenzoate end group, strong rate retardation and poor control over the polymer chains were observed. In contrast, when the trithiocarbonate-functionalized poly(2-ethylhexyl acrylate) was used, the formation of monodisperse micellar aggregates of well-defined self-assembled block copolymers was obtained with fast polymerization rates, irrespective of the RAFT agent concentration. Such differences were explained by the dispersed state of the system rather than by the intrinsic reactivity of the soluble macromolecular RAFT agent.