Synthesis of phosphinodiselenoic acid esters and their application as RAFT agents in styrene polymerization

Phosphinodiselenoic acid esters are synthesized from the reaction of chlorodiphenylphosphine and aryl- or alkyl-magnesium bromide in the presence of selenium powder. They are employed as RAFT agents in thermally initiated, styrene polymerization. The phosphinodiselenoic acid esters 6a and 6b showed some degree of control over the radical polymerization of styrene.     

Synthesis of gradient copolymers with complexing groups by RAFT polymerization and their solubility in supercritical CO2

We report the synthesis of new gradient fluorinated copolymers with complexing groups and soluble in supercritical carbon dioxide (scCO₂). Poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate‐co‐acetoacetoxyethyl methacrylate) (poly(FDA‐co‐AAEM)) and poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate‐co‐vinylbenzylphosphonic acid diethylester) (poly(FDA‐co‐VBPDE)) gradient copolymers were synthesized by reversible addition fragmentation chain transfer polymerization in α,α,α‐trifluorotoluene. Poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate‐co‐vinylbenzylphosphonic diacid) (poly(FDA‐co‐VBPDA)) gradient copolymer was efficiently obtained by cleavage of the phosphonic ester groups of poly(FDA‐co‐VBPDE). The cloud points of these gradient copolymers in dense CO₂ were measured in a variable volume view cell at temperatures between 25 and 65 °C. The gradient copolymers show very good solubility in compressed CO₂ with the decreasing order: poly(FDA‐co‐AAEM) ≈ poly(FDA‐co‐VBPDE) > poly(FDA‐co‐VBPDA). Following a green chemistry strategy, poly(FDA‐co‐AAEM) gradient copolymer was successfully synthesized in scCO₂ with a good control over number‐average molecular weight and composition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5448–5460, 2009     

A simple method to convert atom transfer radical polymerization (ATRP) initiators into reversible addition fragmentation chain-transfer (RAFT) mediators

A simple method to convert atom transfer radical polymerization (ATRP) initiators into reversible addition fragmentation chain-transfer (RAFT) mediators is reported. Poly(methylmethacrylate) (PMMA), poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(ethylene glycol) (PEG) ATRP initiators were converted into their corresponding RAFT analogues using modified ATRP conditions for polymer chain activation in presence of bis(thiobenzoyl) disulphide.     

Phosphonate‐terminated poly(vinyl acetate) synthesized by RAFT/MADIX polymerization

Four different xanthates containing either phosphonate or bisphosphonate moieties were synthesized with high degree of purity. These xanthates were used as chain transfer agents (CTA) in the RAFT/MADIX polymerization of vinyl acetate (VAc) to prepare end‐capped poly(VAc). The rate of VAc polymerization in the presence of these new CTAs was shown to be similar to that obtained with conventional xanthate, that is, (methyl ethoxycarbonothioyl) sulfanyl acetate. Good control of VAc polymerization was also obtained since the molecular weight increased linearly with monomer conversion for each phosphonate‐containing xanthate. Low‐PDI values were obtained, ascribed to efficient exchange during RAFT/MADIX polymerization. C_ex value was therefore calculated to about 25, based on RAFT/MADIX of VAc in the presence of rhodixan A1/VAc adduct. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Facile synthesis of temperature-sensitive ABA triblock copolymers by dispersion RAFT polymerization

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Controlled/living polymerization of methacrylamide in aqueous media via the RAFT process

The polymerization of methacrylamide (MAM) was performed in aqueous media via reversible addition fragmentation chain transfer (RAFT) polymerization with the dithiobenzoate chain‐transfer agent (CTA) 4‐cyanopentanoic acid dithiobenzoate (CTP) and 4,4′‐azobis(4‐cyanopentanoic acid) (V‐501) as initiator. The polymerization in unbuffered water at 70 °C with a CTP/V‐501 ratio of 1.5 was controlled for the first 3 h, after which the molecular weight distribution broadened and a substantial deviation of the experimental from the theoretical molecular weight occurred, presumably because of a loss of CTA functionality at longer polymerization times. Conducting the polymerization in an acidic buffer afforded a well‐defined homopolymer (M_n = 23,800 g/mol, M_w/M_n = 1.08). To demonstrate the controlled/living nature of the system, a block copolymer of MAM and acrylamide was successfully prepared (M_n = 33,800 g/mol, M_w/M_n = 1.25) from a polymethacrylamide macro‐CTA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3141–3152, 2005     

PDEGMA-b-PDIPAEMA copolymers via RAFT polymerization and their pH and thermoresponsive schizophrenic self-assembly in aqueous media

We report on a new doubly responsive polymeric system of amphiphilic diblock copolymers, namely poly(di-[ethylene glycol] methyl ether methacrylate)-b-poly(2-[diisopropylamino] ethyl methacrylate), PDEGMA-b-PDIPAEMA, obtained by the reversible addition-fragmentation chain transfer (RAFT) polymerization technique. Molecular characterization by size exclusion chromatography (SEC), nuclearmagnetic resonance (¹H-NMR) and infrared spectroscopy (FT-IR) confirms the successful synthesis of these novel block copolymers. The PDEGMA-b-PDIPAEMA block copolymers formed aggregates in aqueous media in response to solution pH and temperature changes, as evidenced by dynamic and static light scattering techniques, as well as fluorescence spectroscopy. Aggregates with PDEGMA core and PDIPAEMA corona domains are formed at elevated temperatures and low pH, whereas aggregates with PDIPAEMA cores and PDEGMA coronas are formed at neutral and high pH. Overall structural characteristics and solution behavior of the copolymers are affected by the copolymer composition. The obtained results provide valuable new information on the behavior and design guidelines for the construction of stimuli responsive, “schizophrenic” polymeric nanostructures with potential application in the biomedical field.     

Butyl acrylate RAFT polymerization in miniemulsion

Few successes about butyl acrylate (BA) RAFT miniemulsion homopolymerization were reported, even though styrene, methyl methacrylate, and vinyl acetate had been successfully applied in reversible addition fragmentation transfer (RAFT) miniemulsion polymerization. In this article, four types of RAFT agent with various designed R and Z groups [benzyl dithioisobutyrate (BDIB), 1-phenylethyl phenyldithioacetate (PEPDTA), cumyl dithioisobutyrate (CDIB), benzyl dithiobenzoate] were used to mediate BA miniemulsion polymerization using the conditions (5 wt % hexadance and sodium dodecyl sulfate) effective for styrene and methyl methacrylate systems. All four types of the RAFT agents effectively control over the bulk polymerization. In contrast, only BDIB resulted in a rather narrow molecular weight distribution in the miniemulsion polymerization. A pronounced inhibition and rate retardation were observed in both bulk and miniemulsion polymerizations mediated by CDIB and benzyl dithiobenzoate. When compared with the bulk polymerization, a much longer inhibition period (over eight times) was observed in the CDIB-mediated miniemulsion polymerization. It was concluded that only the RAFT agent with the primary R group and Z group with less stabilizing ability to the intermediate radicals is effective to mediate BA miniemulsion polymerization in terms of achieving a narrow molecular weight distribution and short inhibition period. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2304–2315, 2007     

Glucose oxidase deoxygenation−redox initiation for RAFT polymerization in air

A new methodology based on glucose oxidase (GOx) deoxygenation and hydrogen peroxide/vitamin C (H₂O₂/Vc) redox initiation for conducting RAFT polymerization at low temperature in air is reported. GOx catalyzes reduction of oxygen in the presence of glucose to generate hydrogen peroxide, which is directly used to constitute a redox pair with Vc for the efficient generation of hydroxyl radicals to initiate RAFT polymerization in air. Various experimental parameters including temperature, stirring speed, prepolymerization incubation time, and concentrations of Vc, glucose, and GOx were evaluated with respect to monomer conversion, molecular weight, and dispersity. Efficient removal of oxygen is typically realized within 10 min before polymerization is initiated by addition of Vc, and high conversions are achieved within 5 h. Well‐defined homopolymers and block copolymers have been efficiently synthesized with high monomer conversions and low dispersities (< 1.2). Using this new methodology, it is possible to conduct controlled RAFT polymerizations in both open and sealed vessels, though lower conversions but less termination by oxygen are typically observed for the sealed systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 164–174     

The synthesis of P(MAn-co-St)-b-PS-b-P(MAn-co-St) block copolymers by RAFT polymerization and the nanostructure of their self-assembly aggregates

A series of block copolymers of styrene, maleic anhydride and acrylic acid were synthesized by the reverse addition–fragmentation chain transfer (RAFT) process. The structure, molecular weight and polydispersity index were determined by FTIR, ¹H NMR, SEC&MALLS and DSC analysis. The results showed that the polymerization occurred in a living and controlled manner. Multiple self-assembled nanostructures of these block copolymers were investigated by transmission electron microscopy (TEM). Tetrahydrofuran (THF), N,N-dimethylformamide (DMF) and 1,4-dioxane were used as the common solvents and twice-distilled water as the selective solvent to clarify the effects of the solvent. The results revealed that with the increase of the extension degree of the core, non-spherical aggregates were easily formed, the composition of the copolymers influences the aggregation behavior, and other factors also influence the self-assembly, such as hydrolysis, temperature, annealing time, molecular architecture etc. A mechanism is proposed to illustrate the formation of the various aggregates of P(MAn-co-St)-b-PS-b-P(MAn-co-St) copolymer, which were confirmed by TEM results.     

Synthesis and characterizations of 1,2,3-triazole containing polymers via reversible addition-fragmentation chain transfer (RAFT) polymerization

A novel monomer containing triazole and naphthalene ring, 2-(1-naphthalen-1-ylmethyl-1H-[1,2,3]triazol-4-yl)-ethyl methacrylate (NTEMA), was designed and synthesized via “click” chemistry method. The RAFT polymerization of NTEMA was successfully carried out using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as a RAFT agent, 2,2′-azobisisobutyronitrile (AIBN) as an initiator in tetrahydrofuran (THF) solution. The results showed that the polymerizations exhibited “living”/controlled characteristics. The obtained poly(2-(1-naphthalen-1-ylmethyl-1H-[1,2,3]triazol-4-yl)-ethyl methacrylate) homopolymers, PNTEMAs, were further coordinated with samarium ion to prepare rare earth containing polymers (PNTEMA-Sm(III) complexes) which were characterized by FT-IR, DSC and ICP-AES. The characterization data confirmed that triazole in side chain of the polymer could coordinate with Sm(III). The fluorescence property of the polymers and polymer Sm(III) complexes were investigated in solution and in film.     

Controlled/living radical polymerization of vinylcyclicsilazane by RAFT process and their block copolymers

High molecular weight poly(vinyl)silazane were synthesized successfully by reversible addition fragmentation chain transfer (RAFT) polymerization in toluene at 120 °C, using dithiocarbamate derivatives and 2,2′‐azobis‐isobutyrylnitrile (AIBN) as the RAFT agents and thermal initiator, respectively. The polymerization of a vinylcyclicsilazane oligomer with 82.5% conversion was readily controlled to increase the molecular weight from 1000 to 12,000 g/mol with a narrow polydispersity <1.5. The resulting polymer showed a high ceramic yield of 70 wt % at 1000 °C. Moreover, the approach was extended successfully to the synthesis of poly(vinyl)silazane‐block‐polystyrene as an inorganic–organic diblock copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4594–4601, 2008     

Porphyrinic covalent organic framework designed by molecular engineering as heterogeneous photocatalyst for aerobic mediated RAFT polymerization

Covalent organic frameworks (COFs) have gained increasing attention as heterogeneous materials for their prominent applications in photocatalytic processes. The already tailored structure endows COFs with ordered dimensional channels for the separation and migration of the electro-hole pairs and improves their photocatalytic properties. In this contribution, oxygen-mediated RAFT polymerization was achieved by using M-TCPP-DHTA-COFs (M = H₂ or Zn) as photocatalysts with the assistance of TEA as co-catalyst producing polymers with accurate molecular weight and narrow molecular weight distribution under visible light irradiation. The control experiments revealed excellent dual control behavior of light and gas toward polymerization processes. Notably, porphyrinic COFs can be straightforwardly separated and recycled for recycling experiments and exhibit remarkable compatibility features of controllable polymerization for functional monomers under aerobic conditions. This study offers a promising pathway for the construction of an efficient heterogeneous catalyst of oxygen-mediated RAFT polymerization and extends the novel applications of porphyrin-based COF materials.     

Shell-crosslinked nanoparticles through self-assembly of thermoresponsive block copolymers by RAFT polymerization

A reversible addition-fragmentation chain transfer (RAFT) agent, the methyl-2-(n-butyltrithiocarbonyl)propanoate (MBTTCP) has shown to be efficient in controlling the polymerization of N,N-dimethylacrylamide (DMA), N-isopropylacrylamide (NIPAM) and N-acryloyloxysuccinimide (NAS). Two different strategies have been studied to synthesize block copolymers based on one PNIPAN block and the other a random copolymer of DMA and NAS. When a PNIPAM trithiocarbonate-terminated is used as macromolecular chain transfer agent for the polymerization of a mixture of NAS and DMA, well-defined P(NIPAM-b-(NAS-co-DMA)) block copolymers were obtained with a low polydispersity index. These thermoresponsive block copolymers dissolved in aqueous solution at 25 °C and self-assembled into micelles when the temperature was raised above the LCST of the PNIPAM block. The micelle shell containing NAS units was further crosslinked using a primary diamine in order to get shell-crosslinked nanoparticles. Upon cooling below the LCST of PNIPAM this structure may easily reorganize to form nanoparticles with a water filled hydrophilic core.     

Grafting of silica with sulfobetaine polymers via aqueous reversible addition fragmentation chain transfer polymerization and its use as a stationary phase in HILIC

Porous silica particles of 3 μm diameter and 100 Å nominal pore size were first activated for vinylic polymerization by functionalization with 3-methacryloyloxypropyl trimethoxysilane (MAPTMS) and thereafter dressed with zwitterionic grafts of the sulfoalkylbetaine type in the “grafting through” fashion by polymerizing 3-(2-(N-methacryloyloxyethyl)-N,N-dimethylammonio)propane sulfonate (SPE), using either free radical polymerization or controlled reversible addition fragmentation chain transfer polymerization (RAFT). Particles polymerized using RAFT had a lower overall coating which seemed to be more evenly distributed in the pore volume. Both approaches resulted in columns with similar separation properties in HILIC mode.     

Thermoresponsive NIPAM block copolymers containing densely grafted poly(vinyl ether) brushes synthesized by a combination of living cationic polymerization and RAFT polymerization

Diblock copolymers consisting of a multibranched polymethacrylate segment with densely grafted poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] pendants and a poly(N‐isopropylacrylamide) segment were synthesized by a combination of living cationic polymerization and RAFT polymerization. A macromonomer having both a poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] backbone and a terminal methacryloyl group was synthesized by living cationic polymerization. The sequential RAFT copolymerizations of the macromonomer and N‐isopropylacrylamide in this order were performed in aqueous media employing 4‐cyanopentanoic acid dithiobenzoate as a chain transfer agent and 4,4′‐azobis(4‐cyanopentanoic acid) as an initiator. The obtained diblock copolymers possessed relatively narrow molecular weight distributions and controlled molecular weights. The thermoresponsive properties of these polymers were investigated. Upon heating, the aqueous solutions of the diblock copolymers exhibited two‐stage thermoresponsive properties denoted by the appearance of two cloud points, indicating that the densely grafted poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] pendants and the poly(N‐isopropylacrylamide) segments independently responded to temperature. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

RAFT polymerization of tertiary sulfonium zwitterionic monomer in aqueous media for synthesis of protein stabilizing double hydrophilic block copolymers

The reversible addition-fragmentation chain-transfer (RAFT) polymerization of a tertiary sulfonium-containing zwitterionic monomer (N-acryloyl-L-methionine methyl sulfonium salt: A-Met[S⁺]-OH) was performed in aqueous media in the presence of a water-soluble chain-transfer agent (CTA). Several parameters, such as the radical initiator, nature of the salt used as an additive, polymerization temperature, and solvent (water, buffer solution, and mixed solvents), were studied. The polymerization of A-Met(S⁺)-OH in acetate buffer using a trithiocarbonate-type CTA having two carboxylic acid moieties proceeded in a controlled fashion at 45°C, as confirmed by the low polydispersity of the products (M _w/M _n < 1.1) and pre-determined molecular weights. Poly(ethylene glycol)-based macro-CTA was also employed for the polymerization of A-Met(S⁺)-OH in mixed solvents (H₂O/EtOH and H₂O/DMF = 70/30 vol%) to afford novel nonionic-zwitterionic double hydrophilic block copolymers. The chain extension of the hydrophilic poly(N,N-dimethylacrylamide) macro-CTA with A-Met(S⁺)-OH was well controlled in pure water under the appropriate conditions, resulting in the formation of block copolymers with “as-designed” chain structures and relatively low dispersities (M _w/M _n < 1.3). The resulting sulfonium-containing double hydrophilic block copolymers having optimal nonionic/zwitterionic balance were efficient protein-stabilizing agents.     

Reversible addition-fragmentation chain transfer polymerization initiated with γ-radiation at ambient temperature: an overview

Using γ-radiation as initiation source at ambient temperatures (i.e. T≈20 °C) for reversible addition-fragmentation chain transfer (RAFT) polymerizations allows for the generation of narrowly distributed polymeric material with living characteristics. It is shown that the living characteristics effected by RAFT agent mediated bulk polymerizations using γ-irradiation are associated with a RAFT mechanism rather than with reversible termination processes. Furthermore, γ-radiation as initiation source for an appropriate RAFT agent/monomer system allows for effective radical storage and the generation of long-lived reaction intermediates at ambient temperatures.The current overview further demonstrates how the RAFT process together with γ-radiation as source of initiation can be employed to graft various monomers onto polypropylene surfaces in a controlled manner.