Chun-Yan Hong

Recent advances in RAFT dispersion polymerization for preparation of block copolymer aggregates

Differently from bulk, solution, suspension, emulsion, and miniemulsion polymerizations, the controlled radical dispersion polymerization (CRDP) demonstrates self-assembly of the block copolymers formed in the homogeneous system, forming various kinds of micelles or vesicles. Thus, this technology can prepare both the block copolymers and the polymeric aggregates directly. Among CRDP, the reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization has been studied in relative detail and has been successfully developed to prepare a diverse range of assemblies. Several typical systems for RAFT dispersion polymerization are presented in detail and the factors influencing the polymerization and the in situ self-assembly are also highlighted in this minireview.

One-pot synthesis of nanomaterials via RAFT polymerization induced self-assembly and morphology transition

A simple and facile strategy has been developed for synthesis of nanomaterials via polymerization in high concentration; multiple morphologies can be created and tuned just by variation of the feed ratio and reaction conditions.

Fabrication of smart nanocontainers with a mesoporous core and a pH-responsive shell for controlled uptake and release

A facile and versatile method to prepare mesoporous core-shell nanostructures with a reversibly switchable nanoshell is reported. Reversible addition-fragmentation chain transfer (RAFT) functionalities were anchored to the exterior surface of mesoporous silica nanoparticles (MSNs), forming RAFT agent coated MSNs. RAFT polymerization was then conducted to graft a poly(acrylic acid) (PAA) shell onto the exterior surface of MSNs, producing novel smart nanocontainers with a MSN as the container and a pH-responsive PAA nanoshell as a smart nanovalve. The PAA nanovalve can control the access of guest molecules to and from the MSN nanocontainer. This core-shell nanostructure should have potential applications in drug and gene delivery.

Biocompatible Zwitterionic Sulfobetaine Copolymer-Coated Mesoporous Silica Nanoparticles for Temperature-Responsive Drug Release

A novel nanocontainer, which could regulate the release of payloads, has been successfully fabricated by attaching zwitterionic sulfobetaine copolymer onto the mesoporous silica nanoparticles (MSNs). RAFT polymerization is employed to prepare the hybrid poly(2-(dimethylamino)ethyl methacrylate)-coated MSNs (MSN-PDMAEMA). Subsequently, the tertiary amine groups in PDMAEMA are quaternized with 1,3-propanesultone to get poly(DMAEMA-co-3-dimethyl(methacryloyloxyethyl)ammonium propanesulfonate)-coated MSNs [MSN-Poly(DMAEMA-co-DMAPS)]. The zwitterionic PDMAPS component endows the nanocarrier with biocompatibility, and the PDMAEMA component makes the copolymer shell temperature-responsive. Controlled release of loaded rhodamine B has been achieved in the saline solutions.

Photo‐Initiated Living Free Radical Polymerization in the Presence of Dibenzyl Trithiocarbonate

The polymerizations of styrene (St), methyl acrylate (MA), and butyl acrylate (BuA), carried out under UV irradiation at room temperature in the presence of dibenzyl trithiocarbonate (DBTTC) were found to display living free-radical polymerization characteristics as evidenced by: narrow molecular weight distribution, linear increase of molecular weight with increasing conversion, well-controlled molecular weight, and first-order polymerization kinetics. The triblock copolymer, PMA-PSt-PMA, with narrow polydispersity and well-defined structure was successfully prepared using PMA-S-C(=S)-S-PMA as macro-photoinitiator under UV irradiation at room temperature. Based on GPC, NMR and FT-IR analyses, the structures of the polymers were obtained and the mechanism of the polymerization was proposed.

Formation of the block copolymer aggregates via polymerization-induced self-assembly and reorganization

The self-assembly of block copolymers attracts wide interest due to many potential applications of the polymeric aggregates. Great effort has been made to realize the convenient fabrication of abundant polymeric materials with well-defined nanostructures. This review introduces the development of the in situ preparation of block copolymer aggregates by heterogeneous polymerization. Great emphasis is put on discussing the formation mechanism of aggregates with different morphologies. Some important factors that influence the morphologies are illustrated when different polymerization methods are employed. By demonstrating some recent advances and existing problems in this area, more attention and effort should be paid to this field to facilitate its further progress.

Morphology transitions in RAFT polymerization

Polymerization-induced self-assembly and re-organization (PISR) was used to prepare polymeric nanostructured materials with a variety of morphologies. Reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene in a selective solvent, methanol, was carried out using cyanoisopropyl dithiobenzoate-terminated poly(2-dimethylaminoethyl methacrylate) (PDMAEMA-DBT) as the macro chain transfer agent and stabilizer for investigation of the factors influencing the formation of morphologies. Various morphologies, including spherical micelles, nanostrings, vesicles and large compound vesicles, with different shapes were obtained by changing the feed ratios and reaction conditions. The sequential morphologic transitions from spherical micelles to nanostrings, to vesicles and to large compound vesicles via increasing the chain length ratio of the hydrophobic block to the hydrophilic one in the same system were observed for the first time. This approach can be performed at a high concentration, thus it can be scaled up for the reproducible preparation of nanostructured materials in a relatively high volume.

Directly growing ionic polymers on multi-walled carbon nanotubes via surface RAFT polymerization

RAFT agents were attached to multi-walled carbon nanotubes (MWNTs); subsequently, different kinds of aqueous soluble ionic polymer chains, such as cationic polymer (poly(2-(dimethylamino) ethylmethacrylate)), anionic polymer (poly(acrylic acid)) and zwitterionic polymer (poly{3-[N-(3- methacrylamidopropyl)-N,N-dimethyl] ammoniopropane sulfonate}) were easily to grafted onto the surface of MWNTs directly by surface reversible addition-fragmentation chain transfer (RAFT) polymerization. The produced poly{3-[N-(3-methacrylamidopropyl)-N,N-dimethyl] ammoniopropane sulfonate} functionalized MWNTs, poly(acrylic acid) functionalized MWNTs and poly(2-(dimethylamino) ethyl methacrylate) functionalized MWNTs have good solubility in aqueous solution.

Spiropyran-Based Polymeric Vesicles: Preparation and Photochromic Properties

A direct access to photochromic polymeric vesicles was demonstrated via polymerization-induced self-assembly and reorganization (PISR). The resulting vesicles displayed interesting photochromic behaviors different from that of their free polymer chains in DMF, and the vesicles exhibited stronger fluorescence and excellent photostability due to confinement of conformational flexibility of the polymer chains in aggregates.

Galactose-based amphiphilic block copolymers: synthesis, micellization, and bioapplication.

Redox-responsive amphiphilic diblock copolymers, poly(6-O-methacryloyl-D-galactopyranose-co-2-(N,N-dimethylaminoethyl) methacrylate)-b-poly(pyridyl disulfide ethyl methylacrylate) (P(MAGP-co-DMAEMA)-b-PPDSMA) were obtained by deprotection of poly((6-O-methacryloyl-1,2:3,4-di-O-isopropylidene-D-galactopyranose)-co-DMAEMA)-b-PPDSMA [P(MAlpGP-co-DMAEMA)-b-PPDSMA], which were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization of PDSMA using P(MAlpGP-co-DMAEMA) as macro-RAFT agent. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies showed that diblock copolymers P(MAGP-co-DMAEMA)-b-PPDSMA can self-assemble into micelles. Doxorubicin (DOX) could be encapsulated by P(MAGP-co-DMAEMA)-b-PPDSMA upon micellization and released upon adding glutathione (GSH) into the micelle solution. The galactose functional groups in the PMAGP block had specific interaction with HepG2 cells, and P(MAGP-co-DMAEMA)-b-PPDSMA can act as gene delivery vehicle. So, this kind of polymer has potential applications in hepatoma-targeting drug and gene delivery and biodetection.