RAFT-mediated emulsion polymerization of styrene with a thermoresponsive MacroCTA

Abstract

Heterogeneous RAFT polymerization is an attractive 'living' radical polymerization technique to control not only the molecular weight distribution but also the particles size distribution. Here, we demonstrate the use of a thermoresponsive RAFT macro chain transfer agent (MacroCTA) to form seed particles for the chain extension of styrene to form block copolymer latex particles. By incorporating a few styrene units into the MacroCTA, the polymerizations become faster, producing both narrow particle size and molecular weight distribution. This is due to the 'superswelling effect', in which all the seed particles swell with monomer and nucleated at the same time. The resulting latex particles could then be transformed into a variety of nanostructures by cooling below the lower critical solution temperature of the thermoresponsive block in the presence of a plasticizer for polystyrene.The dominant structure was cylindrical worms with the observation of other structures including jelly fish and the rare disc. Cooling under ultrasound produced either vesicles or cauliflower structures. The work demonstrated that utilizing the 'superswelling effect', control over the rate, and molecular weight and particle size distributions could be obtained, providing design parameters to construct new nanostructures.

Particle by Particle Kinetic Monte Carlo Tracking of Reaction and Mass Transfer Events in Miniemulsion Free Radical Polymerization

“…Emulsion radical polymerizations are extensively used to synthesize dry polymers for rubber production or waterborne latexes with applications such as paints, coatings, adhesives, and drug delivery. − These polymerizations are characterized by an organic phase that is dispersed in an aqueous medium in the presence of emulsifier or surfactant. In the industrial (macro)­emulsion process large monomer droplets (>1 μm), (monomer swollen) micelles (5–10 nm), and polymer nanoparticles ( d p = 10–500 nm) are present, making it a much more dynamic process than conventional bulk polymerization due to the existence of several reaction loci and interphase interactions. − …”

Surfactant-Free RAFT Emulsion Polymerization of Styrene Using Thermoresponsive macroRAFT Agents: Towards Smart Well-Defined Block Copolymers with High Molecular Weights

“…They are, nevertheless, a highly interesting class of materials, for instance as chemical valves [ 28 , 29 ] or drug delivery systems [ 30 , 31 , 32 ]. Therefore, the groups of Davis [ 33 , 34 ] and Monteiro [ 35 , 36 , 37 ] tried to overcome the lack of stabilizing ability of thermoresponsive macroRAFT agents in aqueous emulsion polymerizations by adding the low-molecular-weight anionic surfactant sodium dodecyl sulfate (SDS). Upon cooling of the created latex after completion of the polymerization to temperatures below the PTT of the thermoresponsive block, its rapidly changing hydrophilicity leads to a temperature-induced morphological transformation (TIMT) if an appropriate plasticizer for the core-forming block is added.…”

Controlled radical polymerization in dispersed systems for biological applications

“…While this review is focussed on the synthesis of biologically relevant nanoparticles (not micron sized) using RDRP, an interesting approach to generate nonspherical nanoparticles has arisen using a post-polymerisation strategy pioneered by Monteiro and co-workers using RAFT suspension polymerisation. [154] As mentioned in the previous section, the formation of nonspherical, elongated nanoparticles is becoming increasingly important due to their longer circulation time and thus greater therapeutic efficacy compared to spherical analogues. This approach operates on the use of a thermoresponsive macro-RAFT agents which collapse and become hydrophobic during the high temperatures (70°C) of suspension polymerisations.…”