Showing papers in "Journal of Polymer Science Part A in 2009"
TL;DR: Gandini et al. as discussed by the authors proposed a poly(ethylene 2,5-furandicarboxylate) crystallization method for renewable polymers from renewable resources.
Abstract: ALESSANDRO GANDINI, ARMANDO J. D. SILVESTRE, CARLOS PASCOAL NETO,ANDREIA F. SOUSA, MO´ NICA GOMESDepartment of Chemistry, CICECO, University of Aveiro, Aveiro 3810-193, PortugalReceived 30 September 2008; accepted 7 October 2008DOI: 10.1002/pola.23130Published online in Wiley InterScience (www.interscience.wiley.com).Keywords: crystallization; poly(ethylene 2,5-furandicarboxylate); polytransesterifi-cation; renewable resources; structureINTRODUCTIONThe burgeoning surge of research on polymers fromrenewable resources
445 citations
TL;DR: In this article, the authors have discussed about the recent development of benzoxazine chemistry and discussed several strategies to improve the mechanical properties and processibility of polybenzoxazine based composites or alloys.
Abstract: Polybenzoxazine is a newly developed addition polymerized phenolic system, having a wide range of interesting features and the capability to overcome several shortcomings of conventional novolac and resole type phenolic resins. They exhibit (i) near zero volumetric change upon curing, (ii) low water absorption, (iii) for some polybenzoxazines Tg much higher than cure temperature, (iv) high char yield, (v) no strong acid catalysts required for curing, (vi) release of no byproduct during curing and also possess thermal and flame retarding properties of phenolics along with the mechanical performance. Though benzoxazine based materials possess several advantages, they have not yet became very attractive to the industries. To improve the mechanical properties and processibility several strategies have been reported including (i) synthesis of benzoxazine monomers with additional functionality, (ii) incorporation of benzoxazine in polymer chain, and (iii) benzoxazine based composites or alloys. In this article, we have discussed about the recent development of benzoxazine chemistry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5565–5576, 2009
436 citations
TL;DR: Hydrogels were the first biomaterials designed for clinical use and their discovery and applications as soft contact lenses and implants are presented and pathways to self-assembly of block and graft copolymers into hydrogels of precise 3D structures are introduced.
Abstract: Hydrogels were the first biomaterials designed for clinical use. Their discovery and applications as soft contact lenses and implants are presented. This early hydrogel research served as a foundation for the expansion of biomedical polymers research into new directions: design of stimuli sensitive hydrogels that abruptly change their properties upon application of an external stimulus (pH, temperature, solvent, electrical field, biorecognition) and hydrogels as carriers for the delivery of drugs, peptides, and proteins. Finally, pathways to self-assembly of block and graft copolymers into hydrogels of precise 3D structures are introduced.
345 citations
TL;DR: In this paper, an investigation into the aminolysis of omega-end groups of RAFT-polymers and simultaneous thiol-ene reactions with ene-bearing compounds is described.
Abstract: An investigation into the aminolysis of omega-end groups of RAFT-polymers and simultaneous thiol-ene reactions with ene-bearing compounds is described. Three different polymers, P(MMA), P(HPMA), and P(NIPAAm), with low PDIs were synthesized using dithiobenzoate and trithiocarbonate RAFT agents. P(NIPAAm) synthesized with trithiocarbonate RAFT agent and P(HPMA) synthesized with dithiobenzoate RAFT agent were both functionalized with a methacrylate-modified mannose and a maleimide-modified biotin via one-pot simultaneous aminolysis and thiol-ene reactions with product yields above 85%. The presence of ene-compounds during aminolysis was shown to prevent the formation of disulfide interchain crosslinking. Using the same approach, P(MMA), P(HPMA), and P(NIPAAm) were converted to (meth)acrylate macromonomers with high yields (>80%). In the case of P(MMA), the simultaneous aminolysis and thiol-ene addition prevented any intrachain side reactions, i.e., thiolactone formation. New architectures such as graft and block copolymers were successfully generated from the macromonomers.(C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3773-3794, 2009
230 citations
TL;DR: The addition of a third step, the single-electron transfer living radical polymerization (SET-LRP) of methyl acrylate (MA), was shown to provides access to a three-step “branch” and “grow” divergent approach to dendritic macromolecules wherein poly(methyl acRYlate) (PMA) connects the branching subunits.
Abstract: The development of a novel nucleophilic thio-bromo “Click” reaction, specifically base-mediated thioetherification of thioglycerol with α-bromoesters was reported in an earlier article. The combination of this thio-bromo click reaction with subsequent acylation with 2-bromopropionyl bromide provides an iterative two-step divergent growth approach to the synthesis of a new class of poly(thioglycerol-2- propionate) (PTP) dendrimers. In this article, the addition of a third step, the single-electron transfer living radical polymerization (SET-LRP) of methyl acrylate (MA), was shown to provides access to a three-step “branch” and “grow” divergent approach to dendritic macromolecules wherein poly(methyl acrylate) (PMA) connects the branching subunits. This facile methodology can provide a diversity of dendritic macromolecular topologies and will ultimately provide the means to the development of self-organizable dendritic macromolecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3940–3948, 2009
217 citations
TL;DR: In this paper, a precursor of polyNIPAm (PNIPAm) was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization in DMF at 70 °C using the 1-cyano-1-methylethyl dithiobenzoate/2,2′-azobis(2-methylpropionitrile) chain transfer agent/initiator combination yielding a homopolymer with an absolute molecular weight of 5880 and polydispersity index of 1.18.
Abstract: Sequential thiol-ene/thiol-ene and thiol-ene/thiol-yne reactions have been used as a facile and quantitative method for modifying end-groups on an N-isopropylacrylamide (NIPAm) homopolymer. A well-defined precursor of polyNIPAm (PNIPAm) was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization in DMF at 70 °C using the 1-cyano-1-methylethyl dithiobenzoate/2,2′-azobis(2-methylpropionitrile) chain transfer agent/initiator combination yielding a homopolymer with an absolute molecular weight of 5880 and polydispersity index of 1.18. The dithiobenzoate end-groups were modified in a one-pot process via primary amine cleavage followed by phosphine-mediated nucleophilic thiol-ene click reactions with either allyl methacrylate or propargyl acrylate yielding ene and yne terminal PNIPAm homopolymers quantitatively. The ene and yne groups were then modified, quantitatively as determined by 1H NMR spectroscopy, via radical thiol-ene and radical thiol-yne reactions with three representative commercially available thiols yielding the mono and bis end functional NIPAm homopolymers. This is the first time such sequential thiol-ene/thiol-ene and thiol-ene/thiol-yne reactions have been used in polymer synthesis/end-group modification. The lower critical solution temperatures (LCST) were then determined for all PNIPAm homopolymers using a combination of optical measurements and dynamic light scattering. It is shown that the LCST varies depending on the chemical nature of the end-groups with measured values lying in the range 26–35 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3544–3557, 2009
211 citations
TL;DR: In this paper, a nucleophilic thio-bromo click reaction with subsequent acylation with 2bromopropionyl bromide provides an iterative two-step divergent growth approach to the synthesis of a new class of poly(thioglycerol-2-propionate) (PTP) dendrimers.
Abstract: The development of a novel nucleophilic thio-bromo “Click” reaction, specifically base-mediated thioetherification of thioglycerol with α-bromoesters, is reported. Combination of this thio-bromo click reaction with subsequent acylation with 2-bromopropionyl bromide provides an iterative two-step divergent growth approach to the synthesis of a new class of poly(thioglycerol-2-propionate) (PTP) dendrimers. This approach is demonstrated in the rapid preparation of four generation (G1–G4) of PTP dendrimers with high-structural fidelity. The isolated G1–G4 bromide-terminated dendrimers can be used directly as dendritic macroinitiators for the synthesis of star-polymers via SET-LRP. Additionally, the intermediate hydroxy-terminated dendrimers are analogs of other water-soluble polyester and polyether dendrimers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3931–3939, 2009
209 citations
TL;DR: In this article, the disproportionation of colloidal Cu(I)X mediated by Me-6-TREN in various solvents was studied through UV-vis spectroscopy and Dynamic Light Scattering (DLS).
Abstract: Disproportionation of Cu(I)X is the major step in Single-Electron Transfer Living Radical Polymerization (SET-LRP). The disproportionation of Cu(I)X mediated by Me-6-TREN in various solvents was studied through UV-vis spectroscopy and Dynamic Light Scattering (DLS). UV-vis experiments reveal that disproportionation is dependent on both solvent composition and concentration of Me-6-TREN, consistent with a revised equilibrium expression and corroborated by mathematical models. Electrochemistry data do not accurately predict the extent of disproportionation in the presence of Me6-TREN. Exemplified by DMSO, a favored solvent for SET-LRP, LTV-vis spectroscopy shows that under certain conditions disproportionation is four-orders of magnitude greater than the value reported from electrochemistry experiments. Through LTV-vis and DLS analysis, it was demonstrated that DMSO, DMF, DMAC, and NMP, stabilize colloidal Cu(0), while acetone, EtOH, EC, MeOH, PC, and H2O facilitate agglomeration of Cu(0) particles. Additionally, for colloidal Cu(0) stabilizing solvents, the amount of ligand and solvent composition decide the particle size distribution. Therefore, the kinetics of SET-LRP are cooperatively and synergistically determined by the complex interplay of solvent polarity, the extent of disproportionation in the solvent/ligand mixture, and the ability of that mixture to stabilize colloidal Cu(0) or control particle size distribution. The implications of these results for SET-LRP are discussed. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47:5606-5628, 2009
187 citations
TL;DR: In this paper, a simple approach was developed to synthesize pegylated thermoresponsive core-shell nanoparticles in a minimum of steps, directly in water based on RAFT-controlled radical crosslinking copolymerization of N,N-diethylacrylamide (DEAAm) and N, N′-methylene bisacrylide (MBA) in aqueous dispersion polymerization.
Abstract: A very straightforward approach was developed to synthesize pegylated thermoresponsive core-shell nanoparticles in a minimum of steps, directly in water. It is based on RAFT-controlled radical crosslinking copolymerization of N,N-diethylacrylamide (DEAAm) and N,N′-methylene bisacrylamide (MBA) in aqueous dispersion polymerization. Because DEAAm is water-soluble and poly(N,N-diethylacrylamide) (PDEAAm) exhibits a lower critical solution temperature at 32 °C, the initial medium was homogeneous, whereas the polymer formed a separate phase at the reaction temperature. The first macroRAFT agent was a surface-active trithiocarbonate based on a hydrophilic poly(ethylene oxide) block and a hydrophobic dodecyl chain. It was further extented with N,N-dimethylacrylamide (DMAAm) to target macroRAFT agents with increasing chain length. All macroRAFT agents provided excellent control over the aqueous dispersion homopolymerization of DEAAm. When they were used in the radical crosslinking copolymerization of DEAAm and MBA, the stability and size of the resulting gel particles were found to depend strongly on the chain length of the macroRAFT agent, on the concentrations of both the monomer and the crosslinker, and on the process (one step or two steps). The best-suited experimental conditions to reach thermosensitive hydrogels with nanometric size and well-defined surface properties were determined. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2373–2390, 2009
184 citations
TL;DR: In this article, a library of solvents with different equilibrium constants for disproportionation of Cu(I)X such as DMSO, DMF, DMAC, EC, PC, EtOH, MeOH, methoxyethanol, NMP, acetone and in their binary mixtures with H 2 O was examined.
Abstract: SET-LRP is mediated by a combination of solvent and ligand that promotes disproportionation of Cu(I)X into Cu(0) and Cu(II)X 2 . Therefore, the diversity of solvents suitable for SET-LRP is limited. SET-LRP of MA in a library of solvents with different equilibrium constants for disproportionation of Cu(I)X such as DMSO, DMF, DMAC, EC, PC, EtOH, MeOH, methoxyethanol, NMP, acetone and in their binary mixtures with H 2 O was examined. H 2 O exhibits the highest equilibrium constant for disproportionation of Cu(I)X. The apparent rate constant of the polymerization exhibits a linear increase with the addition of H 2 O. This is consistent with higher equilibrium constants for disproportionation generated by addition of H 2 O to organic solvents. Furthermore, with the exception of alcohols and carbonates, the rate constant of polymerization in binary mixtures could be correlated with the Dimroth-Reichardt solvent polarity parameter. This is consistent with the single-electron transfer mechanism proposed for SET-LRP that involves a polar transition state. These experiments demonstrate that the use of binary mixtures of solvents with H 2 O provides a new, simple and efficient method for the elaboration of a large diversity of reaction media that are suitable for SET-LRP even when one of the two solvents does not mediate disproportionation of Cu(I)X.
177 citations
TL;DR: In this article, a diallyl functional monomer is synthesized through the Mannich and ring closing reaction of 4,4 0 -isopro- pylidenediphenol (bisphenol A), formaldehyde and allylamine.
Abstract: Oligosiloxanes containing thermally curable benzoxazine units in the main chain have been synthesized. For this purpose, first the diallyl functional monomer is synthesized through the Mannich and ring closing reaction of 4,4 0 -isopro- pylidenediphenol (bisphenol A), formaldehyde and allylamine. Hydrosilylation reac- tion of the resulting diallylic monomer (B-ala) with 1,1,3,3-tetramethyldisiloxane (TMDS) in the presence of Pt catalyst yields the corresponding poly(B-ala-tetra- methyl disiloxane)s (PBTMDS) with the molecular weights in the range of 1800- 4100 Da. The structures of the precursor diallyl monomer and the resulting polymers are confirmed by FT-IR and 1 H NMR analysis. Curing behavior of both the monomer and polymers has also been studied by Differential Scanning Calorimetry (DSC). Flexible free standing transparent films of the oligosiloxanes are obtained by solvent casting from dichloromethane solution on Teflon plates. The films preserve shape and, to some extent, toughness after thermal curing between 100 and 180 � C. Ther- mal properties of the cured polymers are also investigated by thermogravimetric analysis (TGA). V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 804-811,
TL;DR: In this paper, the feasibility of postpolymerization modification of poly(pentafluorophenyl methacrylate) (PPFMA) prepared by reversible addition fragmentation chain transfer (RAFT) polymerization was explored.
Abstract: This article explores the feasibility of poly(pentafluorophenyl methacrylate) (PPFMA) prepared by reversible addition fragmentation chain transfer (RAFT) polymerization as a platform for the preparation of diverse libraries of functional polymers via postpolymerization modification with primary amines. Experiments with a broad range of functional amines and PPFMA precursors of different molecular weights indicated that the postpolymerization modification reaction proceeds with good to excellent conversion for a diverse variety of functional amines and is essentially independent of the PPFMA precursor molecular weight. The RAFT end group, which was well preserved throughout the polymerization, is cleaved during postpolymerization modification to generate a thiol end group that provides possibilities for further orthogonal chain-end modification reactions. The degree of postpolymerization modification can be controlled by varying the relative amount of primary amine that is used and random polymethacrylamide copolymers can be prepared via a one-pot/two-step sequential addition procedure. Cytotoxicity experiments revealed that the postpolymerization modification strategy does not lead to any additional toxicity compared with the corresponding polymer obtained via direct polymerization, which makes this approach also of interest for the synthesis of biologically active polymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4332-4345, 2009
TL;DR: The “grafting through” approach offers versatility in the construction of complexmacromolecular systems, but is likely to encounter steric hindrance during the polymerization of high molecular weight or sterically-bulky macromonomers.
Abstract: Of significant interest is the development of synthetic methodologies to prepare complexmacromolecular structures that contain functionalities, allowing for stimuli-responsivecharacteristics and further chemical modifications.1–6 The cylindrical molecular brush,which is composed of many side chain polymers distributed densely along a backbone, hasattracted much attention because its chemical composition, size and morphology can becontrolled precisely by choosing appropriate monomers and tuning the lengths of thebackbone and side chains.7–9 To prepare such structures, three synthetic strategies are oftenemployed: “grafting onto”8,9 (grafting side chains onto a pre-established multifunctionalbackbone by coupling reactions), “grafting from”10–13 (growth of side chains from amultifunctionalized initiating backbone) and “grafting through”14–18 (polymerization ofpreviously synthesized side chains through their terminal groups). Previously, our laboratoryhas demonstrated the compatibility of the three primary living radical polymerizations(nitroxide mediated radical polymerization (NMRP), atom transfer radical polymerization(ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization)together with ring-opening metathesis polymerization (ROMP) in the “grafting from”method.12,19,20 Our interest has focused recently on the “grafting through” method,because it provides exceptional control over the grafting density, the length of the backbone,and the length of the side chains, each independently.Although the “grafting through” approach offers versatility in the construction of complexmacromolecular systems, it is likely to encounter steric hindrance during the polymerizationof high molecular weight or sterically-bulky macromonomers.21,22 To overcome this issue,ROMP has often been used, which is driven by the release of enthalpy from cyclic monomerstructures and affords a polymer backbone with a relatively loose grafting density. Forexample, the syntheses of molecular brushes have been reported using ROMP fromnorbornene-terminated poly(ethylene oxide),16 polystyrene,15 polyphosphazene,14 poly(e-caprolactone),18 and polylactide,17 macromonomers synthesized mainly from anionic
TL;DR: In this paper, a 3D cell scaffold based on vinyl esters was successfully implanted into the distal femoral bone of an adult New Zealand white rabbit, and the obtained histological results approved the excellent biocompatibility of the esters and showed that they are significantly less cytotoxic than methacrylates.
Abstract: Lithography based additive manufacturing technologies (AMT) like stereolithography or digital light processing have become appealing methods for the fabrication of 3D cellular scaffolds for tissue engineering and regenerative medicine. To circumvent the use of (meth)acrylate-based photopolymers, that suffer from skin irritation and sometimes cytotoxicity, new monomers based on vinyl esters were prepared. In vitro cytotoxicity studies with osteoblast-like cells proofed that monomers based on vinyl esters are significantly less cytotoxic than (meth)acrylates. Photoreactivity was followed by photo-differential scanning calorimetry and the mechanical properties of the photocured materials were screened by nanoindentation. Conversion rates and indentation moduli between those of acrylate and methacrylate references could be observed. Furthermore, osteoblast-like cells were successfully seeded onto polymer specimens. Finally, we were able to print a 3D test structure out of a vinyl ester-based formulation by μ-SLA with a layer thickness of 50 μm. For in vivo testing of vinyl esters these 3D scaffolds were implanted into surgical defects of the distal femoral bone of adult New Zealand white rabbits. The obtained histological results approved the excellent biocompatibility of vinyl esters. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009
TL;DR: In this article, it was shown that a similar effect is observed in binary mixtures of organic solvents, wherein the addition of a more polar solvent to a less polar solvent provides a linear increase in the apparent rate constant of propagation, k.
Abstract: SET-LRP requires a combination of ligand and solvent that mediates the disproportionation of Cu(I)X into Cu(O) activator, and Cu(II) deactivator. The solvent also modulates the kinetics of the reaction. More polar solvents, including mixtures of water and organic solvents enhance the rate of polymerization in accord with the Dimroth-Reichardt parameter. Here, it is demonstrated that a similar effect is observed in binary mixtures of organic solvents, wherein the addition of a more polar solvent to a less polar solvent provides a linear increase in the apparent rate constant of propagation, k . However, this linear relationship does not hold for the entire range of volume fraction for binary mixtures when ethylene carbonate (EC) or MeOH are one of the two components. Results herein, suggest that the kinetics of SET-LRP in these solvent mixtures is cooperatively and synergistically determined by polarity, degree of disproportionation, and also by another parameter related to the ability of the solvent to stabilize colloidal Cu(0) and determine its particle size.
TL;DR: In this article, the authors describe the structure-property relationships between poly octahedral oligomeric silsesquioxane (POSS) fillers and the thermomechanical properties of the polymer composites using polystyrene, poly(methyl methacrylate), and ethylene-(vinyl acetate) copolymer.
Abstract: In this article, we describe the structure–property relationships between the polyoctahedral oligomeric silsesquioxane (POSS) fillers and the thermomechanical properties of the polymer composites using polystyrene, poly(methyl methacrylate), and ethylene-(vinyl acetate) copolymer. We used eight kinds of octa-substituted aliphatic and aromatic POSS as a filler, and homogeneous polymer composites were prepared with various concentrations of these POSS fillers. From a series of measurements of thermal and mechanical properties of the polymer composites, it was summarized that the longer alkyl chains and unsaturated bonds at the side chains in POSS are favorable to improve the thermal stability and the elasticity of polymer matrices. It was found that phenyl-POSS can show superior ability to improve the thermomechanical properties of conventional polymers used in this study. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5690–5697, 2009
TL;DR: In this article, a series of double-hydrophilic graft copolymers, consisting of poly(N-isopropylacrylamide)-b-poly(ethyl acrylate) (PNIPAM-b-PEA) backbone and poly(2-(dimethylamino)ethyl Acrylate (PDMAEA) side chains, were synthesized by the combination of singleelectron-transfer living radical polymerization (SET-LRP) and atom-transfer radical polymerisation (ATRP).
Abstract: A series of well-defined double-hydrophilic graft copolymers, consisting of poly(N-isopropylacrylamide)-b-poly(ethyl acrylate) (PNIPAM-b-PEA) backbone and poly(2-(dimethylamino)ethyl acrylate) (PDMAEA) side chains, were synthesized by the combination of single-electron-transfer living radical polymerization (SET-LRP) and atom-transfer radical polymerization (ATRP). PNIPAM-b-PEA backbone was first prepared by sequential SET-LRP of N-isopropylacrylamide and 2-hydroxyethyl acrylate at 25 °C using CuCl/tris(2-(dimethylamino)ethyl)amine as catalytic system followed by the transformation into the macroinitiator by treating the pendant hydroxyls with 2-chloropropionyl chloride. The final graft copolymers with narrow molecular weight distributions were synthesized by ATRP of 2-(dimethylamino)ethyl acrylate initiated by the macroinitiator at 40 °C using CuCl/tris(2-(dimethylamino)ethyl)amine as catalytic system via the grafting-from strategy. These copolymers were employed to prepare stable colloidal gold nanoparticles with controlled size in aqueous solution without any external reducing agent. The morphology and size of the nanoparticles were affected by the length of PDMAEA side chains, pH value, and the feed ratio of the graft copolymer to HAuCl4. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1811–1824, 2009
TL;DR: In this paper, a review of strategies to synthesize p- conjugated polymers and to tune their absorption and emission colors is presented, where a deli-cate interplay between the chem- ical structure and the processing conditions are found, resulting in a high sensitivity of both struc- tural features and optical proper-ties.
Abstract: Fluorene-based p- conjugated polymers and oligo- mers combine several advanta- geous properties that make them well-suited candidates for appli- cations in organic optoelectronic devices and chemical sensors. This review highlights strategies to synthesize these materials and to tune their absorption and emission colors. Furthermore, methods to control their supra- molecular organization will be discussed. In many cases, a deli- cate interplay between the chem- ical structure and the processing conditions are found, resulting in a high sensitivity of both struc- tural features and optical proper- ties. V C 2009 Wiley Periodicals, Inc. J
TL;DR: In this paper, a photoinitiator system consisting of camphorquinone in combination with a benzyl alcohol to generate free radicals by the absorption of visible light was proposed, and the radicals participated in the free radical chain induced decomposition of a diaryliodonium salt.
Abstract: This communication reports the development of an efficient three-component visible light sensitive photoinitiator system for the cationic ring-opening photopolymerization of epoxide monomers and epoxide functional oligomers. The photoinitiator system consists of camphorquinone in combination with a benzyl alcohol to generate free radicals by the absorption of visible light. Subsequently, the radicals participate in the free radical chain induced decomposition of a diaryliodonium salt. The resulting strong Bronsted acid derived from this process catalyzes the cationic ring-opening polymerization of a variety of epoxide substrates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 866–875, 2009
TL;DR: In this article, the formation of one-handed helical poly(triphenylmethyl methacrylate) (PTrMA) was found through the helix-sense-selective polymerization of methacylate using chiral anionic initiators, and the existence of a stable helical polymer without chiral side chains was proved.
Abstract: In 1979, the formation of one-handed helical poly(triphenylmethyl methacrylate) (PTrMA) was found through the helix-sense-selective polymerization of methacrylate using chiral anionic initiators, and the existence of a stable helical polymer without chiral side chains was proved. The chiral polymer exhibited unexpected high chiral recognition of various racemic compounds when used as the chiral packing material (CPM) for HPLC, which was commercialized in 1982 as the first chiral column based on an optically active polymer. This success encouraged us to develop further useful commercial chiral packing materials (CPMs) based on polysaccharides, cellulose, and amylose. By using these polysaccharide-based CPMs, particularly phenylcarbamate derivatives, nearly 90% of chiral compounds can be resolved not only analytically but also preparatively, and several chiral drugs have been produced using the CPMs.
TL;DR: In this paper, a novel mono-and difunctional aliphatic oxyalcohol-based benzoxazines have been synthesized and characterized in detail, and molecular structures of the monomers were investigated by spectral analysis.
Abstract: Novel mono- and difunctional aliphatic oxyalcohol-based benzoxazines have been synthesized and characterized in detail. Molecular structures of the monomers were investigated by spectral analysis. The obtained benzoxazine monomers exhibit fluidic behavior, which makes them particularly useful for many applications compared to other traditional benzoxazines. Differential scanning calorimetry was used to monitor the thermal crosslinking behavior of synthesized monomers. Mono- and bifunctional benzoxazine monomers exhibited low curing exhothermic peak with the onset around 173 and 180 °C, respectively. Relatively, low ring-opening polymerization temperature was due to the hydroxyl groups present in the structure of the monomers. The hydrogen bonding of hydroxyl groups may cause alignment of the monomers in the liquid state. Thermal stabilty of the polybenzoxazines was studied by thermogravimetric analysis. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009
TL;DR: In this paper, the authors present a review of the recent literature on supercritical carbon dioxide (scCO2) based radical polymerization and describe the unique characteristics of scCO2 that allow composite particle formation of unique morphology to be achieved.
Abstract: Supercritical carbon dioxide (scCO2) is an inexpensive and environmentally friendly medium for radical polymerizations. ScCO2 is suited for heterogeneous controlled/living radical polymerizations (CLRPs), since the monomer, initiator, and control reagents (nitroxide, etc.) are soluble, but the polymer formed is insoluble beyond a critical degree of polymerization (Jcrit). The precipitated polymer can continue growing in (only) the particle phase giving living polymer of controlled well-defined microstructure. The addition of a colloidal stabilizer gives a dispersion polymerization with well-defined colloidal particles being formed. In recent years, nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT) polymerization have all been conducted as heterogeneous polymerizations in scCO2. This Highlight reviews this recent body of work, and describes the unique characteristics of scCO2 that allows composite particle formation of unique morphology to be achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3711–3728, 2009
TL;DR: A series of low bandgap conjugated polymers consisting of benzothiadiazole alternating with DTT or DTP unit with or without 3-alkylthiophene bridge have been synthesized.
Abstract: A series of low bandgap conjugated polymers consisting of benzothiadiazole alternating with dithienothiophene (DTT) or dithienopyrrole (DTP) unit with or without 3-alkylthiophene bridge have been synthesized. Effect of the fused rings and 3-alkylthiophene bridge on the thermal, optical, electrochemical, charge transport, and photovoltaic properties of these polymers have been investigated. These polymers show broad absorption extending from 300 to 1000 nm with optical bandgaps as low as 1.2 eV; the details of which can be varied either by incorporating 3-alkylthiophene bridge or by replacing DTT with DTP. The LUMO levels (―2.9 to ―3.3 eV) are essentially unaffected by the specific choice of donor moiety, whereas the HOMO levels (―4.6 to ―5.6 eV) are more sensitive to the choice of donor. The DTT and DTP polymers with 3-alkylthiophene bridge were found to exhibit hole mobilities of 8 x 10 ―5 and 3 x 10 ―2 cm 2 V ―1 s ―1 , respectively, in top-contact organic field-effect transistors. Power conversion efficiencies in the range 0.17―0.43% were obtained under simulated AM 1.5, 100 mW cm ―2 irradiation for polymer solar cells using the DTT and DTP-based polymers with 3-alkylthiophene bridge as donor and fullerene derivatives as acceptor.
TL;DR: In this article, a combination of LPO and AIBN was used to remove the thiocarbonylthio end groups of styrenic or acrylic polymers and minimize the occurrence of self termination.
Abstract: The removal of thiocarbonylthio end groups by radical-addition-fragmentation- coupling from polymers synthesized by RAFT polymerization has been studied. We found that a method, which involves heating the polymer with a large excess (20 molar equivalents) of azobis(isobutyronitrile) (AIBN), while successful with methacrylic polymers, is less effective with styrenic or acrylic polymers and provides only partial end group removal. This is attributed to the propagating radicals generated from the latter polymers being poor radical leaving groups relative to the cyanoisopropyl radical. Similar use of lauroyl peroxide (LPO) completely removes the thiocarbonylthio groups from styrenic or acrylic polymers but, even with LPO in large excess, produces a polymer with a bimodal molecular weight distribution. The formation of a peak of double molecular weight is indicative of the occurrence of self-termination and ineffective radical trapping. We now report that by use of a combination of LPO (2 molar equivalents) and AIBN (20 molar equivalents) we are able to completely remove thiocarbonylthio end groups of styrenic or acrylic polymers and minimize the occurrence of self termination. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6704–6714, 2009
TL;DR: In this paper, a series of alkynyl terminally functionalized PNIPAM (alkyne-PNIPAM) linear precursors with varying degrees of polymerization (DP) were synthesized via atom transfer radical polymerization of N-isopropylacrylamide using propargyl 2-chloropropionate as the initiator.
Abstract: The syntheses of well-defined 7-arm and 21-arm poly(N-isopropylacrylamide) (PNIPAM) star polymers possessing β-cyclodextrin (β-CD) cores were achieved via the combination of atom transfer radical polymerization (ATRP) and click reactions. Heptakis(6-deoxy-6-azido)-β-cyclodextrin and heptakis[2,3,6-tri-O-(2-azidopropionyl)]-β-cyclodextrin, β-CD-(N3)7 and β-CD-(N3)21, precursors were prepared and thoroughly characterized by nuclear magnetic resonance and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. A series of alkynyl terminally functionalized PNIPAM (alkyne-PNIPAM) linear precursors with varying degrees of polymerization (DP) were synthesized via atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using propargyl 2-chloropropionate as the initiator. The subsequent click reactions of alkyne-PNIPAM with β-CD-(N3)7 and β-CD-(N3)21 led to the facile preparation of well-defined 7-arm and 21-arm star polymers, namely β-CD-(PNIPAM)7 and β-CD-(PNIPAM)21. The thermal phase transition behavior of 7-arm and 21-arm star polymers with varying molecular weights were examined by temperature-dependent turbidity and micro-differential scanning calorimetry, and the results were compared to those of linear PNIPAM precursors. The anchoring of PNIPAM chain terminal to β-CD cores and high local chain density for star polymers contributed to their considerably lower critical phase separation temperatures (Tc) and enthalpy changes during phase transition as compared with that of linear precursors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 404–419, 2009
TL;DR: In this paper, S-3-butynyl methane thiosulfonate (MTS) was used for end group functionalization of RAFT polymers, and the disul-fide bond connecting the polymers to the surface could be selectively cleaved and resulted in all surfaces having the same contact angle.
Abstract: Five different polymers, poly[methyl methacrylate] (PMMA), poly[lauryl methacrylate] (PLMA), poly[diethylene glycol methacrylate] (PDEGMA), poly[N-iso-propylacrylamide] (PNIPA), and poly[styrene] (PS) prepared by the RAFT process and thus terminated with dithioesters were aminolyzed in the presence of S-3-butynyl methane thiosulfonate (MTS), which was synthesized in two steps. Analysis of the polymers by 2D NMR, UV–vis absorbance, and gel permeation chromatogra-phy revealed them to quantitatively carry acetylene end groups connected with disul-fide bridges, indicating that functional MTS reagents can be employed for end group functionalization of RAFT polymers. This versatile method is of advantage compared with conjugations with functional maleimides, where isolation of terminal thiols is of-ten required but inexpedient for poly[(meth)acrylates] because their terminal thiols may undergo backbiting and thus avoid conjugation. The acetylene-terminated poly-mers were bound to an azide functionalized glass surface in a Cu(I) catalyzed cyclo-addition. The modified surfaces exhibited water contact angles corresponding to the polarity of the attached polymers. In the case of the stimulus responsive polymers PNIPA and PDEGMA, the surfaces showed temperature-dependent contact angles. The disulfide bond connecting the polymers to the surface could be selectively cleaved and resulted in all surfaces having the same contact angle, independent of the nature of the polymer prior attached to the surface.
TL;DR: In this article, a new model for the kinetics of reversible addition-fragmentation chain transfer (RAFT) polymerization was proposed, which showed that the termination of the radical intermediate formed by the RAFT process occurs only with very short oligomeric radicals.
Abstract: We extend a new model for the kinetics of reversible addition-fragmentation chain transfer (RAFT) polymerization. The essence of this model is that the termination of the radical intermediate formed by the RAFT process occurs only with very short oligomeric radicals. In this work, we consider cross-termination of oligomers up to two monomers and an initiator fragment. This model accounts for the absence of three-armed stars in the molecular weight distribution, which are predicted by other cross-termination models, since the short third arm makes a negligible difference to the polymer's molecular weight. The model is tested against experiments on styrene mediated by cyano-isopropyl dithiobenzoate, and ESR experiments of the intermediate radical concentration. By comparing our model to experiments, we may determine the significance of cross-termination in RAFT kinetics. Our model suggests that to agree with the known data on RAFT kinetics, the majority of cross-terminating chains are dimeric or shorter. If longer chains are considered in cross-termination reactions, then significant discrepancies with the experiments (distinguishable star polymers in the molecular weight distribution) and quantum calculations will result. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3455–3466, 2009
TL;DR: In this article, the synthesis of polyHIPE containing biodegradable poly(e-caprolactone) (PCL) groups through the step-growth reaction of a diisocyanate with a flexible PCL triol to form a crosslinked polyurethane was described.
Abstract: PolyHIPE are highly porous, emulsion-templated polymers typically synthesized via free-radical polymerization within a water-in-oil (W/O) high internal phase emulsion (HIPE) whose dispersed, aqueous phase occupies more than 74% of the volume. The synthesis of a polyHIPE containing biodegradable polymers is not straightforward because the presence of both an organic phase and an aqueous phase within the HIPE limits the type of polymerization reactions that can be used. This article describes the synthesis of polyHIPE containing biodegradable poly(e-caprolactone) (PCL) groups through the step-growth reaction of a diisocyanate with a flexible PCL triol to form a crosslinked polyurethane. The reaction of the diisocyanate with the water in the HIPE produced urea groups and large bubbles from the generation of CO2. The polymer walls between these bubbles consisted of a porous, emulsion-templated structure. Polymerization with an excess of diisocyanate produced a significant enhancement in the amounts of urea and CO2. The reduction in the flexible PCL content and the enhancement in the rigid urea content produced an increase in wall modulus that was over 20-fold. The ability to synthesize polyHIPE through such step-growth reactions is an important advance in the adaptation of polyHIPE for such applications as tissue engineering. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5806–5814, 2009
TL;DR: In this article, the shape-memory properties of poly(e-caprolactone) with a pendent coumarin group were evaluated by means of a cyclic thermomechanical tensile experiments under varying maximum strains (em = 100, 300, and 500).
Abstract: Poly(e-caprolactone) (PCL) with a pendent coumarin group was prepared by solution polycondensation from 7-(3,5-dicarboxyphenyl) carbonylmethoxycoumarin dichloride and α, ω-dihydroxy terminated poly(e-caprolactone) with molecular weights of 1250, 3000, and 10,000 g/mol. These photosensitive polymers underwent a rapid reversible photocrosslinking upon exposure to irradiation with alternating wavelengths (>280/254 nm) without a photoinitiator. The thermal and mechanical properties of the photocrosslinked films were examined by means of differential scanning calorimetry and stress–strain measurements. The crosslinked films exhibited elastic properties above the melting temperature of the PCL segment along with significant decrease in the ultimate tensile strength and Young's modulus. Shape-memory properties such as strain fixity ratio (Rf) and strain recovery ratio (Rr) were determined by means of a cyclic thermomechanical tensile experiments under varying maximum strains (em = 100, 300, and 500%). The crosslinked ICM/PCL-3000 and -10,000 films exhibited the excellent shape-memory properties in which both Rf and Rr values were 88–100% for tensile strain of 100–500%; after the deformation, the films recovered their permanent shapes instantaneously. In vitro degradation was performed in a phosphate buffer saline (pH 7.2) at 37 °C with or without the presence of Pseudomonas cepacia lipase. The presence of the pendent coumarin group and the crosslinking of the polymers pronouncedly decreased the degradation rate. The crosslinked biodegradable PCL showing a good shape-memory property is promising as a new material for biomedical applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2422–2433, 2009
TL;DR: The direct synthesis of novel gluconamidoalkyl methacrylamides by reacting D-gluconolactone with aminoalkyl methamphetamine with the aim of forming nanostructures via the complexation with plasmid DNA is described.
Abstract: We describe here the direct synthesis of novel gluconamidoalkyl methacrylamides by reacting D-gluconolactone with aminoalkyl methacrylamides. The glycomonomers were then successfully polymerized via the reversible addition-fragmentation chain transfer process (RAFT) using 4-cyanopentanoic acid dithiobenzoate (CTP) as chain transfer agent and 4,4′-azobis(4-cyanovaleric acid) (ACVA) as the initiator in aqueous media. Well-defined polymers were obtained as revealed by gel permeation chromatography. Diblock copolymers were then synthesized by the macro-CTA approach. The cationic glycopolymers were subsequently used in the formation of nanostructures via the complexation with plasmid DNA. As noted by dynamic light scattering, monodisperse nanoparticles were obtained via the electrostatic interaction of the cationic glycopolymer with DNA. The sizes of the nanoparticles formed were found to be stable and independent of pH. In vitro cell viability studies of the glycopolymers were carried out using HELA cell lines. The RAFT synthesized glycopolymers and cationic glyco-copolymers revealed to be nontoxic. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 614–627, 2009