Homopolymers of sodium 4-styrenesulfonate have been synthesized directly in aqueous media by reversible addition−fragmentation chain transfer polymerization (RAFT). The resulting homopolymers have narrow molecular weight distributions, with polydispersity indices in the range 1.12−1.25, as determined by aqueous size exclusion chromatography. Using a dithioester-capped sodium 4-styrenesulfonate homopolymer as a macro chain transfer agent, a block copolymer with sodium 4-vinylbenzoate has been prepared in aqueous media. Additionally, a block copolymer of (ar-vinylbenzyl)trimethylammonium chloride with N,N-dimethylvinylbenzylamine has been synthesized, using the same methodology. We believe these represent the first examples of AB diblock copolymers prepared directly in aqueous media via the RAFT process. Both block copolymers are stimuli-responsive and undergo reversible pH-induced micellization in aqueous solution. Micelles with hydrodynamic diameters in the range 18−38 nm were observed by dynamic light scattering.

Herein we disclose a facile method for the preparation of (co)polymer-stabilized transition metal colloids, via the "grafting-to" approach. The method takes advantage of the fact that (co)polymers synthesized in aqueous media, in a controlled fashion, via reversible addition-fragmentation chain transfer bear thiocarbonylthio end groups. These are readily reduced to yield (co)polymers with thiol end groups. When the reduction is performed, with NaBH(4), for example, in aqueous media in the presence of an appropriate transition metal species, (co)polymer-stabilized metal nanoparticles are formed in which the size and size distribution are dependent upon the individual transition metals. Colloid formation is confirmed by transmission electron microscopy and UV-vis spectroscopy.

The syntheses of the novel acrylamido-based RAFT chain transfer agents (CTAs) N,N-dimethyl-s-thiobenzoylthiopropionamide (TBP, 1c) and N,N-dimethyl-s-thiobenzoylthioacetamide (TBA, 1d) for the controlled polymerization of N,N-dimethylacrylamide (DMA) are described. The results from a comparative study of 1c and 1d with two CTAs previously reported for the RAFT polymerization of DMA (benzyl dithiobenzoate (BDB, 1a) and cumyl dithiobenzoate (CDB, 1b)) are disclosed and demonstrate the effectiveness of the newly reported CTAs. Polymerizations at CTA/I ratios of 5/1 yield poly(N,N-dimethylacrylamide) (PDMA) homopolymers with high molecular weight impurity (1b−1d) or bimodal molecular weight distributions (1a). The high molecular weight impurity observed in polymerizations mediated by 1b−1d has been attributed to species arising from bimolecular termination reactions, as determined by multiple detector size exclusion chromatography (SEC). The bimodality observed for 1a-mediated polymerizations is due to the presence of two distinct “active” species, as determined by end group analysis using SEC. We show that it is possible to reduce/eliminate the high molecular weight impurity for 1b−1d-mediated polymerizations simply by increasing the CTA/I ratio to 80/1. Under these conditions, 1a-mediated polymerization still yields a bimodal molecular weight distribution. The differences in the efficiency of the CTAs 1a−1d are rationalized in terms of their structural and electronic characteristics and their relative fragmentation/reinitiation efficiencies.

Introduction. Controlled radical polymerization 1 (CRP) has been the focus of intense research in recent years. Atom transfer radical polymerization (ATRP), 2 nitroxide-mediated polymerization (NMP), 3 and more recently, reversible addition-fragmentation chain transfer polymerization (RAFT) 4 have allowed for the synthesis of (co)polymers with designated molecular weights and narrow molecular weight distributions.Considering the advantages of precisely controlled structures and the need for environmentally viable technologies, we have recently centered our efforts on conducting CRP in aqueous media. We first reported the synthesis, via RAFT, of homopolymers and block copolymers based on the water-soluble styrenic monomers, sodium 4-styrenesulfonate, sodium 4-styrenecarboxylate, N,N-dimethylvinylbenzylamine, and (ar-vinylbenzyl)trimethylammonium chloride. 5 Subsequently, we reported the first example of CRP of anionic acrylamido monomers in aqueous media. 6 As well as ionic monomers, we are interested in polymerizing nonionic hydrophilic/water-soluble species, such as N,N-dimethylacrylamide (DMA) via RAFT. Herein, we report the CRP of DMA, in aqueous media, utilizing two RAFT CTAs, Table 1. As far as we are aware, this constitutes the first report outlining the CRP of this monomer via RAFT in water.The CRP of DMA, and acrylamido monomers in general, has proven to be challenging using techniques such as ATRP and NMP. Li and Brittain reported the polymerization of DMA by NMP using TEMPO, but the process was shown to be uncontrolled. 7 However, with the development of more universal nitroxides, Benoit et al. demonstrated the ability to (co)polymerize DMA via NMP. 8 Teodorescu and Matyjaszewski reported the ATRP of several (meth)acrylamides. 9 However, the authors concluded that these systems were not "living". This was subsequently confirmed by Rademacher et al. 10 Senoo et al. reported the ATRP synthesis of PDMA, employing the RuCl 2 (PPh 3 ) 3 -based initiating system, although resulting polydispersities were typically >1.60. 11 With the discovery of RAFT, a wider range of monomers are now amenable to CRP. Significantly, the CRP of DMA 12 and N-isopropylacrylamide, 13 via RAFT, in organic media have already been demonstrated.In the work reported here, DMA homopolymers were synthesized in water via RAFT. Both sodium 4-cyanopentanoic acid dithiobenzoate (CTPNa) and N,N-dimethyl-s-thiobenzoylthiopropionamide (TBP) were employed as the RAFT chain transfer agents (CTAs). CTPNa was chosen due to its inherent water-solubility

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