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231.
New thermoplastic polyurethaneureas (TPUU) based on polyisobutylene (PIB) and poly(tetramethylene oxide) (PTMO) segments have been synthesized possessing tensile properties comparable to conventional PTMO based TPUs. PIB based TPUU containing 35 weight (wt)% hard segment was synthesized by chain extension of H2N-Allyl-PIB-Allyl-NH2 with 4,4′ -methylene bis(phenylisocyanate) (MDI) and 1,4-butanediol (BDO) in toluene. The ultimate tensile strength (UTS) = 12 MPa and ultimate elongation = 70% were inferior to PTMO based polyurethane (UTS = 35 MPa, elongation at break = 600%). H2N-Allyl-PIB-Allyl-NH2 and HO-PTMO-OH in different proportions were chain extended in presence of MDI and BDO to obtain TPUUs containing 35 wt% hard segment. The polymers exhibited M ns = 84000–138000 with polydispersity indices (PDIs) = 1.7–3.7. The UTS = 23–32 MPa and elongation at break = 250–675% was comparable to that of PTMO based polyurethane and significantly higher than the PIB based TPUU with the same Shore hardness. The Young's modulus of the polymers was strongly dependent and directly proportional to the PIB wt% in the SS of the TPUUs. 相似文献
232.
Robinson Anandakathir Umaprasana Ojha Earl T. Ada Rudolf Faust Jayant Kumar 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):1217-1222
In this paper, we report the synthesis of stilbene-based fluorophore, 3,4-dihydroxy-4′-aminostilbene (DHAS) for the detection of chemical warfare agents such as organophosphorus nerve gases. DHAS was characterized by various spectroscopic methods and grafted on to electrospun nanofibers. The interaction of DHAS with nerve agents simulant, diethyl chlorophosphate (DCP) was investigated in solution and vapor phase by fluorescence spectroscopy. 相似文献
233.
Nidhi VyasAnimesh K. Ojha 《Vibrational Spectroscopy》2011,56(1):42-50
The interaction between divalent metal cations and amino acids plays an important role in many biological processes. In present report, we have examined the effect of metal cations (Be++, Mg++ and Ca++) interaction on structures, binding energies (BE), metal ion affinities (MIA) and infrared (IR) spectra of phenylalanine (Phe) molecule by density functional theory (DFT) calculations at B3LYP/6-311++G(d,p) level. Nine different ground state isomers of Phe molecule have been optimized at B3LYP/6-311++G (d,p) level of theory. The relative ground state energies of these nine isomers are lying between 0.0-1.9 kcal/mol with respect to the ground state energy of most stable Phe isomer. Seven most stable complexes of Phe molecule with Be++, Mg++ and Ca++ [Phe+M]++ (M = Be++, Mg++ and Ca++) were studied. The calculated values of metal ion affinity (MIA), BE and the Gibbs free energies of each [Phe+M] ++ complexes were found to be in the order of Be++ > Mg++ > Ca++. Among the seven [Phe+M]++ complexes, the most stable conformer has charge solvation structure where the metal cations coordinated through tridentate bonds with -N, -O atoms and benzene ring (N/O/Ring). The [Phe+Be]++ complex has maximum MIA value, 353.3 kcal/mol than that of [Phe+Mg]++ and [Phe + Ca]++ complexes. Thus, the complex [Phe+Be]++ is energetically more stable than that of [Phe+Mg]++ and [Phe + Ca]++. The IR spectra of each seven conformers of [Phe+M]++ complexes have been also calculated. The wavnumber position of (-CO) stretching mode was used to determine the charge/salt bridge structures of the [Phe+M]++ complex. The most stable [Phe+M]++ complex has been also verified through the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) analysis. 相似文献
234.
Electromagnetic wave propagation in one-dimensional plasma photonic crystal (PPC) made of alternate thin layers of two materials namely plasma and dielectric materials is theoretically studied. Dispersion relation is obtained. Group velocity, effective group index, reflectivity and superluminal behavior have been studied. The study of the reflectivity plot shows that the designed structure works as a perfect reflector/mirror in a certain range of frequency. Left-right and up-down symmetries (and flip-flop) are observed when we study the variation of group velocity with frequency. Abnormal behavior of group velocity (negative) inside the PPC structure creates the superluminal propagation of electromagnetic waves. The marked existence of symmetries may be exploited for directional switching in optical circuits. 相似文献
235.
A comparative computational analysis of molecular organization in four-nematogenic acids (nOCAC) having two, four, six, and eight carbon atoms in the alkyl chain is carried out with respect to translatory and orientational motions. The evaluation of the atomic charge and dipole moment at each atomic center is performed through the complete neglect differential overlap (CNDO/2) method. The Rayleigh-Schrödinger perturbation theory, along with the multicentered-multipole expansion method, is employed to evaluate the long-range interactions, while the “6-exp” potential function is assumed for short-range interactions. The total interaction-energy values obtained through these computations are used to calculate the probability of each configuration at the phase transition temperature via the Maxwell-Boltzmann formula. Further, the flexibility of various configurations is studied in terms of variation of probability due to small departures from the most probable configuration. A comparative picture of molecular parameters, such as the total energy, binding energy, and total dipole moment, is given. An attempt is made to explain the nematogenic behavior of these liquid crystals in terms of their relative order and, thereby, to develop a molecular model for the liquid crystallinity. 相似文献