| 168. Mori, H.; Chan Seng, D.; Lechner, H.; Zhang, M.; Müller, A.H.E.: Synthesis and Characterization of Branched Polyelectrolytes 1. Preparation of Highly Branched Poly(acrylic acid) via Self-Condensing Atom Transfer Radical Copolymerization, Macromolecules 35, 9270 (2002) | |
| Abstract: 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,  = [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,  1, the degree of branching is given as DB  2/( + 1),
and corresponds to an average number
of tBuA units between branch points. The Mark-Houwink exponents of these
branched PtBuAs obtained at = 0.5-100
are significantly lower ( = 0.38-0.47)
than that of linear PtBuA ( = 0.80).
The nature of the ligand and polymerization temperature affect the molecular
weights and chain architectures, while the comonomer-to-catalyst ratio,  = ([tBuA]0 +
[BPEA]0)/[CuBr]0, has a slight influence only on these
parameters. Subsequent cleavage of the tert-butyl ester moieties by
acidic hydrolysis gave randomly branched polyelectrolytes, PAA, as confirmed by
elemental analyses, 1H 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. |
Prof. Dr. Axel Müller
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