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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.

We present the synthesis of hyperbranched polymer-silica hybrid nanoparticles by self-condensing vinyl polymerization (SCVP) via atom transfer radical polymerization (ATRP) from silica surfaces. ATRP initiators were covalently linked to the surface of silica particles, followed by SCVP of an initiatormonomer ("inimer") which has both a polymerizable acrylic group and an initiating group in the same molecule. Well-defined polymer chains were grown from the surface to yield hybrid nanoparticles comprised of silica cores and hyperbranched polymer shells having multifunctional bromoester end groups, as confirmed by elemental analyses and Fourier transform infrared measurements. Characterization of soluble polymers obtained in solution by gel permeation chromatography (GPC), GPC/viscosity, and NMR suggests the formation of highly branched polymers. Correlation of molecular parameters of the soluble polymers with the polymers grafted on the surface is discussed in view of theoretical considerations. Hydrolysis of the ester functionality of branched poly(tert-butyl acrylate), which was obtained by copolymerization of the inimer and tert-butyl acrylate, created branched poly(acrylic acid)-silica hybrid nanoparticles. The hybrid nanoparticles were characterized using transmission electron microscopy, field emission scanning electron microscopy, scanning force microscopy, and dynamic light scattering.

We present novel intelligent colloidal polymer/silica nanocomposites, in which the complexation of cationic silica nanoparticles and a weak anionic polyelectrolyte can be manipulated simply by pH change through a hydrogen-bonding interaction and ionic complexation caused by hydrogen-transfer interactions between the constituents. Special silica particles which have nanometer size (diameter approximately 3.0 nm) and two independent proton-accepting sites were developed in this study. Both the silica and poly(acrylic acid) form transparent colloidal solutions in water, while a white turbid dispersion was obtained just after mixing the two solutions due to the complexation. The pH-induced association-dissociation behavior was confirmed by the turbidity and potentiometric titration measurements. The assembled structures of the hybrids were visualized by scanning force microscopy.

We report the controlled synthesis of an amino acid based polymer by reversible addition−fragmentation chain transfer (RAFT) polymerization of N-acryloyl-l-phenylalanine (A-Phe-OH), which has a carboxylic acid group. Three chain transfer agents (CTAs), benzyl dithiobenzoate (CTA 1), benzyl 1-pyrrolecarbodithioate (CTA 2), and O-ethyl-S-(1-phenylethyl) dithiocarbonate (CTA 3), were compared for the direct polymerization of A-Phe-OH without protecting chemistry. With 2,2‘-azobis(isobutyronitrile) as an initiator, the dithiocarbamate-type RAFT agent (CTA 2) is efficient for the preparation of poly(A-Phe-OH) with relatively narrow molecular weight distributions. The effects of several parameters, such as solvent, temperature, CTA to initiator molar ratio, etc., were investigated in order to determine the conditions, leading to optimal control of the direct polymerization. Good control of the polymerization in the presence of CTA 2 in methanol was confirmed by the formation of narrow polydispersity products and the linear relationship between the molecular weight and conversion. Depending on the monomer/CTA ratio, the amino acid based polyelectrolytes, poly(A-Phe-OH)s, with number-average molecular weights between 6500 and 54 400 and polydispersities between 1.23 and 1.27 were obtained, as evidenced by size-exclusion chromatography of the methylated samples.