title: Synthesis, multilayer film assembly, and capsule formation of macromolecularly engineered acrylic acid and styrene sulfonate block copolymers.
abstract: We report the use of copolymers synthesized with specific block ratios of weakly and strongly charged groups for the preparation of stable, pH-responsive multilayers. In this study, we utilized reversible addition-fragmentation chain transfer (RAFT) polymerization in the synthesis of novel pH-sensitive copolymers comprising block domains of acrylic acid (AA) and styrene sulfonate (SS) groups. The PAA x- b-SS y copolymers, containing 37%, 55%, and 73% of AA groups by mass (denoted as PAA 37- b-SS 63, PAA 55- b-SS 45, and PAA 73- b-SS 27, respectively), were utilized to perform stepwise multilayer assembly in alternation with poly(allylamine hydrochloride), PAH. The ratio of AA to SS groups, and the effect of the pH of both anionic and cationic adsorption solutions, on multilayer properties, were investigated using ellipsometry and atomic force microscopy. The presence of SS moieties in the PAA x- b-SS y copolymers, regardless of the precise composition, lead to films with a relatively consistent thickness. Exposure of these multilayers to acidic conditions postassembly revealed that these multilayers do not exhibit the characteristic large swelling that occurs with PAA/PAH films. The film stability was attributed to the presence of strongly charged SS groups. PAA x- b-SS y/PAH films were also formed on particle substrates under various adsorption conditions. Microelectrophoresis measurements revealed that the surface charge and isoelectric point of these core-shell particles are dependent on assembly pH and the proportion of AA groups in PAA x- b-SS y. These core-shell particles can be used as precursors to hollow capsules that incorporate weak polyelectrolyte functionality. The role of AA groups in determining the growth profile of these capsules was also examined. The multilayer films prepared may find applications in areas where pH-responsive films are required but large film swelling is unfavorable.
authors.affiliation: Centre for Nanoscience and Nanotechnology, Department of Chemical and Biomolecular Engineering, The University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Heng Pho
authors.initials: HP
authors.lastname: Yap
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Hao
authors.forename: Elvira
authors.initials: E
authors.lastname: Tjipto
authors.forename: Chakravarthy
authors.initials: C
authors.lastname: Gudipati
authors.forename: John F
authors.initials: JF
authors.lastname: Quinn
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Davis
authors.forename: Christopher
authors.initials: C
authors.lastname: Barner-Kowollik
authors.forename: Martina H
authors.initials: MH
authors.lastname: Stenzel
authors.forename: Frank
authors.initials: F
authors.lastname: Caruso