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Well-defined polymers derived from L-proline are synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization and the amino acid-based polymers exhibit thermosensitive phase separation at lower critical solution temperatures (LCST = 15-45 degrees C) in aqueous medium.

We report on the synthesis of randomly branched (arborescent) poly(acrylic acid) (PAA) by self-condensing vinyl copolymerization (SCVCP) of an acrylic AB* inimer, 2-(2-bromopropionyloxy)ethyl acrylate (BPEA), with tert-butyl acrylate (tBuA) via atom transfer radical polymerization (ATRP), followed by hydrolysis of tert-butyl groups. Depending on the comonomer ratio, γ ) [tBuA] 0/[BPEA]0, branched PtBuAs with number-average molecular weights between 8000 and 76 000 and degrees of branching (DB) between 0.48 and 0.02 were obtained by SCVCP, as evidenced by GPC, GPC/viscosity, GPC/MALS, and NMR analysis. For the case of high comonomer ratios, γ . 1, the degree of branching is given as DB ≈ 2/(γ + 1), and γ corresponds to an average number of tBuA units between branch points. The Mark-Houwink exponents of these branched PtBuAs obtained at γ ) 0.5-100 are significantly lower (R ) 0.38-0.47) than that of linear PtBuA (R ) 0.80). The nature of the ligand and polymerization temperature affect the molecular weights and chain architectures, while the comonomer-to-catalyst ratio, µ ) ([tBuA] 0 + [BPEA]0)/[CuBr]0, has a slight influence only on these parameters. Subsequent cleavage of the tertbutyl ester moieties by acidic hydrolysis gave randomly branched polyelectrolytes, PAA, as confirmed by elemental analyses, 1 H NMR, and FT-IR measurements. Aqueous-phase GPC and dynamic light scattering confirm the compact structure of the branched PAAs. Their water solubility and their size depend on the degree of branching and on pH.

The polymerizations of N-vinylimidazolium salts, 1-(3-phenylpropyl)-3-vinylimidazolium bromide (PVI-Br), 1-(6-ethoxycarbonylhexyl)-3-vinylimidazolium bromide (EHVI-Br), and 1-(2-ethoxyethyl)-3-vinylimidazolium bromide (EtOEVI-Br), were performed by reversible addition−fragmentation chain transfer (RAFT)/macromolecular design via interchange of xanthate (MADIX) process. Two xanthate-type chain transfer agents (CTAs), O-ethyl-S-(1-phenylethyl) dithiocarbonate (CTA 1) and O-ethyl-S-(1-ethoxycarbonyl) ethyldithiocarbonate (CTA 2), proved efficient for obtaining poly(PVI-Br)s and (EHVI-Br)s with relatively low polydispersities (M w/M n < 1.4). Poly(EtOEVI-Br)s with moderate molecular weight distributions (M w/M n = 1.5−1.6) were also obtained under the same conditions. Controlled character of the polymerization of PVI-Br was confirmed by the molecular weight controlled by the monomer/CTA molar ratio, a linear increase in the number-average molecular weight (M n) with conversion, and the ability to extend the chain by a second addition of monomer. Polymerizations of the N-vinylimidazolium salts using the dithiocarbonate-terminated poly(N-isopropylacrylamide) as a macro-chain-transfer agent provided well-defined thermoresponsive ionic liquid block copolymers. Thermally induced phase separation behavior and assembled structures of the block copolymers were also studied in aqueous solution.