Rapid formation of natural gas clathrate hydrates has been a significant hazard in off-shore natural gas drilling and gas transport. During operation, polymer inhibitors can serve as low-dosage kinetic inhibitors to prevent the formation of gas hydrates. A comprehensive consideration of the multiple factors involved in the actions of kinetic hydrate inhibitors (KHIs) can elucidate the inhibiting behavior of polymers. Here, amphiphilic poly(N-isopropylmethacrylamide) (PNIPMAm) (or poly(N-isopropylacrylamide)) are found to achieve weak to strong inhibition by the variable superimposed effect of the polymer's amide group and hydrophobic effect of the polymer's alkyl groups on the aqueous phase. The interfacial and bulk water mobility and hydrogen bonding energy in the polymer solutions are compared by low-temperature nuclear magnetic resonance (NMR) relaxometry. The mobility of the water is found to be sensitive to the hydrophobic alpha-methyl side group in PNIPMAm and its molecular weight when a guest molecule tetrahydrofuran is present. The water hydrogen bonding energies measured from NMR are also associated with the nonfreezable bound water amount revealed by differential scanning calorimetry. The alpha-methyl side group leads to a significant reduction of the water mobility, an increase in the hydrogen bonding energies of the interfacial water, and a decrease of the hydrate growth rate constants by 2 to 3 orders of magnitude. The retarded reaction kinetics of heterogeneous hydrate growth can be related to the hydrophobic effect of the polymer's alpha-methyl side group and bound water properties (mobility and amount) in the interface.

We present an efficient approach for the consecutive synthesis of Au-TiO2 nanocomposites with controlled morphologies in a microfluidic chip. The seed-mediated growth method was employed to synthesize Au nanorods as the core, and TiO2 layers of varying thicknesses were deposited on the surface or tip of the Au nanorods. Au-TiO2 nanocomposites with core-shell, dumbbell, and dandelion-like structures can be precisely synthesized in a one-step manner within the microfluidic chip by finely tuning the flow rate of NaHCO3 and the amount of hexadecyl trimethyl ammonium bromide. Furthermore, we have investigated the photocatalytic activity of the synthesized nanocomposites, and it was found that Au NR-TiO2 core-shell nanostructure with a thin TiO2 shell exhibits superior catalytic performance. This work provides an effective and controlled method for the microscale preparation and photocatalytic application of various Au-TiO2 nanocomposite structures.

We prepare metal films with various thicknesses on liquid substrates by thermal evaporation and investigate the annealing effect on these films. Gold films deposited on a silicone oil surface consist of a large number of branched aggregates, which contains plenty of gold nanoparticles. This characteristic morphology is mainly attributed to the isotropic and free-sustained liquid substrate. Thermal annealing results in the reintegration of nanoparticles; thus, the surface morphology and microstructure of gold films change significantly. The dependence of annealing conditions on the surface-enhanced Raman scattering performance of gold films is studied, in which gold films show favorable Raman activity when annealed at certain annealing temperature and the experimental results are verified by simulation analysis. The study on the optimal annealing temperature of surface-enhanced Raman scattering substrate will pave the way for the potential application of films deposited on liquid surfaces in microfluidics and enhanced Raman detection.

Amphiphilic polymers have now been designed to achieve an icephobic performance and have been used for ice adhesion prevention. They may function by forming a strongly bonded but nonfreezable water shell which serves as a self-lubricating interfacial layer that weakens the adhesion strength between ice and the surface. Here, an analogous concept is built to prevent the formation of clathrate hydrate compounds during oil and natural gas production, in which amphiphilic water-soluble polymers act as efficient kinetic hydrate inhibitors (KHIs). A novel group of copolymers with N-vinylcaprolactam and N-acryloylpyrrolidine structural units are investigated in this study. The relationships among the amphiphilicity, lower critical solution temperature, nonfreezable bound water, and kinetic hydrate inhibition time are analyzed in terms of the copolymer compositions. Low-field NMR relaxometry revealed the crucial interfacial water in tightly bound dynamic states which led to crystal growth rates changing with the copolymer compositions, in accord with the rotational rheometric analysis results. The nonfreezable bound water layer confirmed by a calorimetry analysis also changes with the polymer amphiphilicity. Therefore, in the interface between the KHI polymers and hydrate, water surrounding the polymers plays a critical role by helping to delay the nucleation and growth of embryonic ice/hydrates. Appropriate amphiphilicity of the copolymers can achieve the optimal interfacial properties for slowing down hydrate crystal growth.

We report a facile approach for the wettability control of copper (Cu) films grown on a silicone oil surface by thermal evaporation. Characteristic aggregation of deposited Cu atoms was obtained due to the isotropic and free-sustained liquid substrates. Through the fine adjustment of deposition parameters in the growth process, Cu films with controlled morphology from ramified aggregates to continuous films can be prepared. Accompanied with the evolution of morphology, water wettability was effectively reduced and the hydrophilic-to-hydrophobic transition can be achieved. The relationship between the wettability and microstructure of Cu films was investigated. These films with characteristic morphology and controlled wettability may open lots of application avenues in the development of devices with modified surface properties.

Hydrogen gas production can be produced from dimethylamine borane by the catalytic effect of metal nanoparticles. Past research efforts were heavily focused on dehydrogenation in organic solvents. In this study, hydrolysis of the borane in aqueous solutions was investigated, which bears two significant advantages: that two-thirds of the hydrogen generated originate from water and that the hydrogen storage materials are non-flammable. Polymer hydrogels serve as good carriers for metal particles as catalysts in aqueous solutions. Kinetic analysis of hydrogen production was performed for Ni/Pd bimetallic nanoclusters dispersed in a polymer hydrogel with a 3-D network structure. The reaction catalyzed by the bimetallic nanoclusters has an activation energy of only 34.95 kJ/mol, considerably lower than that by Ni or other metal catalysts reported. A significant synergistic effect was observed in the Ni/Pd bimetallic catalysts (Ni–Pd = 20/1) with a higher activity than Pd or Ni alone. This proves the alloy nature of the nanoparticles in the borane hydrolysis and the activation of water and borane by both metals to break the O–H and B–H bonds. The hydrogel with the Ni/Pd metal can be recycled with a much longer lifetime than all the previously prepared catalysts. The aqueous borane solutions with a polymer hydrogel can become a more sustainable hydrogen supplier for long-term use.

Water-soluble amphiphilic polymers are vital chemicals in the oil and gas industry to retard crystal growth of hydrocarbon hydrate via surface adsorption and suppress nucleation of a pristine hydrate nucleus, thereby preventing formation of hydrate blockages in flow lines during oil and natural gas production. Apart from a few theoretical modeling studies, an experimental method to study the polymer/water interface in the crystal growth is critically needed. Here, water motions in the hydration shells of an exemplary kinetic inhibitor, poly(N-vinylcaprolactam), during hydrate formation from the tetrahydrofuran/water system are revealed via nuclear magnetic resonance relaxometry. Unequivocal experiments show that the pivotal interfacial water in the tightly bound state gradually freezes at rates depending on the polymer molecular weight (MW). This is supported by nonfreezable water analysis, which is correlated to the inhibition time. The polymers tune the kinetics of the hydration process via interaction with and perturbation of the water molecules. The free water component in the polymer solution crystallizes at a very slow rate when in partially restricted mobility, whereas the bound water component increases in the reaction, with the polymer/water interface serving as the reaction sites. The appropriate MW (including average MW and polydispersity values) of the inhibitive polymers can give rise to maximal retardation of the hydrate crystal growth. This work will help control other multiphase crystallization kinetic processes through the design of inhibitors or promoters functioning in the interface.

Subsea natural gas drilling and gas transport is challenged by the catastrophic formation of gas clathrate hydrate in production lines. Polymer inhibitors are vital to mitigate this technical problem in subsea gas drilling operation. However, physico- chemical factors affecting their performance are not yet completely known. Herein, we report that the activities of synthetic kinetic inhibitors of clathrate hydrates are correlated to the surrounding water dynamics. Two types of linear polyamide inhibitors are found to be capable of producing immobilized nonfreezable water molecules with fast transverse relaxation in sub-millisecond to millisecond time-scale as revealed by NMR relaxometry. Such a unique state of water can be construed as a form of nonfreezable bound water measured by differential scanning calorimetry. The quantity of such water species can be tuned by the size of the hydrophobic groups introduced to the polyamides and result in longer inhibition time before the rapid growth of the hydrate crystals. Addition of a single hydroxyl side group in the polymer structural unit can also affect the dependence of the kinetic inhibition time on the amount of the supercooled water. Both the hydrophobic and hydrophilic groups in the polymer inhibitors exert coordinated influence on the dynamic properties of the bound water, which are responsible for the early recognition and inhibition of the clathrate hydrate clusters.

Reusable palladium nanoparticles highly dispersed in porous and hydrophilic interpenetrating polymer networks (IPN), i.e., Pd@IPN hybrid gels, are employed for catalysis of Suzuki and Heck coupling reactions. Good yields are obtained with high turnover frequencies when the reactions are run with very low Pd-loadings. The use of IPN gives better recyclability than that of crosslinked polyvinyl alcohol alone. The polymer networks allow the reactants to have easy access to the Pd metals. The catalysts combine high activity with the reusability offered by the heterogeneous system, without the need for strong coordination or chelating ligands.

Kinetic hydrate inhibitors (KHIs) are polymers that play a vital role in gas energy production, transport, and storage. A series of polyaspartamides based on l-aspartic acid were designed to serve as potential KHIs. Tuning the fine structures of the polyaspartamides can inhibit the tetrahydrofuran hydrate formation more effectively than classical KHIs, i.e., poly(N-vinylcaprolactam) (PVCap) and poly(N-vinylpyrrolidone) (PVP). When the hydrophobic side chain is longer, the polyaspartamide is more effective. For elucidation of the polymer structure–property relationships in the inhibition of the clathrate hydrate, the molecular-level interactions between the polyaspartamides and tetrahydrofuran hydrate were studied. Dynamics of water surrounding the polymers probed by NMR relaxometry demonstrate that the polyaspartamides can bind tightly with water molecules in the hydrate, resulting in faster transverse relaxation times of the nonfreezable water. This phenomenon can be interpreted by quantum chemical simul...

Efficient non-precious metal catalysts are crucial for hydrogen production from borohydride compounds in aqueous media via hydrogen atoms in water. A method for preparing magnetic polymer nanoparticles is developed in this study based on the chemical deposition of nickel onto hydrophilic polymer nanogels. High-resolution transmission electron microscopic and XPS analyses show that Ni exists mainly in the form of NiO in nanogels. Excellent catalytic activities of the nanoparticles are demonstrated for hydrogen generation from the hydrolysis of dimethylamine-borane and sodium borohydride in which the initial TOF (turn-over frequencies) are 376 and 1919 h(-1), respectively. Kinetic studies also reveal an Arrhenius activation energy of 50.96 kJ mol(-1) for the hydrolysis of dimethylamine-borane and 47.82 kJ mol(-1) for the hydrolysis of sodium borohydride, which are lower than those catalyzed by Ru metal. Excellent reusability and the use of water for hydrogen production from dimethylamine-borane provide the additional benefit of using a hybrid catalyst. The principle illustrated in the present study offers a new strategy to explore polymer-transition metal hybrid particles for hydrogen energy technology. (C) 2016 Elsevier Ltd. All rights reserved.

Two types of polymer nanocomposite particles were developed through electroless plating of nickel onto polymer nanospheres for hydrogen production from sodium borohydride solution. Different distributions of Ni in the polymer particles can be obtained either in polymer core-metal shell morphology or homogeneously hybridized morphology, depending on the hydrophilicity of the polymers. The Ni-polymer particles exhibited high catalytic activities in hydrogen production reactions with excellent recyclability, which is important in portable clean energy generation technology. (C) 2015 Elsevier Ltd. All rights reserved.

ABSTRACTA novel type of aqueous soluble polyamides were prepared as renewable substitutes for ecologically benign poly(aspartic acid) by polymerization of succinic acid ester and hexamethylene diamine in the presence of citric acid ester. The copolymerization resulted in the formation of poly(amide imide) intermediates, which were hydrolyzed to aqueous solutions of polyamides. The hydrolyzed products were confirmed to be copolymers of succinamide and citramide with COOH side chains, similar to poly(aspartic acid). The polyamides showed strong chelating abilities to Ca2+ and Pb2+ metals, comparable to poly(aspartic acid). Interestingly, they also demonstrated antifreeze activities in water by reducing the ice fractions. The polyamides represent a new class of metal chelators and antifreeze protein mimics derived from succinamide and citramide. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39807.

Catalyzed sodium borohydride hydrolysis is a highly valuable method to produce clean hydrogen energy for portable applications. This study provides a new and fast route to preparation of reusable hybrid materials composed of nickel-boron based nanoclusters dispersed in nanoporous poly(acrylamide) hydrogels for catalyzed hydrogen production. Palladium was added to the Ni-B catalysts during chemical reduction under the protection of poly(N-vinylpyrrolidone). The resulting nanoclusters immobilized in the hydrogels were essentially alloy particles with uni-modal size distributions and average diameters ranging from ca. 4-8 nm. Pd exerted significant promoting effects on the activities of the Ni-B catalysts. The highest activity was achieved for Pd-Ni-B nanoclusters with a charge ratio of Pd/Ni = 1/20 in moles, which exhibited activity nearly twice that of a Ni-B catalyst and good recyclability for consecutive uses. The hydrogen production rates also increased with the decreasing particle sizes. The activation energy, enthalpy and entropy for the reaction were determined to be 31.10 kJ mol(-1), 28.39 kJ mol(-1) and -45.22 J mol(-1) K-1, respectively. The activation energy is lower than that of previously reported polymer-stabilized Co(0), Fe(0), or Ni(0) nanoparticle catalysts. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Hydrogen-bonded interpolymer complexes can be used for development of novel dosage forms. In this study, two types of crosslinked hydrogels, copolymer networks of N-vinyl pyrrolidone and acrylamide (PVP-co-PAM) and interpenetrating polymer networks (IPN) composed of crosslinked PVP-co-PAM and poly(vinyl alcohol) (PVA), were synthesized at three different degrees of crosslinking. The side chain groups in such polymers can form non-ionic complexes through H-bonding, resulting in additional "crosslinks" in the hydrogels. Both kinds of hydrogels have significantly larger swelling sensitivities than the networks formed with ionizable side chains. In the IPNs, introduction of the PVA chains into the PVP-co-PAM networks raises the permeability, indicating more open pores. The permeability decreases with the increasing degree of crosslinking of the copolymer. For probing the drug binding in the hydrogels, Fourier transform infrared spectra (FTIR) difference spectroscopy indicated the presence of significant H-bonding interactions between 5-fluorouracil (5-FU) and the side chains of the polymers. Such interactions are larger in the PVP-co-PAM copolymers than in the IPN hydrogels, thereby causing an additional source of the slower release kinetics in the copolymer hydrogels as revealed by the Peppas model, albeit both types of the networks followed a non-Fickian transport mechanism.

Copolymers of tributyl citrate (TBC) and hexamethylenediamine (HMDA) were synthesized with a solvent-free condensation method with molar ratios of TBC to HMDA varying from 2:1 to 1:2. The reaction led to poly(succinimide-co-citramide) copolymers which were characterized by infrared and Raman spectroscopies, X-ray diffraction, and thermal analyses. Hydrolysis of the copolymers resulted in water soluble polycitramides with number averaged molecular weights ranging from 1.16 x 104 to 5.00 x 103 as determined by gel permeation chromatography. 1H, 13C, and 13C-1H-heteronuclear single quantum coherence NMR spectroscopy has confirmed that the hydrolyzed polycitramides with COOH side chains and amide backbones are structurally similar to biodegradable poly(aspartic acid) (PASP). Interestingly, the polycitramides showed Ca2+ and Pb2+ ion chelating capabilities higher than PASP, citric acidsorbitol copolymers, or conventional resins. Thus, the polycitramides offer promise as a totally new class of metal sequesters and renewable substitutes for PASP and poly(acrylic acid). (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

A novel type of Heck reaction catalyst composed of hydrophilic interpenetrating polymer networks (IPNs) and palladium (Pd) nanoparticles was prepared by simultaneous crosslinking of polyvinyl alcohol and polyacrylamide. The mesh sizes of the IPNs are one order of magnitude smaller than the average sizes of the uniformly dispersed Pd nanoparticles, which functions well to stabilize Pd nanoparticles and prevent aggregation. The Pd particles in the IPNs can catalyze Heck coupling reactions with high activities and be recycled over 20 times, providing more sustainability than any other polymer-stabilized Pd catalyst reported in the literature. The confined reactions inside the IPN nanopores in neat water may provide a green route for C–C coupling reactions.

This study reports properties of a class of biodegradable polyesters based on citric acid and glycerin, both of which are safe ingredients in food, and their usefulness for drug control release applications. Transparent thin films of poly(glycerin citrate) (PGC) prepared by condensation polymerization were characterized by dynamic mechanical analysis, tensile testing, and FTIR spectroscopy. Depending on the acid-to-glycerin molar ratios, the crosslinked films could have glass transition temperatures varying from 30 to 81 degrees C as shown by dynamic mechanical analysis. The ductile PGC films were more prone to hydrolytic degradation than poly(lactic acid). The controlled release properties of the PGC films were evaluated by a permeation study of an exemplary drug theophylline. The diffusion of theophylline in PGC film follows a Super Case II mechanism, but in PGC film modified with PEG4000, the diffusion follows approximately a Case II mechanism (near zero-order release mechanism). (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Poly(N-vinylpyrrolidone) (PVP) hydrogels have become increasingly important materials for pharmaceutical and biomedical applications. UV-light initiated oxidative crosslinking of PVP represents a novel method for producing PVP based hydrogel materials. However, the mechanism of the gelation by this approach is poorly understood. In this study, the reaction mechanism for the crosslinking process is investigated by FTIR, Raman, and solid-state CP/MAS NMR techniques. Both FTIR and Raman spectra indicate that in the process of free radical oxidative crosslinking, the pyrrolidone ring is partially transformed into a succinimide ring. Solid-state NMR data have confirmed this change, and provided evidence that stable intermediates of 4-hydroperoxy-pyrrolidone (PVP–OOH) and its accompanied 4-hydroxy-pyrrolidone (PVP–OH) are formed. The pyrrolidone hydroperoxide intermediate can account for the efficient crosslinking, producing a sufficient level of macroradicals to form stable hydrogels.

This article reviews recent advances in polymer-supported Pd catalysts for heterogeneous C—C coupling reactions.This type of catalysts possesses high activities,selectivities,and multiple reusable performance for Suzuki-,Heck-,Sonogashira-,Stille-,Ullmann-and related coupling reactions,therefore showing great potential in membrane reactors,automatic combinatorial synthesis,and transformation to environmental friendly materials.Microencapsulation and nanocluster formation are useful methods for achieving both high activity and recyclization.Polymeric ligands have several advantages that they can immobilize the metal,adjust and control the activity of the metal,and even demonstrate macromolecular effect,while the polymer chains can present necessary mechanical properties and desired affinities in different reaction media.