Effect of hydrophilic macro-RAFT agent in surfactant-free emulsion polymerization

Heparin-Mimicking Sulfonated Polymer Nanoparticles via RAFT Polymerization-Induced Self-Assembly

Heparin plays a significant role in wound healing and tissue regeneration applications, through stabilization of fibroblast growth factors (FGF). Risks associated with batch-to-batch variability and contamination from its biological sources have led to the development of synthetic, highly sulfonated polymers as promising heparin mimics. In this work, a systematic study of an aqueous polymerization-induced self-assembly (PISA) of styrene from poly(2-acrylamido-2-methylpropane sodium sulfonate) (P(AMPS)) macro reversible addition-fragmentation chain transfer (macro-RAFT) agents produced a variety of spherical heparin-mimicking nanoparticles, which were further characterized with light scattering and electron microscopy techniques. None of the nanoparticles tested showed toxicity against mammalian cells; however, significant hemolytic activity was observed. Nonetheless, the heparin-mimicking nanoparticles outperformed both heparin and linear P(AMPS) in cellular proliferation assays, suggesting increased bFGF stabilization efficiencies, possibly due to the high density of sulfonated moieties at the particle surface.

Recent advances in RAFT-mediated surfactant-free emulsion polymerization

We summarized the RAFT-mediated surfactant-free emulsion polymerization using various RAFT agents and the polymerization types for the preparation of organic/inorganic hybrid materials.

Alizarin Yellow R (AYR) as compatible stabilizer for miniemulsion polymerization

HYPOTHESIS

Many solid particles have been used in Pickering stabilized (mini)emulsions. Stabilizing "particles" can be also formed in situ e.g. by aggregation of dye molecules as reported recently. Among the dyes sodium 2-hydroxy-5-[(E)-(4-nitrophenyl)diazenyl]benzoate (Alizarin Yellow R, (AYR)) is one of the best stabilizers. It is assumed to act as sole stabilizer also in heterophase polymerizations and offers a great potential for applications.

EXPERIMENTS

Aqueous solutions of AYR in varying concentrations (0.3, 0.5, 1.0, 1.5, 2.0mg/mL (dye/water)) were employed as continuous phase in direct miniemulsions. The oil phase comprised ethenylbenzene (styrene) and hexadecane. The effects of AYR concentration and ultrasonication time on size and distribution of the droplets were investigated. The miniemulsions were polymerized with a water-soluble azo-initiator (2,2'-azobis[n-(2-carboxyethyl)-2-methylpropionamidine] n-hydrate, VA-057) and conversion and kinetics were determined.

FINDINGS

The AYR is successfully employed as stabilizer in Pickering-like miniemulsion polymerizations of styrene. The higher the AYR concentrations the more stable the miniemulsions, the smaller the droplet sizes and the narrower the distributions are, ranging from ca. 450 to 180nm and 0.38 to 0.15, respectively. The nucleation mechanism of the polymer particles could be revealed by the number ratio of droplets and particles and follows droplet nucleation. This is confirmed by polymerization kinetics, which is in accordance with classical miniemulsion polymerization, too.

Polyisoprene-Silica Nanoparticles Synthesized via RAFT Emulsifier-Free Emulsion Polymerization Using Water-Soluble Initiators

Polyisoprene-silica (PIP-co-RAFT-SiO₂) nanoparticles were prepared via reversible addition⁻fragmentation chain-transfer (RAFT) emulsifier-free emulsion polymerization using water-soluble initiators, 4,4'-Azobis (4-cyanopentanoic acid) (ACP) and 2,2'-Azobis (2-methylpropionamidine) dihydrochloride (V50). The particle size of emulsion prepared using ACP initiator was smaller than that using V50 initiator because the V50 initiator was more active toward decomposition than the ACP initiator. A high monomer conversion (84%), grafting efficiency (83%) and small particle size (38 nm) with narrow size distribution were achieved at optimum condition. The PIP-co-RAFT-SiO₂ nanoparticles exhibited core⁻shell morphology with silica encapsulated with polyisoprene (PIP). The new PIP-SiO₂ nanoparticles could be applied as effective filler in rubber composites that possess good mechanical and thermal properties.

Fluorinated amphiphilic block copolymers via RAFT polymerization and their application as surf-RAFT agent in miniemulsion polymerization

Preparation of an amphiphilic block copolymer (Am-BCP) based on poly(ethylene glycol) methyl ether methacrylate (PEGMA) and heptafluorobutyl acrylate (HFBA) via RAFT polymerization and application of this Am-BCP as surf-RAFT agent for polymerization of styrene.