The formation of interpolymer complexes and hydrophilic associates of poly(acrylic acid) and non‐ionic copolymers based on 2‐hydroxyethylacrylate in aqueous solutions

It is shown that the reaction between poly(acrylic acid) and a non‐ionic polymer may give two different products. One of them is the well‐known interpolymer complex stabilized by hydrogen bonds, and the other belongs to a relatively new class of compounds named hydrophilic interpolymer associates. Networks occurring in the dynamic mode of formation and destruction of hydrogen bond linkages represent the structure of the hydrophilic associates; a single molecule of polyacid may be linked with two or more molecules of non‐ionic polymer in such associates. The result of the reaction under consideration strongly depends on the ratio of volumes of swollen coils of ionogenic and electrically neutral macromolecules. Classical interpolymer complexes cannot be formed at a high degree of swelling of polyacid coils, which takes place at high pH values. In contrast, hydrophilic associates are formed under such conditions. © 2013 Society of Chemical Industry     

Stabilization of hydrophobic domains in hydrogel by intermolecular hydrogen bonds between carboxylic groups at the distal end of alkyl side-chain

The role of intermolecular hydrogen bond on the stability of hydrophobically associated domains of hydrogel, consisting of 12-acryloyloxydodecanoic acid (ADA; hydrophobic) or 6-acryloyloxyhexanoic acid (AHA; hydrophobic) and acrylic acid (AA; hydrophilic), carrying an alkyl side group terminated by carboxylic acid, was studied by swelling behavior in an organic solvent/water mixture. We chose propionic acid (PAc) and 1-propanol (PrOH) as organic solvents whose solubility parameter, log P, logarithmic partition equilibrium coefficient for octanol/water, is similar. The equilibrated swelling ratio of poly(ADA-co-AA) and poly(AHA-co-AA) gels by PAc was higher than by PrOH at a lower composition (ca. 5–15 mol%) and that of homo-polymer poly(AHA) gel by PAc was higher even at a high composition (up to ca. 70 mol%). The variation in swelling with solvent/water composition indicated a cross-over between the two solvent systems and this phenomenon did not depend on the alkyl side-chain length. Using Fourier transfer infrared spectroscopy, we observed the remarkable shift of the wavelength corresponding to the hydrogen bond in PAc aqueous solutions. Non-dissociated short alkanoic acid, which can penetrate hydrophobic domains and form hydrogen bonds with non-dissociated carboxylic groups of the polymer gel, favors the disruption of hydrophobic domains, causing swelling. Intermolecular hydrogen bonds between carboxylic groups of the alkyl side-chain are thus closely involved in the stability of hydrophobic domains in copolymer gel.     

The investigation on states of water in different hydrophilic polymers by DSC and FTIR

The interaction between polymers and water in four hydrophilic polymer aqueous solutions were investigated by DSC and FTIR. DSC result shows that the different hydrophilic polymer/water mixtures have various water calorimetric behaviors in the melting temperature range of freezable bound water as well as free water. The melting temperature of freezable water and the amount of non-freezable water in the mixtures vary with the change of chemical structure of polymers. The melting point of the freezable bound water doesn’t change with the water content, revealing that water bound weakly to polymer chains can form a stable crystalline structure at high water content. For the three hydrophilic polymer/water mixtures with C=O group, the weight ratio of non-freezable water to polymers is constant, but varies with polymer chemical structures. The FTIR spectra confirmed the formation of the hydrogen bonds and it was found that there exist different states of water based on various strengths of hydrogen bonds. The OH stretching bands indicated the fraction of strongly bound water decreases with increasing water content. It was concluded that at least in hydrophilic polymer aqueous solutions with polar sites in polymer chains, the formation of non-freezable water is ascribed to the hydrogen bonds between hydrophilic polymers and water molecules. Different strengths of hydrogen bonds can affect the thermal behaviors of water in the hydrophilic polymer/water mixtures.     

Grafting poly(t‐butyl acrylate) to poly(allylamine) by inverse microemulsion radical polymerization: From comb‐polymer to amphiphilic shell crosslinked polymer nanocapsule

An interfacial grafting radical polymerization method for amphiphilic comb copolymer and shell crosslinked polymer nanocapsules was reported. Macropolyradicals on a water soluble long chain polyamine were generated with hydrogen peroxide in the water phase and subsequent grafting radical polymerization of a vinylic monomer at the water/oil interface proceeded at 65°C. In the presence of a crosslinker, the resulting graft copolymer formed a defined core‐shell structure with hydrophilic aqueous core functionalized by the polyamine and a hydrophobic crosslinked polymer shell. The structure of the core‐shell material was characterized by NMR, FTIR, DSC, TGA, SEM, TEM, and the mechanism of the graft polymerization is proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1905–1911, 2007     

Molecular Insight into the Self-Assembly Process of Cellulose Iβ Microfibril

The self-assembly process of β-D-glucose oligomers on the surface of cellulose Iβ microfibril involves crystallization, and this process is analyzed herein, in terms of the length and flexibility of the oligomer chain, by means of molecular dynamics (MD) simulations. The characterization of this process involves the structural relaxation of the oligomer, the recognition of the cellulose I microfibril, and the formation of several hydrogen bonds (HBs). This process is monitored on the basis of the changes in non-bonded energies and the interaction with hydrophilic and hydrophobic crystal faces. The oligomer length is considered a parameter for capturing insight into the energy landscape and its stability in the bound form with the cellulose I microfibril. We notice that the oligomer–microfibril complexes are more stable by increasing the number of hydrogen bond interactions, which is consistent with a gain in electrostatic energy. Our studies highlight the interaction with hydrophilic crystal planes on the microfibril and the acceptor role of the flexible oligomers in HB formation. In addition, we study by MD simulation the interaction between a protofibril and the cellulose I microfibril in solution. In this case, the main interaction consists of the formation of hydrogen bonds between hydrophilic faces, and those HBs involve donor groups in the protofibril.     

Synthesis and swelling properties of pH‐ and temperature‐sensitive interpenetrating polymer networks composed of polyacrylamide and poly(γ‐glutamic acid)

Novel hydrogels of interpenetrating polymer networks (IPNs) composed of polyacrylamide and poly(γ‐glutamic acid) were synthesized. In these systems, both polymers were crosslinked independently; this reduced the potential loss of a polymer during the washing process, as often occurs in semi‐IPN systems. Interpolymer interactions were investigated with Fourier transform infrared spectroscopy and differential scanning calorimetry. These studies suggested possible interactions between both polymers by the formation of hydrogen bonds. The swelling behavior of these hydrogels was analyzed by immersion of the hydrogel samples in deionized water at 25 and 37°C and in buffer solutions with pHs of 3, 7, and 10. The kinetics of swelling showed increases in the values of the swelling ratio with increasing immersion time in the swelling medium, molar proportion of the biopolymer in the hydrogel, temperature, and pH of the swelling medium. All of the hydrogels swelled rapidly and reached equilibrium in an average time of 40 min. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Encapsulation and controlled release in polyacrylamide hydrogels

A novel host–guest system was developed by the encapsulation of simple organic guest molecules in the hydrophilic molecular architecture of crosslinked polyacrylamide hydrogels. The crosslinking agents used for the preparation of the host systems were hexanediol dimethacrylate (HDDMA) and divinyl benzene (DVB). This enabled us to construct hydrogels with different hydrophobic–hydrophilic equilibria. The model guest system used for the studies was benzoic acid. The selections gave simple but excellent host–guest systems with fine polar–apolar balancing. Polyacrylamide hydrogels with encapsulated benzoic acid were prepared with varying crosslink densities (5, 10, 15, and 20 mol %) by the solution polymerization technique. The rate of release of the host from the host–guest assembly was studied in different swelling conditions. The rate of release depended on the interaction forces between the polymer and the solvents. Polar forces, dispersion forces, and hydrogen bonding all played a vital role. The swelling behavior of the host‐polymer system and the host–guest assembly was analyzed and compared by the Flory–Rehner method. The amount of benzoic acid encapsulated in the DVB‐crosslinked polymer was higher than in the HDDMA‐crosslinked polymer, and the rate of release was in the order 5 > 15 > 10 > 20% for the DVB‐crosslinked polymer. The rate of release for the HDDMA‐crosslinked host–guest assembly was in the order 10 > 5 > 15 > 20%. These results were in excellent agreement with those of the Flory–Rehner analysis of the swelling properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1816–1824, 2004     

Molecular dynamics simulation of oxygen diffusion in dry and water-containing poly(vinyl alcohol)

The kinetics and mechanisms of diffusion of oxygen and water in dry and water-containing amorphous syndiotactic poly(vinyl alcohol) were studied at 502 K and normal pressure by molecular dynamics simulation. Penetrant molecule trajectories were obtained in a system with 600 repeating units of poly(vinyl alcohol) and 0, 40 (2.6 wt%) and 80 (5.2 wt%) water molecules. Under dry conditions, oxygen molecules jumped in a cage-like fashion. The oxygen molecule diffused in a liquid-like fashion while water diffusion was cage-like in the system with 5.2 wt% water. The hydrogen bond lifetimes among the water molecules were significantly shorter than those formed between water and the polymer and between different polymer segments. The hydrogen bond lifetimes among all species were, within experimental error, unaffected by the content of water, even though the oxygen diffusivity increased exponentially and the water diffusivity increased to some extent with increasing water content. It seemed that the diffusivity was sensitive primarily to the decrease in concentration of polymer-polymer hydrogen bonds, which followed from the increase in water content. This finding was consonant with the analysis of the oxygen molecule motion relative to the nearest polymer backbone, which revealed that it jumped preferentially along the polymer chain and towards the backbone. This behavior was more pronounced when the dynamics were analyzed over longer distances (5 Å) and it was less pronounced in the water-rich systems. The simulations indicated that water clustering was absent and consequently that water was homogeneously distributed in the polymer systems.     

Novel hydrogels based on a high‐molar‐mass water‐soluble dimethacrylate monomer

This report describes the preparation and swelling behaviour of novel hydrogels based on a water‐soluble dimethacrylate monomer (EBisEMA), which is characterized by a relatively high molar mass (M_n ～ 1700 g mol^?1) and contains a high proportion of aliphatic ether bonds in its structure. This feature results in moderately crosslinked and flexible polymer networks. Significant differences were observed in degree of swelling, depending on the synthesis method employed to obtain the hydrogels. The equilibrium water sorption of EBisEMA photopolymerized in bulk was 68 wt% while that of EBisEMA photopolymerized in aqueous solution (0.5 g mL^?1) was 104 wt%. Thiol–methacrylate hydrogels were prepared by visible light photopolymerization of EBisEMA with a tetrafunctional thiol (PETMP) at various EBisEMA‐to‐PETMP molar ratios. These hydrogels contained unreacted thiol groups because of a faster homopolymerization reaction of EBisEMA. Hydrogels were also prepared in bulk by propylamine‐catalysed Michael addition reaction. No significant differences in swelling were observed between EBisEMA homopolymer and photocured EBisEMA–PETMP copolymer. Conversely, a marked increase in water uptake (110 wt%) was observed in the EBisEMA–PETMP hydrogels prepared by the Michael addition reaction catalysed by propylamine. These trends are explained in terms of a balance between the mass fraction of hydrophilic groups and the crosslinking density of the network. EBisEMA–PETMP hydrogels formulated with thiol in excess showed a noticeable tendency to adhere to diverse substrates, including paper, metals, glass and skin. This feature makes them especially attractive in applications for which adhesion is particularly critical such as dermatological patches. © 2018 Society of Chemical Industry     

A Method for the Immobilization of Chitosan onto Urinary Catheters

A method for the immobilization of an antibacterial chitosan coating to polymeric urinary medical catheters is presented. The method comprises a two-step plasma-treatment procedure, followed by the deposition of chitosan from the water solution. In the first plasma step, the urinary catheter is treated with vacuum-ultraviolet radiation to break bonds in the polymer surface film and create dangling bonds, which are occupied by hydrogen atoms. In the second plasma step, polymeric catheters are treated with atomic oxygen to form oxygen-containing surface functional groups acting as binding sites for chitosan. The presence of oxygen functional groups also causes a transformation of the hydrophobic polymer surface to hydrophilic, thus enabling uniform wetting and improved adsorption of the chitosan coating. The wettability was measured by the sessile-drop method, while the surface composition and structure were measured by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Non-treated samples did not exhibit successful chitosan immobilization. The effect of plasma treatment on immobilization was explained by noncovalent interactions such as electrostatic interactions and hydrogen bonds.     

Molecular dynamic simulation of coal-solvent interactions in Permian-aged South African coals

Molecular dynamic simulations were used to examine the initial stages of solvent-coal interactions during solvent swelling. Large-scale (> 10,000 atoms) vitrinite-rich Waterberg and inertinite-rich Highveld coal models used in this study were previously constructed. Isothermal-isobaric molecular dynamics simulated the experimental conditions used for the solvent swelling of these coals. Partially solvent swollen structures were constructed by the addition of solvent molecules to the original coal molecules using an amorphous building approach. The various solvated coal models were simulated using pyridine, N-methylpyrrolidone (NMP) and CS₂/NMP solvents. The changes in bonding and nonbonding energies due to solvent swelling were determined by comparing original coal models to corresponding swollen models. Simulation studies showed that coal-coal nonbonding interactions changed due to disruption of the van der Waals interaction energies. The distributions of hydrogen bonds were calculated and provided a method to evaluate solvent-coal hydrogen interactions. It was found that hydroxyl groups associated with the bituminous coal structure are the dominating hydrogen bond donor in solvent interaction. Therefore, the contributions of nonbonding interactions in coal play an important role during coal-solvent swelling. Molecular modeling and simulation is a useful tool to probe these changes in energies and nonbonding interactions in coal with various solvents.     

氢键对物质性质与化学反应的广泛影响

氢键是一种特殊的化学键合形式,在很多物质体系中存在着广泛的影响.在无机化学、有机化学、分析化学、生物化学、高分子材料等领域中,氢键都显现了特殊的重要性.讨论了氢键对物质的物理性质、酸碱性、物质结构与化学反应等方面的影响.     

Zum kautschukelastischen verhalten von polyurethan-ionomeren

Dispersions of cationic and anionic ionomers of polyurethanes were prepared by the acetone method. Characteristic changes of the viscosity were observed during the addition of water. This change was studied with a cationic ionomer. The ionomers are mainly associated dimeric species in solution of acetone. During the addition of water the ions are solvated while the hydrophobic segments are increasingly associated. At the maximum of the observed viscosity the apparent molecular weight M_max ≈ 3 M_min. In the absence of solvents the ionomers behave like crosslinked materials even if no covalent crosslinks are present. The modulus at small elongations is a linear function of the square of the concentration of the cations. It is concluded that two ionic centers are required per crosslink. The anionic ionomers were also chemically crosslinked since an excess of isocyanate was used. A linear increase of the modulus was observed with increasing amount of chemical crosslinks, while the concentration of ions and hydrogen bonds was constant. The crosslinks formed by ions can be suspended by swelling with water. The portion of the modulus caused by ionic crosslinking can be computed from the difference of the moduli in the dry and swollen state.     

Influence of the environment on swelling of hydrophilic polymers

The influence of water activity on swelling of cross-linked hydrophilic polymers in electrolyte solutions of various concentrations was studied. A heterophase model was proposed to explain the polymer swelling. It was shown that the change in polymer swelling deals with different water sorption, and is described by water vapour sorption isotherm. At the same time, the volume of external solution taken up by polymer at swelling is constant and independent of concentration of the solution. Three models describing the structure of polymer gels were suggested and discussed on the base of the obtained results.     

The effect of oil raw material composition in the synthesis of bio-sorbents based on inverse vulcanization on the ability to remediate hydrocarbon-contaminated water. A novel method for decontaminating water/fuel emulsions

Solid crosslinked biopolymers made by inverse vulcanization of soybean (PSB) or sunflower (PSF) oil with sulfur are characterized and tested to decontaminate water from hydrocarbons (HC): gasoline, diesel, two lubricant oils, and water/gasoline emulsion. The physicochemical structure of the biopolymers is studied by FTIR spectroscopy, Differential scanning calorimetry, contact angle measurement, and mechanical testing. Also, the morphological structure is analyzed by scanning electron microscopy. Moreover, the polymer decontamination capability and reusability are tested gravimetrically. Both biopolymers are formed by C S bonds, and their elastic behavior dominates. However, PSF is more hydrophilic, has a larger amount of free sulfur and a less compact structure, and also sorbs ca. 60% more HC than PSB. The results indicate that the unsaturated feedstock has a strong effect on the polymer structure and the capacity to remediate contaminated water or solids. Also, both materials can be reused to remediate water for more than five consecutive cycles. In addition, inverse vulcanization of oils and sulfur is an ecological way of obtaining environmentally-improved materials with great potential and applications, providing a complete atomic economy and high performance to remediate water from water/HCs dispersed and, more importantly, from water/gasoline emulsions.     

Effect of crosslinked polycarboxylate superplasticizers with varied structures on cement dispersion performance

In order to investigate the effect of double bond content in the crosslinkers on the performance of superplasticizers, three different crosslinked polycarboxylate superplasticizers were synthesized herein with various respective crosslinkers. Their impacts on the fluidity, absorption, and hydration behavior of cement systems were studied. The results showed that the polymer, which was synthesized using a crosslinker with four double bonds and five/six double bonds, had higher fluidity and the highest fluidity reached up to 395 mm at W/C of 0.35. Additionally, thermogravimetric analysis and hydration heat tests showed that the crosslinked polycarboxylate superplasticizers could prolong the hydration process of cement slurries. Among these three kinds of crosslinked polycarboxylate superplasticizers, the induction period of cement slurry containing the polymer with crosslinker of four double bonds was significantly extended to facilitate the processing of the concrete. The purpose of this study is to provide strategies for studying high-performance polycarboxylate superplasticizers with novel topological structure.     

Hydrophilic membranes for pervaporation: An analytical review

An analytical review has been attempted on the issues encountered in selecting polymers for hydrophilic pervaporation (PV) membranes. It is well known that permselectivity is determined by selective sorption and by selective diffusion. Selective sorption is governed by the presence of the active centers in the polymer which are capable of specific interactions with water. The analysis of the influences of the type of interactions of water-active centers of the polymer on the membrane performances are presented. Selective diffusion is governed by the rigidity and the regularity of the polymer structure and also by the constructure of the polymer's interspace. There is a net of bonds and crosslinks in the polymer due to existence of inter- and intramolecular interactions in it. This net is responsible for the stability of the mass transfer properties of the polymer to the feed water. The influences of the degree of swelling and frequencies of the crosslinks in the polymer are analysed. The main role of the selective diffusion in the selective permeation is demonstrated. The possibility of the existence of two different channels (hydrophilic and hydrophobic) for the permeation of water and organics is discussed, and it has been concluded that there are two different channels for friable polymers which have fragments with not so strong inter- and intra-molecular interactions. But in the polymers with strong inter- and intra-molecular interactions and a narrow net of these bonds (e.g., polyelectrolyte complexes), the hydrophobic channels are strongly collapsed. They can be opened only by water at its high feed concentrations. It was concluded that one of the most prospective ways to create highly permeative and highly selective materials for dehydration of organics by PV is using polyelectrolyte complexes (especially for the separation of water with organic molecules, which have more than three carbon atoms in total).     

Hydrogen bond lifetimes and statistics of aqueous mono‐, di‐ and tri‐ethylene glycol

Hydrogen bond statistics, energy distributions of hydrogen bonds and hydrogen bond lifetimes for aqueous monoethylene glycol (MEG), diethylene glycol (DEG), and triethylene glycol (TEG) were investigated at temperatures ranging from 275 to 370 K at 101.325 kPa using molecular dynamics simulations. Each individual type of hydrogen bond were studied separately to better understand how each type of hydrogen bond affected the collective behavior often measured in experiments. We also studied the effects of glycols on water–water hydrogen bond structures and lifetimes. Decay constants for hydroxyl type hydrogen bonds, as well as for water based hydrogen bonds were in the same order, thus indicating that all these hydrogen bonds play an essential role in the process of dielectric relaxation. Correlations between water hydrogen bond distances and angles were not affected markedly by adding glycols. However, hydrogen bond lifetimes increased by 9, 29, and 62 times by adding MEG, DEG, and TEG, respectively. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1674–1689, 2017     

基于分子修饰C-COS的高吸湿保湿机理

采用漆酶/2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)体系氧化壳寡糖制备了一种高吸湿保湿性羧基化壳寡糖(C-COS)。利用低场核磁共振(LF-NMR)、FTIR和13CNMR考察了其分子间氢键的变化并进一步推测出吸湿保湿机理。结果表明:在C-COS的吸湿过程中,聚合物分子与水之间存在着分子间氢键作用力。C-COS分子上极性较强的羧酸根产生了新的氢键效应,结合升温红外中3363、1643 cm~(–1)处吸收峰强度的减小和同样波数下吸收峰频率的蓝移以及溶胀红外中1643cm~(–1)处吸收峰强度的增加,确定了C-COS分子中羧酸根与水之间所形成的水合氢键(H—O—H···O—C==O)。另外,C-COS的保湿机理在于聚合物溶解在水体系中能够形成一种巨大的聚合物-水网状结构,促使水分子以氢键的形式被牢牢地锁住在这种网状结构中。     

微波电场对甘油水溶液体系中氢键的影响

通过分子动力学模拟考察微波电场对不同水含量甘油溶液中氢键的影响。研究发现：甘油含量高时,甘油分子在溶液中以较大的团簇结构存在,水分子以较小的团簇结构或游离状态存在,电场作用下,大的甘油分子团簇变成较小的团簇并且变得更加有序;随着电场强度继续增加,甘油分子整体结构变化不大,但是团簇结构边缘甘油分子氢键断裂,变成游离状态。对于水分子而言,其较小的团簇结构在电场作用下被打开,团簇结构消失,水分子在电场方向上整齐排布,且电场强度继续增大,其结构变化不大,同样个别水分子氢键断裂变成游离状态。因此,甘油浓度高时,水分子间氢键数减少,甘油分子氢键数先增大后略微减少;甘油浓度低时,水分子氢键数先增大后略有减少,甘油分子间氢键减少。