Showing papers in "Journal of Polymer Science Part A in 2011"

Building nanostructures using RAFT polymerization

Abstract: Reversible addition fragmentation chain transfer (RAFT) polymerization is one of the most extensively studied controlled/living radical polymerization methods that has been used to prepare well-defined nanostructured polymeric materials. This review, with more 650 references illustrates the range of well-defined functional nanomaterials that can be accessed using RAFT chemistry. The detailed syntheses of macromolecules with predetermined molecular weights, designed molecular weight distributions, controlled topology, composition and functionality are presented. RAFT polymerization has been exploited to prepare complex molecular architectures, such as stars, blocks and gradient copolymers. The self-assembly of RAFT-polymer architectures has yielded complex nanomaterials or in combination with other nanostructures has generated hybrid multifunctional nanomaterials, such as polymer-functionalized nanotubes, graphenes, and inorganic nanoparticles. Finally nanostructured surfaces have been described using the self-organization of polymer films or by the utilization of polymer brushes. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 551-595, 2011

Synthesis and characterization of poly(2,5-furan dicarboxylate)s based on a variety of diols

Abstract: Novel polyesters from renewable resources based on 2,5-dicarboxylic acid and several diols were synthesized and characterized using different polycondensation techniques. The aliphatic diols were sufficiently volatile to allow the use of polytransesterifications, which gave high-molecular weight semicrystalline materials with good thermal stability. In particular, the polyester based on ethylene glycol displayed properties comparable with those of its aromatic counterpart, poly(ethylene terephthalate), namely, the most important industrial polyester. The use of isosorbide gave rise to amorphous polymers with very stiff chains and hence a high glass transition temperature and an enhanced thermal stability. The interfacial polycondensation between the acid dichloride and hydroquinone produced a semicrystalline material with features similar to those of entirely aromatic polyesters, characterized essentially by the absence of melting and poor solubility, both associated with their remarkable chain rigidity. The replacement of hydroquinone with the corresponding benzylic diol was sufficient to provide a more tractable polyester. This study provided ample evidence in favor of the exploitation of furan monomers as renewable alternatives to fossil-based aromatic homologs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

A fully biobased epoxy resin from vegetable oils: From the synthesis of the precursors by thiol‐ene reaction to the study of the final material

Abstract: A novel vegetable oil-based polyamine issued from grapeseed oil (GSO) was prepared using cysteamine chloride (CAHC) by thiol-ene coupling (TEC). The structure of the polyamine oil (AGSO) was carefully examined using a large range of chemical analyses (FTIR, 1H NMR and 13C NMR, LC-MS…). The effects of the amination of GSO on the vegetable oil properties were also studied using viscosimetry. Then, AGSO was employed as a novel curing agent for bio-based epoxy resin. The thermal crosslinking reaction between AGSO and epoxidized linseed oil (ELO) was studied by DSC and rheology. This study also dealt with the definition of the thermomechanical properties of the final material obtained by the mixing and curing of AGSO with ELO in stoichiometric proportions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis and properties of biobased epoxy resins. part 1. Glycidylation of flavonoids by epichlorohydrin

Abstract: Biobased epoxy resins were synthesized from a cate- chin molecule, one of the repetitive units in natural flavonoid biopolymers also named condensed tannins. The reactivity of catechin toward epichlorohydrin to form glycidyl ether deriva- tives was studied using two model compounds, resorcinol and 4-methylcatechol, which represent the A and B rings of catechin, respectively. These model molecules clearly showed differences in reactivity upon glycidylation, explaining the results found with catechin monomer. The reaction products were character- ized by both FTIR and NMR spectroscopy and chemical assay. The glycidyl ether of catechin (GEC) was successfully cured in various epoxy resin formulations. The GECs thermal properties showed that these new synthesized epoxy resins displayed interesting properties compared to the commercial diglycidyl ether of bisphenol A (DGEBA). For instance, when incorporated up to 50% into the DGEBA resin, GEC did not modify the glass- transition temperature. Epoxy resins formulated with GEC had slightly lower storage moduli but induced a decrease of the swelling percentage, suggesting that GEC-enhanced crosslink- ing in the epoxy resin networks. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2261-2270, 2011

Combining renewable gum rosin and lignin: Towards hydrophobic polymer composites by controlled polymerization

Abstract: Rosin polymer-grafted lignin composites were pre- pared via ''grafting from'' atom transfer radical polymerization (ATRP) with the aid of 2-bromoisobutyryl ester-modified lignin as macroinitiators. Three different monomers derived from dehydroabietic acid (DA) were used for execution of grafting from ATRP, while DA was separately attached onto lignin by a simple esterification reaction. Kinetic studies indicated con- trolled and ''living'' characteristics of all monomer polymeriza- tions. Thermal studies indicated that rosin polymer-grafted lignin composites exhibited glass transition temperatures in a broad temperature range from � 20 to 100 � C. The grafting of both DA and rosin polymers significantly enhanced hydropho- bicity of lignin. Static contact angle measurement of water droplets showed � 90 � for all these rosin modified lignin com- posites. X-ray photoelectron spectroscopy demonstrated that the surface of rosin-lignin composites was dominated with chemical compositions originating from the hydrocarbon rich rosin moiety. The impartation of hydrophobicity of rosin into lignin provided excellent water resistance of this class of renewable polymers, as all rosin-modified lignin com- posites showed water uptake below 1.0 wt %. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3728-3738, 2011

Organocatalytic depolymerization of poly(ethylene terephthalate)

Abstract: We describe the organocatalytic depolymerization of poly(ethylene terephthalate) (PET), using a commercially available guanidine catalyst, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). Postconsumer PET beverage bottles were used and processed with 1.0 mol % (0.7 wt %) of TBD and excess amount of ethylene glycol (EG) at 190 °C for 3.5 hours under atmospheric pressure to give bis(2-hydroxyethyl) terephthalate (BHET) in 78% isolated yield. The catalyst efficiency was comparable to other metal acetate/alkoxide catalysts that are commonly used for depolymerization of PET. The BHET content in the glycolysis product was subject to the reagent loading. This catalyst influenced the rate of the depolymerization as well as the effective process temperature. We also demonstrated the recycling of the catalyst and the excess EG for more than 5 cycles. Computational and experimental studies showed that both TBD and EG activate PET through hydrogen bond formation/activation to facilitate this reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis and properties of poly(butylene succinate): Efficiency of different transesterification catalysts

Abstract: The efficiency of organometal- (Ti, Zr, Sn, Hf, and Bi) and metal oxide- (Ge and Sb) based catalysts was investigated during the transesterification step of the synthesis of poly(butylene succinate) (PBS). PBS was prepared from succinic acid and 1,4-butanediol via a two-stage melt polycondensation process. The catalytic efficiency of the organometal catalysts was as follows: Ti≫Zr∼ Sn>Hf>Sb>Bi. The germanium and antimony metal oxides displayed desirable catalytic efficiency when were associated with hydroxy acids (lactic acid or glycolic acid), which acted as chelating agents. However, this catalytic system exhibited lower efficiency compared to the titanium system. Furthermore, at high concentrations of hydroxy acids the overall transesterification rate decreased. This effect can be explained by the substitution of PBS hydroxyl end groups by a lactic or glycolic unit, both of which are less reactive during the transesterification reaction. The role of catalytic residues during the storage and processing of PBS was also studied. The reduced viscosity of the PBS samples did not vary when processing at 190 °C from 1 to 10 minutes. However, when stored under ambient conditions, all PBS samples were prone to significant hydrolytic degradation, especially those containing a titanium catalyst. This behavior indicates that zirconium- and germanium-based catalysts could be interesting substitutes for titanium-based catalysts. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

Discrete macromolecular constructs via the Diels–Alder “Click” reaction

Abstract: Functional polymeric materials with desired proper- ties can be designed by precise control of macromolecular architectures. Over the recent years, click reactions have enabled efficient synthesis of a variety of polymers with differ- ent topologies via efficient polymer-polymer conjugations. While the copper catalyzed Huisgen type (3þ2) dipolar cycload- dition between azide and alkyne has been widely used toward this goal, the Diels-Alder (DA) reaction offers an alternative click reaction that allow efficient macromolecular conjugations, oftentimes without the need of any additional reagent or cata- lyst. This article highlights, with illustrative examples, the power of the DA ''click'' reaction to efficiently synthesize a vari- ety of different well-defined macromolecular constructs in a modular fashion. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4103-4120, 2011

Poly(allyl glycidyl ether)-A versatile and functional polyether platform.

Abstract: Allyl glycidyl ether, polymerized from potassium alkoxide/naphthalenide initiators under both neat and solution conditions was shown to be a highly-controlled process. In both cases, molar masses (10-100 kg/mol) were determined by the reaction stoichiometry, and low polydispersity indices (1.05-1.33) could be obtained with a full understanding of the dominant side reaction, isomerization of the allyl side chain, being developed. The degree of isomerization of allyl to cis-prop-1-enyl ether groups (0 - 10 % mol.) was not correlated to the molar mass or polydispersity of the polymer but was dictated by the polymerization temperature. This allows the extent of isomerization to be reduced to essentially zero under either melt or solution conditions at polymerization temperatures of less than 40 °C.

An efficient way to functionalize graphene sheets with presynthesized polymer via ATNRC chemistry

Abstract: Graphene nanosheets offer intriguing electronic, thermal and mechanical properties and are expected to find a variety of applications in high-performance nanocomposite materials. The great challenge of exfoliating and dispersing pristine graphite or graphene sheets in various solvents or matrices can be achieved by facilely and properly chemical functionalization of the carbon nanosheets. Here we reported an efficient way to functionalize graphene sheets with presynthesized polymer via a combination of atom transfer nitroxide radical coupling chemistry with the grafting-onto strategy, which enable us to functionalize graphene sheets with well-defined polymer synthesized via living radical polymerization. A radical scavenger species, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), was firstly anchored onto -COOH groups on graphene oxide (GO) to afford TEMPO-functionalized graphene sheets (GS-TEMPO), meanwhile, the GO sheets were thermally reduced. Next, GS-TEMPO reacted with Br-terminated well-defined poly(N-isopropylacrylamide) (PNIPAM) homopolymer, which was presynthesized by SET-LRP, in the presence of CuBr/N,N,N',N',N ''-pentamethyldiethylenetriamineto form PNIPAM-graphene sheets (GS-PNIPAM) nanocomposite in which the polymers were covalently linked onto the graphene via the alkoxy-amine conjunction points. The PNIPAM-modified graphene sheets are easily dispersible in organic solvents and water, and a temperature-induced phase transition was founded in the water suspension of GS-PNIPAM. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1582-1590, 2011

Polybenzoxazines from renewable diphenolic acid

Abstract: The novel benzoxazine monomers, DPA-Bz and MDP-Bz from renewable diphenolic acid (DPA), which mimics the structure of bisphenol A (BPA), were synthesized by traditional approaches. The structure and purity of the monomers was confirmed by FTIR, 1H NMR, and 13C NMR spectra. The thermally activated polymerization of the MDP-Bz and DPA-Bz afforded thermosetting polybenzoxazines with higher Tg's, 270 °C and 208 °C respectively, and higher crosslinking density compared to BPA-Bz, due to the transesterification or esterification reactions occurred during curing process. These reactions are in accordance with the number of independent reactions determined analyzing by SVD the chemical rank of the IR spectra data matrices recorded along the homopolymerization reactions monitored at 200 °C. Spectral and concentration profiles of the active chemical species involved in these processes were obtained by MCR-ALS. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

ADMET: Metathesis polycondensation

Abstract: Although it is well known that Acyclic Diene METathesis (ADMET) describes an olefin metathesis polymerization mode that relies on double-bond substituent interchange of a diolefin, the story behind its discovery is not. The story is divulged here. Olefin metathesis has a rich history dating to the 1950s, but the one particular metathesis mode mentioned, ADMET, has more recent historical roots. ADMET polymerization is easy to do and highlighted here are the particular reaction details for success. Additionally, the most recent advances from the past 5 years are detailed, exemplifying this reaction's wide utility from fundamental structure-property studies to multiple advanced applications.

Hydrophilic dual‐responsive magnetite/PMAA core/shell microspheres with high magnetic susceptibility and ph sensitivity via distillation‐precipitation polymerization

Abstract: A facile and effective approach to preparation of dual-responsive magnetic core/shell composite microspheres is reported. The magnetite(Fe3O4)/poly(methacrylic acid) (PMAA) composite microspheres were synthesized through encapsulat- ing c-methacryloxypropyltrimethoxysilane (MPS)-modified magnetite colloid nanocrystal clusters (MCNCs) with cross- linked PMAA shell. First, the 200-nm-sized MCNCs were fabri- cated through solvothermal reaction, and then the MCNCs were modified with MPS to form active vinyl groups on the surface of MCNCs, and finally, a pH-responsive shell of PMAA was coated onto the surface of MCNCs by distillation-precipita- tion polymerization. The transmission electron microscopy (TEM) and vibrating sample magnetometer characterization showed that the obtained composite microspheres had well- defined core/shell structure and high saturation magnetization value (35 emu/g). The experimental results indicated that the thickness and degree of crosslinking of PMAA shell could be well-controlled. The pH-induced change in size exhibited by the core/shell microspheres reflected the PMAA shell contained large amount of carboxyl groups. The carboxyl groups and high saturation magnetization make these microspheres have a great potential in biomolecule separation and drug carriers. Moreover, we also demonstrated that other magnetic poly- meric microspheres, such as Fe3O4/PAA, Fe3O4/PAM, and Fe3O4/PNIPAM, could be synthesized by this approach. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2725-2733, 2011

Influence of the stirring speed and CaCl2 concentration on the nano‐object morphologies obtained via RAFT‐mediated aqueous emulsion polymerization in the presence of a water‐soluble macroRAFT agent

Abstract: Aqueous emulsion polymerizations of styrene were performed in the presence of a macromolecular reversible addition-fragmentation chain transfer (RAFT) agent (macroRAFT) composed of acrylic acid (AA) and poly(ethylene oxide) methyl ether acrylate (PEOA), end-capped by a reactive dodecyl trithiocarbonate group (P(AA-co-PEOA)-TTC). The influence of the stirring speed or the presence of different amounts of a divalent salt, CaCl2, were investigated in this polymerization-induced self-assembly process, in which spherical and nonspherical nano-objects were formed upon the synthesis of amphiphilic diblock copolymers in situ. It appeared that the addition of CaCl2 led to the controlled formation of different nano-objects such as spheres, fibers or vesicles, whereas an appropriate stirring speed was required for the formation of nanofibers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Side-Chain Ferrocene-Containing (Meth)acrylate Polymers: Synthesis and Properties

Abstract: A comprehensive investigation on the synthesis and properties of a series of ferrocene-containing (meth)acry- late monomers and their polymers that differ in the linkers between the ferrocene unit and the backbone was carried out. The side-chain ferrocene-containing polymers were prepared via atom transfer radical polymerization. The kinetic studies indicated that polymerization of most monomers followed a ''controlled''/living manner. The polymerization rates were affected by the vinyl monomer structures and decreased with an increase of the linker length. Methacrylate polymerization was much faster than acrylate polymerization. The optical absorption of monomers and polymers was affected by the linkers. Thermal properties of these polymers can be tuned by controlling the length of the linker between the ferrocene unit and the backbone. By increasing the length of the linker, the glass transition temperature ranged from over 100 to � 20 � C. Electrochemical properties of both monomers and polymers were characterized. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1409-1420, 2011

End‐group fidelity of copper(0)‐meditated radical polymerization at high monomer conversion: an ESI‐MS investigation

Abstract: Copper(0)-mediated radical polymerization (single electron transfer-living radical polymerization) is an efficient polymerization technique that allows control over the polymerization of acrylates, vinyl chloride and other monomers, yielding bromide terminated polymer. In this contribution, we investigate the evolution of the end-group fidelity at very high conversion both in the presence and in the absence of initially added copper (II) bromide (CuBr2). High resolution electrospray-ionization mass spectroscopy (ESI-MS) allows determination of the precise chemical structure of the dead polymers formed during the polymerization to very high monomer conversion, including post polymerization conditions. Two different regimes can be identified via ESI-MS analysis. During the polymerization, dead polymer results mainly from termination via disproportionation, whereas at very high conversion (or in the absence of monomer, that is, post-polymerization), dead polymers are predominantly generated by chain transfer reactions (presumably to ligand). The addition of CuBr2 significantly reduces the extent of termination by both chain transfer and disproportionation, at very high monomer conversion and under post-polymerization conditions, offering a convenient approach to maintaining high end-group fidelity in Cu(0)-mediated radical polymerization. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

SET‐LRP of methyl acrylate catalyzed with activated Cu(0) wire in methanol in the presence of air

Abstract: Single electron transfer-living radical polymerization (SET-LRP) of methyl acrylate (MA) in methanol, catalyzed with nonactivated and activated Cu(0) wires, was performed in the presence of nondeoxygenated reagents and was investigated under a simple blanket of nitrogen. The addition of a small amount of hydrazine hydrate mediates the deoxygenation of the reaction mixture by the consumption of oxygen through its use to oxidize Cu(0) to CuO, followed by the reduction of CuO with hydrazine back to the active Cu(0) catalyst. SET-LRP of MA in methanol in the presence of air requires a smaller dimension of Cu(0) wire, compared to the nonactivated Cu(0) wire counterpart. Activation of Cu(0) wire allowed the polymerization in air to proceed with no induction period, linear first-order kinetics, linear correlation between the molecular weight evolution with conversion, and narrow molecular weight distribution. The retention of chain-end functionality of α,γ-di(bromo) poly(methyl acrylate) (PMA) prepared by SET-LRP was demonstrated by a combination of experiments including H NMR spectroscopy and matrix-assisted laser desorption ionization-time of flight mass spectrometry after thioetherification of α,γ-di(bromo) PMA with thiophenol. In SET-LRP of MA in the presence of limited air, bimolecular termination is observed only above 85% conversion. However, for bifunctional initiators, the small amount of bimolecular termination observed at high conversion maintains a perfectly bifunctional polymer.

Visible Light Induced Free Radical Promoted Cationic Polymerization Using Thioxanthone Derivatives

Abstract: The free radical promoted cationic polymerization cyclohexene oxide (CHO), was achieved by visible light irradia- tion (kinc ¼ 430-490 nm) of methylene chloride solutions con- taining thioxanthone-fluorene carboxylic acid (TX-FLCOOH) or thioxanthone-carbazole (TX-C) and cationic salts, such as diphe- nyliodonium hexafluorophosphate (Ph2I þ PF � ) or silver hexa- fluorophosphate (Ag þ PF � ) in the presence of hydrogen donors. A feasible initiation mechanism involves the photogeneration of ketyl radicals by hydrogen abstraction in the first step. Subse- quent oxidation of ketyl radicals by the oxidizing salts yields Bronsted acids capable of initiating the polymerization of CHO. In agreement with the proposed mechanism, the polymerization was completely inhibited by 2,2,6,6-tetramethylpiperidinyl-1-oxy and di-2,6-di-tert-butylpyridine as radical and acid scavengers, respectively. Additionally polymerization efficiency was directly related to the reduction potential of the cationic salts, that is, Ag þ PF � (E 1=2 red ¼þ 0.8 V) was found to be more efficient than Ph2I þ PF � (E 1=2

Synthesis and characterization of UV‐curable ladder‐like polysilsesquioxane

Abstract: Various ladder-like structured poly(phenyl-co-methacryl silsesquioxane)s (LPMSQ)s with high molecular weight (Mw = 10,000 ∼ 40,000) were synthesized by direct hydrolysis and polymerization in the presence of base catalyst at 25 °C. Synthesized LPMSQs mainly showed ladder-like structure and photo-cure reaction by 100 mW/cm2 (360 nm) for 10 s without any photo-cure initiators. Chemical composition and structural analysis of the obtained LPMSQs were characterized using 1H NMR, 29Si NMR, Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and X-ray diffraction (XRD). Physical properties of LPMSQs before and after photcuring were analyzed by Nanoindentation. Surface modulus increased to 8GPa and hardness of thin films increased from 100 to 400 MPa. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis and properties of novel triptycene‐based polyimides

Abstract: Two new triptycene-containing bis(ether amine)s, 1,4-bis(4-aminophenoxy)triptycene (4) and 1,4-bis(4-amino-2-trifluoromethylphenoxy)triptycene (6), were synthesized, respectively, from the nucleophilic chloro-displacement reactions of p-chloronitrobenzene and 2-chloro-5-nitrobenzotrifluoride with 1,4-dihydroxytriptycene in the presence of potassium carbonate, followed by palladium-catalyzed hydrazine reduction of the dinitro intermediates. The bis(ether amine)s were polymerized with six commercially available aromatic tetracarboxylic dianhydrides to obtain two series of novel triptycene-based polyimides 8a―f and 9a―f by using a conventional two-step synthetic method via thermal and chemical imidizations. All the resulting polyimides exhibited high enough molecular weights to permit the casting of flexible and strong films with good mechanical properties. Incorporation of trifluoromethyl groups in the polyimide backbones improves their solubility and decreases their dielectric constants. The fluorinated polyimides 9d and 9f derived from diamine 6 with 4,4'-oxydiphthalic anhydride and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), respectively, could afford almost colorless thin films.

Synthesis and structure‐activity relationship of several aromatic ketone‐based two‐photon initiators

Abstract: Several novel aromatic ketone-based two-photon ini- tiators containing triple bonds and dialkylamino groups were syn- thesized and the structure-activity relationships were evaluated. Branched alkyl chains were used at the terminal donor groups to improve the solubility in the multifunctional monomers. Because of the long conjugation length and good coplanarity, the eval- uated initiators showed large two-photon cross section values, while their fluorescence lifetimes and quantum yields strongly depend on the solvent polarity. All novel initiators exhibited high activity in terms of two-photon-induced microfabrication. This is especially true for fluorenone-based derivatives, which displayed much broader processing windows than well-known highly active initiators from the literature and commercially available initiators. While the new photoinitiators gave high reactivity in two-photon- induced photopolymerization at concentration as low as 0.1% wt, these compounds are surprisingly stable under one photon con- dition and nearly no photo initiation activity was found in classical photo DSC experiment. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3688-3699, 2011

Synthesis and characterization of polystyrene‐graphite nanocomposites via surface RAFT‐mediated miniemulsion polymerization

Abstract: Graphite oxide (GO) was prepared and immobilized with dodecyl isobutyric acid trithiocarbonate (DIBTC) reversible addition-fragmentation chain transfer (RAFT) agent. The hydroxyl groups of GO were attached to the DIBTC RAFT agent through an esterification process. The resultant modified GO was used for the preparation of polystyrene (PS)/graphite nanocomposites in miniemulsion polymerization. The RAFT- grafted GO (GO-DIBTC) at various loadings was dispersed in styrene monomer, and the resultant mixtures were sonicated in the presence of a surfactant (sodium dodecylbenzene sulfo- nate) and a hydrophobe (hexadecane) to form miniemulsions. The stable miniemulsions thus obtained were polymerized using azobisisobutyronitrile as the initiator to yield encapsu- lated PS-GO nanocomposites. The molar mass and polydisper- sity index of PS in the nanocomposites depended on the amount of RAFT-grafted GO in the system, in accordance with the features of the RAFT polymerization method. The PS-GO nanocomposites were of exfoliated morphology, as confirmed by X-ray diffraction and transmission electron microscopy measurements. The thermal stability and mechanical proper- ties of the PS-GO nanocomposites were better than those of the neat PS polymer. Furthermore, the mechanical properties were dependent on the modified GO content (i.e., the amount of RAFT-grafted GO). V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1621-1632, 2011

Growing poly(N-vinylcarbazole) from the surface of graphene oxide via RAFT polymerization

Abstract: A new approach on usage of S-1-dodecyl-S'-(α,α'-dimethyl-α"-acetic acid)trithiocarbonate (DDAT)-covalently functionalized graphene oxide (GO) as reversible addition fragmentation chain transfer (RAFT) agent for growing of poly(N-vinylcarbazole) (PVK) directly from the surface of GO was described. The PVK polymer covalently grafted onto GO has M n of 8.05 x 10 3 , and a polydispersity of 1.43. The resulting material PVK-GO shows a good solubility in organic solvents when compared to GO, and a significant energy bandgap of ~2.49 eV. Bistable electrical switching and nonvolatile rewritable memory effect, with a turn-on voltage of about -1.7 V and an ON/OFF state current ratio in excess of 10 3 , are demonstrated in the AI/PVK-GO/ITO structure.

Functionalization of graphene oxide towards thermo‐sensitive nanocomposites via moderate in situ SET‐LRP

Abstract: A mild and efficient strategy is presented for growing thermo-sensitive polymers directly from the surface of exfoliated graphene oxide (GO). This method involves the covalent attachment of Br-containing initiating groups onto the surface of GO sheets followed by in situ growing poly[poly(ethylene glycol) ethyl ether methacrylate] (PPEGEEMA) via single-electron-transfer living radical polymerization (SET-LRP). Considering the lack of reactive functional groups on the surface of GO, exfoliated GO sheets were subjected to an epoxide ring opening reaction with tris(hydroxymethyl) aminomethane (TRIS) at room temperature. The initiating groups were grafted onto TRIS-GO sheets by treating hydroxyls with 2-bromo-2-methylpropionyl bromide at room temperature. PPEGEEMA chains were synthesized by in situ SET-LRP using CuBr/Me6TREN as catalytic system at 40 C in H2O/THF. The resulting materials were characterized using a range of testing techniques and it was proved that polymer chains were successfully introduced to the surface of GO sheets. After grafting with PPEGEEMA, the modified GO sheets still maintained the separated single layers and the dispersibility was significantly improved. This TRIS-GO-PPEGEEMA hybrid material shows reversible self-assembly and deassembly in water by switching temperature at about 34 C. Such smart graphene-based materials promise important potential applications in thermally responsive nanodevices and microfluidic switches. VC 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4747–4755, 2011

A Green Approach Toward Oleic- and Undecylenic Acid-Derived Polyurethanes

Abstract: Naturally occurring oleic and undecylenic acids were used as raw materials for the synthesis of novel polyur- ethanes (PUs). The application of environmentally friendly thiol-ene additions to 10-undecenoate and oleate derivatives was studied with the goal of obtaining renewable diols. The resulting monomers were then polymerized with 4,4 0 -methyle- nebis (phenylisocyanate), in N,N-dimethylformamide solution using tin (II) 2-ethylhexanoate as catalyst, to produce the corre- sponding thermoplastic PUs (TPUs). Also, ultrasound irradia- tion has been tested to improve the synthesis of PU. Under these conditions, TPUs were obtained in high yields (80-99%) with weight-average molecular weights in the 36-83 kDa range. The chemical structures of PUs were assessed by FTIR and NMR spectroscopy. The thermal and mechanical properties of the syn- thesized TPUs have been studied and they showed a clear de- pendence on the structure of the parent diol. MTT test was carried out to asses the potential cytotoxicity of the prepared PUs, indicat- ing no cytotoxic response. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2407-2416, 2011

Poly(L‐glutamic acid) grafted with oligo(2‐(2‐(2‐methoxyethoxy)ethoxy)ethyl methacrylate): Thermal phase transition, secondary structure, and self‐assembly

Abstract: Thermoresponsive and pH-responsive graft copolymers, poly(L-glutamate)-g-oligo(2-(2-(2-methoxyethoxy) ethoxy) ethyl methacrylate) and poly(L-glutamic acid-co-(L-glutamate-g-oligo(2-(2-(2-methoxyethoxy) ethoxy) ethyl methacrylate))), were synthesized by ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) monomers and subsequent atom transfer radical polymerization of 2-(2-(2-methoxyethoxy) ethoxy) ethyl methacrylate. The thermoresponsiveness of graft copolymers could be tuned by the molecular weight of oligo(2-(2-(2-methoxyethoxy) ethoxy) ethyl methacrylate) (OMEO(3)MA), composition of poly(L-glutamic acid) (PLGA) backbone and pH of the aqueous solution. The alpha-helical contents of graft copolymers could be influenced by OMEO(3)MA length and pH of the aqueous solution. In addition, the graft copolymers exhibited tunable self-assembly behavior. The hydrodynamic radius (R(h)) and critical micellization concentration values of micelles were relevant to the length of OMEO(3)MA and the composition of biodegradable PLGA backbone. The R(h) could also be adjusted by the temperature and pH values. Lastly, in vitro methyl thiazolyl tetrazolium (MTT) assay revealed that the graft copolymers were biocompatible to HeLa cells. Therefore, with good biocompatibility, well-defined secondary structure, and mono-, dual-responsiveness, these graft copolymers are promising stimuli-responsive materials for biomedical applications. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2665-2676, 2011

Disproportionating versus nondisproportionating solvent effect in the SET‐LRP of methyl acrylate during catalysis with nonactivated and activated cu(0) wire

Abstract: The disproportionating solvent effect on the kinetics of single electron transfer living radical polymerization (SET-LRP) during catalysis with nonactivated Cu(0) wire coated with Cu2O and activated Cu(0) wire free of Cu2O was studied. In solvents such as dimethyl sulfoxide, MeOH and ethylene carbonate that in conjunction with Me6-TREN promote extensitve disproportionation of Cu(I)X, faster polymerizations were achieved upon switching from nonactivated Cu(0) wire to activated Cu(0) wire. The results showed that the substantial rate enhancement was accompanied with excellent control of molecular weight evolution and distribution, and high fidelity of chain-end functionality. This can be attributed to a more effective equilibrium between activation and deactivation in the presence of Cu(0) free of Cu2O. In nondisproportionating solvents, the kinetics of SET-LRP of methyl acrylate catalyzed by activated Cu(0) wire resembled that of the polymerizations catalyzed by nonactivated wire. This is the result of a competing effect between rapid activation and insufficient disproportionation. The absence of disproportionation effectively leads to the lack of first order kinetics, broad molecular weight distribution, significant loss of bromide chain-end functionality, and therefore, the absence of a living polymerization. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Nonlinear optical side-chain polymers post-functionalized with high-β chromophores exhibiting large electro-optic property

Abstract: Electro-optic side-chain polymers have been synthesized by the post-functionalization of methacrylate isocyanate polymers with novel phenyl vinylene thiophene vinylene bridge (FTC) nonlinear optical chromophores. For this application, FTC-based chromophores were modified in their electronic donor structure, exhibiting much larger molecular hyperpolarizabilities compared with the benchmark FTC. Of these new chromophores, absorption spectra, hyper-Rayleigh scattering experiment, and thermal analysis were carried out to confirm availability as effective nonlinear optical units for electro-optic side-chain polymers. The electro-optic coefficients (r33) of obtained polymers were investigated in the process of in situ poling by monitoring the temperature, current flow, poling field, and electro-optic signal. Compared with the nonsubstituted analogue, benxyloxy modified FTC chromophore significantly achieved higher nonlinear optical property, exhibiting molecular hyperpolarizability at 1.9 μm of 4600 × 10−30 esu and an r33 value of 150 pm/V at the wavelength of 1.31 μm. Synthesized electro-optic polymers showed high glass transition temperature (Tg), so that the temporal stability examination exhibited >78% of the electro-optic intensity remaining at 85 °C over 500 h. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Tuning the size of supramolecular single‐chain polymer nanoparticles

Abstract: In this article we further investigate our recently devised method for folding polymer chains into nanoparticles using intramolecular, supramolecular interactions. Specifically, we show a direct relationship between molecular weight of the parent chain and size of the folded nanoparticle. This is investigated both analytically via the separation and subsequent characterization of a polydisperse nanoparticle sample into high and low molecular weight fractions, and by examining a family of poly(norbornenes) deliberately prepared with varying molecular weights. With these polymer nanoparticles in hand their assembly on surfaces is studied where larger structures are formed as a result of the interplay between the movement of the nanoparticles on the surface and the evaporation of solvent.