title: Disulfide-Functionalized Diblock Copolymer Worm Gels.
abstract: Two strategies for introducing disulfide groups at the outer surface of RAFT-synthesized poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA, or Gx-Hy for brevity) diblock copolymer worms are investigated. The first approach involved statistical copolymerization of GMA with a small amount of disulfide dimethacrylate (DSDMA, or D) comonomer to afford a G54-D0.50 macromolecular chain transfer agent (macro-CTA); this synthesis was conducted in relatively dilute solution in order to ensure mainly intramolecular cyclization and hence the formation of linear chains. Alternatively, a new disulfide-based bifunctional RAFT agent (DSDB) was used to prepare a G45-S-S-G45 (or (G45-S)2) macro-CTA. A binary mixture of a non-functionalized G55 macro-CTA was utilized with each of these two disulfide-based macro-CTAs in turn for the RAFT aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). By targeting a PHPMA DP of 130 and systematically varying the molar ratio of the two macro-CTAs, a series of disulfide-functionalized diblock copolymer worm gels were obtained. For both formulations, oscillatory rheology studies confirmed that higher disulfide contents led to stronger gels, presumably as a result of inter-worm covalent bond formation via disulfide/thiol exchange. Using the DSDB-based macro-CTA led to the strongest worm gels, and this formulation also proved to be more effective in suppressing the thermosensitive behavior that is observed for the nondisulfide-functionalized control worm gel. However, macroscopic precipitation occurred when the proportion of DSDB-based macro-CTA was increased to 50 mol %, whereas the DSDMA-based macro-CTA could be utilized at up to 80 mol %. Finally, the worm gel modulus could be reduced to that of a nondisulfide-containing worm gel by reductive cleavage of the inter-worm disulfide bonds using excess tris(2-carboxyethyl)phosphine (TCEP) to yield thiol groups. These new biomimetic worm gels are expected to exhibit enhanced muco-adhesion.
authors.affiliation: Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, S3 7HF, United Kingdom.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Warren
authors.affiliation: Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, S3 7HF, United Kingdom.
authors.forename: Julien
authors.initials: J
authors.lastname: Rosselgong
authors.affiliation: Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, S3 7HF, United Kingdom.
authors.forename: Jeppe
authors.initials: J
authors.lastname: Madsen
authors.affiliation: Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, S3 7HF, United Kingdom.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Armes
mesh_terms: D004220:Disulfides / Q000737:chemistry*; D005782:Gels / Q000138:chemical synthesis / Q000737:chemistry*; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D012212:Rheology; D012996:Solutions / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D004220:Disulfides; D005782:Gels; D011108:Polymers; D012996:Solutions; D014867:Water