title: Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution.
abstract: Various carboxylic acid-functionalized poly(N,N-dimethylacrylamide) (PDMAC) macromolecular chain transfer agents (macro-CTAs) were chain-extended with diacetone acrylamide (DAAM) by reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization at 70 °C and 20% w/w solids to produce a series of PDMAC-PDAAM diblock copolymer nano-objects via polymerization-induced self-assembly (PISA). TEM studies indicate that a PDMAC macro-CTA with a mean degree of polymerization (DP) of 68 or higher results in the formation of well-defined spherical nanoparticles with mean diameters ranging from 40 to 150 nm. In contrast, either highly anisotropic worms or polydisperse vesicles are formed when relatively short macro-CTAs (DP = 40-58) are used. A phase diagram was constructed to enable accurate targeting of pure copolymer morphologies. Dynamic light scattering (DLS) and aqueous electrophoresis studies indicated that in most cases these PDMAC-PDAAM nano-objects are surprisingly resistant to changes in either solution pH or temperature. However, PDMAC40-PDAAM99worms do undergo partial dissociation to form a mixture of relatively short worms and spheres on adjusting the solution pH from pH 2-3 to around pH 9 at 20 °C. Moreover, a change in copolymer morphology from worms to a mixture of short worms and vesicles was observed by DLS and TEM on heating this worm dispersion to 50 °C. Postpolymerization cross-linking of concentrated aqueous dispersions of PDMAC-PDAAM spheres, worms, or vesicles was performed at ambient temperature using adipic acid dihydrazide (ADH), which reacts with the hydrophobic ketone-functionalized PDAAM chains. The formation of hydrazone groups was monitored by FT-IR spectroscopy and afforded covalently stabilized nano-objects that remained intact on exposure to methanol, which is a good solvent for both blocks. Rheological studies indicated that the cross-linked worms formed a stronger gel compared to linear precursor worms.
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Byard
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: Mark
authors.initials: M
authors.lastname: Williams
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: Beulah E
authors.initials: BE
authors.lastname: McKenzie
authors.affiliation: BASF SE, GMV/P-B001, 67056 Ludwigshafen, Germany.
authors.forename: Adam
authors.initials: A
authors.lastname: Blanazs
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Armes