Supramolecular thermoplastic elastomer with thermally scratch repairable effect from 3‐amino‐1,2,4‐triazole crosslinked maleated polyethylene‐octene elastomer/nylon 12 blends

In this study, nylon 12 (5–25 wt %) was melt blended with a supramolecular thermally repairable thermoplastic elastomer (ATA‐POE), which was generated by crosslinking of maleated polyethylene‐octene elastomer (mPOE) with 3‐amino‐1,2,4‐triazole (ATA), in an internal mixer. The effect of nylon 12 content on the phase morphology, thermomechanical properties, and thermally triggered scratch repairing effects of the ATA‐POE/nylon 12 blends was investigated. Scanning electron microscopy results showed that nylon 12 formed a dispersed phase with submicron scale in a continuous ATA‐POE phase. Fourier transform infrared spectroscopy and differential scanning calorimetry analysis revealed that there are extensive hydrogen bonding interactions between the ATA‐POE and nylon 12 in the blends, which was manifested by a decrease in the melting temperature of each polymer component. Tensile and dynamic mechanical test showed that tensile modulus increased with increasing nylon 12 contents in the blend with maintaining fairly high elastic recoverability. Furthermore, the blends containing up to 20 wt % of nylon 12 showed good scratch repairing effects when they are heated above melting temperature of the ATA‐POE phase in the blend. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41511.     

Supramolecular magnetorheological polymer gels

Novel magnetorheological fluids—supramolecular magnetorheological polymer gels (SMRPGs)— were investigated. Supramolecular polymer deposited on the surface of iron particles was suspended in the carrier fluids. The supramolecular network was obtained by metal coordination between terpyridine monomers and zinc ion. These SMRPGs had such advantages as controllable off‐state viscosity, a reduced iron particle settling rate, and stability. The viscoelastic behavior of SMRPGs with small‐ and large‐amplitude oscillatory shear was investigated using the amplitude and frequency sweep mode. The effects of strain amplitude, frequency, and magnetic field strength on the viscoelastic moduli were measured. The linear viscoelastic (LVE) strain range was obtained by the oscillation and static stress strain methods. The maximum LVE value was equal to the preyield strain point, 0.3%. Microstructural variation of SMRPG is proposed as an explanation of the rheological changes in the oscillation tests. The results of this research indicate that off–state viscosity and particle settling can be controlled by adjusting the concentration of supramolecular polymer gel. Dynamic yield stress significantly increased with an external magnetic field up to ～23,500 Pa under a magnetic flux density of 500 mT. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2464–2479, 2006     

Crosslinking mechanism of supramolecular elastomers based on linear bifunctional polydimethylsiloxane oligomers

Supramolecular elastomers (SESis) were synthesized via a simplified synthesis route on the basis of a linear bifunctional polydimethylsiloxane. Compared with previous synthesis methods, the structure of the product was much clearer. The ¹H‐NMR titration results show that the hydrogen‐bond associations in SESis were relatively weak. During ¹H‐NMR reaction monitoring, the viscosity analysis of SESis and the model reactions demonstrated a previously neglected covalent crosslinking reaction not only during the reaction process but also during the postprocess; this led to a hybrid network, that is, covalent crosslinking and hydrogen association, in SESis. This finding explained the poor solubility of the SESis, and it provides us with an important way to controllably synthesize this material and adjust its properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43385.     

Self‐healing supramolecular elastomers based on the multi‐hydrogen bonding of low‐molecular polydimethylsiloxanes: Synthesis and characterization

Novel self‐healing supramolecular elastomers based on polydimethylsiloxanes (SESi) were synthesized from a mixture of polydimethylsiloxanes derivers with single, di‐, or tri‐carboxylic acid groups (PDMS–COOH_x, where x = 1, 2, and 3, respectively), diethylene triamine, and urea with a two‐stage procedure. The reactions and the final products were tracked, characterized, and confirmed by Fourier transform infrared spectroscopy, ¹H‐NMR, differential scanning calorimetry, dynamic mechanical analysis, and gel permeation chromatography. Compared with a supramolecular rubber based on dimer acid (reported previously) with a similar synthesis procedure, the SESi showed a lower glass‐transition temperature of about ?113°C for the softer chain of polydimethylsiloxane and showed real rubberlike elastic behavior and self‐healing properties at room temperature or even lower temperatures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

NMR water self‐diffusion and relaxation studies on sodium polyacrylate solutions and gels in physiologic ionic solutions

Water self‐diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca²⁺ and Na⁺. Several physical models describing the self‐diffusion of the solvent were applied and compared. A free‐volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non‐linear behavior at higher concentrations. Both the water self‐diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na⁺ on the mobility of water molecules was practically undetectable. In contrast, addition of Ca²⁺ strongly increased the longitudinal relaxation rate while its effect on the self‐diffusion coefficient was much less pronounced. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40001.     

Hydrogen‐bonded supramolecular polymers as self‐healing hydrogels: Effect of a bulky adamantyl substituent in the ureido‐pyrimidinone monomer

In an attempt to generate supramolecular assemblies able to function as self‐healing hydrogels, a novel ureido‐pyrimidinone (UPy) monomer, 2‐(N ′‐methacryloyloxyethylureido)‐6‐(1‐adamantyl)‐4[1H]‐pyrimidinone, was synthesized and then copolymerized with N,N‐dimethylacrylamide at four different feed compositions, using a solution of lithium chloride in N,N‐dimethylacetamide as the polymerization medium. The assembling process in the resulting copolymers is based on crosslinking through the reversible quadruple hydrogen bonding between side‐chain UPy modules. The adamantyl substituent was introduced in order to create a “hydrophobic pocket” that may protect the hydrogen bonds against the disruptive effect of water molecules. Upon hydration to equilibrium, all copolymers generated typical hydrogels when their concentration in the hydrated system was at least 15%. The small‐deformation rheometry showed that all hydrated copolymers were hydrogels that maintained a solid‐like behavior, and that their extrusion through a syringe needle did not affect significantly this behavior, suggesting a self‐healing capacity in these materials. An application as injectable substitutes for the eye's vitreous humor was proposed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39932.     

Preparation and characterization of elastomer‐based nanocomposite gels using an unique latex blending technique

Nanocomposite (NC) gels based on natural rubber (NR) and styrene butadiene rubber (SBR) were prepared by using a unique latex blending technique. These NC gels were prepared by first blending the water swollen unmodified montmorillonite clay (Na⁺‐MMT) suspension into the respective latices followed by prevulcanization to generate crosslinked nanogels. Use of water assisted fully delaminated Na⁺‐MMT suspension resulted in predominantly exfoliated morphology in the NC gels, as revealed by X‐ray diffraction study and transmission electron microscopy. Addition of Na⁺‐MMT significantly improved various physical, mechanical and thermal properties of these NC gels. For example, 6 phr of Na⁺‐MMT loaded NR based NC gels registered 54% and 200% increase in tensile strength and Young's modulus, respectively, compared to the unfilled NR gels. SBR based NC gels also showed similar level of improvement in mechanical properties. Mechanical properties of NC gels prepared using this route were also compared with the NC gels prepared by co‐coagulation and conventional curing technique and found to be superior. In the case of dynamic mechanical properties, NC gels showed higher glass transition temperatures along with a concomitant increase in storage moduli, compared to the unfilled gels. These Na⁺‐MMT reinforced NC gels also exhibited markedly improved thermal stability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Terminally cross-linking polyrotaxane hydrogels applicable for cellular microenvironments

Polyrotaxanes, composed of multiple cyclic molecules threaded onto a polymer chain axis capped with bulky molecules, exhibit unique structural features wherein cyclic molecules can move along a chain. We have previously constructed biointerfaces that utilize the molecular mobility of polyrotaxanes for controlling cellular responses. To implement the features in a three-dimensionally engineered cellular microenvironment, this study developed supramolecular hydrogels using polyrotaxane cross-linkers capped with 4-vinylbenzyl groups at the terminals of a polymer chain axis, where the 4-vinylbenzyl groups in the polyrotaxane allow polymerization with other polyrotaxanes to form polyrotaxane networks. Polyrotaxane hydrogels are successfully prepared without any additional monomers via redox polymerization. The dynamic viscoelasticity and swellability of the hydrogels can be varied depending on the concentration of the polyrotaxanes. When fibroblasts are cultured on hydrogels, sufficient adhesion for cultivation is observed. Therefore, polyrotaxane hydrogels demonstrate suitable potential as new supramolecular biomaterials with dynamic structural features.     

Preparation and physical properties of hyaluronic acid‐based cryogels

Macroporous hydrogels based on hyaluronan (HA), a natural polysaccharide occurring in extracellular matrix, have attracted interest over many years owing to their numerous applications in the biomedical area. However, HA hydrogels produced so far suffer from low mechanical strength and slow rate of response against external stimuli, which limit their applications. Here, we prepared macroporous HA cryogels of high mechanical stability and fast responsivity from aqueous HA solutions at subzero temperatures using ethylene glycol diglycidyl ether as a crosslinking agent. HA cryogels are squeezable and no crack development was exhibited when compressed up to 80% strain. Depending on the synthesis parameters, the cryogels exhibit an elastic modulus between 0.2 and 2 kPa, and show fast swelling/deswelling behavior. The microstructure of the cryogels consists of large, interconnected pores on the order of 100 µm separated by thick pore walls, as observed by scanning electron microscopy and confocal scanning laser microscopy. © 2015 The Authors Journal of Applied Polymer Science Published by Wiley Periodicals, Inc. 2015 , 132, 42194.     

Molecular modeling approach to the prediction of mechanical properties of silica‐reinforced rubbers

Recently, we have suggested a nanomechanical model for dissipative loss in filled elastomer networks in the context of the Payne effect. The mechanism is based on a total interfiller particle force exhibiting an intermittent loop, due to the combination of short‐range repulsion and dispersion forces with a long‐range elastic attraction. The sum of these forces leads, under external strain, to a spontaneous instability of “bonds” between the aggregates in a filler network and attendant energy dissipation. Here, we use molecular dynamics simulations to obtain chemically realistic forces between surface modified silica particles. The latter are combined with the above model to estimate the loss modulus and the low strain storage modulus in elastomers containing the aforementioned filler‐compatibilizer systems. The model is compared to experimental dynamic moduli of silica filled rubbers. We find good agreement between the model predictions and the experiments as function of the compatibilizer's molecular structure and its bulk concentration. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40806.     

Polyether‐based main‐chain‐type polytriazole elastomer with benzoxazine via a 1,3‐dipolar cycloaddition reaction

A novel functional polyether‐based elastomer with a benzoxazine structure in its main chain was successfully synthesized via a 1,3‐dipolar cycloaddition reaction. Benefitting from a facile one‐pot synthesis strategy, the elastomer was prepared at low temperature (80°C) and was characterized clearly afterward. The azide‐terminated polyether and acetylene‐terminated benzoxazine were used as the soft and hard segments, respectively, in the polymer chain. Because the triazole rings served as stable linkage between the soft and hard segments, the elastomer possessed good thermal stability (the 5% weight loss temperature could exceed 350°C) compared to traditional elastomers, such as polyurethane. The rigid benzoxazine rings provided the product with good mechanical properties (the tensile strength of the elastomer could exceed 30 MPa). Furthermore, the ring‐opening polymerization of oxazine rings in the structure gifted the elastomer with possibility of thermally induced structural transformation. The thermally induced structural transformation could conveniently realize the conversion of the elastomer to a thermosetting resin. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42820.     

Water‐soluble polymers and gels from the polycondensation between cyclodextrins and poly(carboxylic acid)s: A study of the preparation parameters

Native cyclodextrins (CDx) and some of their derivatives were reacted with poly(carboxylic acid)s (PCAs) [citric acid (CTR), 1,2,3,4‐butanetetracarboxylic acid (BTCA), and poly(acrylic acid) (PAA)]. These reactions were carried out in the dry state at a temperature greater than 140°C in air or in vacuo. They resulted in water‐soluble and insoluble polymers formed by polyesterification between CDx and PCA. In this study, the parameters of the reaction were studied, and their influence on the water solubility or swellability of the obtained polymers was investigated. High reaction temperatures, high PCA/CDx molar ratios, and long reaction times preferably yielded insoluble gels, whereas softer conditions resulted in very soluble polymers. The gels could swell up to 10 times their initial volume in water, and the water‐soluble fraction had a solubility of 1 g/mL. A reaction mechanism was proposed that required the use of PCA carrying at least three neighboring carboxylic groups (CTR, BTCA, and PAA), and it was confirmed experimentally by the unsuccessful use of some dicarboxylic acids. A preliminary characterization by Fourier transform infrared spectroscopy and size exclusion chromatography was also conducted. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 433–442, 2005     

Temperature‐sensitive switch from composite poly(N‐isopropylacrylamide) sponge gels

Thermally sensitive polymers change their properties with a change in environmental temperature in a predictable and pronounced way. These changes can be expected in drug delivery systems, solute separation, enzyme immobilization, energy‐transducer processes, and photosensitive materials. We have demonstrated a thermal‐sensitive switch module, which is capable of converting thermal into mechanical energy. We employed this module in the control of liquid transfer. The thermally sensitive switch was prepared by crosslinking poly(N‐isopropylacrylamide) (PNIPAAm) gel inside the pores of a sponge to generate the composite PNIPAAm/sponge gel. This gel, contained in a polypropylene tube, was inserted into a thermoelectric module equipped with a fine temperature controller. As the water flux through the composite gel changes from 0 to 6.6 × 10² L m⁻² h, with a temperature change from 23 to 40°C, we can reversibly turn on and off the thermally sensitive switch. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75:1735–1739, 2000     

Synthesis and investigation of properties of thiacalix[4]arene‐based polyurethane elastomers

A series of polyurethane elastomers (PUEs) derived from three thiacalix[4]arene derivatives (TC4As), namely p‐tert‐butylthiacalix[4]arene, tetrasodium thiacalix[4]arenetetrasulfonate and thiacalix[4]arenetetrasulfonic acid, as a portion of chain extender in a mixture with glycerol were synthesized. The effects of the chemical structure of TC4As used as chain extenders on the various properties of the prepared PUEs were investigated and compared with PUE extended with only glycerol as chain extender using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X‐ray diffraction (XRD), scanning electron microscopy and a universal tensile tester. Moreover, the effect of the introduction of TC4As as a portion of chain extender on the hydrophobicity of the PUEs was also evaluated. DSC, FTIR spectroscopy and XRD revealed that the degree of phase separation and crystallinity in TC4A‐based PUEs was much higher than that of the glycerol‐based ones. Thus, it was concluded that the presence of TC4As in TC4A‐based PUEs seems to favour the formation of a more ordered structure due to an increase in the degree of phase separation. The TGA results also showed that, with incorporation of TC4As into the polyurethane backbone, the thermal stability of PUEs was improved. © 2014 Society of Chemical Industry     

Gellan gum–O,O′‐bis(2‐aminopropyl)‐polyethylene glycol hydrogel for controlled fertilizer release

A gellan gum–Jeffamine superabsorbent hydrogel was obtained with different crosslink densities using different amounts of (1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride) and N‐hydroxysuccinimide. Infrared spectroscopy and thermal analysis confirm the crosslinking. A morphology analysis indicates denser structures for samples with higher crosslinking points. The swelling degree in high‐acyl gellan gum hydrogels was equivalent to 145 times their dry weight, and 77 times when low‐acyl gellan gum was used. Hydrogels also showed a 450 min water retention, as opposed to 280 min for pure water, evidencing good humidity control, suitable for use in arid climates. They also demonstrated a maximum release of commercial fertilizer of about 400 mg per gram for KH₂PO₄ and about 300 mg per gram for NPK 20‐5‐20. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45636.     

Cure and scorch in the processing of ethylene‐propylene‐diene terpolymer (EPDM)

The objective of this work is to ascertain the characteristics of desirable (cure) and especially undesirable (scorch) crosslinking when carbon black filled ethylene propylene diene terpolymer (EPDM) is processed using different peroxide initiators. The mixing temperature and the nature of the peroxide initiator are crucial parameters affecting scorch (undesirably premature crosslinking) in this rubber. Processability and properties of EPDM prepared using various mixer set temperatures have been investigated. Dicumyl peroxide (Luperox DC), di(t‐butylperoxy) diisopropylbenzene (Luperox F), and 2,5‐dimethyl‐2,5‐di(t‐butylperoxy) hexane (Luperox 101) were used as crosslinking initiators. Higher mixing temperatures give shorter scorch times, greater scorch magnitudes, greater heterogeneities in crosslink spatial distribution and poorer tensile properties. However, extreme localization of the unwanted crosslinking at the rubber‐filler interface does have a beneficial effect. Luperox DC offers poorer processability and poorer resulting properties than do Luperox F and Luperox 101, due to its shorter half‐life and greater solubility in the rubber phase. This is the first time that the spatial heterogeneity of crosslinking and scorch has been related to the basic thermodynamics of 3‐component 2‐phase systems. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44523.     

Physicomechanical studies and solvent resistance analysis of melt‐blended novel ethylene‐1‐octene elastomer and ethylene‐co‐acrylic acid interpenetrating network hybrids

Polar modification of poly(ethylene‐co‐octene) (POE) elastomer was carried out with a relatively new approach. Poly(ethylene‐co‐acrylic acid) (EAA) was taken as the modifier and POE with a calculated amount of EAA were coextruded with dicumyl peroxide (DCP; used as a crosslinker). The majority of the compositions showed the existence of a crosslinked EAA phase inside POE, although increasing DCP concentrations and extrusion temperatures were possibly capable of crosslinking either of the phases, as observed with a model composition. All of the samples were soft and light in nature. The best composition was the one that contained 13.3 wt % EAA; that composition showed excellent surface polarity and superior mechanical properties. Detailed solvent swelling experiments also yielded the best results for that particular composition. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of side‐chain liquid‐crystalline elastomers containing cholesterol

A series of new smectic and cholesteric liquid‐crystalline elastomers were prepared by graft polymerization of mesogenic monomer with the chiral and nonmesogenic crosslinking agent using polymethylhydrosiloxane as backbone. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared and proton nuclear magnetic resonance spectra. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. M₁ showed cholesteric phase during the heating and the cooling cycle. Polymer P₁, elastomers P₂ and P₃ exhibited smectic phase, elastomers P₄? P₆ showed chiral smectic C phase, P₇ showed cholesteric phase, and P₈ displayed stress‐induced birefringence. The elastomers containing less than 15 mol % M₂ displayed elasticity and reversible phase transition with wide mesophase temperature ranges. Experimental results demonstrated that the glass transition temperatures, the isotropization temperatures, and the mesophase temperature ranges decreased with increasing content of the crosslinking unit. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 383–390, 2005     

Effect of the length of the carbochain on the phase behavior of side‐chain cholesteric liquid‐crystalline elastomers

In this study, we prepared two series of new side‐chain cholesteric liquid‐crystalline elastomers (PI and PII) derived from the same chiral bisolefinic crosslinking units and different nematic liquid‐crystalline monomers. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared and ¹H‐NMR spectroscopy. The phase behavior properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. The effect of the length of the carbochain on the phase behavior of the elastomers was investigated. The polymers of the PI and PII series showed similar properties. Polymer P₁ showed a nematic phase, P₂–P₇ showed a cholesteric phase, and P₄–P₇, with more than 6 mol % of the chiral crosslinking agent, exhibited a selective reflection of light. The elastomers containing less than 15 mol % of the crosslinking units displayed elasticity, a reversible phase transition with wide mesophase temperature ranges, and a high thermal stability. The experimental results demonstrate that the glass‐transition temperatures first decreased and then increased; the isotropization temperatures and the mesophase temperature ranges decreased with increasing content of crosslinking agent. However, because of the different lengths of the carbochain, the glass‐transition temperatures and phase‐transition temperatures of the PI series were higher than those of the PII series, and the PI and PII elastomers had their own special optical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1204–1210, 2005