The mechanical lability of intermolecular hydrogen bonds in stoichiometric mixtures of acidic and basic butadiene copolymers has been studied by both infrared and mechanical methods. Comparison is made between the weight-averaged E(t) and H(τ) spectra of the parent copolymers and those of the mixed copolymers. The results indicate that the maximum contributions of bond-interchange relaxation migrate to shorter times as the concentration of bonding groups increases. 相似文献
Dilute solution properties of copolymers of acrylamide (AM) with N-(1,1-dimethyl-3-oxybutyl)acrylamide (DAAM) and with N,N-dimethylacrylamide (DMAM) have been studied as a function of composition, temperature, time, and added electrolytes sodium chloride and calcium chloride. Unlike the AM-DMAM copolymers, the AM-DAAM copolymers show solution viscosity increases in the presence of added NaCl and CaCl2 and decreases with increasing temperature which are related to copolymer composition. The unusual viscosity behavior of the DAAM-AM copolymers is suspected to be due to chain extension resulting from intramolecular hydrogen bonding and other cooperative associations along the macromolecular backbone. 相似文献
The solubilities of potassium fluoride, chloride, and bromide in ethanol, formamide, and N-methylformamide and in binary mixtures
of these solvents were determined at 25°C. The standard molar Gibbs energies of solution, ΔsolnGo, in the neat solvents were related to their hydrogen bonding abilities. The values of ΔsolnGo in the mixtures were fitted with expressions of the quasilattice quasichemical theory, and the preferential solvation of
the ions was thereby established. 相似文献
FT-IR method was used to study the molecular structure of completely cured network polymers, prepared from stoichiometric mixtures of diglycidyl ethers of Bisphenol-A (DGEBA) or resorcinol with metha-phenylenediamine, as a function of their postcure thermal histories (quenching/sub-Tg annealing). The results obtained allow to conclude that the changes influenced by the recovery phenomena in epoxy polymeric glasses are closely related to the rearrangements of their phenylene rings. Only minor variations in conformational state and hydrogen bonding in aliphatic fragments were detected. Also, the spectroscopic results on the time-dependent variations in the molecular organization of a series of DGEBA-oligomers (with MW ranging from 340 up to 10000) are presented and discussed. 相似文献
Thermal behavior of poly(vinyl alcohol)-graft-polyacrylamide copolymers (PVA-g-PAA), so-called intramolecular polymer-polymer complexes (intraPC), with variable M̄vPAA and constant average number N of grafts is considered in this report. Complete compatibility of PVA and PAA through hydrogen bonding is realized in the range of the graft lengths not exceeding some critical value. The content of adsorbed and trapped water in graft copolymers reflects some features of PVA-g-PAAN structure depending on the graft lengths. The first thermal decomposition region in air for copolymers begins at higher temperatures with growing M̄vPAA, but the total destruction interval reduces. Formal kinetic decomposition parameters of the first decomposition stage appear to be the largest for the PVA-g-PAA with the largest quantity of H-bonds between the main and graft chains. Chemical transformations in graft copolymers, PVA and PAA during thermal decomposition are discussed. 相似文献
Summary: Random copolymers of poly(styrene-co-4-vinylpyridine) (S4VP) and poly (styrene-co-2-hydroxyethyl acrylate) (SHEA) of different compositions were prepared and characterized. An investigation of the effects of solvent and densities of the interacting species incorporated within these copolymers showed that novel and various hydrogen bonding interpolymer complexes of different structures were elaborated when these copolymers are mixed together. The specific interactions that occurred within the SHEA copolymers and the elaborated complexes were evidenced by FTIR qualitatively from the appearance of a new band at 1604 cm−1 and quantitatively using appropriate spectral curve fitting in the carbonyl and pyridine regions. The intermolecular hydrogen bonding interactions that occurred between the hydroxyl groups of the SHEA and the nitrogen atom of the pyridine groups in the S4VP are stronger than the self-associations within the SHEA. In the solid state, a DSC analysis showed that the variation of the glass transition temperatures of these materials with the composition behaved differently with the densities of interacting species and were analyzed quantitatively. A thermal stability study of the synthesized copolymers and of their different mixtures carried by thermogravimetry confirmed a similar behaviour. 相似文献
High-speed color filming was used to study laminar spherical flame propagation at the initial stage in preliminarily mixed
stoichiometric mixtures of natural gas and isobutylene with oxygen containing krypton and carbon dioxide and in hydrogen-air
mixtures at atmospheric pressure in a bomb with a constant volume. Under experimental conditions (T0 = 298 K, p0 = 100 torr, spark discharge energy E0 = 0.91 J), the dilution of mixtures with Kr and CO2 increased the time of formation of a stable flame front by more than 10 times. The introduction of a small chemically active
admixture (1.2% isobutylene) into a stoichiometric mixture of hydrogen and air sharply increased the time of formation of
a stable flame front, which was evidence of an important role played by the chemical mechanism of the reaction in the formation
of the combustion field. 相似文献
A study was conducted of the complementary base pair interactions between various pairs of electron-donor monomers, electron-acceptor monomers, homopolymers and alternating copolymers selected from the following group: ( 1 ) 9-(2-vinyloxyethyl)adenine; ( 2 ) 1-(2-vinyloxyethyl)thymine; ( 3 ) 1-(2-vinyloxyethyl)cytosine; ( 4 ) 9-(2-maleimidoethyl)adenine; ( 5 ) 6-chloro-9-(2-maleimidoethyl)purine; ( 6 ) 1-(2-maleimidoethyl)thymine; ( 7 ) 1-(2-maleimidoethyl)cytosine; ( 8 ) homopolymer of ( 4 ); ( 9 ) homopolymer of ( 6 ); ( 10 ) alternating copolymer of ( 2 ) and maleic anhydride; ( 11 ) alternating copolymer of ( 2 ) and ( 5 ); and ( 12 ) alternating copolymer of ( 2 ) and ( 4 ). By 1H-NMR, in CDCL3, the base pair interactions between ( 1 ) and ( 2 ) were shown to be hydrogen bonding, the extent of which was shown by a calculated binding constant, K = 61.81 L/mol. The nature of this interaction was conformed by IR. Neither monomer pairs ( 1 )/( 2 ) nor ( 4 )/( 6 ) exhibited hydrogen bonding in DMSO-d6. However, hydrogen bonding interaction was observed for DMSO-d6 solutions of homopolymers ( 8 ) and ( 9 ) and for alternating copolymer ( 12 ). On the basis of an upfield chemical shift of the 2- and 8-aromatic protons of ademine of ( 1 ) in D2O, a partial overlap stacking interaction is proposed. No charge-transfer interactions could be observed by UV between donor-acceptor monomer pairs. 相似文献
The objective of this paper is to use molecular dynamics (MD) simulation to study the influence of hydrogen bonding on the structure and glass transition temperature (Tg) of maleimide–isobutene alternating copolymers (poly(RMI‐alt‐IB)), a promising material used in the optoelectronics industry. The Tg obtained by MD simulation shows that the incorporation of hydrogen bonding increased the Tg for 48 K. The static and dynamic properties of poly(RMI‐alt‐IB)s are examined in this study. All the results prove that intermolecular CO…H O is the main hydrogen bond in the copolymers, while negligible intramolecular hydrogen bonding is observed. The segmental mobility and chain mobility are decreased because of the existance of the hydrogen bonds.
The structural and electrical characteristics of polyelectrolyte complex micelles (PCMs) formed by mixing of oppositely charged double hydrophilic copolymers are studied by means of molecular dynamics simulations. In mixtures of linear diblock copolymers we found that the preferential aggregation number Np of PCMs is a universal function of the ratio γ± of the total positive to total negative charges of the mixture. The addition of divalent salts ions induces a secondary micellization. In mixtures of copolymers bearing a common neutral thermoresponsive block, micelles with contracted corona consisting of thermoresponsive blocks and complex polyelectrolyte core are formed at low salt concentration and temperature far away the biphasic regime. At high salt concentration and temperature in the biphasic regime, reversed micelles are obtained. In equimolar mixtures of linear copolymers with miktoarm stars we found that Np of PCMs decreases as the number of charged branches of miktoarm copolymer increases. The shape of micelles progressively changes from spherical to worm-like with the increase of number of branches of miktoarm copolymers. Our findings are in full agreement with existing experimental and theoretical predictions and provides new and additional insights. 相似文献
The mechanical effects of association between pendant ionic groups are investigated in series of butadiene–lithium methacrylate copolymers, butadiene–methyl (2-methyl-5-vinyl)-pyridinium iodide copolymers, and mixtures of these polyelectrolytes. Thermal and mechanical tests reveal a new transition above Tg in the pyridinium copolymers, designated Tt*. Below this temperature the materials behave like covalently crosslinked elastomers. The complex between the metal carboxylates appears thermally dissociable at all temperatures. The mixing of the oppositely charged polyelectrolytes leads to the formation of more stable intermolecular pyridinium carboxylate links. 相似文献
All‐atom molecular dynamics (MD) simulation combined with chemical shifts was performed to investigate the interactions over the entire concentration range of the ethanol (EtOH)‐water system. The results of the simulation were adopted to explain the NMR experiments by hydrogen bonding analysis. The strong hydrogen bonds and weak C–H···O contacts coexist in the mixtures through the analysis of the radial distribution functions. And the liquid structures in the whole concentration of EtOH‐water mixtures can be classified into three regions by the statistic analysis of the hydrogen‐bonding network in the MD simulations. Moreover, the chemical shifts of the hydrogen atom are in agreement with the statistical results of the average number hydrogen bonds in the MD simulations. Interestingly, the excess relative extent of ηrelE calculated by the MD simulations and chemical shifts in the EtOH aqueous solutions shows the largest deviation at xEtOH≈0.18. The excess properties present good agreement with the excess enthalpy in the concentration dependence. 相似文献
The solvent shifts of haloformic protons, (Cl3CH, Br3CH, I3CH), have been measured in 24 n-electron donor solvents consisting of halogenated hydrocarbons, esters, ketones, ethers and amines. Deviations of ΔBr and Δ1 from linear dependence with ΔCl are indicative of the presence of halogen bond formation competitive with hydrogen bonding interactions. Bromoform interacts predominantly by hydrogen bonding, halogen bonding being detected to a small extent in chlorinated hydrocarbons and amines. Iodoform shows halogen bonding interactions which increase in relative importance to hydrogen bonding with solvent basicity. Halogen bonding is predominant for solutions of iodoform in amines. 相似文献
Excess molar enthalpies of binary mixtures for tributyl
phosphate (TBP)+methanol/ethanol were measured with a TAM air Isothermal calorimeter
at 298.15 K and ambient. The results for xTBP+(1–x)CH3OH
are negative in the whole range of composition, while the values for xTBP+(1–x)C2H5OH
change from positive values at low x to
small negative values at high x. The experimental
results have been correlated with the Redlich–Kister polynomial. IR
spectra of the mixtures were measured to investigate the effect of hydrogen
bonding in the mixture. 相似文献
A group of block copolymers containing diacetylenes as chain extenders in their hard segments was prepared, based on urethanes, esters, ureas, and amides as hard segments and polybutadienes, polyethers, polyesters, and polysiloxanes as soft segments. Almost all block copolymers were photoreactive, but there was a wide range of sensitivities. The photoreactivity of the copolymers was found to depend on the reactivity of the monomer unit, on the width of the diacetylene stacks in the hard segments, and on the degree of phase separation in the solid films. To explore the range of monomer reactivities we prepared 15 crystalline monomers. Urethanes were in general the most reactive, and this was attributed in part to the specific effect of hydrogen bonding which brings about a shortening of the C1 to C4 distance between diacetylenes tend to reduce the photoreactivity. The behavior of identical diacetylene units in the monomer crystal, in the homopolymer, and in the block copolymer is discussed in this paper. 相似文献