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.

Phosphonium polymers for gene delivery

Phosphonium salt-containing polymers have very recently started to emerge as attractive materials for engineering non-viral gene delivery systems.

Synthesis of antimicrobial block copolymers bearing immobilized bacteriostatic groups

Antimicrobial block copolymers bearing covalently bonded quaternized ammonium groups were synthesized through atom transfer radical polymerization (ATRP). Moreover, a new class of antimicrobial block copolymers were designed combining two types of biocide incorporation into one system (both contact-based and release-based mechanisms).

Ethanolic RAFT Dispersion Polymerization of 2-(Naphthalen-2-yloxy)ethyl Methacrylate and 2-Phenoxyethyl Methacrylate with Poly[2-(dimethylamino)ethyl Methacrylate] Macro-Chain Transfer Agents

The ethanolic reversible addition-fragmentation chain transfer dispersion polymerization (RAFTDP), at 21 wt-%, of 2-(naphthalen-2-yloxy)ethyl methacrylate (NOEMA) and 2-phenoxyethyl methacrylate (POEMA) with a poly[2-(dimethylamino)ethyl methacrylate] macro-chain transfer agent (CTA) with an average degree of polymerization of 20 (PDMAEMA20) is described. DMAEMA20-b-NOEMAy (y = 20–125) block copolymers were readily prepared under dispersion conditions in ethanol at 70°C. However, the polymerization of NOEMA was not well controlled, with size exclusion chromatograms being distinctly bi or multimodal with measured dispersities . Though NOEMA copolymerization was not ideal, the resulting series of block copolymers did exhibit the anticipated full spectrum of nanoparticle morphologies (spheres, worms, and vesicles). Interestingly, these morphology transitions occurred over a relatively narrow range of block copolymer compositions. In the case of POEMA, copolymerization was also poorly controlled with 1.50 ≤ ĐM ≤ 1.83 for the series of DMAEMA20-b-POEMAy copolymers. In contrast to the NOEMA-based copolymers, the POEMA series only yielded nanoparticles with a spherical morphology whose size increased with increasing average degrees of polymerization of the POEMA block. Collectively, though both NOEMA and POEMA can be utilized in ethanolic RAFT dispersion polymerization formulations, these preliminary studies suggest that neither appears to be an ideal aryl methacrylate choice as comonomer, especially if the goal is to combine the synthesis of well-defined copolymers with efficient nanoparticle formation.

Synthesis of siRNA Polyplexes Adopting a Combination of RAFT Polymerization and Thiol-ene Chemistry

Block copolymers of allyl methacrylate and N-(2-hydroxypropyl)methacrylamide (HPMA) with different block lengths have been synthesized by reversible addition–fragmentation chain transfer polymerization. Allyl groups were modified with cysteamine, via a thiol-ene photoreaction, with a high efficiency (~100%) as evidenced by NMR spectroscopy, yielding cationic copolymers of HPMA. Polyelectrolyte complexes of small interfering RNAs (siRNA) and the cationic block copolymers were then formed at an N/P ratio between 1 and 4 depending on the block length of the copolymers. Increasing the length of the hydrophilic block was found to decrease the efficiency of siRNA complexation. The hydrodynamic diameter of the polyplexes in 130 mM buffer solution was less than 100 nm.

RAFT Polymer End-Group Modification and Chain Coupling/Conjugation Via Disulfide Bonds

End-group modification of polymers prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization was accomplished by the conversion of trithiocarbonate or dithioester end-groups into a pyridyl disulfide (PDS) functionality. Several different polymers, such as poly(methyl methacrylate), polystyrene, poly(oligoethylene glycol-acrylate), poly(hydroxypropylacrylamide), and poly(N-isopropylacrylamide) were prepared by RAFT polymerization, and subjected to aminolysis in the presence of 2,2′-dithiodipyridine to yield thiol-terminated polymers with yields in the range 65–90% dependent on the polymer structure. Furthermore, this PDS end-group was utilized to generate higher-order architectures, such as diblock copolymers with high yields and selectively. In addition, the PDS end-groups were used for the bioconjugation of different biomolecules, such as oligonucleotides, carbohydrates, and peptides. The successful modification of well-defined polymers was confirmed by a combination of UV-vis, NMR spectroscopy, and gel permeation chromatography.