Limitations of cyclodextrin‐mediated RAFT homopolymerization and block copolymer formation

Abstract

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 1 H‐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