Limitations of cyclodextrin‐mediated RAFT homopolymerization and block copolymer formation |
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Authors: | Martin Hetzer Bernhard V K J Schmidt Christopher Barner‐Kowollik Helmut Ritter |
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Institution: | 1. Lehrstuhl für Pr?parative Polymerchemie, Institut für Organische Chemie und Makromolekulare Chemie, Heinrich‐Heine Universit?t, Universit?tsstra?e 1, , 40225 Düsseldorf, Germany;2. Preparative Macromolecular Chemistry, Institut für Technische Chemie und Polymerchemie, Karlsruhe Institute of Technology (KIT), , 76128 Karlsruhe, Germany |
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Abstract: | The design and synthesis of a new hydrophobic monomer, that is, 4‐(tert‐butyl)phenyl 6‐acrylamidohexanoate (TBP‐AA‐HO) and its ability to form supramolecular host/guest complexes with β‐cyclodextrin (CD) is described. The aqueous CD‐mediated reversible addition fragmentation chain transfer (RAFT) polymerization affords molecular masses up to 8600 g mol?1 with polydispersities between 1.2 and 1.4. The surprisingly low molecular weights for higher monomer/chain transfer agent (CTA) ratios are investigated by comparing results obtained from free radical and RAFT radical polymerization in aqueous and organic media. The results indicate a steric hindrance caused by attached CD molecules on the growing polymer chain leading to stagnation of the polymerization process due to a restricted accessibility of the reactive chain end. This hypothesis is supported by matrix‐assisted laser desorption/ionization time of flight mass spectrometry. Furthermore, the CD‐mediated synthesis of amphiphilic diblock copolymers in variable aqueous media is described. Hydrophilic poly(N,N‐dimethylacrylamide) macro‐CTAs with different molecular weights are used to polymerize TBP‐AA‐HO at 50 °C. The diblock copolymers are analyzed by 1H‐nuclear magnetic resonance spectroscopy and size exclusion chromatography. The results confirm the polymer structure and reveal similar limitations of chain growth as observed for the CD‐mediated homopolymerization with a limit of 7000 g mol?1 for efficient chain extension. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2504–2517 |
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Keywords: | amphiphiles aqueous solution block copolymers cyclodextrin reversible addition fragmentation chain transfer (RAFT) |
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