R‐RAFT approach for the polymerization of N‐isopropylacrylamide with a star poly(ε‐caprolactone) core

Reversible addition‐fragmentation chain transfer (RAFT) polymerization is a more robust and versatile approach than other living free radical polymerization methods, providing a reactive thiocarbonylthio end group. A series of well‐defined star diblock [poly(ε‐caprolactone)‐b‐poly(N‐isopropylacrylamide)]₄ (SPCLNIP) copolymers were synthesized by R‐RAFT polymerization of N‐isopropylacrylamide (NIPAAm) using [PCL‐DDAT]₄ (SPCL‐DDAT) as a star macro‐RAFT agent (DDAT: S‐1‐dodecyl‐S′‐(α, α′‐dimethyl‐α″‐acetic acid) trithiocarbonate). The R‐RAFT polymerization showed a controlled/“living” character, proceeding with pseudo‐first‐order kinetics. All these star polymers with different molecular weights exhibited narrow molecular weight distributions of less than 1.2. The effect of polymerization temperature and molecular weight of the star macro‐RAFT agent on the polymerization kinetics of NIPAAm monomers was also addressed. Hardly any radical–radical coupling by‐products were detected, while linear side products were kept to a minimum by careful control over polymerization conditions. The trithiocarbonate groups were transferred to polymer chain ends by R‐RAFT polymerization, providing potential possibility of further modification by thiocarbonylthio chemistry. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Aqueous RAFT polymerization of N‐isopropylacrylamide‐mediated with hydrophilic macro‐RAFT agent: Homogeneous or heterogeneous polymerization?

Aqueous RAFT polymerization of N‐isopropylacrylamide (NIPAM) mediated with hydrophilic macro‐RAFT agent is generally used to prepare poly(N‐isopropylacrylamide) (PNIPAM)‐based block copolymer. Because of the phase transition temperature of the block copolymer in water being dependent on the chain length of the PNIPAM block, the aqueous RAFT polymerization is much more complex than expected. Herein, the aqueous RAFT polymerization of NIPAM in the presence of the hydrophilic macro‐RAFT agent of poly(dimethylacrylamide) trithiocarbonate is studied and compared with the homogeneous solution RAFT polymerization. This aqueous RAFT polymerization leads to the well‐defined poly(dimethylacrylamide)‐b‐poly(N‐isopropylacrylamide)‐b‐poly(dimethylacrylamide) (PDMA‐b‐PNIPAM‐b‐PDMA) triblock copolymer. It is found, when the triblock copolymer contains a short PNIPAM block, the aqueous RAFT polymerization undergoes just like the homogeneous one; whereas when the triblock copolymer contains a long PNIPAM block, both the initial homogeneous polymerization and the subsequent dispersion polymerization are involved and the two‐stage ln([M]_o/[M])‐time plots are indicated. The reason that the PNIPAM chain length greatly affects the aqueous RAFT polymerization is discussed. The present study is anticipated to be helpful to understand the chain extension of thermoresponsive block copolymer during aqueous RAFT polymerization. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Polymerization-induced self-assembly of amino-acid-based nano-objects by reversible addition–fragmentation chain-transfer dispersion polymerization

A series of amino-acid-based amphiphilic diblock copolymer nano-objects having different morphologies were developed by reversible addition–fragmentation chain-transfer (RAFT) dispersion polymerization of styrene (St) in methanol. This was mediated by six different hydrophilic poly(N-acryloyl amino acid) macro-chain transfer agents (CTAs), including three carboxylic-acid-containing ones, poly(N-acryloyl-l -proline) (PAProOH), poly(N-acryloyl-4-trans-hydroxy-l -proline) (PAHypOH), and poly(N-acryloyl-l -threonine) (PAThrOH) prepared by RAFT polymerization, and their methyl ester forms, PAProOMe, PAHypOMe, and PAThrOMe. The effects of polymerization conditions on RAFT dispersion polymerization of St using a dithiocarbamate-terminated PAProOH was investigated. A systematic study of the effects of monomer conversion and concentration afforded the formation of various morphologies (i.e., spheres, worms, and vesicles). The effects of hydrogen-bonding and ionic interactions of the macro-CTAs on the assembled structures of the nano-objects were evaluated using six different macro-CTAs. Transforming the products from methanol to water via dialysis produced amino-acid-based block copolymer nano-objects, exhibiting pH-responsive morphological change, in aqueous solution.     

Thermo‐responsive fluorescent micelles from amphiphilic A3B miktoarm star copolymers prepared via a combination of SET‐LRP and RAFT polymerization

A novel amphiphilic A₃B miktoarm star copolymer poly(N‐isopropylacrylamide)₃‐poly(N‐vinylcarbazole) ((PNIPAAM)₃(PVK)) was successfully synthesized by a combination of single‐electron transfer living radical polymerization (SET‐LRP) and reversible addition‐fragmentation chain transfer (RAFT) polymerization. First, the well‐defined three‐armed poly(N‐isopropylacrylamide) (PNIPAAM)₃ was prepared via SET‐LRP of N‐isopropylacrylamide in acetone at 25 °C using a tetrafunctional bromoxanthate iniferter (Xanthate‐Br₃) as the initiator and Cu(0)/PMDETA as a catalyst system. Secondly, the target amphiphilic A₃B miktoarm star copolymer ((PNIPAAM)₃(PVK)) was prepared via RAFT polymerization of N‐vinylcarbazole (NVC) employing (PNIPAAM)₃ as the macro‐RAFT agent. The architecture of the amphiphilic A₃B miktoarm star copolymers were characterized by GPC, ¹H‐NMR spectra. Furthermore, the fluorescence intensity of micelle increased with the temperature and had a good temperature reversibility, which was investigated by dynamic light scattering (DLS), fluorescent and UV‐vis spectra. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4268–4278, 2010     

Thermoresponsive diblock copolymer micellar macro‐RAFT agent‐mediated dispersion RAFT polymerization and synthesis of temperature‐sensitive ABC triblock copolymer nanoparticles

The micellar macro‐RAFT agent‐mediated dispersion polymerization of styrene in the methanol/water mixture is performed and synthesis of temperature‐sensitive ABC triblock copolymer nanoparticles is investigated. The thermoresponsive diblock copolymer of poly(N,N‐dimethylacrylamide)‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] trithiocarbonate forms micelles in the polymerization solvent at the polymerization temperature and, therefore, the dispersion RAFT polymerization undergoes as similarly as seeded dispersion polymerization with accelerated polymerization rate. With the progress of the RAFT polymerization, the molecular weight of the synthesized triblock copolymer of poly(N,N‐dimethylacrylamide)‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine]‐b‐polystyrene linearly increases with the monomer conversion, and the PDI values of the triblock copolymers are below 1.2. The dispersion RAFT polymerization affords the in situ synthesis of the triblock copolymer nanoparticles, and the mean diameter of the triblock copolymer nanoparticles increases with the polymerization degree of the polystyrene block. The triblock copolymer nanoparticles contain a central thermoresponsive poly [N‐(4‐vinylbenzyl)‐N,N‐diethylamine] block, and the soluble‐to‐insoluble ‐‐transition temperature is dependent on the methanol content in the methanol/water mixture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2155–2165     

“Living”/controlled free radical polymerization of MMA in the presence of cobalt(II) 2‐ethylhexanoate: A switch from RAFT to ATRP mechanism

A metal complex, cobalt(II) 2‐ethylhexanoate (CEH), was added to the system of thermal‐initiated reversible addition‐fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as the RAFT agent at 115 °C. The polymerization rate was remarkably enhanced in the presence of CEH in comparison with that in the absence of CEH, and the increase of the CPDN concentration also accelerated the rate of polymerization. The polymerization in the concurrence of CPDN and CEH demonstrated the characters of “living”/controlled free radical polymerization: the number‐average molecular weights (M_n) increasing linearly with monomer conversion, narrow molecular weight distributions (M_w/M_n) and obtained PMMA end‐capped with the CPDN moieties. Meanwhile, CEH can also accelerate the rate of RAFT polymerization of MMA using the PMMA as macro‐RAFT agent instead of CPDN. Similar polymerization profiles were obtained when copper (I) bromide (CuBr)/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine was used instead of CEH. Extensive experiments in the presence of butyl methacrylate, bis(cyclopentadienyl) cobalt(II) and cumyl dithionaphthalenoate were also conducted; similar results as those of MMA/CPDN/CEH system were obtained. A transition of the polymerization mechanism, from RAFT process without CEH addition to atom transfer radical polymerization in the presence of CEH, was possibly responsible for polymerization profiles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5722–5730, 2007     

Synthesis of Hyperbranched Polyethylene Amphiphiles by Chain Walking Polymerization in Tandem with RAFT Polymerization and Supramolecular Self‐Assembly Vesicles

A novel polymerization methodology for efficient synthesis of hyperbranched polyethylene amphiphiles by chain walking polymerization (CWP) followed by RAFT polymerization has been developed. Hyperbranched polyethylene with hydroxyl ends (HBPE‐OHs) is first synthesized via chain walking copolymerization of ethylene with 2‐hydroxyethyl acrylate with Pd‐α‐diimine catalyst. The hydroxyl groups of hyperbranched polyethylene are then converted into thiocarbonyl thio moieties by an esterification reaction with trithiocarbonate 3‐benzylsulfanylthiocarbonyl sulfanylpropionic acid (BSPA). The hyperbranched polyethylene with thiocarbonyl thio moiety ends (HBPE‐BSPAs) is used as a macro‐RAFT agent for the synthesis of hyperbranched polyethylene amphiphiles, HBPE‐PDMAEMAs, by RAFT polymerization of N,N‐dimethylaminoethyl methacrylate (DMAEMA). The resultant HBPE‐PDMAEMAs can self‐assemble to form supramolecular polymer vesicles in aqueous solution. A preliminary investigation on thermo‐ and pH‐responsive behaviors of the polymer is also reported.     

Polymerization of styrene in alcohol/water mediated by a macro‐RAFT agent of poly(N‐isopropylacrylamide) trithiocarbonate: From homogeneous to heterogeneous RAFT polymerization

The reversible addition fragmentation chain transfer (RAFT) polymerization of styrene in alcohol/water mixture mediated with the poly(N‐isopropylacrylamide) trithiocarbonate macro‐RAFT agent (PNIPAM‐TTC) is studied and compared with the general RAFT dispersion polymerization in the presence of a small molecular RAFT agent. Both the homogeneous/quasi‐homogeneous polymerization before particle nucleation and the heterogeneous polymerization after particle nucleation are involved in the PNIPAM‐TTC‐mediated RAFT polymerization, and the two‐stage increase in the molecular weight (M_n) and nanoparticle size of the synthesized block copolymer is found. In the initial homogeneous/quasi‐homogeneous polymerization, the M_n and nanoparticle size slowly increase with monomer conversion, whereas the M_n and particle size quickly increase in the subsequent heterogeneous RAFT polymerization, which is much different from those in the general RAFT dispersion polymerization. Besides, the PNIPAM‐TTC‐mediated RAFT polymerization runs much faster than the general RAFT dispersion polymerization. This study is anticipated to be helpful to understand the polymer chain extension through RAFT polymerization under dispersion conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of low grafting density molecular brush from a poly(N‐alkyl urea peptoid) backbone

The synthesis of a molecular brush was accomplished by combining step‐growth polymerization and reversible addition fragmentation chain transfer (RAFT) polymerization in a “grafting from” methodology. A symmetrical N‐alkyl urea peptoid sixmer containing alkyne functional groups was prepared using a divergent strategy, and the structure of the product was confirmed using NMR spectroscopy and mass spectrometry. A step‐growth process was used to prepare a linear poly(N‐alkyl urea peptoid) by reacting the diamine‐functionalized N‐alkyl urea peptoid sixmer with a diisocyanate. RAFT chain transfer agents were coupled to the poly(N‐alkyl urea peptoid) backbone through a copper‐catalyzed azide/alkyne cycloaddition reaction. The afforded macro‐RAFT agent was used to sequentially polymerize styrene and tert‐butyl acrylate block copolymer arms from the poly(N‐alkyl urea peptoid) backbone. The tert‐butyl groups were removed using dilute trifluoroacetic acid affording hydrophilic polyacrylic acid segments. The molecular brushes were observed to generate micelles in aqueous solution. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of thermoresponsive polymers bearing amino acid diamide derivatives via RAFT polymerization

We report here the synthesis of well‐defined homopolymer bearing amino acid diamide, poly(N‐acryloyl‐L ‐valine N′‐methylamide), via reversible addition fragmentation chain transfer (RAFT) polymerization using alkynyl‐functionalized 2‐dodecylsulfanylthiocarbonylsulfanyl‐2‐methyl‐propionic acid propargyl alcohol ester as chain transfer agent (CTA) and 2,2′‐azobis(isobutyronitrile) as initiator. The effects of a variety of parameters, such as temperature and solvent, on RAFT polymerization were examined to determine the optimal control of the polymerization. The controlled nature of RAFT polymerization was evidenced by the controllable molecular weight and low‐molecular‐weight polydispersity index (M_w/M_n) of resulting homopolymers and further demonstrated to have retained end‐group functionality by the fact of the successful formation of block copolymers from further RAFT polymerization by using the resultant polymer as macro‐CTA, as well as from “click” chemistry. Thermoresponsive property of the prepared polymer was evaluated in terms of the lower critical solution temperature in aqueous solution by measuring the transmittance variation at 500 nm from UV/vis spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3573–3586, 2010     

Synthesis of cationic N‐[3‐(dimethylamino)propyl]methacrylamide brushes on silicon wafer via surface‐initiated RAFT polymerization

Surface‐initiated reversible addition‐fragmentation chain transfer (SI‐RAFT) polymerization of N‐[3‐(dimethylamino)propyl]methacrylamide (DMAPMA) on the silicon wafer was conducted in attempt to create controllable cationic polymer films. The RAFT agent‐immobilized substrate was prepared by the silanization of hydroxyl groups on silicon wafer with 3‐aminopropylthriethoxysilane (APTS) and by the amide reaction of amine groups of APTS with ester groups of 4‐cyano‐4‐((thiobenzoyl) sulfanyl) pentanoic succinimide ester (CPSE); followed by the RAFT polymerization of DMAPMA using a “free” RAFT agent, that is, 4‐cyanopentanoic acid dithiobenzoate (CPAD) and an initiator, that is, 4,4′‐azobis‐4‐cyanopentanoic acid (CPA). The formation of homogeneous tethered poly(N‐[3‐(dimethylamino)propyl]methacrylamide) [poly(DMAPMA)] brushes, whose thickness can be tuned by reaction time varying, is evidenced by using the combination of grazing angle attenuated total reflectance‐Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, and water contact‐angle measurements. The calculation of grafting parameters from the number‐average molecular weight, M _n (g/mol) and ellipsometric thickness, h (nm) values indicated the synthesis of densely grafted poly(DMAPMA) films and allowed us to predict a polymerization time for forming a “brush‐like” conformation for the chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A strategy for synthesis of ion‐bonded amphiphilic miktoarm star copolymers via supramolecular macro‐RAFT agent

Amphiphilic supramolecular miktoarm star copolymers linked by ionic bonds with controlled molecular weight and low polydispersity have been successfully synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization using an ion‐bonded macromolecular RAFT agent (macro‐RAFT agent). Firstly, a new tetrafunctional initiator, dimethyl 4,6‐bis(bromomethyl)‐isophthalate, was synthesized and used as an initiator for atom transfer radical polymerization (ATRP) of styrene to form polystyrene (PSt) containing two ester groups at the middle of polymer chain. Then, the ester groups were converted into tertiary amino groups and the ion‐bonded supramolecular macro‐RAFT agent was obtained through the interaction between the tertiary amino group and 2‐dodecylsulfanylthiocarbonylsulfanyl‐2‐methyl propionic acid (DMP). Finally, ion‐bonded amphiphilic miktoarm star copolymer, (PSt)₂‐poly(N‐isopropyl‐acrylamide)₂, was prepared by RAFT polymerization of N‐isopropylacrylamide (NIPAM) in the presence of the supramolecular macro‐RAFT agent. The polymerization kinetics was investigated and the molecular weight and the architecture of the resulting star polymers were characterized by means of ¹H‐NMR, FTIR, and GPC techniques. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5805–5815, 2008     

Synthesis of diblock copolymers containing poly(N‐vinylcarbazole) by reversible addition‐fragmentation chain transfer polymerization

The reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐vinylcarbazole (NVK) mediated by macromolecular xanthates was used to prepare three types of block copolymers containing poly(N‐vinylcarbazole) (PVK). Using a poly(ethylene glycol) monomethyl ether based xanthate ( PEG‐X ), the RAFT polymerization of NVK proceeded in a controlled way to afford a series of PEG‐b‐PVK with different PVK chain lengths. Successive RAFT polymerization of NVK and vinyl acetate (VAc) with a small molecule xanthate ( X1 ) as the chain transfer agent was tested to prepare PVK‐b‐PVAc. Though both monomers can be homopolymerized in a controlled manner with this xanthate, only by polymerizing NVK first could give well‐defined block copolymers. The xanthate groups in the end of PVK could be removed by radical‐induced reduction using tributylstannane, and PVK‐b‐PVA was obtained by further hydrolysis of PVK‐b‐PVAc under basic conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

New Route to Polymeric Nanoparticles by Click Chemistry Using Bifunctional Cross-Linkers

A new route to functional polymeric nanoparticles (PNPs) of different chemical nature in the 3 to 20 nm size range is reported by combining both radical addition fragmentation chain transfer (RAFT) polymerization and “click” chemistry (CC) techniques. RAFT polymerization was employed for the synthesis of well-defined statistical copolymers with pending –Cl groups along the macromolecular chain. After transformation of the –Cl groups to –N₃ groups by treatment with sodium azide, an appropriate bifunctional cross-linker is employed to obtain PNPs under CC conditions promoting intramolecular cycloaddition (cross-linking). Following this new route, polystyrene, poly(alkyl (meth)acrylate), polymethacrylic acid, poly(sodium styrenesulfonate) and poly(N-isopropyl) NPs have been synthesized and in-deep characterized.     

RAFT‐mediated batch emulsion polymerization of styrene using poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] trithiocarbonate as both surfactant and macro‐RAFT agent

Poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] trithiocarbonate, which contains the reactive trithiocarbonate group and the appending surface‐active groups, is used as both surfactant and macromolecular reversible addition‐fragmentation chain transfer (macro‐RAFT) agent in batch emulsion polymerization of styrene. Under the conditions at high monomer content of ～20 wt % and with the molecular weight of the macro‐RAFT agent ranging from 4.0 to 15.0 kg/mol, well‐controlled batch emulsion RAFT polymerization initiated by the hydrophilic 2‐2′‐azobis(2‐methylpropionamidine) dihydrochloride is achieved. The polymerization leads to formation of nano‐sized colloids of the poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride]‐b‐ polystyrene‐b‐poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] triblock copolymer. The colloids generally have core‐shell structure, in which the hydrophilic block forms the shell and the hydrophobic block forms the core. The molecular weight of the triblock copolymer linearly increases with increase in the monomer conversion, and the values are well‐consistent with the theoretical ones. The molecular weight polydispersity index of the triblock copolymer is below 1.2 at most cases of polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Heterofunctional RAFT‐derived PNIPAM via cascade trithiocarbonate removal and thiol‐yne coupling click reaction

An efficient one‐pot process to functionalize the α‐ and ω‐positions of RAFT‐derived poly(N‐isopropylacrylamide) (PNIPAM) by two inherently different mechanistic pathways is reported. The method relies on the RAFT polymerization of NIPAM using a new alkyne‐based RAFT agent, namely 2‐cyano‐5‐oxo‐5‐(prop‐2‐yn‐1‐ylamino)pentan‐2‐yl dodecyltrithiocarbonate (COPYDC) and the combination of thiol‐yne click chemistry and thiocarbonylthio chain‐end removal reactions. COPYDC was prepared in good yield and used as an efficient chain transfer agent during the RAFT polymerization of NIPAM. Well‐defined polymers with controlled molar masses ( = 7500–14,700 g.mol^?1) and narrow dispersities (? = 1.18–1.26) are thus obtained. Cascade thiol‐yne click reaction at the alkyne α‐chain end and trithiocarbonate removal at the ω‐chain end are successfully achieved using benzyl mercaptan and excess AIBN. The reported method provides a facile and mild route to heterofunctional telechelic RAFT polymers with predictable molar masses and low dispersities. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3597–3606     

One‐step synthesis of poly(N‐vinylpyrrolidone)‐b‐poly(l‐lactide) block copolymers using a dual initiator for RAFT polymerization and ROP

Amphiphilic, biocompatible poly(N‐vinylpyrrolidone)‐b‐poly(l ‐lactide) (PVP‐b‐PLLA) block polymers were synthesized at 60 °C using a hydroxyl‐functionalized N,N‐diphenyldithiocarbamate reversible addition–fragmentation chain transfer (RAFT) agent, 2‐hydroxyethyl 2‐(N,N‐diphenylcarbamothioylthio)propanoate (HDPCP), as a dual initiator for RAFT polymerization and ring‐opening polymerization (ROP) in a one‐step procedure. 4‐Dimethylamino pyridine was used as the ROP catalyst for l ‐lactide. The two polymerization reactions proceeded in a controlled manner, but their polymerization rates were affected by the other polymerization process. This one‐step procedure is believed to be the most convenient method for synthesizing PVP‐b‐PLLA block copolymers. HDPCP can also be used for the one‐step synthesis of poly(N‐vinylcarbazole)‐b‐PLLA block copolymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1607–1613     

Encapsulated clay particles in polystyrene by RAFT mediated miniemulsion polymerization

RAFT grafted montmorillonite (MMT) clays [i.e., N,N‐dimethyl‐N‐(4‐(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium‐MMT (PCDBAB‐MMT) and N‐(4‐((((dodecylthio)carbonothioyl)thio)methyl)benzyl)‐N,N‐dimethylethanammo‐nium‐MMT (DCTBAB‐MMT)] of various loadings were dispersed in styrene (S) monomer and the resultant mixtures emulsified and sonicated in the presence of a hydrophobe (hexadecane) into miniemulsions. The stable miniemulsions thus obtained were polymerized to yield encapsulated polystyrene‐clay nanocomposites (PS‐CNs). The molar mass and polydispersity index (PDI) of the PS‐CNs depended on the amount of RAFT agent in the system, in accordance with the features of the RAFT process. The morphology of the PS‐CNs ranged from partially exfoliated to an intercalated morphology, depending on the percentage clay loading. The thermomechanical properties of the PS‐CNs were better than those of the neat PS polymer, and were dependent on the molar mass, PS‐CN morphology and clay loading. The similarities and differences of the PS‐CNs prepared here by miniemulsion polymerization were compared to those prepared using the same RAFT agents and polymer system by bulk polymerization (as reported by us in a previous article). © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7114–7126, 2008     

Living free‐radical polymerization of sterically hindered monomers: Improving the understanding of 1,1‐disubstituted monomer systems

The sterically hindered, 1,1‐disubstituted monomers di‐n‐butyl itaconate (DBI), dicyclohexyl itaconate (DCHI), and dimethyl itaconate (DMI) were polymerized with reversible addition–fragmentation chain transfer (RAFT) free‐radical polymerization and atom transfer radical polymerization (ATRP). Cumyl dithiobenzoate, cumyl phenyl dithioacetate, 2‐cyanoprop‐2‐yl dithiobenzoate, 4‐cyanopentanoic acid dithiobenzoate, and S‐methoxycarbonylphenylmethyl dithiobenzoate were employed as RAFT agents to mediate a series of polymerizations at 60 °C yielding polymers ranging in their number‐average molecular weight from 4500 to 60,000 g mol^?1. The RAFT polymerizations of these hindered monomers displayed hybrid living behavior (between conventional and living free‐radical polymerization) of various degrees depending on the molecular structure of the initial RAFT agent. In addition, DCHI was polymerized via ATRP with a CuCl/methyl benzoate/N,N,N′,N″,N″‐pentamethyldiethylenetriamine/cyclohexanone system at 60 °C. Both the ATRP and RAFT polymerization of the hindered monomers displayed living characteristics; however, broader than expected molecular weight distributions were observed for the RAFT systems (polydispersity index = 1.15–3.35). To assess the cause of this broadness, chain‐transfer‐to‐monomer constants for DMI, DBI, and DCHI were determined (1.4 × 10^?3, 1.3 × 10^?3, and 1.0 × 10^?3, respectively) at 60 °C. Simulations carried out with the PREDICI program package suggested that chain transfer to monomer contributed to the broadening process. In addition, the experimental results indicated that viscosity had a pronounced effect on the broadness of the molecular weight distributions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3692–3710, 2006     

Solution and aqueous miniemulsion polymerization of vinyl chloride mediated by a fluorinated xanthate

Solution and aqueous miniemulsion polymerizations of vinyl chloride (VC) mediated by (3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctyl‐2‐((ethoxycarbonothioyl)thio) propanoate) (X1) were studied. The living characters of X1‐mediated solution and miniemulsion polymerizations of VC were confirmed by polymerization kinetics. The miniemulsion polymerization exhibits higher rate than solution polymerization. Final conversions of VC in the reversible addition‐fragmentation chain transfer (RAFT) miniemulsion polymerization reach as high as 87% and are independent of X1 concentration. Initiation process of X1‐mediated RAFT miniemulsion polymerization is controlled by the diffusion–adsorption process of prime radicals. Due to the heterogeneity of polymerization environments and concentration fluctuation of RAFT agent in droplets or latex particles, PVCs prepared in RAFT miniemulsion exhibit relatively broad molecular weight distribution. Furthermore, chain extensions of living PVC (PVC‐X) with VC, vinyl acetate (VAc), and N‐vinylpyrrolidone (NVP) reveal that PVC‐X can be reinitiated and extended, further confirming the living nature of VC RAFT polymerization. PVC‐b‐PVAc diblock copolymer is successfully synthesized by the chain extension of PVC‐X in RAFT miniemulsion polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2092–2101