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481.
Darwin P. R. Kint Antxon Martínez De Ilarduya Sebastin Muoz‐Guerra 《Journal of polymer science. Part A, Polymer chemistry》2000,38(11):1934-1942
Poly(ethylene terephthalate‐co‐5‐nitroisophthalate) copolymers, abbreviated as PETNI, were synthesized via a two‐step melt copolycondensation of bis(2‐hydroxyethyl) terephthalate and bis(2‐hydroxyethyl) 5‐nitroisophthalate mixtures with molar ratios of these two comonomers varying from 95/5 to 50/50. Polymerization reactions were carried out at temperatures between 200 and 270 °C in the presence of tetrabutyl titanate as a catalyst. The copolyesters were characterized by solution viscosity, GPC, FTIR, and NMR spectroscopy. They were found to be random copolymers and to have a comonomer composition in accordance with that used in the corresponding feed. The copolyesters became less crystalline and showed a steady decay in the melting temperature as the content in 5‐nitroisophthalic units increased. They all showed glass‐transition temperatures superior to that of PET with the maximum value at 85 °C being observed for the 50/50 composition. PETNI copolyesters appeared stable up to 300 °C and thermal degradation was found to occur in two well‐differentiated steps. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1934–1942, 2000 相似文献
482.
David Zanuy Carlos Alemn Sebastin Muoz‐Guerra 《Macromolecular theory and simulations》2000,9(8):543-549
We present a molecular dynamics study of the helical conformation of the naturally occurring poly(γ‐D ‐glutamic acid) in the un‐ionized state. The study was conducted in both aqueous solution and gas‐phase considering a 20 residue polypeptide. The results indicated that the left‐handed helix with 19‐membered ring hydrogen bonds set between the CO of the amide group i and the NH of amide group i + 3 is very stable in aqueous solution. This conformation was recently proposed for this poly(γ‐amino acid) from a conformational search study. A detailed picture of the most relevant structural details of the helical conformation of poly(γ‐D ‐glutamic acid) is provided. 相似文献
483.
484.
Pellegrino Musto Simona Tavone Gaetano Guerra Claudio De Rosa 《Journal of Polymer Science.Polymer Physics》1997,35(7):1055-1066
Fourier transform infrared (FTIR) spectra of syndiotactic polystyrene (s-PS) semicrystalline samples have been examined by using the spectral subtraction approach. For the crystalline forms including trans-planar chains (trigonal α and orthorhombic β) a number of conformational and structural order effects, not previously described in the literature, have been identified. A method based on the results of the spectral subtraction analysis has been developed for the determination of the crystallinity degree and compared with the standard method based on the wide-angle X-ray diffraction patterns. The spectral subtraction analysis on FTIR spectra allows also an easy evaluation of the amount of α and β crystalline phases (often simultaneously present in melt-crystallized samples) although both contain chains in a same conformation. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1055–1066, 1997 相似文献
485.
A new concept of duality is proposed for multiobjective linear programs. It is based on a set expansion process for the computation of optimal solutions without scalarization. The duality gap qualifications are investigated; the primal–dual balance set and level set equations are derived. It is demonstrated that the nonscalarized dual problem presents a cluster of optimal dual vectors that corresponds to a unique optimal primal vector. Comparisons are made with linear utility, minmax and minmin scalarizations. Connections to Pareto optimality are studied and relations to sensitivity and parametric programming are discussed. The ideas are illustrated by examples. 相似文献
486.
In this paper, we study the high temperature or low connectivity phase of the Viana–Bray model in the absence of magnetic field. This is a diluted version of the well known Sherrington–Kirkpatrick mean field spin glass. In the whole replica symmetric region, we obtain a complete control of the system, proving annealing for the infinite volume free energy and a central limit theorem for the suitably rescaled fluctuations of the multi-overlaps. Moreover, we show that free energy fluctuations, on the scale 1/N, converge in the infinite volume limit to a non-Gaussian random variable, whose variance diverges at the boundary of the replica-symmetric region. The connection with the fully connected Sherrington– Kirkpatrick model is discussed. 相似文献
487.
C. De Rosa G. Guerra R. Napolitano V. Petraccone B. Pirozzi 《European Polymer Journal》1984,20(10):937-941
Transitions between structural modifications of isotactic polypropylene, characterized by increasing degrees of order in respect to the up and down positioning of the chains, have been studied for samples having different previous thermomechanical histories or containing small amounts of ethylenic units. The annealing temperature ranges, in which such transitions are observed, are strictly related to the positions of the melting endotherm positions for the various samples. For all the recrystallized samples, the same relation has been found between the increases in the melting peak positions and the increases in the parameter selected as a measure of the up-down degree of order. 相似文献
488.
J. E. García-Ramos J. M. Arias J. Dukelsky E. Moya de Guerra P. van Isacker 《Czechoslovak Journal of Physics》1998,48(6-7):703-706
A Hartree-Bose mean-field approximation for the IBM-3 is presented. A Hartree-Bose transformation from the spherical to the
deformed bosons with charge-dependent parameters is proposed which allows bosonic pair correlations and includes higher angular
momentum bosons. The formalism contains previously proposed IBM-2 and IBM-3 intrinsic states as particular limits.
Presented by J.E. García-Ramos at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September
1–5, 1997.
This work has been supported in part by the Spanish DGICYT under contracts No. PB 95/0123 and PB95-0533, a DGICYT-IN2P3 agreement
and by the European Commission under contract CI1*-CT94-0072. 相似文献
489.
A theorem about the Radon-Nikodym property and the convergence of bounded martingales is proved for a bilinear integral in locally convex spaces. 相似文献
490.