Showing papers in "Journal of Polymer Science Part A in 2007"

A structural definition of polymer brushes

Abstract: In this article, we consolidate several literature re- ports in an attempt to provide a structural definition of a polymer brush as a tethered polymer layer with a high grafting density of poly- mer chains. We will try to distin- guish a brush from grafted polymer layers and coated layers and provide a reasonable approach to the descrip- tion of the brush regime with a single parameter S—reduced grafting den- sity. Furthermore, we will attempt to describe the relevance of this description to applications. This arti- cle is timely given the continuing interest relating to brushes on flat substrates, nanoparticles, and the walls of micro-channels. V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3505-3512, 2007

Recent advances in the synthesis of well-defined glycopolymers

Abstract: Glycopolymers are receiving increasing interest due to their application in areas, such as glycomics, medicine, biotechnology, sensors, and separation science Consequently, new methods for their synthesis are constantly being developed, with an increasing emphasis on the preparation of well-defined polymers and on the production of complex macromolecular architectures such as stars This review covers recent developments in the synthesis of glycopolymers, with a particular emphasis on (i) the use of controlled radical polymerization to prepare well-defined glycopolymers from unprotected monomers and (ii) postpolymerization modification strategies using reactive polymer precursors (including "click" reactions) Recent work on the production of glycosylated polypeptides, which are under investigation as mimics of naturally occurring glycoproteins, is also included The authors offer some suggestions as to future developments and remaining challenges in this topical area of polymer chemistry (C) 2007 Wiley Periodicals, Inc

Engineering functional materials by halogen bonding

Abstract: Engineering functional materials endowed with unprecedented properties require the exploitation of new intermolecular interactions, which can determine the characteristics of the bulk materials. The great potential of Halogen Bonding (XB), namely any noncovalent interaction involving halogens as electron acceptors, in the design of new and high-value functional materials is now emerging clearly. This Highlight will give a detailed overview on the energetic and geometric features of XB, showing how some of them are quite constant in most of the formed supramolecular complexes (e.g., the angle formed by the covalent and the noncovalent bonds around the halogen atom), while some others depend strictly on the nature of the interacting partners. Then, several specific examples of halogen-bonded supramolecular architectures, whose structural aspects as well as applications in fields as diverse as enantiomers' separation, crystal engineering, liquid crystals, natural, and synthetic receptors, will be fully described. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: PolymChem 45: 1–15, 2007

Perfluorocarbons: Life sciences and biomedical uses Dedicated to the memory of Professor Guy Ourisson, a true RENAISSANCE man.

Abstract: Perfluorocarbons are primarily characterized by outstanding chemical and biological inertness, and intense hydrophobic and lipophobic effects. The latter effects provide a powerful noncovalent, labile binding interaction that can promote selective self-assembly. Perfluoro compounds do not mimic nature, yet they can offer abiotic building blocks for the de novo design of functional biopolymers and alternative solutions to physiologically vital issues. They offer new tags useful for molecular recognition, selective sorting, and templated binding (e.g., selective peptide and nucleic acid pairing). They also stabilize membranes and provide micro-and nanocompartmented fluorous environments. Perfluorocarbons provide inert, apolar carrier fluids for lab-on-a-chip experiments and assays using microfluidic technologies. Low water solubility, combined with high vapor pressure, allows stabilization of injectable microbubbles that serve as contrast agents for diagnostic ultrasound imaging. High gas solubilities are the basis for an abiotic means for intravascular oxygen delivery. Other biomedical applications of fluorocarbons include lung surfactant replacement and ophthalmologic aids. Diverse colloids with fluorocarbon phases and/or shells are being investigated for molecular imaging using ultrasound or magnetic resonance, and for targeted drug delivery. Highly fluorinated polymers provide a range of inert materials (e.g., fluorosilicons, expanded polytetrafluoroethylene) for contact lenses, reconstructive surgery (e.g., vascular grafts), and other devices.

Temperature-induced spontaneous sol–gel transitions of poly(D,L-lactic acid-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(D,L-lactic acid-co-glycolic acid) triblock copolymers and their end-capped derivatives in water

Abstract: The spontaneous hydrogel formation of a sort of biocompatible and biodegradable amphiphilic block copolymer in water was observed, and the underlying gelling mechanism was assumed. A series of ABA-type triblock copolymers [poly(D,L-lactic acid-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(D,L-lactic acid-co-glycolic acid)] and different derivatives end-capped by small alkyl groups were synthesized, and the aqueous phase behaviors of these samples were studied. The virgin triblock copolymers and most of the derivatives exhibited a temperature-dependent reversible sol-gel transition in water. Both the poly(D,L-lactic acid-co-glycolic acid) length and end group were found to significantly tune the gel windows in the phase diagrams, but with different behaviors. The critical micelle concentrations were much lower than the associated critical gel concentrations, and an intact micellar structure remained after gelation. A combination of various measurement techniques confirmed that the sol-gel transition with an increase in the temperature was induced not simply via the self-assembly of amphiphilic polymer chains but also via the further hydrophobic aggregation of micelles resulting in a micelle network due to a large-scale self-assembly. The coarsening of the micelle network was further suggested to account for the transition from a transparent gel to an opaque gel.

A density functional theory computational study of the role of ligand on the stability of CuI and CuII species associated with ATRP and SET‐LRP

Abstract: Atom transfer radical polymerization (ATRP) and single electron-transfer living radical polymerization (SET-LRP) both utilize copper complexes of various oxidation states with N-ligands to perform their respective activation and deactivation steps. Herein, we utilize DFT (B3YLP) methods to determine the preferred ligand-binding geometries for Cu/N-ligand complexes related to ATRP and SET-LRP. We find that those ligands capable of achieving tetrahedral complexes with CuI and trigonal bipyramidal with axial halide complexes with [CuIIX]+ have higher energies of stabilization. We were able to correlate calculated preferential stabilization of [CuIIX]+ with those ligands that perform best in SET-LRP. A crude calculation of energy of disproportionation revealed that the same preferential binding of [CuIIX]+ results in increased propensity for disproportionation. Finally, by examining the relative energies of the basic steps of ATRP and SET-LRP, we were able to rationalize the transition from the ATRP mechanism to the SET-LRP mechanism as we transition from typical nonpolar ATRP solvents to polar SET-LRP solvents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4950–4964, 2007

Synthesis of perfectly bifunctional polyacrylates by single-electron-transfer living radical polymerization

Abstract: Poly(methyl acrylate)s, poly(ethyl acrylate)s, and poly(butyl acrylate)s with α,ω-di(bromo) chain ends and Mn from 8500 to 35,000 were synthesized by single-electron-transfer living radical polymerization (SET-LRP). The analysis of their chain ends by a combination of 1H and 2D-NMR, GPC, MALDI-TOF MS, chain end functionalization, chain extension, and halogen exchange experiments demonstrated the synthesis of perfectly bifunctional polyacrylates by SET-LRP. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4684–4695, 2007

Chemical surface modification of poly(ethylene terephthalate) fibers by aminolysis and grafting of carbohydrates

Abstract: PET is a semicrystalline thermoplastic polyester used in many fields. For a variety of applications, however, it is necessary to impart desired properties by introducing specific functional groups on the surface. Aminolysis of PET fibers with diamines (1,2-diaminoethane, 1,6-diaminohexane, 3,6-dioxa-1,8-diaminooctane, and 4,9-dioxa-1,12-diaminododecane) gives amino functional groups on the surface. The effects of temperature, reaction time, diamine concentration, and solvent employed for the grafting were studied. The graft yield was observed to increase with temperature, reaction time, and diamine concentration. Aminolysis affects greatly the geometry and surface morphology of PET fibers as observed by scanning electronic microscopy and atomic force microscopy in tapping mode. A decrease of fibers diameter and an increase of surface heterogeneity and roughness due to chemical degradation is observed. Amino groups on the surface were used to prepare glycosylated fibers by reductive amination or amidation with different carbohydrates as maltose, maltotriose, and maltohexaose. The study reveals that the yield is dependent on the initial amino groups' surface concentration and the molar mass of the carbohydrate. These surfaces could benefit to a wide range of applications in the biomedical field. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2172–2183, 2007

Thermally curable benzoxazine monomer with a photodimerizable coumarin group

Abstract: A new monomer, 4-methyl-9-p-tolyl-9,10-dihydrochromeno[8,7-e][1,3]oxazin-2(8H)-one, possessing both benzoxazine and coumarin rings in its structure was synthesized by the reaction of 4-methyl-7-hydroxycoumarin, paraformaldehyde, and p-toluidine in methanol at 40 °C and characterized with spectral analysis. Upon photolysis around 300 nm, this monomer underwent dimerization via the [2πs+2πs] cycloaddition reaction. Photodimerization reactions were investigated with UV and 1H NMR spectroscopy measurements. The thermal ring-opening reaction of the benzoxazine ring was demonstrated with differential scanning calorimetry measurements. The thermal behavior of the cured product was also investigated with thermogravimetric analysis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1670–1676, 2007

Segmented sulfonated poly(arylene ether sulfone)-b-polyimide copolymers for proton exchange membrane fuel cells. I. Copolymer synthesis and fundamental properties

Abstract: Segmented disulfonated poly(arylene ether sulfone)-b-polyimide copolymers based on hydrophilic and hydrophobic oligomers were synthesized and evaluated for use as proton exchange membranes (PEMs). Amine terminated sulfonated poly (arylene ether sulfone) hydrophilic oligomers and anhydride terminated naphthalene based polyimide hydrophobic oligomers were synthesized via step growth polymerization including high temperature one-pot imidization. Synthesis of the multiblock copolymers was achieved by an imidization coupling reaction of hydrophilic and hydrophobic oligomers oligomers in a m-cresol/NMP mixed solvent system, producing high molecular weight tough and ductile membranes. Proton conductivities and water uptake increased with increasing ion exchange capacities (IECs) of the copolymers as expected. The morphologies of the multiblock copolymers were investigated by tapping mode atomic force microscopy (TM-AFM) and their measurements revealed that the multiblock copolymers had well-defined nano-phase separated morphologies which were clearly a function of block lengths. Hydrolytic stability test at 80 °C water for 1000 h showed that multiblock copolymer membranes retained intrinsic viscosities of about 80% of the original values and maintained flexibility which was much improved over polyimide random copolymers. The synthesis and fundamental properties of the multiblock copolymers are reported here and the systematic fuel cell properties will be provided in a separate article. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4879–4890, 2007

Synthesis and biological application of glycopolymers

Abstract: Saccharides on the cell surfaces participate in a number of biochemical phenomena via the protein–saccharide interaction. Synthetic glycopolymers mimic the function of the cell-surface saccharides and efficiently interact with proteins, cells, and pathogens based on the multivalent effect. Since the biological functions of saccharides are paid much attention, the glycopolymers are being increasingly explored as biomaterials for medicinal application and tissue engineering. This review presents a practical approach of glycopolymers. The glycopolymers were prepared by the facile syntheses of poly(vinyl saccharide)s and the physical and biological properties were introduced. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5031–5036, 2007

Preparation, Tg improvement, and thermal stability enhancement mechanism of soluble poly(methyl methacrylate) nanocomposites by incorporating octavinyl polyhedral oligomeric silsesquioxanes

Abstract: The soluble poly(methyl methacrylate-co-octavinyl-polyhedral oligomeric silsesquioxane) (PMMA–POSS) hybrid nanocomposites with improved Tg and high thermal stability were synthesized by common free radical polymerization and characterized using FTIR, high-resolution 1H NMR, 29Si NMR, GPC, DSC, and TGA. The POSS contents in the nanocomposites were determined based on FTIR spectrum, revealing that it can be effectively adjusted by varying the feed ratio of POSS in the hybrid composites. On the basis of the 1H NMR analysis, the number of the reacted vinyl groups on each POSS molecules was determined to be about 6–8. The DSC and TGA measurements indicated that the hybrid nanocomposites had higher Tg and better thermal properties than the pure PMMA homopolymer. The Tg increase mechanism was investigated using FTIR, displaying that the dipole–dipole interaction between PMMA and POSS also plays very important role to the Tg improvement besides the molecular motion hindrance from the hybrid structure. The thermal stability enhances with increase of POSS content, which is mainly attributed to the incorporation of nanoscale inorganic POSS uniformly dispersed at molecular level. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5308–5317, 2007

Modular synthesis of ABC type block copolymers by “click” chemistry

Abstract: Heterotelechelic polystyrene (PS), poly(tert-butyl acrylate) (PtBA), and poly (methyl acrylate) (PMA), containing both azide and triisopropylsilyl (TIPS) protected acetylene end groups, were prepared in good control (Mw/Mn � 1.24) by atom transfer radical polymerization (ATRP). The end groups were independently applied in two suc- cessive ''click'' reactions, that is: first the azide termini were functionalized and, after deprotection, the acetylene moieties were utilized for a second conjugation step. As a proof of concept, PS was consecutively functionalized with propargyl alcohol and azido- acetic acid, as confirmed by MALDI-ToF MS. In addition, the same methodology was employed to modularly build up an ABC type triblock terpolymer. Size exclusion chro- matography measurements demonstrated first coupling of PtBA to PS and, after the deprotection of the acetylene functionality on PS, connection of PMA, yielding a PMA-b- PS-b-PtBA triblock terpolymer. The reactions were driven to completion using a slight excess of azide functionalized polymers. Reduction of the residual azide groups into amines allowed easy removal of this excess of polymer by column chromatography.

Kinetic simulation of single electron transfer–living radical polymerization of methyl acrylate at 25 °C

Abstract: A mechanistic comparison of the ATRP and SET-LRP is presented. Subsequently, simulation of kinetic experiments demonstrated that, in the heterolytic outer-sphere single-electron transfer process responsible for the SET-LRP, the activation of the initiator and of the propagating dormant species is faster than of the homolytic inner-sphere electron-transfer process responsible for ATRP. In addition, simulation experiments suggested that in both polymerizations the rate of deactivation is similar. In SET-LRP, the Cu(II)X2/L deactivator is created by the disproportionation of Cu(I)X/L inactive species, while in ATRP its concentration is mediated by the bimolecular termination. The combination of higher rate of activation with the creation of deactivator via disproportionation provides, via SET-LRP, an ultrafast synthesis of polymers with very narrow molecular weight distribution at room temperature. SET-LRP is mediated by a catalytic amount of Cu(0), and under suitable conditions, bimolecular termination is virtually absent. Kinetic and simulation experiments have also demonstrated that the amount of water available in commercial solvents and monomers is sufficient to induce the disproportionation of Cu(I)X/L into Cu(0) and Cu(II)X2/L and, subsequently, to change the polymerization mechanism from ATRP to SET-LRP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1835–1847, 2007.

Role of Architecture and Molecular Weight in the Formation of Tailor-Made Ultrathin Multilayers Using Dendritic Macromolecules and Click Chemistry

Abstract: The high efficiency and mild reaction conditions associated with the Cu(I) catalyzed cycloaddition of azides and alkynes were exploited for the covalent layer-by-layer synthesis of dendritic thin films on silicon wafers. The preparation of azide and alkyne-terminated dendrimers based on bisMPA was accomplished by a divergent strategy; combinations of these monodisperse building blocks from the 2nd to the 5th generation were used for construction of the thin films. The layer-by-layer self assembly process proceeds under ambient conditions and was monitored by ellipsometry, XPS, and ATR-IR, which showed extremely regular growth of the dendritic thin films. Film thickness could be accurately controlled by both the size/generation number of the dendrimers as well as the number of layers. In comparison with linear analogues, the growth of the dendritic films was significantly more controlled and defect-free with each layer being thinner than the corresponding films prepared from the isomeric linear polymers, demonstrating the well-defined, three-dimensional nature of the dendritic architecture.

High‐molecular‐weight AB‐type benzoxazines as new precursors for high‐performance thermosets

Abstract: Novel high-molecular-weight polybenzoxazine precursors, namely AB-type benzoxazine precursors, were synthesized from aminophenols and formaldehyde. Both 1H NMR and IR confirmed the structure of the precursors, indicating the presence of a cyclic benzoxazine structure in the backbone of the precursors. The weight-average molecular weight was estimated by size exclusion chromatography to be to in the range of 1300–4500. The precursors gave self-standing thin films when their solutions were cast in dioxane over glass plates and dried, and upon a gradual thermal cure up to 250 °C, they afforded polybenzoxazine films. The viscoelastic analyses showed that the glass transition temperatures of the polybenzoxazine films obtained from these novel precursors were as high as 260–300 °C. Thermogravimetric analysis results indicated that the onset of decomposition and the char yield of the thermosets derived from these AB-type precursors were higher than those of traditional polybenzoxazine. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1878–1888, 2007.

Doping phosphoric acid in polybenzimidazole membranes for high temperature proton exchange membrane fuel cells

Abstract: Polybenzimidazole (PBI) membranes were doped in phosphoric acid solutions of different concentrations at room temperature. The doping chemistry was studied using the Scatchard method. The energy distribution of the acid complexation in polymer membranes is heterogeneous, that is, there are two different types of sites in PBI for the acid doping. The protonation constants of PBI by phosphoric acid are found to be 12.7 L mol -1 (K 1 ) for acid complexing sites with higher affinity, and 0.19 L mol -1 (K 2 ) for the sites with lower affinity. The dissociation constants for the complexing acid onto these two types of PBI sites are found to be 5.4 X 10 -4 and 3.6 X 10 -2 , respectively, that is, about 10 times smaller than that of aqueous phosphoric acid in the first case but 5 times higher in the second. The proton conducting mechanism is also discussed.

Synthesis of core-shell silver–polyaniline nanocomposites by gamma radiolysis method

Abstract: Core-shell silver (Ag)–polyaniline (PAni) nanocomposites have been synthesized by the in-situ gamma radiation-induced chemical polymerization method. Aqueous solution of aniline, a free-radical oxidant, and/or silver metal salt were irradiated by γ-rays. Reduction of the silver salt in aqueous aniline leads to the formation of silver nanoparticles which in turn catalyze oxidation of aniline to polyaniline. The resultant Ag-PAni nanocomposites were characterized by using different spectroscopy analyses like X-ray photoelectron, UV–visible, and infrared spectroscopy. The optical absorption bands revealed that the bands at about 400 nm are due to the presence of nanosilver and the blue-shifted peak at ∼ 555 nm is due to the presence of metallic silver within the PAni matrix. X-ray diffraction pattern clearly indicates the broad amorphous polymer and the sharp metal peaks. Scanning electron microscopy and transmission electron microscopy of the nanocomposite showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the composites have a higher degradation temperature than polyaniline alone. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5741–5747, 2007

Preparation of poly(styrene-co-acrylonitrile)-grafted multiwalled carbon nanotubes via surface-initiated atom transfer radical polymerization

Abstract: The in situ grafting-from approach via atom transfer radical polymerization was successfully applied to polystyrene, poly(styrene-co-acrylonitrile), and polyacrylonitrile grafted onto the convex surfaces of multiwalled carbon nanotubes (MWCNTs) with (2-hydroxyethyl 2-bromoisobutyrate) as an initiator. Thermogravimetric analysis showed that effective functionalization was achieved with the grafting approach. The grafted polymers on the MWCNT surface were characterized and confirmed with Fourier transform infrared spectroscopy and nuclear magnetic resonance. Raman and near-infrared spectroscopy revealed that the grafting of polystyrene, poly(styrene-co-acrylonitrile), and polyacrylonitrile slightly affected the sidewall structures. Field emission scanning electron microscopy showed that the carbon nanotube surface became rough because of the grafting of the polymers. Differential scanning calorimetry results indicated that the polymers grafted onto MWCNTs showed higher glass-transition temperatures. The polymer-grafted MWCNTs exhibited relatively good dispersibility in an organic solvent such as tetrahydrofuran.

A Diels‐Alder/retro Diels‐Alder strategy to synthesize polymers bearing maleimide side chains

Abstract: Polymers containing thiol-reactive maleimide groups on their side chains have been synthesized by utilization of a novel methacrylate monomer containing a masked maleimide. Diels-Alder reaction between furan and maleimide was adapted for the protection of the reactive maleimide double bond prior to polymerization. AIBN initiated free radical polymerization was utilized for synthesis of copolymers containing masked maleimide groups. No unmasking of the maleimide group was evident under the polymerization conditions. The maleimide groups in the side chain of the polymers were unmasked into their reactive form by utilization of retro Diels-Alder reaction. This cycloreversion was monitored by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and 1H and 13C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4545–4551, 2007

A comparative computational study of the homolytic and heterolytic bond dissociation energies involved in the activation step of ATRP and SET‐LRP of vinyl monomers

Abstract: A quantum-chemical calculation of the homolytic and heterolytic bond dissociation energies of the model compounds of the monomer and dimer is reported. These model compounds include the dormant chloride, bromide, and iodide species for representative activated and nonactivated monomers containing electron-withdrawing groups as well as for a nonactivated monomer containing an electron-donor group. Two examples of sulfonyl and N-halide initiators are also reported. The homolytic inner-sphere electron-transfer bond dissociation is known as atom transfer and is responsible for the activation step in ATRP. The heterolytic outer sphere single electron transfer bond dissociation is responsible for the activation step in single electron transfer mediated living radical polymerization (SET-LRP). The results of this study demonstrated much lower bond dissociation energies for the outer sphere single electron transfer processes. These results explain the higher rate constant of activation, the higher apparent rate constant of propagation, and the lower polymerization temperature for both activated and nonactivated monomers containing electron-withdrawing groups in SET-LRP.

Science and technology of perfluorocyclobutyl aryl ether polymers

Abstract: This article highlights the preparation of perfluorocyclobutyl (PFCB) aryl ether polymers for a multitude of commercial technologies that are of academic and commercial global interest. In this account, the synthesis of various aryl trifluorovinyl ether (TFVE) monomers tailored for specific applications is discussed. The preparation of PFCB aryl ether polymers and their properties is then presented. Topics of PFCB aryl ether polymers and their applications include photonics, polymer light emitting diodes (PLEDs), proton exchange membranes (PEMs) for fuel cells, atomic oxygen (AO) resistant coatings, and hybrid composites.

Well-controlled polymerization of 2-azidoethyl methacrylate at near room temperature and click functionalization

Abstract: A functional monomer with a pendant azide moiety, 2-azidoethyl methacrylate (AzMA), was polymerized via reversible addition-fragmentation chain transfer (RAFT) polymerization with excellent control over the molecular weight distribution (PDI = 1.05–1.15). The subsequent copper-catalyzed Huisgen 1,3-dipolar cycloadditions of phenyl acetylene with polyAzMA was achieved at room temperature with high conversion. The resulting functional polymer exhibited identical 1H NMR and IR spectra with the polymer of the same molecular structure but prepared by a prefunctionalization approach, confirming the retention of the azide side chains during the RAFT polymerization of AzMA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4300–4308, 2007

Thiourethane‐based thiol‐ene high Tg networks: Preparation, thermal, mechanical, and physical properties

Abstract: Thiourethane-based thiol-ene (TUTE) films were prepared from diisocyanates, tetrafunctional thiols and trienes. The incorporation of thiourethane linkages into the thiol-ene networks results in TUTE films with high glass transition temperatures. Increases of Tg were achieved by aging at room temperature and annealing the UV cured films at 85 °C. The aged/annealed film with thiol prepared from isophorone diisocyanate and cured with a 10,080-mJ/cm2 radiant exposure had the highest DMA-based glass transition temperature (108 °C) and a tan δ peak with a full width at half maximum (FWHM) of 22 °C, indicating a very uniform matrix structure. All of the initially prepared TUTE films exhibited good physical and mechanical properties based on pencil hardness, pendulum hardness, impact, and bending tests. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5103–5111, 2007

Thiol–norbornene materials: Approaches to develop high Tg thiol–ene polymers

Abstract: The ability to prepare high Tg low shrinkage thiol–ene materials is attractive for applications such as coatings and dental restoratives. However, thiol and nonacrylated vinyl materials typically consist of a flexible backbone, limiting the utility of these polymers. Hence, it is of importance to synthesize and investigate thiol and vinyl materials of varying backbone chemistry and stiffness. Here, we investigate the effect of backbone chemistry and functionality of norbornene resins on polymerization kinetics and glass transition temperature (Tg) for several thiol–norbornene materials. Results indicate that Tgs as high as 94 °C are achievable in thiol–norbornene resins of appropriately controlled chemistry. Furthermore, both the backbone chemistry and the norbornene moiety are important factors in the development of high Tg materials. In particular, as much as a 70 °C increase in Tg was observed in a norbornene–thiol specimen when compared with a sample prepared using allyl ether monomer of analogous backbone chemistry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5686–5696, 2007

Synthesis and characterization of highly refractive polyimides from 4,4′-thiobis[(p-phenylenesulfanyl)aniline] and various aromatic tetracarboxylic dianhydrides

Abstract: An aromatic sulfur-containing diamine 4,4′-thiobis[(p-phenylenesulfanyl) aniline] (3SDA) was synthesized and polymerized with a sulfur-containing dianhydride 4,4′-[p-thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) and three nonsulfur aromatic tetracarboxylic dianhydrides, respectively to afford four poly(amic acid)s (PAAs) with the inherent viscosities of 0.54–1.04 dL/g. Flexible and tough polyimide (PI) films obtained from the PAA precursors showed good thermal, mechanical, and optical properties. The glass transition temperatures (Tgs) of the PIs ranged from 179.1–227.2 °C determined by differential scanning calorimetry (DSC), and 173.8–227.3 °C by dynamic mechanical analysis (DMA), depending on the dianhydride used. The 10% weight loss temperatures were in the range of 500–536 °C, showing high intrinsic thermal-resistant characteristics of the PI films. The PI films also showed good optical transparency above 500 nm, which agreed well with the calculated absorption spectra using the time-dependent density functional theory. The average refractive indices (nav) measured at 632.8 nm were 1.7191–1.7482, and the in-plane/out-of-plane birefringences (Δn) were 0.0068–0.0123. The high refractive indices originate from the high sulfur contents, good molecular packing, and the absence of bulky structures. The relatively small birefringence mainly results from the flexible thioether linkages structures of the diamine. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5606–5617, 2007

Click chemistry in materials synthesis. III. Metal‐adhesive polymers from Cu(I)‐catalyzed azide–alkyne cycloaddition

Abstract: 1,2,3-Triazole-based polymers generated from the Cu(I)-catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007

Aging of a donor conjugated polymer: Photochemical studies of the degradation of poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene]

Abstract: This article is devoted to the study of the photoaging and thermal aging of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV; also called OC1C10-PPV) used in organic solar cells. Thin MDMO-PPV films (thickness 300 nm) in the presence of air or thermooxidized at 60°C. The modifications of the chemical structure of the matrix were analyzed with ultraviolet-visible and infrared spectroscopy. The oxidation products that formed were identified by postirradiation treatments, including chemical derivatization reactions. On the basis of the identification of the various products formed, a two-step radical mechanism is proposed to account for the modification of the chemical structure of the polymeric matrix. It involves first the oxidation of the ether substituent followed by the oxidation of the double bonds. These reactions are responsible for a loss of conjugation of MDMO-PPV, chain scissions, and a decrease in the visible absorbance, which are anticipated to drastically impair the photovoltaic properties of the material.

A tailor‐made polymethacrylate bearing a reactive diene in reversible diels–alder reaction

Abstract: A tailor-made polymethacrylate bearing a pendant furfuryl group was prepared by atom transfer radical polymerization (ATRP), an important method of recent advances in controlled radical polymerization. It was otherwise difficult to prepare via conventional radical polymerization, because of several side reactions involving the reactive diene functionality of the furfuryl group. Successful Diels–Alder (DA) chemistry was carried out using this reactive furfuryl group of the tailor-made polymer as diene and a bismaleimide as a dienophile. Interestingly, the resultant material was observed to be thermoreversible as evidenced by FT-IR and DSC studies. This example of application of a tailor-made polymer having controlled molecular architecture and with reactive diene functionality in DA chemistry will open new possibilities to prepare newer tailor-made reversible materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4441–4449, 2007

Fast degradable poly(L-lactide-co-ε-caprolactone) microspheres for tissue engineering: Synthesis, characterization, and degradation behavior

Abstract: Polymeric scaffolds play a crucial role in engineering process of new tissues and effect the cell growth and viability. PLCL copolymers are found to be very useful during cell growth due to their elastic behavior and mechanical strength. Thus, low molecular weight PLCL copolymers of various ratios viz. PLCL(90/10), PLCL(75/25), PLCL(50/50) and PCL were synthesized by ring opening polymerization using stannous octoate as a catalyst. Synthesized polymers were characterized by GPC, 1H-NMR, FTIR and XRD. The thermal properties of the copolymers were studied using TGA and DSC. Microspheres of about 100 μm diameter were prepared for different copolymers and their in vitro degradation behaviors were studied up to 108 days. It was observed that degradation of PLA content in polymer backbone occurs faster than PCL component which is also indicated by corresponding change in ratios of PLA/PCL, as determined by 1H-NMR. SEM images of microspheres depicted the surface morphology during degradation and suggested the faster degradation for PLCL (50:50). Copolymers of different thermal, mechanical properties and different degradation behaviors can be prepared by adjusting the composition of copolymers. Various synthesized polymers from this work have been tested in our laboratory as polymeric scaffold for soft tissue engineering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2755–2764, 2007