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Synthesis, characterization and swelling behaviour of poly(methacrylic acid) brushes synthesized using atom transfer radical polymerization |
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| Authors: | Andrew J Parnell Simon J Martin Mark Geoghegan Colin J Crook Anthony J Ryan |
| Affiliation: | a Department of Physics and Astronomy, The University of Sheffield, The Hicks Building, Sheffield S3 7RH, UK b IPTME, Loughborough University, Loughborough LE11 3TU, UK c Department of Chemistry, The University of Sheffield, Sheffield S3 7HF, UK d Department of Chemical and Process Engineering, The University of Sheffield, Sheffield S1 3JD, UK |
| Abstract: | Poly(methacrylic acid) brushes have been prepared utilizing the “grafting from” technique and a living radical synthesis route using a two stage process. Firstly a poly(1-ethoxyethyl methacrylate) brush was synthesized by atom transfer radical polymerization and then thermally decomposed to poly(methacrylic acid). The swelling behaviour of the weak polyacid brush was investigated as a function of pH and salt concentration in aqueous solutions using atomic force microscopy. Force pulling measurements were used to establish the molecular weight and the grafted chain density. The swelling transition was found to be at pH 9; which is significantly different to the pKa (5.5) of untethered poly(methacrylic acid). We attribute this large shift in pKa to the high grafting density of these brushes. This can be explained as a result of the Coulombic repulsion of neighbouring charges. High salt concentrations (0.3 M Na+) also collapse the brush layer. Conversely low salt concentrations cause an increase in the thickness of the brush, a behaviour expected for osmotic brushes. |
| Keywords: | AFM Brush Polyelectrolyte |
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