Main Chain (main + chain)

Distribution by Scientific Domains

Kinds of Main Chain

  • conjugated main chain
  • polymer main chain

  • Selected Abstracts

    Electroactive Polymer with Oligoanilines in the Main Chain: Synthesis, Characterization and Dielectric Properties

    Junfeng Zhang
    Abstract An electroactive polymer with well-defined oligoanilines in the main chain has been prepared by oxidative coupling polymerization. The detailed characteristics of the polymer were systematically studied by FT-IR, 1H NMR, GPC and XRD. Its electrochemical behavior was explored with UV-Vis spectra and cyclic voltammetry showing that its intrinsic electroactivity was maintained and exhibited three distinct reversible oxidative states. Its electrical conductivity is about 3.91,,10,4,S,,cm,1 in HCl-doped form at room temperature. Furthermore, the polymer displays a dielectric constant of 48.4 and 13.6 at 10 and 1,MHz, respectively, mainly attributed to the improvement in delocalized charge density and electrical conductivity of the polymer by introduction of the conjugated oligoaniline segments. [source]

    Electroactive Copolymers with Oligoanilines in the Main Chain via Oxidative Coupling Polymerization

    Danming Chao
    Abstract Summary: By oxidative coupling polymerization of the macromonomer of oligoaniline and p -phenylenediamine, we have prepared an electroactive copolymer, exhibiting an exciting molecular structure, and interesting spectroscopic and electrochemical properties. The polymerization characteristics and structure of the copolymer were systematically studied by gel permeation chromatography (GPC), Fourier-transform infrared (FTIR) spectroscopy, 1H NMR spectroscopy and X-ray powder diffraction (XRD). UV-vis spectra were used to monitor the chemical oxidation process of the reduced copolymer. The electrochemical activity of the copolymer was tested in 1.0 M H2SO4 aqueous solution. Three redox peaks were shown, which is different to that for polyaniline. The thermal properties of the copolymer were also evaluated, by thermogravimetric analysis (TGA); the electrical conductivity is about 5.53,,10,5 Scm,1 at room temperature, upon a preliminarily, proton-doped experiment. Synthesis of the copolymer. [source]

    Synthesis and Light-Emitting Properties of New Polyimides Containing Ethynylene Units in the Main Chain

    Jun Ho Chi
    Abstract Two new polyimides (ODA-PI and HDA-PI) having 1,4-phenylenediethynylene unit and octyloxy groups were synthesized. Judging from inherent viscosities of their precursor PAAs (1.42 and 1.62 dL,,g,1), the two PIs were very high in molecular weight. Casting and thermal imidization of PAAs results polyimides with good-quality films. They were stable up to 364,C and showed no crystallites. UV-vis and PL spectra in NMP solutions of both PIs showed maxima at 442 and 501 nm, respectively, while PL spectra in ,10 m thick films exhibited a maximum at 540 nm. CV indicates that two PIs were electrochemically active in redox region. The devices with construction of ITO/PEDOT/PIs/BAlq3/LiF/Al exhibited turn-on voltages of 6.5 V in ODA-PI and 7.5 V in HDA-PI and emitted a bright bluish-green light. ODA-PI and HDA-PI showed maximum luminescence of 256 and 316 cd,,cm,2, respectively, at the same voltage of 12 V. [source]

    Linear Azo Polymer Containing Conjugated 5,5,-Azodisalicylic Acid Segments in the Main Chain: Synthesis, Characterization, and Degradation

    Junying Lai
    Abstract Summary: Copolymers of poly(ethylene oxide) (PEO) and 5,5,-azodisalicylic acid (Olsalazine, OLZ) were synthesized and evaluated by hydrolysis and in-vitro biodegradation with azoreductase. It was found that changing the molecular weight of the PEO blocks affected the loading ratio of OLZ, and resulted in significant differences in the hydration and degradability of the copolymers. These novel azo-containing copolymers can be used in colon-specific drug delivery. Release of 5-ASA from OLZ and PEO-OLZ copolymers incubated with rat cecum content in the presence of benzyl viologen and , - D -glucose. [source]

    New , -Conjugated Polymers Containing 1,3,5-Triazine Units in the Main Chain: Synthesis and Optical and Electrochemical Properties of the Polymers,

    Shijie Ren
    Abstract Summary: Three new soluble , -conjugated polymers containing 1,3,5-triazine units in the main chain, Pa,Pc, were synthesized. The polymers showed optical properties in solution that were mainly dependant on the properties of the substituting R groups, on the triazine ring. Hence, Pa and Pb (R,=,H and OCH3, respectively) showed blue photoluminescent (PL) emission with high quantum yields (QY) even in polar solvents, whereas Pc (R,=,N,N -dimethylamino) gave green-blue PL emission with very low QY. The PL spectra of the polymers in solution were concentration and polarity dependent, which suggested the formation of an exciplex. The three new soluble , -conjugated polymers containing 1,3,5-triazine units in the main chain synthesized here. [source]

    The crystal structure of a xyloglucan-specific endo-,-1,4-glucanase from Geotrichum sp.

    FEBS JOURNAL, Issue 18 2009
    M128 xyloglucanase reveals a key amino acid residue for substrate specificity
    Geotrichum sp. M128 possesses two xyloglucan-specific glycoside hydrolases belonging to family 74, xyloglucan-specific endo-,-1,4-glucanase (XEG) and oligoxyloglucan reducing-end-specific cellobiohydrolase (OXG-RCBH). Despite their similar amino acid sequences (48% identity), their modes of action and substrate specificities are distinct. XEG catalyzes the hydrolysis of xyloglucan polysaccharides in endo mode, while OXG-RCBH acts on xyloglucan oligosaccharides at the reducing end in exo mode. Here, we determined the crystal structure of XEG at 2.5 resolution, and compared it to a previously determined structure of OXG-RCBH. For the most part, the amino acid residues that interact with substrate are conserved between the two enzymes. However, there are notable differences at subsite positions ,1 and +2. OXG-RCBH has a loop around the +2 site that blocks one end of the active site cleft, which accounts for its exo mode of action. In contrast, XEG lacks a corresponding loop at this site, thereby allowing binding to the middle of the main chain of the substrate. At the ,1 site in OXG-RCBH, Asn488 interacts with the xylose side chain of the substrate, whereas the ,1 site is occupied by Tyr457 in XEG. To confirm the contribution of this residue to substrate specificity, Tyr457 was substituted by Gly in XEG. The wild-type XEG cleaved the oligoxyloglucan at a specific site; the Y457G variant cleaved the same substrate, but at various sites. Together, the absence of a loop in the cleft and the presence of bulky Tyr457 determine the substrate specificity of XEG. [source]

    Hysteresis in Conjugated Polymer Thin Film Transistors Generated by Chain Relaxation

    Neng-Jye Yang
    Abstract The hysteresis phenomenon in a polymer thin film transistor (PTFT) with either poly(3-hexylthiophene), poly(3-dodecylthiophene), or poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] is investigated over a wide range of temperatures, and found to be generated by the delay in main chain ring distortion with an applied electric field. In the temperature range for side chain relaxation, main chain motion induced by side chain motion already starts such that polarization of the main chain by the applied electric field is permitted but in a limited extent and is not in phase with the variation in electric field. In the main chain relaxation temperature range, the extent of segmental motion increases, which leads to the main chain being more realignable by the applied electric field and thus a reduced hysteresis. After main chain relaxation is complete, the ring can distort more freely and chain segments are able to realign in phase with the applied electric field, which leads to a leveling off of the hysteresis. This investigation shows for first time that the chain relaxation in conjugated polymers is the origin of the hysteresis in PTFT devices. [source]

    Red-Emitting Polyfluorenes Grafted with Quinoline-Based Iridium Complex: "Simple Polymeric Chain, Unexpected High Efficiency"

    Zhihua Ma
    Abstract A series of red-light emitting electrophosphorescent polyfluorenes (PFs) with varying content of a quinoline-based iridium complex, (PPQ)2Ir(acac) (bis(2,4-diphenylquinolyl-N,C2,) iridium(acetylacetonate)), in the side chain are synthesized by Suzuki polycondensation. Because of the efficient Frster energy transfer from the PF main chain to (PPQ)2Ir(acac) and direct charge trapping on the complex, the electroluminescent emission from PF is nearly completely quenched, even though the amount of iridium complex incorporated into the polymers is as low as 1,mol %. Based on a single-layer device configuration, a luminous efficiency of up to 5.0,cd A,1 with a luminance of 2000,cd m,2 and Commission Internationale de L'Eclairage coordinates of (0.63, 0.35) (x, y) is realized, which is far superior to that of previously reported red-light emitting PFs containing benzothiazole- and isoquinoline-based iridium complexes. This result is beyond expectations, especially when considering that the simple polymeric chain involved has no additional charge-transporting moieties. Noticeably, the device efficiency remains as high as 4.2,cd A,1 with a luminance of 4000,cd m,2 even at current densities of 100,mA cm,2. Further optimization of the device configuration by incorporating an additional electron-injection layer leads to improved efficiencies of 8.3 and 7.5,cd A,1 at luminances of 100 and 1000,cd m,2, respectively. This state-of-the-art performance indicates that covalently attaching quinoline-based iridium complexes to a PF backbone is a simple and effective strategy to develop high-efficiency red-light emitting electrophosphorescent polymers. [source]

    Electron-Rich Alcohol-Soluble Neutral Conjugated Polymers as Highly Efficient Electron-Injecting Materials for Polymer Light-Emitting Diodes

    Fei Huang
    Abstract We report the design and synthesis of three alcohol-soluble neutral conjugated polymers, poly[9,9-bis(2-(2-(2-diethanolaminoethoxy) ethoxy)ethyl)fluorene] (PF-OH), poly[9,9-bis(2-(2-(2-diethanol-aminoethoxy)ethoxy)ethyl)fluorene- alt -4,4,-phenylether] (PFPE-OH) and poly[9,9-bis(2-(2-(2-diethanolaminoethoxy) ethoxy)ethyl)fluorene- alt -benzothiadizole] (PFBT-OH) with different conjugation length and electron affinity as highly efficient electron injecting and transporting materials for polymer light-emitting diodes (PLEDs). The unique solubility of these polymers in polar solvents renders them as good candidates for multilayer solution processed PLEDs. Both the fluorescent and phosphorescent PLEDs based on these polymers as electron injecting/transporting layer (ETL) were fabricated. It is interesting to find that electron-deficient polymer (PFBT-OH) shows very poor electron-injecting ability compared to polymers with electron-rich main chain (PF-OH and PFPE-OH). This phenomenon is quite different from that obtained from conventional electron-injecting materials. Moreover, when these polymers were used in the phosphorescent PLEDs, the performance of the devices is highly dependent on the processing conditions of these polymers. The devices with ETL processed from water/methanol mixed solvent showed much better device performance than the devices processed with methanol as solvent. It was found that the erosion of the phosphorescent emission layer could be greatly suppressed by using water/methanol mixed solvent for processing the polymer ETL. The electronic properties of the ETL could also be influenced by the processing conditions. This offers a new avenue to improve the performance of phosphorescent PLEDs through manipulating the processing conditions of these conjugated polymer ETLs. [source]

    Cationic Conjugated Polyelectrolytes with Molecular Spacers for Efficient Fluorescence Energy Transfer to Dye-Labeled DNA,

    Y. Woo
    Abstract Two water-soluble conjugated polyelectrolytes, poly(9,9,-bis(6- N,N,N -trimethylammoniumhexyl)fluorene- alt -1,4-(2,5-bis(6- N,N,N -trimethylammoniumhexyloxy))phenylene) tetrabromide (P1i) and poly((10,10,-bis(6- N,N,N -trimethylammoniumhexyl)-10H-spiro(anthracene-9,9,-fluorene))- alt -1,4-(2,5-bis(6- N,N,N -trimethylammoniumhexyloxy))phenylene) tetrabromide (P2i) are synthesized, characterized, and used in fluorescence resonance energy transfer (FRET) experiments with fluorescein-labeled single-stranded DNA (ssDNA-Fl). P1i and P2i have nearly identical ,-conjugated backbones, as determined by cyclic voltammetry and UV-vis spectroscopy. The main structural difference is the presence of an anthracenyl substituent, orthogonal to the main chain in each of the P2i repeat units, which increases the average interchain separation in aggregated phases. It is possible to observe emission from ssDNA-Fl via FRET upon excitation of P2i. Fluorescein is not emissive within the ssDNA-Fl/P1i electrostatic complex, suggesting Fl emission quenching through photoinduced charge transfer (PCT). We propose that the presence of the anthracenyl "molecular bumper" in P2i increases the distance between optical partners, which decreases PCT more acutely relative to FRET. [source]

    Influence of Side-Chain Structure and Irradiation Condition on Photoalignment of Ladder-Like Polysiloxane Films,

    H.-W. Gu
    Abstract In this paper we consider the photo-induced aligning capability of various ladder-like polysiloxane-based photoalignment films,which could be used in liquid-crystal displays,bearing different photoreactive side chains, i.e., laterally grafted cinnamate/azobenzene-based dual photoreactive side chains with a short or longer spacer, and terminally fixed coumarin-containing side chains. Results from polarized optical microscopy (POM), Fourier-transform infrared (FTIR) spectroscopy, surface-enhanced Raman scattering (SERS), atomic force microscopy (AFM), etc., are integrated to elucidate the influence of side-chain structure and the irradiation conditions on the photoalignment of ladder-like polysiloxane films. It is demonstrated that the film containing the dual photoreactive group with a longer spacer exhibits better alignment properties. Reasonably, the concerted photoreactions of the dual photoreactive group and the longer spacer are beneficial to the cooperative motion of chromophores at the "domain level", resulting in improved alignment facility and stability. The complicated effects of irradiation conditions and moderate annealing are also discussed. High-quality alignment of the polysilsesquioxane (LPS)-based photoalignment film LPS-CA11 with a longer spacer between the LPS main chain and cinnamoyl/azobenzene side chains can be achieved only within an optimal range of exposure (5,8,J,cm,2), while the pretilt angles can be adjusted in the range 0.5,7 by varying the incident light intensity. Additionally, moderate annealing before and after illumination can markedly improve the alignment uniformity by self-healing of defects. [source]

    Structural stability of Sclerotium rolfsii ATCC 201126 ,-glucan with fermentation time: a chemical, infrared spectroscopic and enzymatic approach

    J.I. Faria
    Abstract Aims:,Sclerotium rolfsii ATCC 201126 exopolysaccharides (EPSs) recovered at 48 h (EPS I) and 72 h (EPS II) of fermentation, with differences in rheological parameters, hydrogel topography, salt tolerance, antisyneresis, emulsifying and suspending properties, were subjected to a polyphasic characterization in order to detect structural divergences. Methods and Results:, Fermenter-scale production led to productivity (Pr) and yield (YP/C) values higher at 48 h (Pr = 0542 g l,1 h,1; YP/C = 074) than at 72 h (Pr = 0336 g l,1 h,1; YP/C = 050). Both EPSs were neutral glucose-homopolysaccharides with a ,-(1,3)-glycosidic backbone and single ,-(1,6)-glucopyranosyl sidechains regularly attached every three residues in the main chain, as revealed by chemical analyses. The infra-red diagnostic peak at 890 cm,1 confirmed ,-glycosidic linkages, while gentiobiose released by ,-(1,3)-glucanases confirmed single ,-1,6-glycosidic branching for both EPSs. Conclusions:, The true modular repeating unit of S. rolfsii ATCC 201126 scleroglucan could be resolved. Structural stability was corroborated and no structural differences could be detected as to account for the variations in EPSs behaviour. Significance and Impact of the Study:, Recovery of S. rolfsii ATCC 201126 scleroglucan at 48 h might be considered based on better fermentation kinetic parameters and no detrimental effects on EPS structural features. [source]

    Synthesis and characterization of new unsaturated polyesters containing cyclopentapyrazoline moiety in the main chain

    Ismail A. Alkskas
    Abstract 3-p -Hydroxyphenyl-6- p -hydroxybenzylidene cyclopentapyrazoline (III) and 3-vanillyl-7-vanillylidene cyclopentapyrazoline (IV) were used as new starting materials for preparing new unsaturated polyesters. The polyesters were prepared by reacting (III) or (IV) with adipoyl, sebacoyl, isophthaloyl, and terephthaloyl dichlorides utilizing the interfacial polycondensation technique. The polyester samples have been characterized by elemental and spectral analyses. The polyesters have inherent viscosities of 0.55,0.97 dL/g. All the polyesters are semicrystalline and most of them are partially soluble in most common organic solvents but freely soluble in concentrated sulfuric acid. Their glass transition temperatures (Tg) range from 103.34 to 208.81C, and the temperatures of 10% weight loss as high as 190 to 260C in air, indicating that these aromatic polyesters have high Tg and excellent thermal stability. Doping with iodine dramatically raised the conductivity and produced dark brown colored semiconductive polymers with a maximum conductivity in the order of 3.1 10,7 ,,1 cm,1. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    Polyesters based on two silarylene or germarylene moieties: Synthesis under phase-transfer conditions

    L. H. Tagle
    Abstract Polyesters (PEs) containing two heteroatoms (Si and/or Ge) in the main chain, derived from the acid dichlorides bis(4-chloroformylphenyl) ethylmethylsilane, bis(4-chloroformylphenyl) diethylsilane, bis(4-chloroformylphenyl) diethylgermane, and bis(4-chloroformylphenyl) di- nbutylgermane and from the diphenols bis(4-hydroxyphenyl) ethylmethylsilane, bis(4-hydroxyphenyl) diethylsilane, bis(4-hydroxyphenyl) diethylgermane, and bis(4-hydroxyphenyl) di- nbutylgermane, were synthesized under phase-transfer conditions with three quaternary ammonium salts as phase-transfer catalysts and three NaOH concentrations in the aqueous phase. PEs were characterized with IR and NMR spectroscopy, including 29Si-NMR. In general, the yields and intrinsic viscosities were low, and in some cases, an increase in these parameters was shown as a result of the catalyst effect. An increase in the NaOH concentration caused a decrease in the yields because of a hydrolytic process. PEs with Si were thermally more stable than those with Ge. The glass-transition temperatures decreased when the side chains bonded to the heteroatoms were longer. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

    Synthesis and properties of homopolyamide and copolyamides fibers based on 2,6-bis(p -aminophenyl)benzo[1,2-d;5,4- d,]bisoxazole

    Xiangqun Chen
    Abstract A novel aromatic homopolyamide with benzobisoxazole units in the main chain was synthesized with 2,6-bis(p -aminophenyl)benzo[1,2- d;5,4- d,]bisoxazole and terephthaloyl chloride by low temperature solution polycondensation, the inherent viscosity of which was 1.98 dL/g. The diamine and p -phenylendiamine with terephthaloyl chloride were used to synthesize the copolyamides. The structures of homopolyamide and copolyamides were characterized by IR spectra, elemental analysis, and wide-angle X-ray diffraction. Wide-angle X-ray diffraction measurements showed that homopolyamide and copolyamides were predominantly crystallinity. The results of thermal analysis indicated that the thermal stabilities of the copolymer increased with an increase of the molar fraction of benzobisoxazole in the copolymers. The thermal stability of the copolyamides with decomposition temperatures (at 10% weight loss) above 570C was better than that of poly(p -phenylene terephthalamide) (PPTA). Fibers of homopolyamide and copolyterephthalamides were spun from lyotropic liquid crystal dope in 100% H2SO4. When compared with PPTA fibers prepared under the same conditions, the tensile strengths of copolyamides fibers improved by 20,33% with tensile strengths of 1.81 GPa, tensile moduli of 76 GPa, and elongations at break of 3.8,4.1%, which indicated that copolyamides fibers had outstanding mechanical properties. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Synthesis and crystallization behavior of acetal copolymer/silica nanocomposite by in situ cationic ring-opening copolymerization of trioxane and 1,3-dioxolane

    Lanhui Sun
    Abstract The acetal copolymer/silica nanocomposite was prepared by in situ bulk cationic copolymerization of trioxane and 1,3-dioxolane in the presence of nanosilica. The crystallization behavior of acetal copolymer/silica nanocomposite was studied by AFM, DSC, XRD, and CPOM, and the macromolecular structure of acetal copolymer/silica nanocomposite was characterized by FTIR and 1H-NMR. The 1H-NMR results showed that the macromolecular chain of acetal copolymer had more than two consecutive 1,3-dioxolane units in an oxymethylene main chain, while that of acetal copolymer/silica nanocomposite had only one 1,3-dioxolane unit in an oxymethylene main chain. There existed interaction between the macromolecular chains and nanoparticles (such as hydrogen bonds and coordination). On one hand, nanoparticles acted as nucleation center, which accelerated the crystallization rate but reduced the crystallinity. The spherulite sizes also decreased with addition of nanoparticles attributed to the nucleation effect. On the other hand, the presence of nanoparticles interrupted the spherical symmetry of the crystallite. In conclusion, the high surface energy and small scale of nanoparticles have a prominent impact on the polymerization mechanism and crystallization behavior of nanocomposite. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Effective preparation and characterization of montmorillonite/poly(,-caprolactone)-based polyurethane nanocomposites

    Eun Hwan Jeong
    Abstract In this study, montmorillonite (MMT)/poly(,-caprolactone)-based polyurethane cationomer (MMT/PCL-PUC) nanocomposites were prepared and their mechanical properties, thermal stability, and biodegradability were investigated. PCL-PUC has 3 mol % of quaternary ammonium groups in the main chain. The MMT was successfully exfoliated and well dispersed in the PCL-PUC matrix for up to 7 wt % of MMT. The 3 mol % of quaternary ammonium groups facilitated exfoliation of MMT. The 1 wt % MMT/PCL-PUC nanocomposites showed enhanced tensile properties relative to the pure PCL-PU. As the MMT content increased in the MMT/PCL-PUC nanocomposites, the degree of microphase separation of PCL-PUC decreased because of the strong interactions between the PCL-PUC chains and the exfoliated MMT layers. This resulted in an increase in the Young's modulus and a decrease in the elongation at break and maximum stress of the MMT/PCL-PUC nanocomposites. Biodegradability of the MMT/PCL-PUC nanocomposites was dramatically increased with increasing content of MMT, likely because of the less phase-separated morphology of MMT/PCL-PUC. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Synthesis and characterization of soluble copolyimides containing chalcone and phosphine oxide moieties in the main chain

    Wei Wang
    Abstract The functional diamines 3,3,-diaminochalcone and bis(3-aminophenyl)-3,5-bis(trifluoromethyl)phenyl phosphine oxide were successfully prepared by simple and convenient procedures with short reaction times, and the overall yields were 78 and 70%, respectively. Copolyimides prepared from 3,3,-diaminochalcone, bis(3-aminophenyl)-3,5-bis(trifluoromethyl)phenyl phosphine oxide, and 4,4,-(hexafluoroisopropylidene)diphthalic anhydride exhibited excellent solubility in several organic solvents, such as dimethyl sulfoxide, N,N -dimethylformamide, N -methyl pyrrolidone, tetrahydrofuran, and acetone. They also showed very good thermal stability even up to 450C for 5% weight loss (by thermogravimetric analysis) in nitrogen and a high glass-transition temperature up to 274C (by differential scanning calorimetry) in nitrogen. The copolymers' adhesive and photoreactive properties were also investigated, and it was confirmed that the copolyimide containing chalcone and phosphine oxide moieties in the main chain had good adhesiveness and photoreactivity. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Relation between thermal conductivity and network formation with polymerizable liquid crystals

    Takashi Kato
    Abstract The molecules with the mono- and bi-function at the sides in the acrylic PLC mixtures were aligned by the rubbing method. The alignment was immobilized by the photo polymerization to result the homogeneous acrylic films, which have good alignment with the higher order parameters. The thermal conductivity along the molecular long axis direction showed the larger magnitude of 0.62 W/m K, which is independent on ratio of the main chain and the side chain fractions. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3169,3174, 2007 [source]

    Collagen structure: The molecular source of the tendon magic angle effect

    Gary D. Fullerton PhD
    Abstract This review of tendon/collagen structure shows that the orientational variation in MRI signals from tendon, which is referred to as the "magic angle" (MA) effect, is caused by irreducible separation of charges on the main chain of the collagen molecule. These charges are held apart in a vacuum by stereotactic restriction of protein folding due in large part to a high concentration of hydroxyproline ring residues in the amino acids of mammalian collagen. The elevated protein electrostatic energy is reduced in water by the large dielectric constant of the highly polar solvent (, , 80). The water molecules serve as dielectric molecules that are bound by an energy that is nearly equivalent to the electrostatic energy between the neighboring positive and negative charge pairs in a vacuum. These highly immobilized water molecules and secondary molecules in the hydrogen-bonded water network are confined to the transverse plane of the tendon. Orientational restriction causes residual dipole coupling, which is directly responsible for the frequency and phase shifts observed in orientational MRI (OMRI) described by the MA effect. Reference to a wide range of biophysical measurements shows that native hydration is a monolayer on collagen hm = 1.6 g/g, which divides into two components consisting of primary hydration on polar surfaces hpp = 0.8 g/g and secondary hydration hs = 0.8 g/g bridging over hydrophobic surface regions. Primary hydration further divides into side-chain hydration hpsc = 0.54 g/g and main-chain hydration hpmc = 0.263 g/g. The main-chain fraction consists of water that bridges between charges on the main chain and is responsible for almost all of the enthalpy of melting ,H = 70 J/g-dry mass. Main-chain water bridges consist of one extremely immobilized Ramachandran water bridge per tripeptide hRa = 0.0658 g/g and one double water bridge per tripeptide hdwb = 0.1974 g/g, with three water molecules that are sufficiently slowed to act as the spin-lattice relaxation sink for the entire tendon. J. Magn. Reson. Imaging 2007. 2007 Wiley-Liss, Inc. [source]

    Synthesis and characterization of a thiadiazole/benzoimidazole-based copolymer for solar cell applications

    Guan-yu Chen
    Abstract In this study, we synthesized a new polymer, PCTDBI, containing alternating carbazole and thiadiazole-benzoimidazole (TDBI) units. This polymer (number-average molecular weight = 25,600 g mol,1), which features a planar imidazole structure into the polymeric main chain, possesses reasonably good thermal properties (Tg = 105 C; Td = 396 C) and an optical band gap of 1.75 eV that matches the maximum photon flux of sunlight. Electrochemical measurements revealed an appropriate energy band offset between the polymer's lowest unoccupied molecular orbital and that of PCBM, thereby allowing efficient electron transfer between the two species. A solar cell device incorporating PCTDBI and PCBM at a blend ratio of 1:2 (w/w) exhibited a power conversion efficiency of 1.20%; the corresponding device incorporating PCTDBI and PC71BM (1:2, w/w) exhibited a PCE of 1.84%. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source]

    Benzoxazine containing polyester thermosets with improved adhesion and flexibility

    Alev Tuzun
    Abstract High molecular weight polyesters containing thermally curable benzoxazine units in the main chain have been synthesized. For this purpose, first the diol functional monomer is synthesized through the Mannich and subsequent ring closure reactions of bisphenol-A, paraformaldehyde, and 5-amino-1-pentanol. Polycondensation of the resulting benzoxazine and pyromellitic dianhydride or 4-4,-(hexafluoroisopropylidene) diphatalic anhydride with or without dibutyltin laurate yielded the corresponding polyesters with the molecular weights between 5800 and 7000 Da. The structures of the precursor diol monomer and the resulting polyesters are confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy analysis. Curing behavior of both the monomer and polymers has also been studied by differential scanning calorimetry. Flexible films of the polyesters were obtained by solvent casting on tin plates and crosslinked by heating in the absence of any catalyst. The cured films exhibited high flexibility and adhesion on the tin plates as determined by ASTM and DIN tests. Thermal properties of the cured polymers were also investigated by thermogravimetric analysis (TGA). 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4279,4284, 2010 [source]

    Asymmetric anionic polymerization of 7-cyano-7-ethoxycarbonyl-1,4-benzoquinone methide

    Noboru Nakagaki
    An optically active polymer having configurational chirality in the main chain was synthesized from a prochiral monomer, 7-cyano-7-ethoxycarbonyl-1,4-benzoquinone methide (1), by asymmetric anionic polymerization using various chiral anionic initiators. The effects of the chiral ligand and solvent polarity on the specific rotations of the resulting polymers were investigated. The polymerization of 1 using iPrPhOLi/(,)-PhBox complex initiator in a mixture solution of dichloromethane/toluene ratio of 30/70 (in vol %) at ,78 C afforded an optically active polymer with a large positive specific rotation ([,]435 = +90.4). [source]

    Water-soluble anionic conjugated polymers for metal ion sensing: Effect of interchain aggregation

    Yi Chen
    Abstract Three sulfonato-containing fluorene-based anionic water-soluble conjugated polymers, which are specially designed to link fluorene with alternating moieties such as bipyridine (P1), pyridine (P2), and benzene (P3) have been synthesized via the Pd-catalyzed Sonogashira-coupling reaction, respectively. These polymers had good solubility in water and showed different responses for transition metal ions with different valence in aqueous environments: the fluorescence of bipyridine-containing P1 can be completely quenched by addition of all transition metal ions selected and showed a good selectivity for Ni2+; the pyridine-containing P2 had a little response for monovalent and divalent metal ions while showed good quenching with the addition of trivalent metal ions (with a special selectivity for Fe3+); P3 had responses only for the trivalent metal ions within the ionic concentration we studied. After investigation of the UV-vis absorption spectra, PL emission spectra, DLS, and fluorescence lifetime of P1,P3 in aqueous solution when adding transition metal ions, we found that the different spectrum responses of these polymers are attributed to the different coordination ability of the units linked with fluorene in the main chain. The energy or electron-transfer reactions were the main reason for fluorescence quenching of P1 and P2. On the other hand, interchain aggregation caused by trivalent metal ions lead to fluorescence quenching for P3 and also caused partly fluorescence quenching of P1 and P2. These results revealed the origin of ionochromic effects of these polymers and suggested the potential application for these polymers as novel chemosensors with higher sensing sensitivity in aqueous environments. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5057,5067, 2009 [source]

    New fluorene-based copolymers containing oxadiazole pendant groups: Synthesis, characterization, and polymer stability

    Dmitrij Bondarev
    Abstract A series of fluorene-based copolymers containing hole blocking/electron transporting diphenyloxadiazole units were synthesized by means of Suzuki-Miyaura coupling of selected aromatic dibromo- and diboronato- derivatives catalyzed with a Pd(PPh3)4 catalyst. All of the copolymers with various composition of main-chain units were characterized by SEC chromatography, NMR, UV,vis, fluorescence and IR spectroscopy, and DSC. The emission stability of fluorene copolymers was improved by the replacement of alkyl groups on the C-9 carbon of fluorene with aryl groups or by the incorporation of anthracene units into the copolymer main chain. A comparison of luminescence properties of pristine and annealed thin layers of studied copolymers was performed. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4532,4546, 2009 [source]

    Synthesis and properties of conjugated polymers containing 3,9- and 2,9-linked carbazole units in the main chain

    Kosaku Tamura
    Abstract Novel conjugated polymers containing 3,9- or 2,9-linked carbazole units in the main chain were synthesized by the polycondensation of ethynyl- and iodo-substituted 9-arylenecarbazolylene monomers, and their optical and electrical properties were studied. Polymers with weight-average molecular weights of 3400,12,000 were obtained in 76,99% yields by the Sonogashira coupling polycondensation in piperidine or tetrahydrofuran (THF)/piperidine at 30 C for 48 h. All the 3,9-linked polymers absorbed light around 300 nm. The para -phenylene-linked polymer also absorbed light around 350 nm, while meta -phenylene-linked one did not. The 3,9-linked polymers absorbed light at a wavelength longer than the 2,9-linked one. The polymers emitted blue fluorescence with high quantum yields (0.21,0.78) upon excitation at the absorption maxima. The polymers were oxidized around 0.6 V, and reduced around 0.5 V. Poly(1) showed the dark conductivity of 3.7 10,11 S/cm (103 V/cm). 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3506,3517, 2009 [source]

    Liquid crystalline conjugated polymers and their applications in organic electronics

    Sheng-Hsiung Yang
    Abstract This article describes the syntheses and electro-optical applications of liquid crystalline (LC) conjugated polymers, for example, poly(p -phenylenevinylene), polyfluorene, polythiophene, and other conjugated polymers. The polymerization involves several mechanisms: the Gilch route, Heck coupling, or Knoevenagel condensation for poly(p -phenylenevinylene)s, the Suzuki- or Yamamoto-coupling reaction for polyfluorenes, and miscellaneous coupling reactions for other conjugated polymers. These LC conjugated polymers are classified into two types: conjugated main chain polymers with long alkyl side chains, namely main-chain type LC polymers, and conjugated polymers grafting with mesogenic side groups, namely side-chain type LC conjugated polymers. In general, the former shows higher transition temperature and only nematic phase; the latter possesses lower transition temperature and more mesophases, for example, smectic and nematic phases, depending on the structure of mesogenic side chains. The fully conjugated main chain promises them as good candidates for polarized electroluminescent or field-effect devices. The polarized emission can be obtained by surface rubbing or thermal annealing in liquid crystalline phase, with maximum dichroic ratio more than 20. In addition, conjugated oligomers with LC properties are also included and discussed in this article. Several oligo-fluorene derivatives show outstanding polarized emission properties and potential use in LCD backlight application. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2713,2733, 2009 [source]

    Synthesis and characterization of fluorene-based copolymers containing siloxane or distilbene moieties on their main chain

    Hoon-Je Cho
    Abstract Two novel types of polyfluorene copolymers containing siloxane linkages or distilbene moieties on their main-chains were synthesized by Ni(0)-mediated Yamamoto coupling polymerization. These polymers, designated P2Silo05, P2Silo15, PF-P02, and PF-P05 were prepared by copolymerization between 2,7-dibromo-9,9,-dihexylfluorene and bis(bromobenzene)-terminated disiloxane monomer (for P2Silo05 and P2Silo15) or dibromodistilbene monomer (for PF-P02 and PF-P05). All of the polymers were highly soluble in common organic solvents such as chloroform, toluene, and p -xylene. The glass transition temperatures of the polymers were between 92 and 113 C, and the decomposition temperatures for a 5% weight loss (Td) were above 420 C for all of the polymers, demonstrating high thermal stability. The molecular weight (Mw) of the polymers ranged from 4.2 104 to 8.8 104. The blue shift of the maximum in the UV-visible absorption was greater in polymers with a higher molar percentage of siloxane linkages or distilbene moieties than in homo poly (dihexylfluorene) (PDHF). However, the photoluminescence spectra of the polymers were similar to those of PDHF in terms of the onsets and patterns. Single-layer light-emitting diodes were fabricated with a configuration of ITO/PEDOT:PSS/polymers/Ca/Al. The maximum electroluminescence emission wavelengths of the polymers were 425,450 nm, corresponding to pure blue light. The CIE co-ordinates of the polyfluorenes containing siloxane linkages or distilbene moieties ranged from (0.21, 0.21) to (0.17, 0.10), indicating deeper blue light than that of PDHF {CIE co-ordinates of (0.25, 0.29)}, with P2Silo15 giving the deepest blue-light {CIE co-ordinates of (0.17, 0.10)}. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1595,1608, 2009 [source]

    Ring-opening polymerization of benzylated 1,6-anhydro-,- D -lactose and specific biological activities of sulfated (1,6)-,- D -lactopyranans

    Shuqin Han
    Abstract A new anhydro disaccharide monomer, 1,6-anhydro-2,3-di- o -benzyl-4- o -(2,,3,,4,,6,-tetra- o -benzyl-,- D -galactopyranosyl)-,- D -glucopyranose (benzylated 1,6-anhydro lactose (LSHBE)), was synthesized from D -lactose to investigate the polymerizability and biological activities of the resulting branched polysaccharides. The ring-opening polymerization of LSHBE was carried out with phosphorus pentafluoride as a catalyst under high vacuum to give a stereoregular benzylated (1 , 6)-,- D -lactopyranan. The molecular weights of poly(LSHBE)s increased with an increase in the amount of CH2Cl2 solvent, and polymerization temperatures were affected in both molecular weights and yields of the polymers. The copolymerization of LSHBE with benzylated 1,6-anhydro-,- D -glucopyranose (LGTBE) gave the corresponding copolysacchrides having different proportions of lactose and glucose units in good yields. After debenzylation to recover hydroxyl groups and then sulfation, sulfated homopoly(lactose)s and copoly(lactose and glucose)s were obtained. Sulfated homopoly(lactose)s had moderate anti-HIV (EC50 = 5.9 and 1.3 ,g/mL) and blood anticoagulant activities (AA = 18 and 13 unit/mg), respectively. Sulfated copoly(lactose and glucose) having 15 mol % lactose units gave high anti-HIV and blood anticoagulant activities of 0.3 ,g/mL and 54 unit/mg, respectively. These biological results suggest that the distance between branched units on the main chain plays an important role in the anti-HIV and blood anticoagulant activities. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 913,924, 2009 [source]

    Stilbene-containing polyactylenes: Molecular design, synthesis, and relationship between molecular structure and NLO properties

    Xinyan Su
    Abstract Polyacetylenes (P1,P4) containing different stilbene groups, [(CHC) PhCHCHPhR]n(ROCmH2m+1 (m = 4 (P1), 10 (P2), 16 (P3)), or NO2 (P4)) were designed and synthesized, respectively, using [Rh(nbd)Cl]2 as a catalyst. Their structures and properties were characterized and evaluated by FTIR, 1H-NMR, 13C-NMR, GPC, and UV, PL, respectively. The optical limiting and nonlinear optical properties were investigated by using a frequency doubled, Q-switched, mode-locked Continuum ns/ps Nd:YAG laser system and their optical limiting mechanism was discussed. It is surprising to see that the stilbene pendants endow the polyacetylenes with a high thermal stability (Td , 270 C), novel optical limiting properties and large third-order nonlinear optical susceptibilities (up to 4.61 10,10 esu). The optical limiting mechanism is mainly originated from reverse saturable absorption of molecules. In addition, it is found that the polymer with electron accepted NO2 moiety exhibits better optical properties than that with electron donated alkoxy group because of larger , electron delocalization and dipolar effect. The strong interaction between stilbene pendants and the polyene main chain significantly results in red-shift of fluorescence emitting peak. 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4529,4541, 2008 [source]