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.

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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Well-defined poly(sodium 2-(acrylamido)-2-methylpropanesulfonate-block-sodium 6-acrylamidohexanoate) (pNaAMPS-AaH) was synthesized by reversible addition−fragmentation chain transfer (RAFT) radical polymerization of sodium 6-acrylamidohexanoate (AaH) using the sodium 2-(acrylamido)-2-methylpropanesulfonate-based macrochain transfer agent. The “living” polymerization of AaH was evidenced by the fact that the number-average molecular weight increased linearly with monomer conversion while the molecular weight distribution remained narrow independent of the conversion. pH-induced association and dissociation behavior of the diblock copolymers was investigated by quasi-elastic light scattering (QELS), static light scattering (SLS), 1H NMR spin−spin relaxation time, and fluorescence probe techniques. At pH < 4, the diblock copolymers exhibited large values of the hydrodynamic radius and small values of the 1H NMR spin−spin relaxation time. These observations indicated that micellization occurred to form polymer micelles comprising hydrophobic protonated AaH cores and hydrophilic NaAMPS coronas at pH < 4. On the other hand, these diblock copolymers dissolved in aqueous solutions as a state of unimer under high-pH conditions. 8-Anilino-1-naphthalenesulfonic acid, ammonium salt hydrate (ANS), as a fluorescence probe could be incorporated into the protonated AaH core of diblock copolymer micelles at low pH and released upon dissociation of the micelles at high pH, which was completely reversible.