Ab Initio Emulsion Polymerization by RAFT-Controlled Self-Assembly

Abstract

A method is developed to enable emulsion polymerization to be performed under RAFT control to give living character without the problems that often affect such systems: formation of an oily layer, loss of colloidal stability, or loss of molecular weight control. Trithiocarbonate RAFT agents are used to form short stabilizing blocks from a water-soluble monomer, from which diblocks can be created by the subsequent polymerization of a hydrophobic monomer. These diblocks are designed to self-assemble to form micelles. Polymerization is initially performed under conditions that avoid the presence of monomer droplets during the particle formation stage and until the hydrophobic ends of the diblocks have become sufficiently long to prevent them from desorbing from the newly formed particles. Polymerization is then continued at any desired feed rate and composition of monomer. The polymer forming in the reaction remains under RAFT control throughout the polymerization; molecular weight polydispersities are generally low. The number of RAFT-ended chains within a particle is much larger than the aggregation number at which the original micelles would have self-assembled, implying that in the early stages of the polymerization, there is aggregation of the micelles and/or migration of the diblocks. The latexes resulting from this approach are stabilized by anchored blocks of the hydrophilic monomer, e.g., acrylic acid, with no labile surfactant present. Sequential polymerization of two hydrophobic monomers gives completely novel core−shell particles where most chains extend from the core of the particles through the shell layer to the surface.

Effect of stirring rate on particle formation in emulsifier-free, organotellurium-mediated living radical emulsion polymerization (emulsion TERP) of styrene

“…[18][19][20] As a solution of the problem, Hawkett and coworkers recently proposed an emulsifier-free reversible addition-fragmentation chain transfer emulsion polymerization method utilizing self-assembly. 21,22 Following this proposal, nitroxide-mediated radical polymerization [23][24][25][26][27][28] and reversible addition-fragmentation chain transfer [29][30][31][32][33][34][35] in emulsion polymerization systems have been successfully studied.…”

Supramolecular thermoplastics and thermoplastic elastomer materials with self-healing ability based on oligomeric charged triblock copolymers

“…A solution of 2-(((butylsulfanyl)carbonothioyl)sulfanyl)propanoic acid 38 (16.90 g, 71 mmol) and ethylene glycol (2.00 g, 32 mmol) in dichloromethane (300 ml) was cooled in an ice bath. A solution of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (16.57 g, 81 mmol) and 4-(dimethylamino)pyridine (0.79 g, 0.64 mmol) in dichloromethane (100 ml) was added dropwise, and the reaction was stirred overnight at room temperature.…”

Controlled/living heterogeneous radical polymerization in supercritical carbon dioxide

“…The polymer-philic segment of the block copolymer anchors to the forming particles, while the CO 2 -philic segment extends into the continuous phase as a steric stabilizer. It is conceivable that micelle formation would occur based on self-assembly once the PMMA segments have become sufficiently long 110,111 and/or the chains may simply precipitate, eventually leading to particle formation. The polymerizations reached 71 and 91% in 24 h using 5 and 10 wt % inistab rel.…”

“…The use of CLRP to prepare core-shell particles is often based on the self-assembly technique in aqueous ab initio emulsion polymerizations, whereby a diblock copolymer is formed in situ with the second block being insoluble in the continuous phase. 110,111 Micelles form when the second block has grown sufficiently long, and subsequently these micelles swell with monomer and grow ''inwards,'' resulting in core-shell particles. An important difference between such particles and those generated by conventional seeded polymerization is that in the former, the core and the shell are covalently linked.…”