Chitosan–organosilane hybrids—Syntheses,characterization, copper adsorption,and enzyme immobilization

New organic–inorganic hybrids SiGCX (X = 1 to 3) were prepared from the biopolymer chitosan with a degree of the deacetylation of 86% and three distinct silylating agents of the type (CH₃O)₃Si R NH₂ [R =  (CH₂)₃ ,  (CH₂)₃NH(CH₂)₂ and  (CH₂)₃NH(CH₂)₂NH(CH₂)₂ ]. Both chitosan and silylating agents have the amine groups crosslinking through linear glutaraldehyde units. Two stages were proposed for this synthetic method: crosslinking, and sol‐gel processes. The resulting dried hydrogels are amorphous, insoluble in organic as well as acidic or alkaline aqueous media, and exhibited a lamellae‐like surface morphology. The hybrids SiGCX (X = 2 and 3) have a larger adsorption capacity for copper ion than natural chitosan, with very similar kinetics of adsorption, defining a plateau after 1 h. The adsorption of copper increases with the organic chain length of the silylating agents: [(1.72 ± 0.05); (1.98 ± 0.06) and (2.49 ± 0.07)] × 10⁻² mmol/g for SiGCX (X = 1 to 3), respectively, and chitosan adsorbed (1.72 ± 0.05) × 10⁻² mmol/g. These hybrids presented a good capacity for immobilizing enzymes, which decreased with the increase of the organic chain length of the silylating agents, that is, from SiGC3 to SiGC1. The amount of catalase immobilized for the hybrids SIGCX (X = 1 to 3) is 29.03 ± 0.87; 25.79 ± 0.77, and 17.94 ± 0.54 mg g⁻¹, respectively, which is larger than the value of 12.21 ± 0.37 mg g⁻¹ obtained for chitosan. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 797–804, 2000     

Antiswelling and robust supramolecular polyurea hydrogels induced by the synergy of hydrogen bond and hydrophobic interaction for constructing durable underwater anti-oil-fouling coatings

Hydrogels are attractive materials for constructing underwater antifouling coatings on solid substrates. However, the application of hydrogel coatings usually faces the obstacles of complex preparation process and poor durability. Herein, we present a facile method to prepare durable hydrogel coatings on metal foils based on rationally designed supramolecular polyurea (PU) hydrogels. PU hydrogels are designed to be cross-linked with hydrogen bonds (H-bonds) and hydrophobic interactions in the hard segment domains by using dihydrazides with different alkyl spacer lengths ( (CH₂)_m ) as chain extender. The synergy of H-bond and hydrophobic interaction can stabilize H-bonds in water, as confirmed by Raman spectroscopy. As a result, PU hydrogels exhibit antiswelling capacity and robustness in both deionized water and seawater. Subsequently, PU hydrogel coatings on Cu/Al foils are prepared by convenient brush coating and subsequent swelling. The resulting hydrogel coatings exhibit excellent underwater anti-oil-adhesion and self-cleaning property, and are durable enough to withstand various static and dynamic damaging tests. The good durability of PU hydrogel coatings should be ascribed to the robust adhesion interface and excellent antiswelling capacity of PU hydrogels. The combination of facile preparation and good durability makes PU hydrogel coatings promising candidates for reliable underwater antifouling.     

Spectroscopic and thermal characterization of poly(glycidyl azide) converted from polyepichlorohydrin

Poly(glycidyl azide) (PGA) was synthesized by reaction of polyepichlorohydrin (PECH) with sodium azide (NaN₃) by using phase-transfer catalysis. A detailed analysis was performed to follow the polymer–polymer conversion reaction. Conversion of  CH₂ CL to  CH₂  N₃ was achieved completely in 6 h, as determined from FTIR assignment, UV-VIS spectroscopy, and thermal analysis. In FTIR and UV-VIS spectroscopy studies, the reaction was followed from the change in characteristic peak intensities. Thermal analysis also showed that the first thermal decomposition process of PGA, which is due to the exothermic clevage of pendant N₃ groups, was shifted to higher temperatures, and the exothermicity was increased as the conversion proceeded. It was also found that the extent and completion of CL to N₃ conversion could be easily followed by measuring the glass transition temperature and exothermic decompostion of the polymers. The quantitative analysis of the data collected from FTIR and DSC measurements showed that PECH → PGA conversion is a first-order reaction with a rate constant of k = 0.74 h⁻¹. © 1996 John Wiley & Sons, Inc.     

Rapid formation of methane hydrates with compact agglomeration via regulating the hydrophilic groups of nanopromoters

Gas hydrates have been endowed with great potential as the medium for natural gas storage & transportation. In this work, we prepared novel nanopromoters by grafting hydrophilic groups ( SO₃⁻,  COO⁻ and  N[CH₃]₃⁺) covalently on polystyrene nanospheres (Group@PSNS), and for the first time achieved rapid formation of methane hydrates together compact agglomeration by regulating the hydrophilic groups on the surface of nanopromoters. When  SO₃⁻@PSNS was used, methane hydrates formed rapidly but loosely in the reactor; while for  COO⁻@PSNS and  N(CH₃)₃⁺@PSNS, even the hydrate formation rate was seriously reduced, the formed hydrates agglomerated compactly in the reactor bottom. Interestingly, when both  SO₃⁻ and  COO⁻ were fixed on the nanospheres, both the hydrate growth rate and agglomeration compactness were controlled. Especially, the nanopromoter with the  SO₃⁻/ COO⁻ molar ratio of 2:1 resulted in the formation of methane hydrates with compact agglomeration morphology within 1–2 hr and with the storage capacity reaching 140–145 vol/vol.     

Gas permeability of model polyurethane networks and hybrid organic-inorganic materials: Relations with morphology

Various polyurethane (PU) and hybrid organic-inorganic networks based on isocyanate chemistry were synthesized using a two-stage method. All the networks were amorphous. For PU membranes the morphology and the permeability coefficients of different gases (H₂, N₂, O₂) were a function of the polarity and the chain length of the soft segment and a function of the composition of the networks. The membranes based on the same soft segment chain length and on the same molar composition were structurally nanoheterogeneous systems for the less polar soft segments (α, ω-hydroxy-terminated hydrogenated polybutadiene and a fatty acid oligoester). They were homogeneous for a polycaprolactone type soft segment. The gas diffusion was appreciably hindered in the case of better miscibility between the soft chains and the hard crosslinks. Decreasing the soft segment length decreased the gas permeability coefficient of the network. As the chemical compositions were changed by increasing the soft segment content, an increase in permeability coefficients was observed. The morphology and transport properties of PU networks and hybrid organic-inorganic networks with low inorganic content were compared for the same soft segment content. The similarities observed between the two types of networks led us to conclude that the organic or inorganic nature of the crosslinking agent has no influence on the gas transport properties of these networks. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2579–2587, 1997     

Role of the interactions between carbonate groups on the phase separation and properties of waterborne polyurethane dispersions prepared with copolymers of polycarbonate diol

Different aliphatic waterborne polyurethane dispersions (PUDs) were synthesized by using different polyols (M_w: 1000 Da) of randomly copolymerized polycarbonate diols with hexamethylene and pentamethylene (C6–C5), tetramethylene (C6–C4) and trimethylene (C6–C3); these copolymers differed in the length of the methylene groups and the structural regularity due to the combination of even and odd units. Brookfield viscosity, extent of particle crowding and broadening of the particle size distribution of the PUD synthesized with C6–C4 polyol followed a different trend than for the other because of the even number of methylene units in the polyol. The PUDs showed monomodal particle size distribution which was narrower in C6–C4 (i.e. the dispersion with higher structural regularity) and the mean particle size decreased by decreasing the length of the methylene unit of the copolymer.The properties of the polyurethanes were affected by the phase separation between the hard and soft segments, the more regular packing of even methylene units in the copolymer and the crystallized polar segments due to carbonate groups. Thus, the glass transition values of the soft segments in the polyurethanes were similar because of the more regular packing of even methylene units in C6–C4 polyol and the crystallized segments produced by interactions of carbonate groups. PU(C6–C5) and PU(C6–C4) showed similar degree of phase separation, the higher degree of phase separation corresponded to PU(C6–C3). Furthermore, the crystallinity of the polyurethanes increased with decreasing the number of methylene units in the polyol, but PU(C6–C4) was the most crystalline because of the more regularly packed even methylene groups in the polyol chain. The thermal stability of the polyurethanes increased from PU(C6–C5) to PU(C6–C3) because the more net interactions between the carbonate groups in the soft segments. The lower was the number of methylene groups between carbonate units in the copolymer, the higher was the elastic modulus of the polyurethanes. The tensile strength and elongation-at-break values of the polyurethanes increased by increasing the number of methylene groups between carbonate units in the copolymer. Finally, the peel strength was maximal in the joint made with PU(C6–C5) and the shear strength was the highest in the joint made with PU(C6–C3), in agreement with the variation of the viscoelastic and mechanical properties of the polyurethanes.     

Generation of antifouling layers on stainless steel surfaces by plasma‐enhanced crosslinking of polyethylene glycol

Polyethylene glycol (PEG) structures were deposited onto stainless steel (SS) surfaces by spin coating and argon radio frequency (RF)‐plasma mediated crosslinking. Electron spectroscopy for chemical analysis (ESCA) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR) indicated the presence of  CH₂ CH₂ O structure and C C C linkage, as a result of the plasma crosslinking, on PEG‐modified SS surfaces. Scanning electron microscopy (SEM) indicated complete deposition, and water contact angle analysis revealed higher hydrophilicity on PEG‐modified surfaces compared to unmodified SS surfaces. Surface morphology and roughness analysis by atomic force microscopy (AFM) revealed smoother SS surfaces after PEG modification. The evaluation of antifouling ability of the PEG‐modified SS surfaces was carried out. Compared to the unmodified SS, PEG‐modified surfaces showed about 81–96% decrease in Listeria monocytogenes attachment and biofilm formation (p < 0.05). This cold plasma mediated PEG crosslinking provided a promising technique to reduce bacterial contamination on surfaces encountered in food‐processing environments. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 485–497, 2005     

Improved adhesion of silicone rubber to polyurethane by surface grafting

Polyurethane (PU) has widespread applications in implantable devices because of its excellent mechanical and biocompatible properties, whereas weak biostability limits its long‐term implantation. The introduction of silicone rubber (SR) onto the PU surface is an effective method for improving the biostability of PU, but the adhesion of these two polymers is unsatisfactory. In this study, the surface modification of PU via grafting through the introduction of vinyl and Si H groups onto the PU surface was attempted to improve the adhesion of PU to SR. Fourier transform infrared, energy‐dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy were employed to investigate the graft reaction on the PU surface. The interfacial and surface morphology was characterized with scanning electron microscopy. Different PU/SR interfaces after oscillation and shear were compared as well. The results indicated that the PU surface was activated by diisocyanate, which generated free isocyanate groups for the further grafting of vinyl and Si H groups. When addition‐type, room‐temperature‐vulcanized SR was poured onto the PU surface, the vinyl and Si H groups on the PU surface underwent an addition reaction, which improved the adhesion of PU and SR by connecting them with chemical bonds. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Rheological,thermal, and morphological properties of ABS–PA1010 blends

Noncompatibilized and compatibilized ABS–nylon1010 blends were prepared by melt mixing. Polystyrene and glycidyl methacrylate (SG) copolymer was used as a compatibilizer to enhance the interfacial adhesion and to control the morphology. This SG copolymer contains reactive glycidyl groups that are able to react with PA1010 end groups ( NH₂ or  COOH) under melt conditions to form SG‐g‐Nylon copolymer. Effects of the compatibilizer SG on the rheological, thermal, and morphological properties were investigated by capillary rheometer, DSC, and SEM techniques. The compatibilized ABS–PA1010 blend has higher viscosity, lower crystallinity, and smaller phase domain compared to the corresponding noncompatibilized blend. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 683–688, 1999     

Structure analysis in polyurethane foams at interfaces

The aim of this study was to investigate the structure and morphology of polyurethane (PU) foams at the interface with a thermoplastic material. Fourier transform infrared/attenuated total reflectance spectroscopy was used to study the reaction of 4,4′‐diphenylmethane diisocyanate (MDI) with polyether‐based polyols with water as a blowing agent via the absorption intensity of the ν(NCO, 2265 cm^?1) vibrational band of MDI in three different PU foam systems. The data revealed that MDI reacted simultaneously with two different species in the reaction mixture having different reaction rates. These were the reactions of isocyanate functional groups with water (fast reaction) and polyol (slow reaction). A structure analysis at the PU foam interface (i.e., PU formed a compact film 110 ± 30 μm thick at the interface) with a thermoplastic material plate was carried out with small‐angle X‐ray scattering (SAXS), transmission electron microscopy (TEM), and neutron reflection (NR) techniques. From SAXS measurements, a typical hard‐segment–segment distance of 10 ± 0.3 nm was observed. The TEM and NR data of the compact PU film revealed an internal layered structure (parallel to the surface) with a typical layer thickness of 260–400 nm. The formation of a layered morphology (macrophase‐separated structures) was assumed to be due to the difference in the polarities of the hard and soft segments. Furthermore, the layer thickness increased when D₂O was used as the blowing agent instead of H₂O. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1280–1289, 2005     

Preparation of silicon dioxide/polyurethane nanocomposites by a sol–gel process

Aqueous emulsions of cationic polyurethane ionomers, based on poly(?‐caprolactone glycol) as soft segment, isophorone diisocyanate as hard segment, 3‐dimethylamino‐1,2‐propanediol as chain extender and potential ionic center, and hydrochloric acid as neutralizer, were mixed with tetraethoxysilane to prepare silicon dioxide–polyurethane (SiO₂/PU) nanocomposites by a sol–gel process during which the inorganic mineral is deposited in situ in the organic polymer matrix. The sizes and distributions of the particles were measured by dynamic light scattering, and the structure and morphology of the nanocomposites were observed by transmission electron microscope and FTIR spectrum. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2013–2016, 2004     

Synthesis of polyurethane–imide (PU–imide) copolymers with different dianhydrides and their properties

This study reports the synthesis of polyurethane–imide (PU–imide) copolymers using 4,4′-diphenylmethane diisocyanate (MDI) polytetramethylene glycols (PTMGs) and different aromatic dianhydrides. Differential scanning calorimetry (DSC) results indicate that PU–imide copolymers had two phase structures containing four transition temperatures (T_gs, T_ms, T_gh and T_mh). However, only PU–imide copolymers were formed by soft PTMG(2000) segments possessing a T_ms (melting point of soft segment). When different aromatic dianhydrides were introduced into the backbone chain of the polyurethane, although the T_gs (glass transition temperature of the soft segment) of some of PU–imide copolymers did not change, the copolymers with long soft segments had low T_gs values. The T_gh (glass transition temperature of hard segment) values of PU–imide copolymers were higher than that of polyurethane (PU). In addition, the high hard segment content of PU–imide copolymer series also had an obvious T_mh (melting point of hard segment). According to thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA), the PU–imide copolymers had at least two stages of degradation. Although the T_di (initial temperature of degradation) depended on the hard segment content and the composition of hard segment, the different soft segment lengths did not obviously influence the T_di. However, PU–imide copolymers with a longer soft segment had a higher thermal stability in the degradation temperature range of middle weight loss (about T_d 5%–50%). However, beyond T_d 50% (50% weight loss at temperature of degradation), the temperature of degradation of PU–imide copolymers increased with increasing hard segment content. Mechanical properties revealed that the modulus and tensile strength of PU–imide copolymers surpassed those of PU. Wide angle X-ray diffraction patterns demonstrated that PU–imide copolymers are crystallizable. © 1999 Society of Chemical Industry     

Revealing the pyrolysis mechanism of polypropylene cable insulation: A combined study of TG-GC experiments and RMD/DFT simulations

Styrene grafted polypropylene (PP-g-St) is one of the insulating materials for high voltage power cables. However, the process of pyrolysis gas generation in polypropylene cable insulation remains poorly understood. To address this knowledge gap, this study employed a combination of thermogravimetric-gas chromatography experiments, density functional theory, and reactive molecular dynamics simulations. The experimental findings revealed that the pyrolysis gases primarily consisted of H₂, CO, C₂H₄, and CH₄. Higher temperatures were found to increase the yields of H₂ and CO. The simulation results indicated that H₂ and CO were generated through the rupture of less reactive olefins and radicals, while C₂H₄ was primarily produced by the rupture of C C bonds in the polypropylene chain. Additionally, CH₄ was formed when  CH₃ groups captured hydrogen from other molecules. By the chain reaction mechanism, we enable the calculation of the activation energy of PP-g-St. This study provides a theoretical foundation for understanding the pyrolysis gas generation.     

Hydroxyethyl starch with high surface activity via ethylene carbonate functionalization

Biosurfactants-hydroxyethyl starches (HES-EC) with the total degree of substitution (DS_t) of 26, 37, and 46% are prepared via ethylene carbonate functionalization. GC–MS semi-quantitative analysis results show that monosubstituents, especially, C-2 monosubstituents are predominant in all substituents. A small amount of disubstituents with  O(CH₂CH₂O)₂H group per polyethylene chain exist in HES-EC. The structural characteristics of HES-EC demonstrate that hydroxyethyl groups distribute more uniformly on starch main chains as compared with corresponding HES-EO. The even distribution of hydroxyethyl groups further promotes the formation of the hydrophilic–hydrophobic structure inside HES-EC. HES-EC exhibits lower surface tension and more notable emulsion ability than HES-EO and traditional petroleum-based surfactant NP-10. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48807.     

Preparation and characterization of polyurethane–gold nanocomposites prepared using encapsulated gold nanoparticles

Gold nanoparticles (GNPs) have been widely studied due to their unique properties. Although many research groups have developed the synthesis of GNPs using various polymers as stabilizing or reducing agents, the effects of GNPs on the structures and properties of polymer matrices have been less reported. We propose a new design for the preparation of polyurethane–gold (PU–Au) nanocomposites. 11‐Mercapto‐1‐undecanol‐coated GNPs acted as the chain extenders and reacted with isocyanates to form covalent bonds between PU and GNPs. PU–Au nanocomposites were successfully synthesized, and the effects of multifunctional GNPs on the structures, morphology and properties of poly(ester urethane) were investigated. Scanning electron microscopy images suggested the GNPs can be dispersed uniformly in the PU matrix. Maltese‐cross of spherical crystals was observed in the PU–Au nanocomposites, and the size of the crystals decreased with an increase in gold content. As the gold content increased, the thermal decomposition temperature and the temperature of the maximum decomposition rate increased. The glass transition temperature, crystal melting temperature and melting enthalpy of the soft segment also increased progressively. The results showed that multifunctional GNPs concentrated hard segments and resulted in an increase of heterogeneous nucleation, phase separation and elasticity. Copyright © 2010 Society of Chemical Industry     

Thermoplastic polyurethanes with controlled morphology based on methylenediphenyldiisocyanate/isosorbide/butanediol hard segments

Isosorbide, a cyclic, rigid and renewable diol, was used as a chain extender in two series of thermoplastic polyurethanes (PUs). Isosorbide was used alone or in combination with butanediol to examine the effects on the morphology of PU. Two series of materials were prepared – one with dispersed hard domains in a matrix of polytetramethylene ether glycol soft segments of molecular weight 1400 g mol^?1 (at 70 wt% soft segment concentration, SSC) and the other with co‐continuous soft and hard phases at 50 wt% SSC. We investigated the detailed morphology of these materials with optical and atomic force microscopy, as well as ultra‐small‐angle X‐ray scattering. The atomic force microscopy measurements confirmed the different morphologies in PUs with 50 wt% SSC and with 70 wt% SSC. Small‐angle X‐ray scattering data showed that in PU with 70 wt% SSC, the hard domain size varied between 2.4 and 2.9 nm, and decreased with increasing isosorbide content. In PU with 70 wt% SSC, we found that the correlation length and average repeat distances became smaller with increasing isosorbide content. We estimated the thickness of the diffuse phase boundary for PU with 70 wt% SSC to be ca 0.5 nm, decreasing slightly with increasing isosorbide content. © 2015 Society of Chemical Industry     

The effect of the incorporation of polystyrene‐based chain extenders on the properties of the shape memory polyurethanes

In this work, the idea of modulating the shape memory properties of polyurethanes by changing their macromolecular architecture through the incorporation of polystyrene‐based moieties was investigated. To study these effects, poly(styrene‐co‐maleic anhydride) (SMA) was incorporated during the synthesis of PU as a potential chain extender. Two sample groups were produced: (i) PU, produced with hydrazine as a chain extender and (ii) PU_SMA, produced with the addition of SMA instead of hydrazine. The results suggest that the SMA incorporation in the PU_SMA chains occurred by the reaction between NCO groups of the PU and maleic anhydride (MA) of the SMA. The presence of SMA was useful in modulating the structure of PU by reducing the soft segment crystallinity and molar mass. These changes in the structure and macromolecular architecture due to the presence of SMA moieties in PU chains led to pronounced improvements in strength, toughness, and the shape recovery ratio. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44471.     

Adjustment of Cell Adhesion on Polyurethane Structures via Control of the Hard/Soft Segment Ratio

Creating substrates with a similar composition that can either prevent or promote cell adhesion is still a challenging feat. Here, it is shown that a strikingly simple method of tuning the amount of hard segments or isocyanate index (NCO_ind) of a polyurethane (PU) film allows to modulate cell adhesiveness. PU films are synthesized with NCO_ind of 75, 100, 200, 300 and 400 corresponding to ratios of isocyanate to hydroxyl functions of 0.75, 1, 2, 3, 4, respectively. The adhesive capacity of NIH 3T3 fibroblasts (3T3) and Wharton's jelly mesenchymal stem cells (WJMSCs) are dependent on the NCO_ind. For NCO_ind below 300, no cell adhesion can be observed regardless of the cell type, whereas for NCO_ind of 300 and 400 cells adhere to the PU surface. WAXS and small angle X‐ray scattering (SAXS) studies reveal that variations of NCO_ind allows to modulate the phase separation in PU films. Porod's law shows that for NCO_ind of 300 and 400, the hard–soft segment interface is sharp. Conversely, samples with smaller NCO_ind present diffuse interfaces. Hence, the morphology of the interface between hard and soft domains appears to be a critical feature that correlates with the adhesion capacity of cells.     

聚氨酯结晶性的研究进展

概述了聚氨酯(PU)结晶性的研究方法,讨论了软硬段种类和结构、硬段含量、软段相对分子质量、带电离子及其它基团和热处理等对PU结晶性的影响,并介绍了结晶性PU在形体记忆材料中的应用状况。     

FTIR equivalent weight determination of perfluorosulfonate polymers

Fourier transform infrared (FTIR) and attenuated total reflectance (ATR) spectroscopy studies of the sulfonyl fluoride, potassium salt, and sulfonic acid forms of long and short side chain perfluorosulfonate polymers revealed bands indicative of the sidegroup and backbone compositions, endgroups on the main chain, water content, monomer concentration, and degree of salt hydrolysis. The equivalent weight (EW) of the polymer was obtained by titration and NMR measurements which were then calibrated to either the C F/C O C absorbance band ratio for thin (<1.1 mil) films or to a C F/SO₂F absorbance band ratio for thick films (5 to 25 mils). An FTIR measurement of the film thickness based on the C F group concentration was found to be both a function of the actual thickness and the EW; a method for compensating for this EW dependence is described. Esterification and fluorination of the polymers yielded FTIR measurements of the endgroup compositions on the polymer backbone which were shown to consist of  COF,  COOH,  CO₂CH₃, and  CFCF₂ groups. Thermogravimetric Analysis Infrared (TGA‐IR) spectroscopy of the acid form polymers indicates that degradation begins by the decomposition of the  SO₃H group at 320°C followed by bulk deterioration above 400°C. The FTIR techniques detailed herein have been developed for accurate, reproducible, and rapid compositional measurements of Nafion® and other perfluorosulfonate polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011