Macro Reversible Addition-fragmentation Chain Transfer Agent Research Articles

Flame Retardant Submicron Particles via Surfactant-Free RAFT Emulsion Polymerization of Styrene Derivatives Containing Phosphorous.

The reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of diethyl-(4-vinylbenzyl) phosphate (DEVBP) was performed using PEG-TTC as a macro RAFT agent. PEG-TTC (MW 2000, 4000) was synthesized by the esterification of poly (ethylene glycol) methyl ether with a carboxylic-terminated RAFT agent, composed a hydrophilic poly (ethylene glycol) (PEG) block and a hydrophobic dodecyl chain. The RAFT emulsion polymerization of DEVBP was well–controlled with a narrow molecular size distribution. Dynamic light scattering and confocal laser scanning microscopy were used to examine the PEG-b-PDVBP submicron particles, and the length of the PEG chain (hydrophilic block) was found to affect the particle size distribution and molecular weight distribution. The submicron particle size increased with increasing degree of polymerization (35, 65, and 130), and precipitation was observed at a high degree of polymerization (DP) using low molecular weight PEG-TTC (DP 130, A3). The flame retardant properties of the PEG-b-PDVBP were evaluated by thermogravimetric analysis (TGA) and micro cone calorimeter (MCC). In the combustion process, the residue of PEG-b-PDEVBP were above 500 °C was observed (A1 ~ B3, 27 ~ 38%), and flame retardant effect of PEG-b-PDEVBP submicron particles/PVA composite were confirmed by increasing range of temperature and decreasing total heat release with increasing contents of PEG-b-PDEVBP. The PEG-b-PDEVBP submicron particles can provide flame retardant properties to aqueous, dispersion and emulsion formed organic/polymer products.

Polymerization‐Induced Thermal Self‐Assembly of Functional and Thermo‐Responsive Diblock Copolymer Nano‐Objects via RAFT Aqueous Polymerization

AbstractThe polymerization‐induced self‐assembly (PISA) of amphiphilic diblock copolymer nano‐objects, which are synthesized via reversible addition‐fragmentation chain‐transfer (RAFT) aqueous polymerization, is discussed. First, the effectiveness of the (S)‐2‐(ethyl propionate)‐(O‐ethyl xanthate) as a RAFT chain transfer agent for the polymerization of N,N‐dimethylacrylamide (DMAm) yielding a water‐soluble macro RAFT agent is investigated. In a second step, poly(DMAm) macro‐CTA is chain‐extended with acrylate monomers in water inducing a PISA process. Besides the use of pentafluorophenyl acrylate (PFPA) as core‐forming block, the thermo‐responsive nature of N‐isopropylacrylamide (NIPAm) and the reactive character of pentafluorophenyl acrylate (PFPA) for a subsequent post‐modification is exploited. Monomer conversion and reaction kinetics are determined via nuclear magnetic resonance spectroscopy, while gel permeation chromatography is used to evaluate the molecular weight distribution of the polymers. The obtained spherical nanostructures are analyzed via dynamic light scattering, scanning electron microscopy, transmission electron microscopy and atomic force microscopy.

Preparation of pH- and reductive-responsive prodrug nanoparticles via polymerization-induced self-assembly

pH- and reductive-responsive prodrug nanoparticles are constructed via a highly efficient strategy, polymerization-induced self-assembly (PISA). First, reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-(diisopropylamino) ethyl methacrylate (DIPEMA) and camptothecin prodrug monomer (CPTM) using biocompatible poly( N -(2-hydroxypropyl) methacrylamide) (PHPMA-CPDB) as the macro RAFT agent is carried out, forming prodrug diblock copolymer PHPMA-P(DIPEMA- co -CPTM). Then, simultaneous fulfillment of polymerization, self-assembly, and drug encapsulation are achieved via RAFT dispersion polymerization of benzyl methacrylate (BzMA) using the PHPMA-P(DIPEMA- co -CPTM) as the macro RAFT agent. The prodrug nanoparticles have three layers, the biocompatible shell (PHPMA), the drug-conjugated middle layer (P(DIPEMA- co -CPTM)) and the PBzMA core, and relatively high concentration (250 mg/g). The prodrug nanoparticles can respond to two stimuli (reductive and acidic conditions). Due to reductive microenvironment of cytosol, the cleavage of the conjugated camptothecin (CPT) within the prodrug nanoparticles could be effectively triggered. pH-Induced hydrophobic/hydrophilic transition of the PDIPEMA chains results in faster diffusion of GSH into the CPTM units, thus accelerated release of CPT is observed in mild acidic and reductive conditions. Cell viability assays show that the prodrug nanoparticles exhibit well performance of intracellular drug delivery and good anticancer activity.

Facile One-Pot Synthesis of Functional Giant Polymeric Vesicles Controlled by Oscillatory Chemistry.

We introduce a novel application of an oscillatory chemical reaction to the synthesis of block copolymers. The Belousov-Zhabotinsky (B-Z) reaction is coupled with the polymerization of an amphiphilic block copolymer. Radicals generated in the B-Z reaction initiate the polymerization between a polyethylene glycol (PEG) macroreversible addition-fragmentation chain-transfer agent and butyl acrylate monomers. The attachment of a hydrophobic block on PEG leads to self-assembly and formation of spherical micelles. The nanoscale micelles transform into submicrometer vesicles and grow to giant vesicles as a consequence of the oscillatory behavior of the B-Z reaction. The one-pot synthesis of an amphiphilic di-block copolymer and retention of oscillatory behavior for the B-Z reaction with the formation of giant vesicles bring a new insight into possible pathways for the synthesis of active functional microreactors in the range from hundreds of nanometers to tens of micrometers.

Template‐Directed Fabrication of Anatase TiO2 Hollow Nanoparticles and Their Application in Photocatalytic Degradation of Methyl Orange

Polymerization‐induced self‐assembly (PISA) was used to fabricate polymeric nanoparticles via reversible addition‐fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) using diblock copolymer poly(glycerol monomethacrylate)‐block‐poly(2‐dimethylaminoethyl methacrylate) (PGMMA‐ PDMAEMA‐CTA) as the macro RAFT agent. The dispersion of polymeric nanoparticles with a final concentration of about 210 mg/g (solid content of 21%) was obtained via this efficient method (PISA). The resultant polymeric nanoparticles consisting of corona‐shell‐core three layers with weak polyelectrolyte PDMAEMA as the shell were used as sacrificial template to fabricate TiO2 hollow nanoparticles. The negatively charged titanium precursor was absorbed into the PDMAEMA shell via the electrostatic interaction, and hydrolyzed to form polymer/TiO2 hybrid nanoparticles. Anatase TiO2 hollow nanoparticles were formed after removing the polymeric templates by calcination at 550 °C. The experiments of photocatalytic degradation of methyl orange showed that the resultant anatase TiO2 hollow nanoparticles had high photocatalytic activity and good reusability.

Spiropyran-Based Hyperbranched Star Copolymer: Synthesis, Phototropy, FRET, and Bioapplication

Photo- and pH-responsive amphiphilic hyperbranched star copolymers, poly(6-O-methacryloyl-1,2;3,4-di-O-isopropylidene-d-galactopyranose)[poly(2-(N,N-dimethylaminoethyl) methacrylate)-co-poly(1'-(2-methacryloxyethyl)-3',3'-dimethyl-6-nitro-spiro(2H-1-benzo-pyran-2,2'-indoline))](n)s [HPMAlpGP(PDMAEMA-co-PSPMA)(n)], were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of the DMAEMA and the SPMA using hyperbranched PMAlpGP as a macro RAFT agent. In aqueous solution, the copolymers self-assembled to form core-shell micelles with HPMAlpGP core and PDMAEMA-co-PSPMA shell. The hydrophobic fluorescent dye nitrobenzoxadiazolyl derivative (NBD) was loaded into the spiropyran-containing micelles. The obtained micelles not only have the photochromic properties, but also modulate the fluorescence of NBD through fluorescence resonance energy transfer (FRET), which was also observed in living cells. Slight fluorescence intensity decrease of the spiropyran in merocyanine (ME) form was observed after five UV-visible light irradiation cycles. The cytotoxicity of the HPMAlpGP(PDMAEMA-co-PSPMA)(n) micelles was lower than that of 25k PEI. All the results revealed that these photoresponsive nanoparticles are a good candidate for cell imaging and may find broad applications in biological areas such as biological diagnosis, imaging, and detection.

Synthesis of Surface-Functionalized Poly(styrene-co-butadiene) Nanoparticles via Controlled/Living Radical Mini-emulsion Copolymerization Stabilized by Ammonolyzed Poly(styrene-alt-maleic anhydride) (SMA) RAFT Agent

A process for reversible addition-fragmentation chain transfer (RAFT) radical polymerization in a mini-emulsion system stabilized by ammnolyzed poly(styrene-alt- maleic anhydride) copolymer (SMA) as an amphiphilic macro RAFT agent has been applied to the copolymerization of styrene and butadiene to prepare nanoparticles. First, for the RAFT polymerization of styrene, the results of molecular weights (Mns) and polydispersity index (PDIs) determined by GPC showed that the RAFT mini-emulsion polymerization of styrene exhibited good controlled/living nature with a lower degree of aminolysis (∼30%). Second, for the copolymerization of styrene and butadiene, before the gel point the molecular weight growth was followed during the polymerization by GPC and the results revealed that the GPC curve moves to the higher molecular weight indicating the formation of the copolymer. At low conversion, molecular weights (Mns) are in good agreement with theoretical prediction. The microphase separation of the copolymer nanoparticles was confirmed by transmission electron microscopy (TEM).

Preparation of Self-Crosslinking Core-Shell Latex at Ambient Temperature

A reversible addition fragmentation chain transfer (RAFT) agent, 2- (dodecylthiocarbonothioylthio)propanoic acid (RAFT-1), was synthesized and characterized. Equimolar doses of acrylic acid (AA) and n-butyl acrylate were successively polymerized in the presence of RAFT-1 to give an amphiphilic macro RAFT agent (RAFT-2), which had a calculated average degree of polymerization of ten. Core-shell poly (butyl acrylate-co-diacetoneacrylamide) latex was prepared by using RAFT-2 as a reactive surfactant. The latex was narrowly distributed and very stable, which had a solid concentration as high as 45 wt.% and an average diameter of about 50 nm, Latex films were prepared with the core-shell emulsion and small amount of cross-linking agent, adipic dihydrazide. Results showed that cross-linking reaction occurred with the evaporation of water. The resulting cross-linked latex film was tough and transparent.

One-pot synthesis of polymeric nanomaterials via RAFT dispersion polymerization induced self-assembly and re-organization

A novel strategy for preparation of multiple nanostructural materials, which is the creation of such materials directly from controlled radical dispersion polymerization in one pot, has been developed. In the formation of polymeric nanomaterials, the chain length ratio of the hydrophobic to hydrophilic blocks is altered continuously, which induces two phase transitions, phase separation to form spherical micelles and re-organization of the resulting spheres to yield multiple morphologies including nanorods, nanotubes, vesicles and doughnuts. This is quite different from self-assembly of the block copolymer in a selective solvent, where nature and solubility parameter of the solvents are changed. In the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene in methanol using poly(4-vinylpyridine) as macro RAFT agent, the resultant polymeric nanomaterials with various morphologies coexisted generally, however, uniform nanowires and vesicles could be prepared by appropriately selecting concentration of monomer and feed ratio, as well as by strict control of reaction conditions. One advantage of this strategy is that the nanomaterials with a concentration as high as 0.5 g mL−1 can be achieved, this provides possibility for studying extensive applications of the various nanomaterials.

Preparation and Characterization of Nano-Sized Silver Particles

This study presents an approach to prepare nano-sized silver particles via in-situ reduction process. First, a reversible addition fragmentation chain transfer (RAFT) agent, 2-(dodecylthiocarbonothioylthio)propanoic acid (DTPA), was synthesized and characterized. Acrylic acid (AA) was polymerized in the presence of DTPA to afford an amphiphilic macro RAFT agent (DTPA-AC-10) with a calculated average degree of polymerization of ten. Latex particles with a sodium salt-containing shell were prepared by using sodium DTPA-AC-10 as a reactive surfactant. Then, through silver ion-exchange processs of the latex particles, the latex particles with silver salt at the surface were obtained. Finally, the silver salt at the particle surface was reduced through chemical reduction to give the silver-coated polymer particles. Dynamic Laser Scattering (DLS) was used to measure the particle size and distribution; X ray diffraction analysis (XRD) was employed to characterize the formed silver crystal in the particle surface. The diameter of the silver particles was about 76 nm and was narrowly distributed. The silver nanoparticles might be used to prepare conductive ink for ink-jet applications.

Preparation of poly(styrene‐block‐acrylamide)/organic montmorillonite nanocomposites via reversible addition–fragmentation chain transfer

AbstractUsing dithioester as a chain‐transfer agent and azobisisobutyronitrile as an initiator, we synthesized amphiphilic poly(styrene‐block‐acrylamide) [P(St‐b‐Am)] by the reversible addition–fragmentation chain transfer (RAFT) polymerization method. To improve the heat stability of the block polymers, amphiphilic P(St‐b‐Am)/organic montmorillonite (O‐MMT) nanocomposites were successfully prepared by the addition of O‐MMT during the preparation of the block polymer. The nanocomposites were tested by gel permeation chromatography, IR spectroscopy, X‐ray diffraction, transmission electron microscopy, and thermogravimetry. As for polystyrene (PSt)/O‐MMT, RAFT polymerization could control the molecular weight and the molecular weight distribution of PSt. PSt/O‐MMT was used as a macro RAFT agent to conduct the polymerization of acrylamide, and P(St‐b‐Am)/O‐MMT nanocomposites were prepared. Nanosize layers of montmorillonite were dispersed in the block polymer matrix, and exfoliative nanocomposites were formed. Therefore, the P(St‐b‐Am)/O‐MMT nanocomposites had a better heat stability than before. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Preparation of star polymers based on polystyrene or poly(styrene- b- N-isopropyl acrylamide) and divinylbenzene via reversible addition-fragmentation chain transfer polymerization

Star polymers based on styrene/divinyl benzene (St/DVB) and PSt- b-poly( N-isopropyl acrylamide) (NIPAAM)/DVB have been successively prepared by ‘arm-first’ method via reversible addition-fragmentation chain transfer (RAFT) polymerization. The linear macro RAFT agent PSt-SC(S)Ph was prepared by RAFT polymerization of St using benzyl dithiobenzoate and AIBN as RAFT agent and initiator. Successive RAFT polymerization of NIPAAM with PSt-SC(S)Ph as macro RAFT agent to afford diblock copolymer, PSt-b-PNIPAAM-SC(S)Ph. The coupling reactions of PSt-SC(S)Ph or PSt-b-PNIPAAM-SC(S)Ph in the presence of DVB produced the star copolymers, C(PSt) n or C(PSt-b-PNIPAAM) n . The molar ratio of DVB/PSt-SC(S)Ph and polymerization time influenced the yields, molecular weight and distribution of the star-shaped polymers, which was characterized by 1H NMR and IR spectra, GPC measurements as well as DLS.