title: pH-responsive non-ionic diblock copolymers: ionization of carboxylic acid end-groups induces an order-order morphological transition.
abstract: A carboxylic acid based reversible additionfragmentation transfer (RAFT) agent is used to prepare gels composed of worm-like diblock copolymers using two non-ionic monomers, glycerol monomethacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA). Ionization of the carboxylic acid end-group on the PGMA stabilizer block induces a worm-to-sphere transition, which in turn causes immediate degelation. This morphological transition is fully reversible as determined by TEM and rheology studies and occurs because of a subtle change in the packing parameter for the copolymer chains. A control experiment where the methyl ester derivative of the RAFT agent is used to prepare the same diblock copolymer confirms that no pH-responsive behavior occurs in this case. This end-group ionization approach is important for the design of new pH-responsive copolymer nano-objects as, unlike polyacids or polybases, only a minimal amount of added base (or acid) is required to drive the morphological transition.
authors.affiliation: Dainton Building, Department of Chemistry, The University of Sheffield, Sheffield, South Yorkshire, S3 7HF (UK).
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Lovett
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Warren
authors.forename: Liam P D
authors.initials: LP
authors.lastname: Ratcliffe
authors.forename: Marzena K
authors.initials: MK
authors.lastname: Kocik
authors.forename: Steven P
authors.initials: SP
authors.lastname: Armes
keywords: RAFT polymerization; block copolymers; morphological transitions; nanoparticles; self-assembly