Limitations of cyclodextrin-mediated RAFT homopolymerization and block copolymer formation

Hetzer, M., Schmidt, B. V.K.J. , Barner-Kowollik, C. and Ritter, H. (2013) Limitations of cyclodextrin-mediated RAFT homopolymerization and block copolymer formation. Journal of Polymer Science Part A: Polymer Chemistry, 51(11), pp. 2504-2517. (doi: 10.1002/pola.26644)

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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.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Schmidt, Dr Bernhard
Authors: Hetzer, M., Schmidt, B. V.K.J., Barner-Kowollik, C., and Ritter, H.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Journal of Polymer Science Part A: Polymer Chemistry
ISSN (Online):1099-0518
Published Online:13 March 2013

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