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.
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.
A library of eight sequence-defined model oligomers, whose sequence is based on a (0,1) binary code, is prepared through chemoselective repeating cycles of amidification and copper-assisted alkyne-azide cycloaddition reactions from a non-modified Wang resin. This library is constructed from two AB (A = acid, B = alkyne) building blocks, i.e., 4-pentynoic acid and 2-methyl-4-pentynoic acid acting, respectively, as non-coding (0) and coding (1) monomer, and 1-amino-11-azido-3,6,9-trioxaundecane as complementary CD (C = amine, D = azide) spacer building block. In particular, encoded triads are synthesized by consecutive covalent attachment of five building blocks (i.e., three coding/non-coding monomers and two spacers). In this communication, optimal protocols for the synthesis of the targeted oligomers are reported along with their full characterization by (1) H NMR, MALDI-TOF mass spectrometry, and size-exclusion chromatography. It is found that all possible encoded triads (i.e., eight possibilities) could be synthesized using this approach. Indeed, monodisperse sequence-defined oligomers are prepared and characterized in all cases.
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