Noncovalent binding interactions of polyacrylamide and clay in nanocomposite hydrogels

The interactions between organic and inorganic components in pregel solution for polyacrylamide (PAAm)/clay nanocomposite hydrogels (NC gels) and in prepared NC gels are investigated. Besides, a kind of self‐crosslinked PAAm gels with excellent mechanical properties is fabricated in the absence of any cross‐linking agents, the hydrogen bonding interactions among PAAm chains are acted as the cross‐linking force. It is revealed that the binding interactions of PAAm and clay in NC gels are owing to the noncovalent interactions between amide groups on PAAm chains and clay platelets, which afford the cross‐linking force for NC gels network formation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis and properties of waterborne self‐crosslinkable sulfo‐urethane silanol dispersions

A novel type of crosslinkable waterborne polyurethane ionomer was prepared by the acetone process. Two new types of sulfonated diols compatible with this process were synthesized from dimethyl 5‐sodium sulfo isophthalate using a one‐ or two‐stage method. Isocyanate‐terminated polyurethane oligomers were prepared from the sulfonated diols with various combinations of diols and diisocyanates and subsequently reacted with amino silane derivatives. Stable, low‐volatile organic chemical, waterborne dispersions of the sulfo‐urethane silanol polymers spontaneously crosslink upon drying without extra additives or processing steps. Despite the lack of organic coalescing solvents, the dispersions have minimum film‐forming temperatures below 10 °C, regardless of glass‐transition temperature. Tensile strengths up to 6000 psi with elongations between 300 and 600% were obtained for the crosslinked films. The hard‐segment content of the films can be controlled to produce films with a Sward–Rocker hardness value up to 42. Through silane end‐group modification, the crosslinking density of the films can also be modified to produce polyurethanes with a wide range of physical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3037–3045, 2002     

Synthesis and physical properties of layered silicates/polyurethane nanocomposites

Samples of polyurethane nanocomposites were synthesized using diphenylmethane diisocyanate, poly(ε‐caprolactone) diol, di(ethylene glycol), and a clay functionalized by hydroxyl groups. The inorganic content in the hybrids was 2 wt %, 4 wt %, and 8 wt %. The X‐ray analysis showed that exfoliation occurred for clay content equal to 2% (w/w), whereas for higher contents, the inorganic phase rearranges in an intercalated structure. FTIR analysis suggested that the degree of hydrogen bonding in the hard segments was greatly reduced because of the amount of silicate layers and their dispersion. The dynamic‐mechanical analysis showed that the presence of clay lamellae extends very much the temperature range before the hard domain transition, causing the loss of mechanical consistency of the samples. It is less than 100 °C for the pure polymer, and increases up to 200 °C for the nanocomposites. The permeability of water vapor decreases linearly with inorganic content up to 4% of inorganic phase, and levels off at higher concentrations. The permeability behavior, at low activities, is largely dominated by the diffusion phenomenon. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2454–2467, 2005     

UV curable waterborne polyurethane acrylate dispersions based on hyperbranched aliphatic polyester: effect of molecular structure on physical and thermal properties

A novel waterborne hyperbranched polyurethane acrylate for aqueous dispersions (WHPUDs) based on hydroxy‐functionalized hyperbranched aliphatic polyester Boltorn? H20 was investigated. The effects of structural composition and crosslinking density have been studied in terms of swellability by water, thermal degradation, viscosity changes as well as transmission electron microscopy (TEM) morphology. The swell ratio showed an increasing trend with the higher concentration of ionic group, which is due to the increased total surface area of particles. The results of thermogravimetric analysis (TGA) for cured WHPUD films indicated good thermal stability with no appreciable weight loss until 200°C. The activation energies were evaluated and were found in the range 154–186 kJ mol^?1. It was observed that an increase in hard segment content provoked the increases in thermal degradation temperature and activation energy of waterborne dispersions. The transmission electron photographs revealed that the average particle sizes of aqueous dispersions were in the range 30–125 nm. Owing to the enlargement of the stabilization site, the particle size decreased as the content of carboxyl group and degree of neutralization increased. The viscosity of WHPUDs increased rapidly with increasing the degree of neutralization. Moreover, water showed a favorable viscosity reduction effect. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of organophilic clay on the solvent‐maintaining capability,dimensional stability,and electrochemical properties of gel poly(vinylidene fluoride) nanocomposite electrolytes

Four quaternary alkyl ammonium salts were used in an organophilic procedure, performed on montmorillonite clay, and resulted in intercalation in dimethylformamide (DMF) or ethylene carbonate (EC)/propylene carbonate (PC) as a cosolvent between poly(vinylidene fluoride) (PVdF) and the organophilic clay. An examination using X‐ray diffraction revealed that PVdF entered galleries of montmorillonite clay, and it exhibited exfoliation and intercalation phenomena when it was analyzed with transmission electron microscopy. Gel PVdF nanocomposite electrolyte materials were successfully prepared by the addition of the appropriate percentages of DMF or PC/EC as a cosolvent, organophilic clay, and lithium perchlorate to PVdF. The maximum ionic conductivity was 1.03 × 10^?2 S/cm, and the materials exhibited better film formation, solvent‐maintaining capability, and dimensional stability than electrolyte films without added organophilic clays. The results of cyclic voltammetry testing showed that the addition of the organophilic clays significantly enhanced the electrochemical stability of the polymer electrolyte system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3873–3882, 2002     

Effects of polymerization method on structure and properties of thermoplastic polyurethanes

The effects of the dynamic polymerization method and temperature on the molecular aggregation structure and the mechanical and melting properties of thermoplastic polyurethanes (TPUs) were successfully clarified. TPUs were prepared from poly (ethylene adipate) glycol (M_n = 2074), 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol by the one‐shot (OS) and the prepolymer (PP) methods in bulk at dynamic polymerization temperatures ranging from 140 to 230 °C. Glass‐transition temperatures (T_gs) of the soft segment and melting points (T_ms) of the hard segment domains of OS‐TPUs increased and decreased, respectively, with increasing polymerization temperatures, but those of PP‐TPUs were almost independent of the polymerization temperature. T_gs of the soft segment and T_ms of the hard segment domains of these TPUs polymerized above 190 °C were almost the same regardless of the polymerization method. Solid‐state nuclear magnetic resonance spectroscopy (NMR) analyses of OS‐ and PP‐TPUs showed that the relative proton content of fast decay components, which corresponds to the hard segment domains, in these TPUs decreased with increasing polymerization temperatures. These results clearly show that the degree of microphase separation becomes weaker with increasing polymerization temperatures. The temperature dependence of dynamic storage modulus and loss tangent of OS‐TPUs coincided with those of PP‐TPUs at polymerization temperature above 190 °C. The apparent shear viscosity for OS‐ and PP‐TPUs polymerized above 190 °C approached a Newtonian behavior at low shear rates regardless of the polymerization method. These results indicate that TPUs polymerized at higher temperatures form almost the same molecular aggregation structures irrespective of the dynamic polymerization method. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 800–814, 2007     

Hydrogen bonding,mechanical properties,and surface morphology of clay/waterborne polyurethane nanocomposites

A novel clay/waterborne polyurethane (WPU) nanocomposite was synthesized from polyurethane and saponite organoclay. The clay was organically modified with various swelling agents, the effect of which has been investigated. Hydrogen bonding between organic and inorganic materials was characterized with Fourier transform infrared (FTIR) spectroscopy. The results implied that hydrogen bonding increased when organoclay was added. Mechanical and wear property studies revealed that introducing clay into waterborne polyurethane will enhance the Young's modulus (from 56 to 126 MPa), the maximum stress (from 3.9 to 7.6 MPa), and the elongation at break (from 27.7 to 58.7%) of the nanocomposite by a factor of two, whereas the wear loss will be only one third of the neat waterborne polyurethane. Atomic force microscopy (AFM) was used to analyze the surface morphology of the nanocomposite. An AFM microphotograph showed that the surface of the clay/waterborne polyurethane nanocomposite was smoother when clay was added in waterborne polyurethane. The average roughness (R_a) decreased from 1.00 to 0.12. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1–12, 2005     

Effect of clay modification on the structure and mechanical properties of polyamide-6 nanocomposites

Polyamide-6 nanocomposites were prepared from a new phosphonium organoclay obtained at pilot scale in supercritical carbon dioxide (scCO₂) and a commercially available ammonium modified-silicate. The composites were homogenised by twin-screw extrusion, then specimens for testing were prepared by injection moulding. The clay content of the composites was varied from 0 to 7 vol.% in 7 steps. The clays were characterised in detail; they differed in their surface coverage and gallery structure, while their particle size was similar and their surface energy differed only slightly. X-ray diffraction, electronic microscopy and rheology were used for the characterisation of composite structure. Different gallery structure of the clays led to dissimilar extent of exfoliation. The phosphonium organoclay exfoliated better in PA than the silicate treated with the ammonium salt in spite of its smaller surface coverage. The nanocomposites showed the usual complex structure: besides individual platelets and intercalated stacks, large particles were also present and the development of a silicate network could be shown at large clay contents. Quantitative determination of the extent of reinforcement revealed two determining factors: contact surface and strength of interaction. The first increases with exfoliation, but the latter decreases as an effect of organophilisation. The extent of exfoliation was also estimated quantitatively, and the calculation confirmed the results of qualitative evaluation showing larger extent of exfoliation for the scCO₂-prepared phosphonium clay.     

Influence of interaction between poly(methyl methacrylate) and clay on the properties of nanocomposites prepared by a heterocoagulation method

To have a better insight into the effect of interaction between polymer matrix and clay on the properties of nanocomposite, poly(methyl methacrylate)/clay nanocomposites were prepared by a heterocoagulation method. Using a reactive cationic emulsifier, methacryloyloxyethyltrimethyl ammonium chloride (METAC), a strong polymer–clay interaction was obtained with the advantage of keeping a consistent polymer matrix property. X‐ray diffraction and transmission electronic microscopy indicated an exfoliated structure in nanocomposites. The glass transition temperature (T_g) of the nanocomposites was measured by DSC and DMA. The DMA results showed that with a strong interaction, PMMA–METAC nanocomposite showed a 20 °C enhancement in glass transition temperature (T_g), whereas a slight increase in T_g was observed for PMMA–cetyl trimethylammonium bromide (CTAB)/clay nanocomposite with a weak interaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 733–738, 2010     

Synthesis of a novel one‐pot approach of hyperbranched polyurethanes and their properties

A new method for the synthesis of hyperbranched polymers involving the use of AB_x macromonomers containing linear units have been investigated. Two types of novel hyperbranched polyurethanes have been synthesized by a one‐pot approach. The structures of monomers and polymers were characterized by elemental analysis, ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. The hyperbranched polymers have been proven to be extremely soluble in a wide range of solvents. Polymer electrolytes were prepared with hyperbranched polymer, linear polymer as the host, and lithium perchlorate (LiClO₄) as the ion source. Analysis of the isotherm conductivity dependence of the ion concentration indicated that these hyperbranched polymers could function as a “solvent” for the lithium salt. The conductivity increased with the increasing concentration of hyperbranched polymers in the host polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 344–350, 2002     

Application of a new separation analyzer for the characterization of dispersions stabilized with clay derivatives

The performance of a newly developed separation analyzer is demonstrated by characterization of the sedimentation kinetics and the swelling behavior of organoclays in binary solvent mixtures (toluene/cyclohexane) as well as by investigation of oil-in-water and water-in-oil emulsions stabilized by clay derivatives. The automatic measuring system – LUMiFuge 114 – is based on a special centrifuge with an integrated optoelectronic sensor system which allows the measuring of spatial and temporal changes of light transmission during the rotation in a variable centrifugal field (12–1200g). By using the new device a fast and reproducible characterization of settling behavior and dispersion stability was possible. Moreover, the evaluation of the long-term stability of samples with high separation stability as well as of the heterogenity of the separation process, the sample transparency and the elasticity of the sediment as a function of alternating centrifugal force could be carried out. Received: 27 August 1999/Accepted in revised form: 24 November 1999     

Clay dispersibility and mechanical property of the epoxy/clay nanocomposites prepared by different treatment methods

The bisphenol‐A type epoxy resin was combined with layered clays. Three types of epoxy/clay nanocomposites were prepared by different clay pretreatment methods, that is, the slurry (clay swelling with polar solvent), organo, and solubilization (organoclay swelling with polar solvent) methods. The organo and solubilization systems showed good dispersibility. The basal spacing of the layered clays in the obtained nanocomposites was evaluated by XRD and TEM observations. The basal spacing of the nanoclay in the solubilization system drastically increased. The mechanical properties were improved with the increase in the clay dispersion. A high modulus and fracture toughness were obtained by improvement of the clay dispersion into the matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1753–1761, 2009     

Mechanical and thermal properties of attapulgite clay reinforced polymethylmethacrylate nanocomposites

To investigate the dispersion and nanofillers' interaction of rod‐like silicates (attapulgite, ATT) in the polymethylmethacrylate (PMMA) matrix, a novel in situ modification of ATT by toluene‐2,4‐di‐isocyanate (TDI) using mechanical mixing was exploited, which resulted in homogeneous dispersion and rod‐like texture of ATT nanorods. As a consequence, organo‐modified ATT/PMMA nanocomposites were prepared, which provided prominent improvements in strength, toughness, and thermal stability. High grafting efficiency of TDI on ATT surface was confirmed by FTIR spectra and SEM observations. The uniform dispersion of in situ TDI modified ATT nanorods in the PMMA which was clearly visible in the TEM micrographs, influenced the mechanical and thermal properties of the nanocomposites. The fibrous nanoparticles significantly confined the segmental motion, causing a 13.20°C increase in the glass transition temperature of 2 wt% in situ TDI modified ATT/PMMA nanocomposites. But at higher loadings little or no differences were observed for the reinforcement benefits provided by the in situ TDI modified ATT clay. By comparison, pre‐treated ATT clay severely fractured during mechanical mixing and showed little reinforcement benefits. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of process variables on mechanical properties of polyurethane/clay nanocomposites

This paper addresses the effects of operating variables on mechanical properties of polyurethane/clay nanocomposites including tensile strength, abrasion resistance, and hardness. The variables were prepolymer type, clay cation, clay content, and prepolymer–clay mixing time. The experiments were carried out based on the design of experiments using Taguchi methods. The nanocomposites were synthesized via in situ polymerization starting from two different types of prepolymers (polyether‐ and polyester‐types of polyol reacted with toluene diisocyanate), and methylene‐bis‐ortho‐chloroanilline (MOCA) as a chain extender/hardener. Montmorillonite with three types of cation (Na⁺, alkyl ammonium ion, and MOCA) were examined. Among the parameters studied, prepolymer type and clay cation have the most significant effects on mechanical properties. Polyester nanocomposites showed larger improvements in mechanical properties compared to polyether materials due to higher shear forces exerted by polymer matrix on clay aggregates during polymer–clay mixing. The original MMT with Na⁺ cation results in weak improvements in mechanical properties compared to organoclays. It is observed that the stress and elongation at break, and abrasion resistance of the nanocomposite samples can be optimized with 1.5% of clay loading. The morphology and chemical structure of the optimum sample were examined by X‐ray diffraction and FT‐IR spectroscopy, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of electron-beam-modified surface coated clay fillers and their influence on physical properties of rubbers

A novel process of surface modification of clay filler has been developed by coating this with an acrylate monomer, trimethylol propane triacrylate (TMPTA) or a silane coupling agent, triethoxy vinyl silane (TEVS) followed by electron beam irradiation. Characterization of these surface modified fillers has been carried out by Fourier-transform infrared analysis (FTIR), electron spectroscopy for chemical analysis (ESCA), wettability by dynamic wicking method measuring the rise of a liquid through a filler-packed capillary tube and water flotation test, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). Presence of the acrylate and the silane coupling agent on the modified fillers has been confirmed from FTIR, ESCA, and EDX studies, which has also been supported by TGA studies. The contact angle measurement by dynamic wicking method suggests improvement in hydrophobicity of the treated fillers, which is supported by water flotation test especially in the case of silanized clay. However, XRD studies demonstrate that the entire modification process does not affect the bulk properties of the fillers. Finally, both unmodified and modified clay fillers have been incorporated in styrene butadiene rubber (SBR) and nitrile rubber (NBR). Rheometric and mechanical properties reveal that there is a definite improvement using these modified fillers specially in the case of silanized clay compared to the control sample, probably due to successful enhancement in interaction between the treated clay and the base polymer.     

Effect of phase separation on the crystallization of soft segments of green waterborne polyurethanes

Effect of phase separation on the crystallization of soft segments of green waterborne polyurethanes (WPUs) was discussed in this paper. Phase separation was studied through dynamic mechanical analysis and energy dispersive spectrometer. Energy dispersive spectrometer was employed originally for the study of phase separation of polyurethanes in our study. Crystallization of soft segments of green WPUs was characterized by differential scanning calorimetry, X-ray diffraction and polarizing optical microscope. Characterization results indicated that phase separation hindered the crystallization of soft segments of green WPUs; higher phase separation degree gave rise to lower crystallization capacity, lower crystallinity and smaller crystals of soft segments.     

Effects of clay on polymorphism of polypropylene in polypropylene/clay nanocomposites

The effects of clay on polymorphism of polypropylene (PP) in PP/clay nanocomposites (PPCNs) under various thermomechanical conditions were studied. In extruded PP and PPCN pellet samples, only α-phase crystallites existed, as they were prepared by rapidly cooling the melt extrudates to room temperature. Under compression, β-phase crystallites can develop in neat PP under various thermal conditions, of which isothermal crystallizing at 120 °C gave the highest content of β-phase crystallites. In contrast, no β-phase crystallite was detected in the PPCN samples prepared under the same conditions. This indicated that clay significantly inhibits the formation of β-phase crystallites. The likely reason is that the presence of clay in PPCNs greatly sped up the crystallization process of the α phase, whereas it had an insignificant effect on the crystallization rates of the β phase. The results also showed that clay may slightly promote the formation of γ-phase PP crystallites in PPCNs. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1810–1816, 2004     

Preparation of fluorinated methacrylate/clay nanocomposite via in‐situ polymerization: Characterization,structure, and properties

Novel fluorinated coating containing well‐dispersed silicate nanolayers is successfully produced via in‐situ free radical polymerization of 2,2,2‐trifluoroethyl methacrylate in the presence of vinylbenzyl‐functionalized montmorillonite with different loading. The organic modification of sodium montmorillonite is achieved through an ion exchange reaction with triphenylvinylbenzylphosphonium chloride as surfactant prepared before use by reaction with vinylbenyl chloride and phosphine. The following in‐situ polymerization in the presence of organomodified clay leads to fluorinated nanocomposites with of partially exfoliated and intercalated morphologies, as determined via XRD and TEM analysis. The nanoscale dispersion of clay layers is also evidenced by thermal analysis; a moderate decrease of the glass transition temperature about 2–8 °C compared to their virgin PMATRIF and an improvement of their thermal stability as evidenced by TGA. The wettability of the nanocomposite films is also studied by contact angle measurements with water. The incorporation of organomodified clays not only increases the hydrophobicity of the fluorinated polymers but also improves the surface properties of obtained nanocomposites. Compared the virgin homopolymer, the mechanical properties of the nanocomposites are reduced by addition of organomodifed clay at temperature from 30 to 60 °C, whereas this trend is gradually decreased at higher temperature. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 411–418     

Synthesis of ionic polyurethanes with pyrene rings: Spectral properties and fluorescence quenching study

Hydrophilic ionic polyurethanes with 4‐chloromethylphenylcarbamoyl‐1‐oxymethylpyrene located on the quaternary ammonium structure from a polymer based on poly(ethylene glycol), isophorone diisocyanate, and N‐methyldiethanolamine were prepared by a quaternization reaction, in which the amount of pyrene covalently attached to the polymeric backbone ranged from 1.14 to 19.82 mmol of fluorophore/100 g of polymer. It was interesting to compare the photoluminescence of the pyrene polyurethane carrying a few mole percent of pyrene moieties with that of a third polymer resulting from its subsequent quaternization with benzyl chloride up to a concentration of ionic groups as in the latter (quaternization degree = 14.15%). The process of excimer formation between the pyrene molecules attached to the ionic polyurethane was investigated in tetrahydrofuran (THF), dimethylformamide, film, and THF/H₂O to illustrate the expected differences in the polymer behavior compared with that of the starting pyrene derivative. The formation of aggregates or core–shell micelles was sustained by the fluorescence data, which indicated the existence of pyrene units in the ground state of the molecule, giving rise thus to an explanation for the high excimer‐to‐monomer intensity ratio. The fluorescence decay of pyrene polyurethanes in the presence of various concentrations of nitrobenzene used as a quencher was analyzed too when the fluorescence quenching in the polymer solution normally followed Stern–Volmer kinetics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3945–3956, 2005     

Effects of organic modifications of clay on the ultraviolet‐curing behavior and structure of a polyester‐acrylate/clay nanocomposite system

A pristine clay (Na⁺‐montmorillonite (MMT) and three different organoclays (20A‐MMT, vinylbenzyl dimethyldodecyl ammonium (VDA)‐MMT, and siloxane diamine ammonium (SDA)‐MMT) that originated from the pristine clay were used to prepare polyester‐acrylate (PEA)/clay nanocomposites by in situ ultraviolet (UV)‐curing. Except for the commercial organoclay (20A‐MMT), VDA‐MMT, and SDA‐MMT were prepared in this study by ion exchange method. The effects of organic modifications of the pristine clay on the UV‐curing behavior and structure of the nanocomposite system were investigated. The organic modifications of the clay affected considerably the UV‐curing behavior and structure of the nanocomposite system. Copyright © 2008 John Wiley & Sons, Ltd.