title: RAFT polymerization of temperature- and salt-responsive block copolymers as reversible hydrogels.
abstract: Reversible-addition fragmentation chain transfer (RAFT) polymerization enabled the synthesis of novel, stimuli-responsive, AB and ABA block copolymers. The B block contained oligo(ethylene glycol) methyl ether methacrylate (OEG) and was permanently hydrophilic in the conditions examined. The A block consisted of diethylene glycol methyl ether methacrylate (DEG) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (TMA). The A block displayed both salt- and temperature-response with lower critical solution temperatures (LCSTs) dependent on the molar content of TMA and the presence of salt. Higher TMA content in the AB diblock copolymers increased the critical micelle temperatures (CMT) in HPLC-grade water due to an increased hydrophilicity of the A block. Upon addition of 0.9 wt% NaCl, the CMTs of poly(OEG-b-DEG95TMA5) decreased from 50 °C to 36 °C due to screening of electrostatic repulsion between the TMA units. ABA triblock copolymers displayed excellent hydrogel properties with salt- and temperature-dependent gel points. TMA incorporation in the A block increased the gel points for all triblock copolymers, and salt-response increased with higher TMA composition in the A block. For example, poly(DEG98TMA2-b-OEG-b-DEG98TMA2) formed a hydrogel at 40 °C in HPLC-grade water and 26 °C in 0.9 wt% NaCl aqueous solution. These salt- and temperature-responsive AB diblock and ABA triblock copolymers find applications as drug delivery vehicles, adhesives, and hydrogels.
authors.affiliation: Department of Chemistry, Macromolecules and Interfaces Institute, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Sean T
authors.initials: ST
authors.lastname: Hemp
authors.affiliation: Department of Chemical Engineering, The University of Mississippi, University, MS 38677, USA.
authors.forename: Adam E
authors.initials: AE
authors.lastname: Smith
authors.affiliation: Department of Material Science, Corporate Research & Engineering, Kimberly-Clark Corporation, 2100 Winchester Road, Neenah, WI 54956, USA.
authors.forename: W Clayton
authors.initials: WC
authors.lastname: Bunyard
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Rubinstein
authors.affiliation: Department of Chemistry, Macromolecules and Interfaces Institute, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Long
keywords: Hydrogels; RAFT polymerization; Stimuli-responsive