The direct synthesis of sulfobetaine-containing amphiphilic block copolymers and their self-assembly behavior

Diblock copolymers containing the thermo-responsive sulfobetaine, [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (DMAPS), were synthesized by the aqueous RAFT polymerization of DMAPS, followed by direct chain extension in hexafluoroisopropanol (HFIP) with methyl methacrylate (MMA). This was shown to give lower dispersity polymers than RAFT emulsion polymerization. The diblock copolymers self-assembled in water to form micelles, as analyzed by light scattering (LS) and transmission electron microscopy (TEM). Micelles formed from diblocks bearing a long PDMAPS block were shown to swell with temperature, rather than display a traditional UCST cloud point. This was due to the polymers retaining hydrophilicity, even at temperatures well below the UCST for the corresponding PDMAPS homopolymer, as shown by variable temperature NMR. This swelling behavior was utilized in the release of a hydrophobic dye in response to temperature. This approach has great potential for applications in controlled release whilst maintaining the structure of the carrier nanoparticles

One-pot synthesis of responsive sulfobetaine nanoparticles by RAFT polymerisation: the effect of branching on the UCST cloud point

We describe the one-pot synthesis of temperature-responsive branched polymer nanoparticles. Reversible addition–fragmentation chain transfer (RAFT) polymerisation has been utilised to synthesise ultra-high molecular weight sulfobetaine polymers (up to ca. 500 kDa) with good control over molecular weight (Mn) and dispersity (Mw/Mn). The UCST cloud points of these linear polymers were found to increase with both Mn and concentration, and represent one of the few recent descriptions of polymers exhibiting UCST behaviour in aqueous solution. The incorporation of difunctional monomers results in branched polymers which display vastly reduced transition temperatures compared to their linear counterparts. Furthermore, the incorporation of a permanently hydrophilic monomer results in the formation of stable core–shell particles which no longer exhibit a cloud point in water, even at very high concentrations (ca. 50 mg mL−1). The branched polymers are shown to form discrete well-defined nanoparticles in aqueous solution, and these have been characterised by DLS, SLS, TEM and DOSY. Their reversible swelling behaviour in response to temperature is also demonstrated

Advantages of block copolymer synthesis by RAFT-controlled dispersion polymerization in supercritical carbon dioxide

Reversible addition-fragmentation chain transfer (RAFT)-controlled block copolymer synthesis using dispersion polymerization in supercritical carbon dioxide (scCO2) shows unprecedented control over blocking efficiency. For PMMA-b-PBzMA and PMMA-b-PSt the blocking efficiency was quantified by measuring homopolymer contaminants using the techniques of GPC deconvolution, gradient polymer elution chromatography (GPEC), and GPC dual RI/UV detection. A new, promising method was also developed which combined GPC deconvolution and GPEC. All techniques showed that blocking efficiency was significantly improved by reducing the radical concentration and target molecular weight. Estimated values agreed well with (and occasionally exceeded) theory for PMMA-b-PBzMA. The heterogeneous process in scCO2 appeared to cause little or no further hindrance to the block copolymerization procedure when reaction conditions were optimized. High blocking efficiencies were achieved (up to 82%) even at high conversion of MMA (>95%) and high molecular weight. These data compare favorably to numerous published reports of heterogeneous syntheses of block copolymers

Synthesis and self-assembly of amphiphilic chiral poly(amino acid) star polymers

Reversible addition-fragmentation chain transfer (RAFT) polymerization techniques were utilized to polymerize N-acryloyl-l-phenylalanine methyl ester (l-Phe-OMe) and tetrahydropyranyl acrylate to afford amphiphilic star polymers (with 4 and 6 arms). These copolymer stars have a chiral hydrophobic core domain and can undergo further solution self-assembly to form well-defined nanostructures, which have been characterized using DLS, TEM, and cryo-TEM analysis. The characterization and properties of these novel chiral assemblies and their potential in racemic resolution are reported