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Chain Segments (chain + segment)
Selected AbstractsMolecular thermodynamic model of the glass transition temperature: dependence on molecular weightPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2008Yong Woo Kim Abstract A new molecular thermodynamic model to predict the dependency of the glass transition temperature (Tg) of polymer on its molecular weight was developed based on the configurational entropy model and the Flory,Huggins theory. In this model, the disorientation entropy of the polymer (Sdis) has been taken into account. Quantitative descriptions according to the proposed model are consistent with experimental Tg data of several polymers against the number of chain segment (r). At the same Tg., (Tg of polymer at a infinite r value), the degree of polymer disorientation is strongly correlated with the slope of straight line at lower r regions in the Tg versus r plot, which is quantitatively identified by physical parameter (,dis) in this model. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hysteresis in Conjugated Polymer Thin Film Transistors Generated by Chain RelaxationADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Neng-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] The incorporation of rigid diol monomers into poly(butylene terephthalate) via solid-state copolymerization and melt copolymerization,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2008M. A. G. Jansen Abstract Incorporation of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane (Dianol 220®) into poly(butylene terephthalate) (PBT) via solid-state copolymerization (SSP) showed that Dianol, besides being the reactant, also acts as a swelling agent for rigid amorphous PBT chain segments. Being swollen, these amorphous chain segments become sufficiently mobile to contribute to the SSP process. The thermal behavior of the resulting copolyesters is comparable with melt copolymerized copolymers, although having a different chemical microstructure. The main reason is a full miscibility in the melt of unmodified PBT chain segments and modified chain segments, which eliminates the advantages of a blocky microstructure for the SSP copolyesters. However, incorporation of 2,2,-biphenyldimethanol (BDM) into PBT resulted in a higher crystallization temperature compared with PBT,Dianol copolymers of equal composition. Preordering of polymer chains in the melt by incorporating rigid, phase separating BDM-moieties, preferably via SSP to obtain a non-random distribution, may be the origin of the enhanced crystallization temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1203,1217, 2008 [source] Ideal tetrafunctional amphiphilic PEG/PDMS conetworks by a dual-purpose extender/crosslinker.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2005Abstract The synthesis of a new type of amphiphilic conetwork (APCN) consisting of well-defined hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) segments is described. The conetwork is ideal (the lengths of each PEG and PDMS chain segments, respectively, are identical) and tetrafunctional (exactly four chains emanate from each crosslink site). The synthesis of the conetworks was achieved by the use of a novel dual-purpose extender/crosslinker Y (bis [(dimethylsilyl)oxy]-[(etoxydimethylsilyl)oxy]phenylsilane, (SiPh(SiH)2OEt)), in two steps: (1) Synthesis of a new linear random multiblock copolymer (MBC) (AY)n(BY)m, where A is the hydrophilic PEG and B is the hydrophobic segment, and (2) Crosslinking the multiblocks by catalytic condensation of the SiOEt groups in the Y units. The extender/crosslinker fulfills two totally different functions: First, it extends two incompatible hydrophilic and hydrophobic prepolymers (PEG and PDMS) to a random MBC, and, subsequently, it cross-links the multiblocks to the target APCN. The synthesis and characterization of the extender/crosslinker is also presented. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4953,4964, 2005 [source] Methacrylic Polymers Containing Optically Active Side-Chain Carbazole: Synthesis, Characterization and Photoconductive PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2008Luigi Angiolini Abstract Two novel optically active polymethacrylates bearing in the side chain a cyclic chiral group of one prevailing absolute configuration linked to the carbazole chromophore, deriving from the related monomers (S)-(,)-3-methacryloyloxy- N -[3-(9-ethylcarbazolyl)]pyrrolidine [(S)-(,)-MECP] and (S)-(+)-2-methacryloyloxy- N -[3-(9-ethylcarbazolyl)]succinimide [(S)-(+)-MECSI], have been prepared and characterized with the aim to obtain materials suitable to photoconductive applications. Poly[(S)-(,)-MECP] and poly[(S)-(+)-MECSI] exhibit remarkable thermal stability, with glass transition temperature around 200,°C and decomposition temperatures in the range 330,350,°C. Spectroscopic, thermal and chiroptical characterizations indicate the occurrence of dipolar interactions among the side chain moieties and the presence of chiral conformation at least for chain segments of the macromolecules. The photoconductive properties are discussed in terms of extent of conjugation in the side chain based on the electron-acceptor or electron-donator properties of the optically active ring linked to the carbazole group. [source] Characterization of PVA and Chitosan/PVA Blends Prepared from Aqueous Solutions of Various Na2SO4 ConcentrationsMACROMOLECULAR SYMPOSIA, Issue 1 2006Petronela Drambei Abstract Uniplaner orientation of a particular crystal plane along the surface of a film was investigated for poly (vinyl alcohol) (PVA) film prepared by a coagulation bath with concentrated aqueous solution containing 100,,,300g of Na2SO4 against 1 , of water. The orientation distribution functions of the three crystallographic principal axes of the dried films were obtained by the X-ray diffraction technique. The same treatment was carried out for the films prepared by stretching biaxially of the fresh gel and then by drying the resultant fresh gel. The very high preferential orientation of the crystal chain axes and amorphous chain segments could be realized by the biaxially elongation. Accordingly, the techniques were applied to the biaxially stretching of chitosan and PVA blend films with high Young's modulus. The planer orientation of the chain axes of chitosan and PVA crystallites could be confirmed. The morphology of the film surface was estimated by measurements of contact angle and electron spectroscopy for chemical analysis. The results suggested that the admixture of chitosan decreases wet ability of the specimen and this tendency was slightly enhanced by the biaxially elongation. [source] Electrospinning of polyamides with different chain compositions for filtration applicationPOLYMER ENGINEERING & SCIENCE, Issue 6 2008Pirjo Heikkilä Electrospinning of several polyamides, PA6, PA66, PA612, PA614, PA1012, and PA1014, having different chain compositions and lengths of diacid and diamine segments, was demonstrated. Electrospinnability and fiber production rate of these polyamides were evaluated. Electrospun fibers were characterized with regard to their use in air filtration by measuring fiber diameter and filtration efficiency of fiber coating. Longer nonpolar chain segments of higher polyamides could in theory indicate higher dielectricity compared to PA6 and PA66, which would be an advantage in filtration applications. The solubility in polar formic acid and electrospinnability of higher polyamides, on the other hand, were clearly impaired with increased length of chain segments. Hence, PA66 is our best choice, and PA612 and PA6 our second options for commercial filtration applications if fiber electrospinnability, production rate, fiber diameter, and its distribution are concerned. Filtration efficiency of more than 95% of the particles having a diameter of 0.16 ,m and above was achieved with 0.5 g/m2 coating of PA66 nanofibers. Further increase in coating weight mainly increased the pressure drop to an unusable range without a significant further improvement of filtration efficiency. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers. [source] Effect of side-chain length of succinic anhydride on coefficient of thermal expansion behavior of epoxy resinsPOLYMER INTERNATIONAL, Issue 11 2006Fan-Long Jin Abstract The effect of an alkenyl side-chain of succinic anhydride (SA) on the thermal behavior and the coefficient of thermal expansion (CTE) of diglycidylether of bisphenol A (DGEBA) epoxy resins was studied. The number of carbons in the side-chain of SA was varied from 6 to 14 and N,N -Dimethylbenzylamine was used as an accelerator. As a result, the reactivity of SA with epoxide groups was decreased on increasing the length of the alkenyl side-chain of SA. The thermal stabilities of cured DGEBA/SA samples were approximately constant with varying alkenyl side-chain of SA. Also, the CTE of the systems was increased as the length of the alkenyl side-chain of SA increased. This could be attributed to the increased motion of the chain segments in the epoxy network structure induced by the longer alkenyl side-chain of SA. The effect of amount anhydride, thermoplastics, and fillers on the CTE of the epoxy resins was also discussed. Copyright © 2006 Society of Chemical Industry [source] Thermal and mechanical properties of diglycidylether of bisphenol A/ trimethylolpropane triglycidylether epoxy blends cured with benzylpyrazinium saltsPOLYMER INTERNATIONAL, Issue 5 2002Soo-Jin Park Abstract The effect of blend composition on thermal stability and mechanical properties of diglycidylether of bisphenol A (DGEBA)/trimethylolpropane triglycidylether (TMP) epoxy blends cured with benzylpyrazinium salts (N -benzylpyrazinium hexafluoroantimonate, BPH) as a thermal latent catalyst was investigated. The thermal stability, characterized by the initial decomposition temperature, temperature of maximum rate of weight loss, integral procedural decomposition temperature, and activation energy for decomposition, increase in DGEBA-rich compositions. This could be due to the long repeat unit and stable aromatic ring in the DGEBA. The mechanical properties are also discussed in terms of the fracture toughness (KIC), flexural and impact tests for the blend composition studied. The addition of TMP into DGEBA gives systematic improvements in fracture toughness, which results from the increase in aliphatic and flexible chain segments of TMP. © 2002 Society of Chemical Industry [source] Physical-chemical determinants of turn conformations in globular proteinsPROTEIN SCIENCE, Issue 8 2007Timothy O. Street Abstract Globular proteins are assemblies of ,-helices and ,-strands, interconnected by reverse turns and longer loops. Most short turns can be classified readily into a limited repertoire of discrete backbone conformations, but the physical,chemical determinants of these distinct conformational basins remain an open question. We investigated this question by exhaustive analysis of all backbone conformations accessible to short chain segments bracketed by either an ,-helix or a ,-strand (i.e., ,-segment-,, ,-segment-,, ,-segment-,, and ,-segment-,) in a nine-state model. We find that each of these four secondary structure environments imposes its own unique steric and hydrogen-bonding constraints on the intervening segment, resulting in a limited repertoire of conformations. In greater detail, an exhaustive set of conformations was generated for short backbone segments having reverse-turn chain topology and bracketed between elements of secondary structure. This set was filtered, and only clash-free, hydrogen-bond,satisfied conformers having reverse-turn topology were retained. The filtered set includes authentic turn conformations, observed in proteins of known structure, but little else. In particular, over 99% of the alternative conformations failed to satisfy at least one criterion and were excluded from the filtered set. Furthermore, almost all of the remaining alternative conformations have close tolerances that would be too tight to accommodate side chains longer than a single ,-carbon. These results provide a molecular explanation for the observation that reverse turns between elements of regular secondary can be classified into a small number of discrete conformations. [source] Effects of denaturants and substitutions of hydrophobic residues on backbone dynamics of denatured staphylococcal nucleasePROTEIN SCIENCE, Issue 7 2003Satoshi Ohnishi NOE, nuclear Overhauser effect; RDC, residual dipolar coupling Abstract Analysis of residual dipolar couplings (RDCs) in the ,131, fragment of staphylococcal nuclease has demonstrated that its ensemble-averaged structure is resistant to perturbations such as high concentrations of urea, low pH, and substitution of hydrophobic residues, suggesting that its residual structure is encoded by local side-chain/backbone interactions. In the present study, the effects of these same perturbations on the backbone dynamics of ,131, were examined through 1H- 15N relaxation methods. Unlike the global structure reported by RDCs, the transverse relaxation rates R2 were quite sensitive to denaturing conditions. At pH 5.2, ,131, exhibits an uneven R2 profile with several characteristic peaks involving hydrophobic chain segments. Protonation of carboxyl side chains by lowering the pH reduces the values of R2 along the entire chain, yet these characteristic peaks remain. In contrast, high concentrations of urea or the substitution of 10 hydrophobic residues eliminates these peaks and reduces the R2 values by a greater amount. The combination of low pH and high urea leads to further decreases in R2. These denaturant-induced increases in backbone mobility are also reflected in decreases in 15N NOEs and in relaxation interference parameters, with the former reporting an increase in fast motions and the latter a decrease in slow motions. Comparison between the changes in chain dynamics and the corresponding changes in Stokes radius and the patterns of RDCs suggests that regional variations in backbone dynamics in denatured nuclease arise primarily from local contacts between hydrophobic side chains and local interactions involving charged carboxyl groups. [source] The architecture of the GroEL,GroES,(ADP)7 chaperonin complex.ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2003The heptagrammal forms derived in part I [Janner (2003a). Acta Cryst. D59, 783,794] enclose chain segments of symmetry-related monomers in the GroEL,GroES,(ADP)7 chaperonin complex. A chain reaching the boundary of a given form either ends, proceeds to a neighbouring form or has to fold. C, atoms corresponding to these folding points are identified in each of the nine forms of the chaperonin and are approximated by ideal positions having integral coordinates (the indices) with respect to a symmetry-adapted basis. Mutual structural relations between the indexed positions are derived in terms of integral scale-rotations (similar to those that leave the form invariant). The magnesium ions at the binding sites of the nucleotides ADP and ATP are shown to be symmetry-related to these folding points. The change in folding (polymorphism) observed in the cis ring of GroEL arising from binding to GroES is discussed. In particular, the form segmentation is conserved in the polymorphic transition. The geometric and algebraic restrictions imposed on the indexed positions and on their structural relations by the integrality condition are presented in an appendix. [source] | |||||||||||||