Synthesis and characters of hyperbranched poly(vinyl acetate) by RAFT polymeraztion

Reversible addition-fragmentation chain transfer (RAFT) polymerization of VAc in the presence of ECTVA, which capable of both reversible chain transferable through a xanthate moiety and propagation via a vinyl group, led to highly branched copolymers by a method analogous to self-condensing vinyl polymerization (SCVP). The ECTVA acted as a vinyl acetate AB^∗ inimer. It was copolymerized with vinyl acetate (VAc) in ratios selected to tune the distribution and length of branches of resulting hyperbranched poly(vinyl acetate). The degree of branching increased with chain ECTVA concentration, as confirmed by NMR spectroscopy. The polymer structure was characterized via MALDI–TOF. Retention of the xanthate compound during the polymerization was evidenced by successful chain extension of a branched (PVAc) macroCTA by RAFT polymerization. The branched PVAc led to better dissolution as compared to linear PVAc, an effect attributed primarily to an increased contribution of end groups.     

Synthesis of poly(tert‐butyl acrylate‐block‐vinyl acetate) copolymers by combining ATRP and RAFT polymerizations

The synthesis of poly(tert‐butyl acrylate‐block‐vinyl acetate) copolymers using a combination of two living radical polymerization techniques, atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation chain transfer (RAFT) polymerization, is reported. The use of two methods is due to the disparity in reactivity of the two monomers, viz. vinyl acetate is difficult to polymerize via ATRP, and a suitable RAFT agent that can control the polymerization of vinyl acetate is typically unable to control the polymerization of tert‐butyl acrylate. Thus, ATRP was performed to make poly(tert‐butyl acrylate) containing a bromine end group. This end group was subsequently substituted with a xanthate moiety. Various spectroscopic methods were used to confirm the substitution. The poly(tert‐butyl acrylate) macro‐RAFT agent was then used to produce (tert‐butyl acrylate‐block‐vinyl acetate). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7200–7206, 2008     

Synthesis of IONP's decorated graft copolymers and study of their magnetic force–induced wastewater treatment

Our work is focused on facile synthesis and modification of amylopectin‐grafted block copolymers by using reversible addition?fragmentation chain transfer (RAFT) polymerization technique. This technique yields polymers with controlled molecular weight and low polydispersity indexes and is feasible with a wide range of monomers. Five different grades of amylopectin‐grafted polymethacrylic acid and polyacrylamide block copolymers have been synthesized via RAFT, by varying the amount of acrylamide employing amylopectin‐based macro chain transfer agent. Graft copolymers have been upgraded as smart responsive graft copolymers, through the incorporation of iron oxide nanoparticles (IONPs) via condensation reaction. The polymeric materials have been extensively characterized by energy‐dispersive X‐ray analysis, Fourier transform infrared spectroscopy, proton magnetic resonance spectroscopy, scanning electron microscopy, ultraviolet‐visible spectroscopy, gel permeation chromatography, transmission electron microscopy, thermogravimetric analysis, and X‐ray diffraction analysis. Normal and responsive graft copolymers have been studied for removal of model contaminant (kaolin), and responsive graft copolymers have been used to remove methylene blue dye (without using any adsorbent) from water by applying external magnetic field. The upgraded block copolymers have shown best performance in wastewater treatment.     

Synthesis and characterization of graft copolymers based on polyepichlorohydrin via reversible addition-fragmentation chain transfer polymerization

In this study, synthesis of poly(epichlorohydrin-g-methyl methacrylate) graft copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization was reported. For this purpose, epichlorohydrin was polymerized by using HNO₃ via cationic ring-opening mechanism. A RAFT macroinitiator (macro-RAFT agent) was obtained by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin. The graft copolymers were synthesized using macro-RAFT agent as initiator and methyl methacrylate as monomer. The synthesis of graft copolymers was conducted by changing the time of polymerization and the amount of monomer-initiator concentration that affect the RAFT polymerization. The effects of these parameters on polymerization were evaluated via various analyses. The characterization of the products was determined using ¹H-nuclear magnetic resonance (¹H-NMR), Fourier-transform infrared spectroscopy, gel-permeation chromatography, thermogravimetric analysis, elemental analysis, and fractional precipitation techniques. The block lengths of the graft copolymers were calculated by using ¹H-NMR spectrum. It was observed that the block length could be altered by varying the monomer and initiator concentrations.     

Photoinitiated RAFT polymerization of vinyl acetate

A photoinitiation process was investigated to develop a rapid and well‐controlled RAFT polymerization method applied to vinyl acetate (VAc) using methyl (ethoxycarbonothioyl)sulfanyl acetate (MESA) and bis(2,4,6‐trimethylbenzoyl)phenylphosphine oxide as the RAFT agent and photoinitiator, respectively. MESA was selected as the photochemically inert RAFT agent to minimize photolysis of the thiocarbonylthio groups during polymerization. Poly(vinyl acetate) with a prespecified well‐controlled molecular weight (MW) and a narrow MW distribution was successfully synthesized. The polymerization reaction proceeded as a living polymerization and was remarkably rapid compared with approaches that use thermally initiated processes with a very short induction period. A detailed kinetic study of the mechanism underlying the polymerization reaction, however, revealed that the chain ends containing xanthate moieties were not perfectly stable upon UV‐irradiation, and they generated radicals via homolytic cleavage. This reaction appeared to proceed by a combination of a degenerative transfer RAFT mechanism and a dissociation‐combination mechanism. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Systematic parallel investigation of RAFT polymerizations for eight different (meth)acrylates: A basis for the designed synthesis of block and random copolymers

Poly(acrylate)s as well as poly(methacrylate)s were successfully synthesized via reversible addition‐fragmentation chain‐transfer (RAFT) polymerizations using 2‐cyano‐2‐butyl dithiobenzoate (CBDB) as RAFT‐agent. Four different ratios of RAFT to initiator were screened for four acrylates and four methacrylates using automated parallel synthesizer robots. The reactions were monitored by gel permeation chromatography (GPC) and gas chromatography (GC). The knowledge obtained during this screening was used for the designed synthesis of block and random copolymers containing a water‐ and a non water‐soluble monomer. The results obtained from GPC analysis together with ¹H NMR spectroscopy demonstrate the possibility to design and prepare well‐defined block and random copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3831–3839, 2005     

Synthesis of amphiphilic block copolymers via ring opening polymerization and reversible addition-fragmentation chain transfer polymerization

Amphiphilic block copolymers were synthesized via a dual initiator chain transfer agent (inifer) that successfully initiated the ring opening polymerization (ROP) of l -lactide (LLA) and subsequently mediated the reversible addition-fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA). The formation of each polymer block was confirmed using ¹H nuclear magnetic resonance spectroscopy, as well as gel permeation chromatography, and comprehensive kinetics studies provide valuable insights into the factors influencing the synthesis of well-defined block copolymers. The effect of monomer concentration, reaction time, and molar ratios of inifer to catalyst on the ROP of LLA are discussed, as well as the ability to produce poly(lactide) blocks of different molecular weights. The synthesis of hydrophilic PPEGEEMA blocks was also monitored via kinetics to provide a better understanding of the role the chain transfer agent plays in facilitating the complex and sterically demanding RAFT polymerization of PEGEEMA.     

Synthesis and characterization of surface‐initiated polymer brushes on silicon substrates by reversible addition fragmentation chain transfer polymerization

Polymer brushes were prepared by using the reversible addition fragmentation chain transfer (RAFT) technique. The silicon substrates (Si (111) surface) were modified with ethyl xanthate groups which were introduced by the treatment of Si (111) surface with sodium ethyl xanthate. The polymer brushes were then prepared under RAFT conditions from the Si (111) wafer. Its “living” characteristics were determined by a series of characterizations including gel permeation chromatography (GPC), ellipsometry, and contact angle measurements. The results showed a well‐defined graft layer consisting of polymer brushes with low‐polydispersity could be prepared directly on Si (111)‐X surface (where X represents an ethyl xanthate groups). The structure of the polymer brushes was characterized and confirmed with the surface sensitive techniques such as X‐ray photoelectron spectroscopy (XPS) and scanning probe microscopy (SPM). Copyright © 2007 John Wiley & Sons, Ltd.     

One‐step synthesis of block‐graft copolymers via simultaneous reversible‐addition fragmentation chain transfer and ring‐opening polymerization using a novel macroinitiator

One‐step synthesis of block‐graft copolymers by reversible addition‐fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) by using a novel initiator was reported. Block‐graft copolymers were synthesized in one‐step by simultaneous RAFT polymerization of n‐butylmethacrylate (nBMA) and ROP of ε‐caprolacton (CL) in the presence of a novel macroinitiator (RAFT‐ROP agent). For this purpose, first epichlorohydrin (EPCH) was polymerized by using H₂SO₄ via cationic ring‐opening mechanism. And then a novel RAFT‐ROP agent was synthesized by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin (poly‐EPCH). By using the RAFT‐ROP agent, poly[CL‐b‐EPCH‐b‐CL‐(g‐nBMA)] block‐graft copolymers were synthesized. The principal parameters such as monomer concentration, initiator concentration, and polymerization time that affect the one‐step polymerization reaction were evaluated. The block lengths of the block‐graft copolymers were calculated by using ¹H‐nuclear magnetic resonance (¹H NMR) spectrum. The block length could be adjusted by varying the monomer and initiator concentrations. The characterization of the products was achieved using ¹H NMR, Fourier‐transform infrared spectroscopy, gel‐permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, elemental analysis, and fractional precipitation (γ) techniques. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2651–2659     

Synthesis and characterization of silica–polyvinyl imidazole core–shell nanoparticles via combination of RAFT polymerization and grafting‐to method

The silica–polyvinyl imidazole core–shell nanoparticles (silica/PVI NPs) with controlled shell thickness and narrow distribution size were fabricated via “grafting‐to” method. First, O‐ethyl xanthate terminated PVI with various chain lengths was produced via the reversible addition–fragmentation chain transfer (RAFT) polymerization using O‐ethyl‐S‐phenyl dithiocarbonate (EPDC) as RAFT agent. Next, three synthesized PVI of different molecular weights (3.4, 6.6, and 11 kg/mol) were successfully grafted to the methacrylate modified silica NPs from solution by radical mediated grafting‐to method. These core–shell NPs were then characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectrum measurements (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Polyvinyl imidazole molecular weight, reaction time, polymer concentration, and reaction temperature were all used to control the grafting reaction for PVI grafting densities and shell thicknesses. The highest grafting density obtained was close to 1.2 chains/nm² and was achieved for 3.4 kg/mol PVI at 80°C. The prepared silica/PVINP displayed efficient antifouling properties and stability in concentrated sodium chloride aqueous solutions over a broad pH range for a period of at least 7 days. Copyright © 2017 John Wiley & Sons, Ltd.     

Organic–inorganic poly(N‐vinylpyrrolidone) copolymers with double‐decker silsesquioxane in the main chains: Synthesis,glass transition,and self‐assembly behavior

An organic–inorganic copolymer with polyhedral oligomeric silsesquioxane (POSS) and xanthate moieties in the main chain was synthesized via the polycondensation between 3,13‐di(2‐bromopropionate)propyl double‐decker silsesquioxane (DDSQ) and 1,4‐di(xanthate potassium)butane. This hybrid copolymer was used as the macromolecular chain transfer agent to obtain the organic–inorganic poly(N‐vinylpyrrolidone) (PVPy) copolymers via a reversible addition fragmentation chain transfer/macromolecular design via the interchange of xanthates (RAFT/MADIX) polymerization approach; the polymerization behavior of N‐vinyl pyrrolidone was investigated by means of gel permeation chromatography. It was found that the polymerization was in a living and controlled manner. Transmission electron microscopy (TEM) showed that the organic–inorganic PVPy copolymers with DDSQ in the main chains were microphase‐separated in bulks. Compared to plain PVPy, the organic–inorganic PVPy copolymers displayed the decreased glass transition temperatures (T_gs); the decreased T_gs are attributable to the effect of the introduced DDSQ cages on the packing of PVPy chains as evidenced by means of Fourier transform infrared spectroscopy (FTIR). In water, the organic–inorganic PVPy copolymers can self‐assemble into the spherical nano‐objects with the size of 20–50 nm in diameter. In the self‐assembled nano‐objects, the aggregates of the hydrophobic DDSQ constituted the cores of the polymeric micelles whereas the PVPy chains between the DDSQ behaved as the coronas of the polymeric micelles. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2949–2961     

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     

Latices of poly(fluoroalkyl mathacrylate)‐b‐poly(butyl methacrylate) copolymers prepared via reversible addition–fragmentation chain transfer polymerization

Poly(fluoroalkyl mathacrylate)‐block‐poly(butyl methacrylate) diblock copolymer latices were synthesized by a two‐step process. In the first step, a homopolymer end‐capped with a dithiobenzoyl group [poly(fluoroalkyl mathacrylate) (PFAMA) or poly(butyl methacrylate) (PBMA)] was prepared in bulk via reversible addition–fragmentation chain transfer (RAFT) polymerization with 2‐cyanoprop‐2‐yl dithiobenzoate as a RAFT agent. In the second step, the homopolymer chain‐transfer agent (macro‐CTA) was dissolved in the second monomer, mixed with a water phase containing a surfactant, and then ultrasonicated to form a miniemulsion. Subsequently, the RAFT‐mediated miniemulsion polymerization of the second monomer (butyl methacrylate or fluoroalkyl mathacrylate) was carried out in the presence of the first block macro‐CTA. The influence of the polymerization sequence of the two kinds of monomers on the colloidal stability and molecular weight distribution was investigated. Gel permeation chromatography analyses and particle size results indicated that using the PFAMA macro‐CTA as the first block was better than using the PBMA RAFT agent with respect to the colloidal stability and the narrow molecular weight distribution of the F‐copolymer latices. The F‐copolymers were characterized with ¹H NMR, ¹⁹F NMR, and Fourier transform infrared spectroscopy. Comparing the contact angle of a water droplet on a thin film formed by the fluorinated copolymer with that of PBMA, we found that for the diblock copolymers containing a fluorinated block, the surface energy decreased greatly, and the hydrophobicity increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 471–484, 2007     

Reversible addition‐fragmentation chain transfer polymerization of vinyl acetate under high pressure

In this work, high molecular weight polyvinyl acetate (PVAc) (M_n,GPC = 123,000 g/mol, M_w/M_n = 1.28) was synthesized by reversible addition‐fragmentation chain transfer polymerization (RAFT) under high pressure (5 kbar), using benzoyl peroxide and N,N‐dimethylaniline as initiator mediated by (S)‐2‐(ethyl propionate)‐(O‐ethyl xanthate) (X1) at 35 °C. Polymerization kinetic study with RAFT agent showed pseudo‐first order kinetics. Additionally, the polymerization rate of VAc under high pressure increased greatly than that under atmospheric pressure. The “living” feature of the resultant PVAc was confirmed by ¹H NMR spectroscopy and chain extension experiments. Well‐defined PVAc with high molecular weight and narrow molecular weight distribution can be obtained relatively fast by using RAFT polymerization at 5 kbar. © 2015 Wiley Periodicals, Inc. J. Polym. Sci. Part A: Polym. Chem. 2015 , 53, 1430–1436     

Polymethylene‐block‐polystyrene copolymers: A new synthetic approach using a combination of polyhomologation and reversible addition‐fragmentation chain‐transfer polymerization and their microfibers and microspheres fabricated through electrospinning process

Well‐defined polymethylene‐block‐polystyrene (PM‐b‐PS) diblock copolymers were synthesized via a combination of polyhomologation of ylides and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization of styrene. Trithiocarbonate‐terminated polymethylenes (PM‐TTCB) (M_n = 1400 g mol^?1; M_w/M_n = 1.09 and M_n = 2100 g mol^?1; M_w/M_n = 1.20) were obtained via an esterification of S?1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐acetate) trithiocarbonate with hydroxyl‐terminated polymethylene synthesized via polyhomologation of ylides followed by oxidation. Then, a series of PM‐b‐PS (M_n = 5500–34,000 g mol^?1; M_w/M_n = 1.12–1.25) diblock copolymers were obtained by RAFT polymerization of styrene using PM‐TTCB as a macromolecular chain‐transfer agent. The chain structures of all the polymers were characterized by proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography, and Fourier transform infrared spectroscopy. The thiocarbonylthio end‐group of PM‐b‐PS was transformed into thiol group by aminolysis and confirmed by UV–vis spectroscopy. In addition, microfibers and microspheres of such diblock copolymers were fabricated by electrospinning process and observed by scanning electron microscopy (SEM). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2892–2899     

Well‐defined amphiphilic graft copolymer consisting of hydrophilic poly(acrylic acid) backbone and hydrophobic poly(vinyl acetate) side chains

A series of well‐defined amphiphilic graft copolymers containing hydrophilic poly(acrylic acid) (PAA) backbone and hydrophobic poly(vinyl acetate) (PVAc) side chains were synthesized via sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization followed by selective hydrolysis of poly(tert‐butyl acrylate) backbone. A new Br‐containing acrylate monomer, tert‐butyl 2‐((2‐bromopropanoyloxy)methyl) acrylate, was first prepared, which can be polymerized via RAFT in a controlled way to obtain a well‐defined homopolymer with narrow molecular weight distribution (M_w/M_n = 1.08). This homopolymer was transformed into xanthate‐functionalized macromolecular chain transfer agent by reacting with o‐ethyl xanthic acid potassium salt. Grafting‐from strategy was employed to synthesize PtBA‐g‐PVAc well‐defined graft copolymers with narrow molecular weight distributions (M_w/M_n < 1.40) via RAFT of vinyl acetate using macromolecular chain transfer agent. The final PAA‐g‐PVAc amphiphilic graft copolymers were obtained by selective acidic hydrolysis of PtBA backbone in acidic environment without affecting the side chains. The critical micelle concentrations in aqueous media were determined by fluorescence probe technique. The micelle morphologies were found to be spheres. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6032–6043, 2009     

Poly(N‐vinyl pyrrolidone)‐block‐Poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) triblock copolymers: Synthesis via RAFT/MADIX process,self‐assembly behavior,and photophysical properties

Poly(N‐vinyl pyrrolidone)‐block‐poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) (PVP‐b‐PVK‐b‐PVP) triblock copolymers were synthesized via sequential reversible addition‐fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process. First, 1,4‐phenylenebis(methylene)bis(ethyl xanthate) was used as a chain transfer agent to mediate the radical polymerization of N‐vinyl carbazole (NVK). It was found that the polymerization was in a controlled and living manner. Second, one of α,ω‐dixanthate‐terminated PVKs was used as the macromolecular chain transfer agent to mediate the radical polymerization of N‐vinyl pyrrolidone (NVP) to obtain the triblock copolymers with various lengths of PVP blocks. Transmission electron microscopy (TEM) showed that the triblock copolymers in bulks were microphase‐separated and that PVK blocks were self‐organized into cylindrical microdomains, depending on the lengths of PVP blocks. In aqueous solutions, all these triblock copolymers can self‐assemble into the spherical micelles. The critical micelle concentrations of the triblock copolymers were determined without external adding fluorescence probe. By analyzing the change in fluorescence intensity as functions of the concentration, it was judged that the onset of micellization occurred at the concentration while the FL intensity began negatively to deviate from the initial linear increase with the concentration. Fluorescence spectroscopy indicates that the self‐assembled nanoobjects of the PVP‐b‐PVK‐b‐PVP triblock copolymers in water were capable of emitting blue/or purple fluorescence under the irradiation of ultraviolet light. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1852–1863     

Synthesis and characterization of well‐defined block and statistical copolymers based on lauryl methacrylate and 2‐(acetoacetoxy)ethyl methacrylate using RAFT‐controlled radical polymerization

Four well‐defined diblock copolymers and one statistical copolymer based on lauryl methacrylate (LauMA) and 2‐(acetoacetoxy)ethyl methacrylate (AEMA) were prepared using reversible addition‐fragmentation chain transfer (RAFT) polymerization. The polymers were characterized in terms of molecular weights, polydispersity indices (ranging between 1.12 and 1.23) and compositions by size exclusion chromatography and ¹H NMR spectroscopy, respectively. The preparation of the block copolymers was accomplished following a two‐step methodology: First, well‐defined LauMA homopolymers were prepared by RAFT using cumyl dithiobenzoate as the chain transfer agent (CTA). Kinetic studies revealed that the polymerization of LauMA followed first‐order kinetics demonstrating the “livingness” of the RAFT process. The pLauMAs were subsequently used as macro‐CTA for the polymerization of AEMA. The glass transition (T_g) and decomposition temperatures (ranging between 200 and 300 °C) of the copolymers were determined using differential scanning calorimetry and thermal gravimetric analysis, respectively. The T_gs of the LauMA homopolymers were found to be around ?53 °C. Block copolymers exhibited two T_gs suggesting microphase separation in the bulk whereas the statistical copolymer presented a single T_g as expected. Furthermore, the micellization behavior of pLauMA‐b‐pAEMA block copolymers was investigated in n‐hexane, a selective solvent for the LauMA block, using dynamic light scattering. pLauMA‐b‐pAEMA block copolymers formed spherical micelles in dilute hexane solutions with hydrodynamic diameters ranging between 30 and 50 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5442–5451, 2008     

Statistical copolymers of N-vinylpyrrolidone and benzyl methacrylate via RAFT: Monomer reactivity ratios,thermal properties and kinetics of thermal decomposition

Statistical copolymers of N-vinylpyrrolidone (NVP) with benzyl methacrylate (BzMA) were prepared by Reversible Addition-Fragmentation chain Transfer Polymerization (RAFT), employing three different xanthates as RAFT agents: [(O-ethylxanthyl)methyl]benzene, [1-(O-ethylxanthyl)ethyl]benzene and O-ethyl S-(phthalimidylmethyl) xanthate. The reactivity ratios were estimated using the Fineman-Ross, inverted Fineman-Ross, Kelen-Tüdos and extended Kelen-Tüdos linear graphical methods, as well as the computer program COPOINT. Structural parameters of the copolymers were obtained by calculating the dyad sequence fractions and the mean sequence length. All the methods are in agreement that the probability for the incorporation of BzMA units is much greater than for that of NVP units. The glass-transition temperature (Tg) values of the copolymers were measured by Differential Scanning Calorimetry and examined by means of several theoretical equations, allowing for the prediction of these Tg values. Subsequently, a systematic and detailed investigation of the thermal degradation of these copolymers compared with that of the respective homopolymers, was carried out by Thermogravimetric Analysis, within the framework of the Ozawa-Flynn-Wall and Kissinger methodologies. As expected, the thermal stability of the copolymers is influenced by the structure of the substituents of the thiocarbonylthio end groups due to the RAFT agents.     

An efficient avenue to poly(styrene)‐block‐poly(ε‐caprolactone) polymers via switching from RAFT to hydroxyl functionality: Synthesis and characterization

The recently introduced procedure of quantitatively switching thiocarbonyl thio capped (RAFT) polymers into hydroxyl terminated species was employed to generate narrow polydispersity (PDI ≈ 1.2) sulfur‐free poly(styrene)‐block‐poly(ε‐caprolactone) polymers (26,000 ≤ M_n/g·mol^?1 < 45,000). The ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) was conducted under organocatalysis employing 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD). The obtained block copolymers were thoroughly analyzed via size exclusion chromatography (SEC), NMR, as well as liquid adsorption chromatography under critical conditions coupled to SEC (LACCC‐SEC) to evidence the block copolymer structure and the efficiency of the synthetic process. The current contribution demonstrates that the RAFT process can serve as a methodology for the generation of sulfur‐free block copolymers via an efficient end group switch. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010