Molecular dynamics simulations of the hydration of poly(vinyl methyl ether):Hydrogen bonds and quasi-hydrogen bonds

Atomistic detailed hydration structures of poly(vinyl methyl ether)(PVME) have been investigated by molecular dynamics simulations under 300 K at various concentrations. Both radial distribution functions and the distance distributions between donors and acceptors in hydrogen bonds show that the hydrogen bonds between the polymer and water are shorter by 0.005 nm than those between water molecules. The Quasi-hydrogen bonds take only 7.2% of the van der Waals interaction pairs. It was found the hydrogen bonds are not evenly distributed along the polymer chain,and there still exists a significant amount(10%) of ether oxygen atoms that are not hydrogen bonded to water at a concentration as low as 3.3%. This shows that in polymer solutions close contacts occur not only between polymer chains but also between chain segments within the polymer,which leads to inefficient contacts between ether oxygen atoms and water molecules. Variation of the quasi-hydrogen bonds with the concentration is similar to that of hydrogen bonds,but the ratio of the repeat units forming quasi-hydrogen bonds to those forming hydrogen bonds approaches 0.2. A transition was found in the demixing enthalpy at around 30% measured by dynamic testing differential scanning calorimetry(DTDSC) for aqueous solutions of a mono-dispersed low molecular weight PVME,which can be related to the transition of the fractions of hydrogen bonds and quasi-hydrogen bonds at ～27%. The transition of the fractions of hydrogen bonds and quasi-hydrogen bonds at ～27% can be used to explain the demixing enthalpy transition at 30% at a molecular scale. In addition,at the concentration of 86%,each ether oxygen atom bonded with water is assigned 1.56 water molecules on average,and 'free' water molecules emerge at the concentration of around 54%.     

Polymer‐solvent interactions during phase transition in poly(vinyl methyl eiher)/D2O solutions as studied by NMR methods

The structural‐dynamic changes and polymer‐solvent interactions during temperature‐induced phase transition in poly(vinyl methyl ether) (PVME)/D₂O solutions in a broad range of concentrations (0.1‐30 wt.‐%) were studied by ¹H NMR methods. In the whole concentration range the phase transition is manifested by line broadening (linewidth 350‐500 Hz) of a major part of PVME units, evidently due to the formation of globular‐like structures. Above the LCST transition, the fraction of phase‐separated PVME segments is equal to 0.8±0.1, independent of polymer concentration. While at low concentrations the transition is virtually discontinuous, at high concentrations the transition region is ∼ 3 K broad. Measurements of nonselective and selective ¹H spin‐lattice relaxation times T₁ of solvent (HDO) molecules evidenced that at elevated temperatures, where most PVME forms globular structures, a part of solvent molecules is bound to PVME forming a complex; the lifetime of the bound water (HDO) molecules is ≤2 s.     

Application of Ultrasonic Attenuation Measurements in the Studies on Macromolecular Conformational Behaviors

——Phase Behavior of the Aqueous Solution of Poly(vinyl methyl ether) Sensitive to Temperature and the Modification of the Behavior by Using Poly(acrylic acid) The phase behavior of the aqueous solution of poly(vinyl methyl ether) (PVME) sensitive to temperature and the modification of the behavior by using poly(acrylic acid) (PAA) have been studied by ultrasonic attenuation measurements and fluorescence probe techniques. It has been observed that PVME solution is transparent at room temperature and becomes turbid upon heating. The solution turns clear again as soon as the temperature is decreased to room temperature. The heating and cooling process can be repeated for many times. The phase behavior of the solution sensitive to temperature is attributed to the conformational changes of the polymer. PVME may adopt an open coil conformation at room temperature. With this conformation, the polymer is well miscible with the solvent, water, and thereby the system is a real solution. The polymer may adopt a compact coil conformation when the temperature is higher than a specific value, which is called the LCST (the lower critical solution temperature) of PVME. In this case, the polymer tangles to each other and forms various aggregates, which can scatter incident light and ultrasonic waves greatly, resulting in the phase separation. Introduction of PAA decreases the temperature sensitivity of the phase behavior of the polymer. The nature of the inhibition is attributed to the complexation of PAA with PVME and the strong hydrophilicity of PAA. Results from fluorescence probe studies are in accordance with those from ultrasonic attenuation measurements, indicating again that the ultrasonic attenuation method can be successfully used for the qualitative studies of polymer conformations and complexation between polymers.     

Application of Ultrasonic Attenuation Measurements in the Studies on Macromolecular Conformational Behaviors——Phase Behavior of the Aqueous Solution of Poly(vinyl methyl ether) Sensitive to Temperature and the Modification of the Behavior by Using Pol

Introduction Studies on the conformational and aggregation be-haviors of macromolecules in aqueous solution and at solid/liquid interfaces have been highlighted in colloid and interface science since the early 1990s.1-3 It was mentioned in the first part of this series of studies that development of new methods, which are characterized by being in time and non-destructive and can be used for monitoring the conformational and aggregation be-havior of macromolecules, is of critical importance fo…     

Immiscibility,upper critical solution temperature,and miscibility in blends of poly(vinyl ether)s with polyacrylics: Effects of pendant groups

Various phase behavior of blends of poly(vinyl ether)s with homologous acrylic polymers (polymethacrylates or polyacrylates) were examined using differential scanning calorimetry, optical microscopy (OM), and Fourier‐transformed infrared spectroscopy. Effects of varying the pendant groups of either of constituent polymers on the phase behavior of the blends were analyzed. A series of interestingly different phase behavior in the blends has been revealed in that as the pendant group in the acrylic polymer series gets longer, polymethacrylate/poly(vinyl methyl ether) (PVME) blends exhibit immiscibility, upper critical solution temperature (UCST), and miscibility, respectively. This study found that the true phase behavior of poly(propyl methacrylate)/PVME [and poly(isopropyl methacrylate)/PVME)] blend systems, though immiscible at ambient, actually displayed a rare UCST upon heating to higher temperatures. Similarly, as the methyl pendant group in PVE is lengthened to ethyl (i.e., PVME replaced by PVEE), phase behavior of its blends with series of polymethacrylates or polyacrylates changes correspondingly. Analyses and quantitative comparisons on four series of blends of PVE/acrylic polymer were performed to thoroughly understand the effects of pendant groups in either polyethers (PVE's) or acrylic polymers on the phase behavior of the blends of these two constituents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1521–1534, 2007     

Upper critical solution temperature phase behavior, composition fluctuations, and complex formation in poly (vinyl methyl ether)/D2O solutions: small-angle neutron-scattering experiments and wertheim lattice thermodynamic perturbation theory predictions

Small-angle neutron-scattering measurements are presented for homogeneous mixtures of poly (methyl vinyl ether) (PVME) and deuterium oxide (D(2)O) at high polymer concentrations and for temperatures lower than the equilibrium melting point of the solvent. The experimental data are analyzed to give values for the second-order compositional derivative of the Gibbs energy and the Ornstein-Zernike correlation length. The experimental data together with earlier SANS data determined at higher temperatures cannot be represented with an extended Flory-Huggins (F-H) interaction function depending on composition and temperatures. The experimental data confirm the existence of a narrow upper critical solution temperature (UCST) miscibility gap at high concentrations in agreement with theoretical predictions of the Wertheim lattice thermodynamic perturbation theory (LTPT). The Wertheim LTPT incorporates the influence of hydrogen bonding and predicts not only the existence of bimodal lower critical solution temperature (LCST) phase behavior but also the occurrence of highly unconventional two narrow adjacent UCST miscibility gaps. Finally, the experimental data do not support the existence of a stable molecular complex at the investigated temperatures and compositions. Even at the lowest investigated temperature, the energy required to induce typical Ornstein-Zernike-like concentration fluctuations is smaller than the thermal energy. Also, in this case, the Wertheim LTPT provides a theoretical basis to understand the formation of polymer solvent associations in PVME/water.     

1H NMR relaxation study of polymer-solvent interactions during thermotropic phase transition in aqueous solutions

The dynamic-structural changes and polymer - solvent interactions during the thermotropic phase transition in poly(vinyl methyl ether) (PVME)/D₂O solutions in a broad range of polymer concentrations (c = 0.1-60 wt.-%) were studied combining the measurements of ¹H NMR spectra, spin-spin (T₂) and spin-lattice (T₁) relaxation times. Phase separation in solutions results in a marked line broadening of a major part of polymer segments, evidently due to the formation of compact globular-like structures. The minority (∼15%) mobile component, which does not participate in the phase separation, consists of low-molecular-weight fractions of PVME, as shown by GPC. Measurements of spin-spin relaxation times T₂ of PVME methylene protons have shown that globular structures are more compact in dilute solutions in comparison with semidilute solutions where globules probably contain a certain amount of water. A certain portion of water molecules bound at elevated temperatures to (in) PVME globular structures in semidilute and concentrated solutions was revealed from measurements of spin-spin and spin-lattice relaxation times of residual HDO molecules.     

Hydrogen bonding and the cryoprotective properties of glycerol/water mixtures

Molecular dynamics simulations and infrared spectroscopy were used to determine the hydrogen bond patterns of glycerol and its mixtures with water. The ability of glycerol/water mixtures to inhibit ice crystallization is linked to the concentration of glycerol and the hydrogen bonding patterns formed by these solutions. At low glycerol concentrations, sufficient amounts of bulk-like water exist, and at low temperature, these solutions demonstrate crystallization. As the glycerol concentration is increased, the bulk-like water pool is eventually depleted. Water in the first hydration shell becomes concentrated around the polar groups of glycerol, and the alkyl groups of glycerol self-associate. Glycerol-glycerol hydrogen bonds become the dominant interaction in the first hydration shell, and the percolation nature of the water network is disturbed. At glycerol concentrations beyond this point, glycerol/water mixtures remain glassy at low temperatures and the glycerol-water hydrogen bond favors a more linear arrangement. High glycerol concentration mixtures mimic the strong hydrogen bonding pattern seen in ice, yet crystallization does not occur. Hydrogen bond patterns are discussed in terms of hydrogen bond angle distributions and average hydrogen bond number. Shift in infrared frequency of related stretch and bend modes is also reviewed.     

Characterization of phase separation of polystyrene/poly(vinyl methyl ether) blends using fluorescence

We have investigated the fluorescence emission spectra of pyrene and anthracene dyes covalently bonded to polystyrene (PS) upon phase separation from poly(vinyl methyl ether) (PVME). The specific chemical structure of the fluorescent labels is found to affect the measured phase separation temperature T_S, with fluorophores covalently attached in closer proximity to the PS backbone identifying phase separation a few degrees earlier. The sharp increase in fluorescence intensity upon phase separation that occurs for all fluorophores with little change in spectral shape is consistent with a mechanism of static fluorescence quenching resulting from the specific interaction with a nearby quenching molecular unit. Based on recent work that has identified a weak hydrogen bond occurring between the aromatic hydrogens of PS and the ether oxygen of PVME, we believe a similar weak hydrogen bond is likely occurring between the PVME oxygen and the aromatic dyes providing a local (few nanometer) sensitivity to phase separation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

A molecular dynamics simulation study of three polysulfones in dry and hydrated states

Molecular dynamics (MD) simulations of three polysulfones (poly(ether sulfone) PESU, poly(phenylene sulfone) PPSU and polysulfone PSU) in dry and hydrated states were undertaken in order to study the specific interactions between water and glassy polymer matrices of the same structural family. Dry polysulfone models were generated using a hybrid pivot Monte Carlo‐MD single‐chain sampling technique and the resulting relaxed densities were found to be in close agreement with experimental data. Hydrated systems are found to reproduce quite well volumetric changes experimentally observed. The concentrations of sulfonic groups can explain qualitatively their different water solubilities. Water is preferentially hydrogen‐bonded to two sites which either link two polymer sites, or one polymer site and another water, or two other waters. A detailed analysis of these water bridges that are formed is presented. Only a small quantity of potential bridging sites are occupied for water contents near the experimental saturation. The free fractional volumes, the probe accessible volumes, the swelling of the polymers, the water‐polymer interactions and the hydrogen bond lifetimes, are also presented for these polysulfones. Water‐water interactions and water clusters are found to be more important in the more hydrophilic PESU in comparison to the less hydrophilic PSU. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Monitoring the hygrothermal response of poly(vinyl methyl ether) submicron films using AFM

Films with submicron thickness of the thermoresponsive polymer poly(vinyl methyl ether) (PVME) are prepared by spin-coating and measured with AFM. The change of film thickness, work of adhesion (WOA), and modulus of elasticity (MOE) are monitored below and above the lower critical solution temperature (LCST) in controlled atmosphere. The film thickness decreases above the LCST at high relative humidity, but not at low humidity. Simultaneously, the MOE increases by 3 orders of magnitude due to conformational transition. The WOA shows a hysteretic behavior due to changes in surface wettability and film compressive strength. Hygrothermal cycling is found to facilitate the relaxation of initially arrested entanglements. The proposed hypothesis of hygrothermally induced partial disentanglement is further supported with cyclic DSC measurements of concentrated aqueous PVME solutions. This work is an important contribution to understand the local and macroscopic behavior of thermoresponsive polymers in dry and humidified atmosphere.     

确定分子量的聚丙烯酸-β-羟乙酯的合成及其水溶液中水氢键缺损的拉曼光谱学研究

水溶性高分子经化学交联可得水凝胶 ,水凝胶也可由水溶性高分子经物理交联如部分结晶微区 ,疏水相互作用及缠绕交联得到 .线型水溶性高分子在水中以高浓度溶解时 ,高分子链之间相互搭迭缠绕也能形成物理“交联” .Ｋｉｔａｎｏ[1～ 4 ] 等研究了聚环氧乙烷、聚丙烯酸、聚丙烯酰胺和聚乙烯基吡咯烷酮等亲水性高分子水溶液中水分子间的氢键缺损情况 ,在重量浓度相同的情况下 ,随着分子量的增大 ,水分子间的氢键缺损加剧 .他们认为分子量大 ,高分子之间的缠绕就比较严重 ,在水溶液中就会形成许多小的微区 ,水分子在这些小微区中形成分子间氢键…     

Dynamics of Poly(vinylmethyl ether) Blends with a Strongly Interassociating Copolymer

We apply broadband dielectric relaxation spectroscopy to probe the dynamics of hydrogen bonded polymer blends. A copolymer consisting of 2,3-dimethylbutadiene (DMB) [86%] and p-(hexafluoro-2-hydroxyl-2-propyl)styrene (HFS) [14%] was synthesized and blended with poly(vinylmethyl ether) (PVME). The copolymer is capable of forming strong intermolecular hydrogen bonds, while minimizing the degree of intramolecular associations, and its blends with PVME are predicted to be miscible over the entire composition range. Two segmental processes, α and α₁, are present in blends containing 26, 50, and 76 weight percent copolymer. The slower process (α₁) is assigned to the segmental motion of the intermolecularly associated copolymer, and the faster process (α) to segmental motions of PVME modified by the HFS:DMB copolymer. A relaxation associated with residual water is present in the glassy state. A local process due to motions of the PVME ether groups (β) is also present in the glassy state, and does not change with blend composition.     

Complexation between poly(maleic acid/octyl vinyl ether) and poly(vinyl caprolactam) in aqueous solution and at the alumina/water interface

Solution and interfacial properties of binary polymer mixtures of poly(maleic acid/octyl vinyl ether) (PMAOVE) and poly(vinyl caprolactam) (PVCAP) have been studied for the alumina/water system. To test the hydrophobic effect, mixtures of poly(maleic acid/methyl vinyl ether) (PMAMVE) and PVCAP are also investigated and compared to the behavior of PMAOVE/PVCAP. At low pH, both polymer mixtures become turbid upon mixing. The turbidity increases at low mixing ratios of PVCAP to the vinyl ether component, reaches a maximum, and then decreases at higher mixing ratios. Upon shifting the pH to the alkaline range, i.e., pH 7.5 and above, the turbid solution becomes clear for both the polymer mixtures. Cloud point measurements indicate the absence of complexation of PVCAP with PMAMVE under the alkaline conditions, but strong interaction with PMAOVE. This is attributed to the different forces involved in the complexation among the polymers: H bonding for PVCAP/PMAMVE and both H bonding and hydrophobic effects for PVCAP/PMAOVE. At the alumina/water interface, the normally nonadsorbing PVCAP is triggered to adsorb by PMAOVE, attributed to the hydrophobic complexation between the two. However, the adsorption of PVCAP shows a maximum as a function of the concentration of PMAOVE. At concentrations of PMAOVE above the onset of its own plateau adsorption, the amount of PVCAP triggered to adsorb is reduced possibly due to the polymer complex formation in solution.     

Relative log P and solution structure for small organic solutes in the chloroform/water system using monte carlo methods

Relative log P values of dimethylether to methanol and dimethylamine to methylamine were calculated in the chloroform/water system using Monte Carlo simulations and statistical perturbation theory. Correct ordering of the calculated relative log Ps was obtained for the two pairs although the method leads to an overestimation of these values. In aqueous solution, both dimethyl ether and dimethylamine solutes are proton acceptors forming a single hydrogen bond to water. Dimethylamine forms a stable N? H-Ow hydrogen bond while the water hydrogen is poorly localized in the O? H-Ow bond to the ether. In chloroform, the solvent molecules are less ordered around the solutes than was found around methanol and methylamine.     

Hydrophilic films based on poly(acrylic acid)–poly(vinyl methyl ether) blends cross-linked by gamma-radiation

Hydrophilic polymeric films based on blends of poly(acrylic acid) and poly(vinyl methyl ether) (PVME) were prepared by casting technique and were cross-linked by gamma-radiation. The films are soft and elastic in a dry state and form hydrogels upon immersion in water. Effect of absorbed dose on the gel fraction as well as on the swelling of the films in aqueous solutions of different pH is studied. It was found that addition of lower molecular weight PVME decreases the gelation dose, which is likely related to a decrease in glass transition temperature of the blends. In acidic media the films have low swelling degree because of suppression of carboxylic groups ionisation and formation of additional physical cross-links via interpolymer hydrogen bonding.     

掺杂聚合物对溶致液晶结构的影响

利用聚合物大分子作构建组分,将其掺杂到不同类型表面活性剂构成的溶致液晶中,考察对液晶相结构的影响．利用小角X射线散射及偏光显微镜对聚合物掺杂前后液晶的结构进行表征,并讨论了聚合物与液晶模板间的相互作用．对阴离子型表面活性剂琥珀酸二异辛酯磺酸钠(AOT)／水液晶体系,聚合物的嵌入使层间距d增大;而对非离子表面活性剂十二烷基聚氧乙烯醚(C12EO4)／水体系,除小分子量的聚乙二醇PEG400外,其它聚合物嵌入使d减小,表明聚合物分子类型、大小及浓度对溶致液晶的结构参数甚至组装方式有不同的影响机制．     

Simulation of Polymer Aggregates as a Method to Investigate the Solvent Effect on Blend Complexation and the Relative Strength of H‐Bonding Groups in Blends

Simulations of polymer‐solvent and polymer‐polymer aggregates, in which the study of hydrogen bonding plays an important role, have been carried out with two blend systems. The aim was to examine the influence of the solvent on blend complexation and to compare the strength of different hydrogen bonds in a blend system. We quantified the strength of one hydrogen bond in the blend environments. For this we used the EVOCAP software, developed by our institute. It allows the building of large molecular aggregates with realistic and homogeneous densities, with an implemented positioning algorithm of the molecules under consideration and their excluded volume, and a charge equilibration method for the partial charge calculation. In the simulated aggregates the specific interaction energy of the hydrogen atom forming the hydrogen bond was a useful indicator for our studies. Through a direct correlation of this specific‐interaction energy with the strength of the hydrogen bond, we supported the experimental result that, in toluene, complex formation between poly(methyl methacrylate) (PMMA) and PSOH, a hydroxyl‐modified polystyrene, is possible, but not in tetrahydrofuran. Varying the proton‐donor polymer, also a hydroxyl‐modified polystyrene, in blends of poly(vinyl methyl ether) (PVME) with groups of different donor strength, we reconstructed the experimental row of increasing hydrogen‐bond strengths.     

Interaction of water with poly(vinyl methyl ether) in aqueous solution

Near-infrared, viscometric, and calorimetric measurements were made on aqueous poly(vinyl methyl ether) (PVME) solutions at temperatures between 15 and 43°C. We found a hydrogen-bonded structure of water around the polymer chain (a polymer-water complex), which is characterized by two distinct hydration numbers (i.e., 2.7 and 5.0 water molecules on each monomer unit of the chain) by analyzing the concentration dependence of endothermic enthalpies at a cloud point temperature, ca. 35°C. In particular, the 2.7 water-polymer complex has been suggested to be cooperatively formed by using data of the near-infrared (nir) absorption spectrum around 1930 nm. Furthermore, the peak-wavelength of the nir spectrum has been observed to change drastically at the cloud point when the temperature is raised. This can be interpreted as a cooperative collapse of the hydrogen-bonded water structure to free water, resulting in the aggregation of the polymer chains due to the exposure of their hydrophobic groups at the cloud point. © 1994 John Wiley & Sons, Inc.     

Quasielastic neutron scattering study of hydrogen motions in an aqueous poly(vinyl methyl ether) solution

We present a quasielastic neutron scattering (QENS) investigation of the component dynamics in an aqueous Poly(vinyl methyl ether) (PVME) solution (30% water content in weight). In the glassy state, an important shift in the Boson peak of PVME is found upon hydration. At higher temperatures, the diffusive-like motions of the components take place with very different characteristic times, revealing a strong dynamic asymmetry that increases with decreasing T. For both components, we observe stretching of the scattering functions with respect to those in the bulk and non-Gaussian behavior in the whole momentum transfer range investigated. To explain these observations we invoke a distribution of mobilities for both components, probably originated from structural heterogeneities. The diffusive-like motion of PVME in solution takes place faster and apparently in a more continuous way than in bulk. We find that the T-dependence of the characteristic relaxation time of water changes at T ? 225 K, near the temperature where a crossover from a low temperature Arrhenius to a high temperature cooperative behavior has been observed by broadband dielectric spectroscopy (BDS) [S. Cerveny, J. Colmenero and A. Alegri?a, Macromolecules, 38, 7056 (2005)]. This observation might be a signature of the onset of confined dynamics of water due to the freezing of the PVME dynamics, that has been selectively followed by these QENS experiments. On the other hand, revisiting the BDS results on this system we could identify an additional "fast" process that can be attributed to water motions coupled with PVME local relaxations that could strongly affect the QENS results. Both kinds of interpretations, confinement effects due to the increasing dynamic asymmetry and influence of localized motions, could provide alternative scenarios to the invoked "strong-to-fragile" transition.