Conductive stretchable shape memory elastomers combining with electrical stimulation for synergistic osteogenic differentiation

The natural extracellular matrix (ECM) possessed varying biomechanical properties which played important roles in the dynamic cellular microenvironment. However, for the conventional bone tissue engineering scaffolds, stretchability and shape memory property were normally absent. Thus, the behaviors of responsive changes required in dynamic physiological settings were unsatisfactory. Herein, a series of conductive polyurethane shape memory elastomers (PCL-IPDI-AT) were synthesized, which based on conductive amino capped aniline trimer (AT), isophorone diisocyanate (IPDI) and poly(ԑ-caprolactone) (PCL). The conductive elastomers possessed high elasticity and flexibility, especially, the breaking elongation of copolymer with 15% AT content was up to 570 ± 56%. The mechanical properties of elastomers could be adjusted by regulating the content of AT in copolymers. The conductive elastomers exhibited excellent shape fixity ratio and good shape recovery ability at 37 °C. The electrical conductivity of elastomers was measured via the standard van der Pauw four-probe method. They were all around 10⁻⁷ S/cm and similar to that in human physiological environments. On the one hand, excellent cytocompatibility was demonstrated by the viability and proliferation results of MC3T3-E1 pre-osteoblasts seeded on the elastomer. On the other hand, the elastomer could synergistically promote the osteogenic differentiation compared to PCL in terms of ALP activity, calcium deposition, and bone-related protein and gene expression levels as combined with electrical stimulation (ES). Specifically, the ALP activity for conductive elastomer under ES was notably improved by 1.4-fold compared to PCL at 7 days. Overall, the conductive elastomers displayed excellent stretchability, shape memory property, fatigue resistance and osteogenic bioactivity. They may be applied as bone substitutes for electrical-signal-sensitive bone tissue engineering.     

Dynamic elastomers based on bio-derived crosslinker

Petroleum-derived monomers are the most common building blocks for ester-based thermosets. Bio-derived thermoset elastomers are becoming viable alternatives to conventional thermosets. Herein, we developed a biobased vitrimer-type thermoset elastomers using abundant and sustainable raspberry ketone as feedstock. We utilize raspberry ketone to create building blocks for dynamic oxime chemistry and crosslinked these through free radical polymerization with poly(ethylene glycol) methyl ether methacrylate as a comonomer. In contrast to other dynamic networks based on ester bonds, which need catalysts, this is undesirable since catalyst deactivation or leaching lowers its effect over time and may impair reuse. This network incorporates catalyst-free bond exchange reactions in catalyst-dependent polyester networks by substituting oxime-esters for typical ester linkages. The elastomer exhibits stress relaxation, a low glass transition temperature (T_g) (−55 to −40.2°C) and tensile strength up to 5.2 ± 3.0 kPa. Furthermore, the dynamic oxime transesterification exchange mechanism allows elastomers to be reprocessed using a hot press at 160°C and 8 × 10³ kPa pressure. After reprocessing, the tensile strength of elastomers can be recovered up to 78.1 ± 10.9%. This work integrates the principles of catalyst-free dynamic exchange process and mechanical recycling coupled with biobased components to provide a rational solution towards conventional elastomers. In the future, these elastomers can be exploited for the development of hydrogels, recyclable elastomers, and commodity plastics.     

Synthesis and characterization of polyaniline filled PU/PMMA interpenetrating polymer networks

A series of conducting interpenetrating polymer networks (IPNs), are prepared by sequential polymerization of castor oil based polyurethane (PU) with poly(methyl methacrylate) (PMMA) and polyaniline doped with camphor sulphonic acid (PAni)_CSA. The effect of different amount of PAni (varies from 2.5-12.5%) on the properties of PU/PMMA (50/50) IPNs such as electrical properties like conductivity, dielectric constant and dissipation factor; mechanical properties like tensile strength and percentage elongation at break have been reported. (PAni)_CSA filled IPNs shows improved tensile strength than the unfilled IPN system. The thermal stability and surface morphology of unfilled and (PAni)_CSA filled PU/PMMA (50/50) IPN sheets were investigated using a thermogravimetric analyzer (TGA) and a scanning electron microscope (SEM). TGA thermograms of (PAni)_CSA filled PU/PMMA (50/50) IPNs show a three-step thermal degradation process. SEM micrograms of filled PU/PMMA IPN system shows spherulitic structure at higher concentration of (PAni)_CSA.     

Ion conduction in poly(crown ethers), polyglucosan gels and macroporous polyethylene films

Much work has been reported on ion conduction in solid solutions of salts dissolved in linear and comb-branched poly(ethylene oxide) analogues. There appears to be a limit to the conductivity levels achieved in such systems, and conductivity values rarely exceed σ ∼ 10⁻⁴ Scm⁻¹ at room temperature. To overcome this there has been a move towards more mobile plasticized systems and polymer gel electrolytes are receiving some attention. Gels prepared from N-methyl-2-pyrrolidinone/LiCl and polyglucosans such as cellulose and amylose have been studied and show some promise with ambient σ Ge; 10⁻⁴ Scm⁻¹. Macroporous polyethylene has also been used to support fluid polyethylene glycol/salt systems, but these only reached σ ≥ 10⁻⁵ Scm⁻¹ at ambient temperature. Comb-branch polymers with crown ethers provide systems with respectable room temperature conductivities of between 10⁻⁴ and 10⁻⁵ Scm⁻¹, but these might be improved if the crown ethers could be arranged in regular channels. Ways to achieve this are briefly discussed.     

Implementation of low temperature physical changes on silicone elastomers to achieve sensitivity gains through CPMAS NMR

Nuclear Magnetic Resonance Spectroscopy (NMR) has been used on several occasions to investigate the biodurability of silicone elastomers used in silicone breast implants. In all of these cases conclusions have been convoluted by lack of sensitivity. We have improved the sensitivity of solid state NMR characterizations of silicone elastomers used in silicone breast implants by changing the physical state of the elastomer. This was achieved by cooling the sample to −90 ^∘C, below its crystalline transition temperatures, and acquiring ²⁹Si Cross Polarization MAS (CPMAS) NMR. This approach yielded signal to noise enhancements as high as 8.5 fold for the elastomer backbone and modest improvements for (CH₃)₂RSiO_1/2 and silica filler signals.     

Interfacially modified LDPE/GTR composites with non-polar elastomers: From microstructure to macro-behavior

This paper provides some new insights into the mechanism of interaction and modifications in thermoplastic composites based on low density polyethylene (LDPE), ground tire rubber (GTR) and non-polar elastomer. The composites were prepared using a co-rotating twin-screw extruder at variable LDPE/GTR ratio and constant elastomer content. Two types of commercial elastomer were applied: styrene-butadiene-styrene (SBS) block copolymers (Kraton^®) with different topologies (linear/branched) and partially cross-linked butyl rubbers (Kalar^®) with different Mooney viscosities. Processing characteristics, static mechanical properties (tensile strength, elongation at break, hardness), dynamic mechanical properties, thermal properties and morphology of the resulting thermoplastic composites were investigated. Microstructure analysis shows that modification of LDPE/GTR composites with non-polar elastomers caused encapsulation of GTR particles within the elastomer phase. This phenomenon has significant influence on macro-behavior of thermoplastic composites based on LDPE/GTR blends. The results indicate that SBS copolymer improves interfacial interactions between GTR and LDPE, which enhances mechanical and thermal properties of the composites. On the other hand, cross-linked butyl rubber showed partial compatibility with LDPE and low compatibility with GTR particles.     

Enzymatic synthesis and properties of novel biodegradable and biobased thermoplastic elastomers

Novel biodegradable and biobased thermoplastic elastomers, poly[dodecanolide-12-hydroxystearate (12HS)], poly(pentadecanolide-12HS) and poly(hexadecanolide-12HS) with M_ws of 140,000-290,000 g mol⁻¹ were prepared by the enzymatic copolymerization of a macrolide as the hard segment and methyl 12HS as the soft segment. Their thermal properties, such as T_m and T_c, were measured by DSC. Physicochemical and mechanical properties, such as crystallinity, were also measured. The polymer structures were analyzed with respect to the sequence of the two monomers by ¹H NMR spectroscopy using an europium shift reagent. The randomness of the two monomer units in the polymer chain increased with the polymerization time. Both Young’s modulus and tensile strength decreased with increasing 12HS content in the copolymer. In contrast, elongation at break increased with increasing 12HS content, thus demonstrating the copolymers’ elastomeric properties. These copolymers showed biodegradabilities by activated sludge, which also increased with increasing 12HS content.     

Fading memory of deformation history in carbon black-filled thermoplastic elastomers

Observations are reported on a carbon black–reinforced thermoplastic elastomer in multistep uniaxial tensile cyclic tests with a mixed deformation program (oscillations between maximum elongation ratios k_max and various minimum stresses σ_min with k_max monotonically increasing with number of cycles n). Fading memory of deformation history is demonstrated: when specimens are subjected to two loading programs that differ along the first n −1 cycles of deformation and coincide afterwards, their stress–strain diagrams become identical starting from the nth cycle. A constitutive model is developed in cyclic viscoplasticity with finite deformations, and its adjustable parameters are found by fitting the observations. Ability of the stress–strain relations to describe the fading memory phenomenon and to predict the mechanical response of polymer composites in multi-step cyclic tests with large strains is confirmed by numerical simulation.     

MC-determination in elastomers by 1H-NMR relaxation and 2H-NMR spectroscopy

We show how ¹H–NMR transversal relaxation and ²H–NMR spectroscopy can be used for the determination of the number average molecular mass M_C in typical elastomers at temperatures well above the glass transition temperature. M_C-results of the different NMR methods are compared among one another and with M_C-results of other common independent methods. Moreover, the NMR measurements provide a number of additional useful parameters: correlation times, portions of dangling chain ends and of sol molecules, molecular order.     

Blend polyolefin elastomers based on a stereoblock elastomeric PP

The principles of the creation of new blend polyolefin elastomers with a controlled complex of properties based on a stereoblock elastomeric PP synthesized in the presence of asymmetric ansa-metallocenes are proposed. Original blend polymer materials with reduced hardness that are based on elastomeric PPs with different characteristics and a 50–70 wt % oil-extended ternary ethylene-propylene-diene elastomer were prepared through the method of dynamic vulcanization. The molecular-mass characteristics of PP have a considerable effect on the rheological properties of polyolefin elastomers. For successful processing of the resulting blends, the pristine component, the elastomeric PP, must have a weight-average molecular mass of M _w = (8?14) × 10⁴ and a low crystallinity.     

Thiol-yne photoclick polymerization as a method for preparing imidazolium-containing ionene networks

Herein, the thiol-yne photoclick reaction was utilized as a method for synthesizing imidazolium-containing ionene networks whereby a bisalkynyl-functionalized imidazolium [NTf₂] ionic liquid was polymerized with the tetrafunctional thiol PTMP (pentaerythritol tetrakis(3-mercaptopropionate)). The thiol:yne functional group ratio was varied in order to examine the breadth of thermal, mechanical, and conductive properties available from the resulting networks. The stoichiometric 1:1 thiol:yne network exhibited very high thiol and alkyne conversions by FT-IR spectroscopy and a gel fraction greater than 95%. The highest T_g value (3.5°C) and stress at break (1.13 MPa) were also observed for this network. As either thiol or alkyne functional group concentration was increased, the networks were noticeably lower in T_g and stress at break with a modest increase in % elongation. Ionic conductivities were found to be on the order of 10⁻⁹ to 10⁻⁷ S/cm at 30°C. Normalization of the ionic conductivity curves did not lead to a complete collapse meaning that the observed differences in conductivity are not solely dependent upon T_g. When compared to analogous imidazolium-containing, thiol-ene ionene networks, the thiol-yne networks were found to be slightly more mechanically robust, but approximately one order of magnitude lower in terms of ionic conductivity.     

Ion conductivity of poly(ethylene oxide)-based polyurethane networks containing alkali metal salts

Ion conductivity of poly(ethylene oxide) (PEO)-based polyurethane networks containing alkali metal salts has been investigated. Consequently, it has been revealed that the conductivity is dependent on the following parameters: lattice energy of the alkali metal salt, concentration of alkali metal salt, and the cross-linking density of the network polymer (which is a function both of the amount of cross-linking agent and the molecular weight of PEO). Under optimal conditions, the conductivity at ambient temperature corresponded to 2.51 × 10^?5 Scm^?1, which is greater than that of a typical alkali metal-PEO system by a factor of about 10² to 10³. Moreover, from the standpoint of the application to electrochromic displays (ECD), tensile bond strength between the polymer electrolytes and tungsten trioxide (WO₃), which is the most promising electrochromic material, has been evaluated. The bonding strength of the bond of WO₃ with the present electrolyte has been found to be much larger than that of the alkali metal-PEO system.     

Threshold fracture energies for elastomers

Fracture energies have been measured for two types of polybutadiene elastomer, crosslinked to various extents and torn under various conditions. Threshold values, ranging from 40 to 80 jm^?2, were observed for samples torn at extremely low rates of tearing, at high temperatures, and in the swollen state. These values were found to be independent of temperature and rate of tearing, and also of the degree of swelling and the nature of the swelling liquid, provided a correction is made for the reduced areal concentration of molecular chains. They decreased somewhat with increased crosslinking, in good agreement with theoretical predictions of Lake and Thomas.⁶ The results for the two elastomers were substantially the same. These observations are strikingly different from those made at normal temperatures and rates of tearing, when large differences in fracture energy were observed between the elastomers, and between samples crosslinked to different extents, due to energy losses from nonequilibrium deformation processes in addition to the energy required for fracture.     

Ionic Liquid Based Polymer Gel Electrolytes for Use with Germanium Thin Film Anodes in Lithium Ion Batteries

Thermally stable, flexible polymer gel electrolytes with high ionic conductivity are prepared by mixing the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (C₄mpyrTFSI), LiTFSI and poly(vinylidene difluoride-co-hexafluoropropylene (PVDF-HFP). FT-IR and Raman spectroscopy show that an amorphous film is obtained for high (60 %) C₄mpyrTFSI contents. Thermogravimetric analysis (TGA) confirms that the polymer gels are stable below ∼300 °C in both nitrogen and air environments. Ionic conductivity of 1.9×10⁻³ S cm⁻² at room temperature is achieved for the 60 % ionic liquid loaded gel. Germanium (Ge) anodes maintain a coulombic efficiency above 95 % after 90 cycles in potential cycling tests with the 60 % C₄mpyrTFSI polymer gel.     

New elastomers based on uralkyd/polyethyl methacrylate semi- and full interpenetrating polymer networks

Two-component semi- and full interpenetrating polymer networks (IPNs) of soybean-oil-based uralkyd resin (UA) and polyethyl methacrylate (PEMA) were synthesized by the sequential technique. The elastomers obtained were characterized by mechanical properties such as tensile strength, elongation, and hardness (Shore A). The apparent densities of these samples were determined and compared. Glass-transition studies were carried out using differential scanning calorimetry. The thermal characterization of the elastomers was undertaken with the aid of thermogravimetric analysis. Phase morphology was studied by scanning electron microscopy. The effect of the compositional variation on the aforementioned properties was examined. The maximum elongation for both the semi- and full IPNs was observed at 60% UA and 40% PEMA. Glass-transition studies revealed that there was a phase separation in the semi-IPNs as two T_gs were obtained, whereas the full IPNs showed one T_g, indicating a single phase transition. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4302–4308, 1999     

Room temperature synthesis and mechanical properties of two kinds of elastomeric interpenetrating polymer networks based on castor oil

Two kinds of interpenetrating polymer networks (IPNs) composed of two-component polyurethane (PU) and vinyl or methacrylic polymer (PV), namely, (polyether-castor oil)PU/PV IPN(I) and (polybutadiene-castor oil)PU/PV IPN(II), were synthesized at room temperature using benzoyl peroxide and N,N-dimethylaniline as redox initiator and dibutyltin dilaurate as catalyst. The former IPN was prepared by polymerization of castor oil, NCO-terminated polyether and vinyl or methacrylic monomer together and the latter IPN was obtained by polymerization of castor oil, NCO-terminated polybutadiene, NCO-terminated castor oil and vinyl or methacrylic monomer together. Various synthesis conditions affecting mechanical properties of the two kinds of IPNs were studied. Acrylonitrile (AN) is a good monomer for synthesizing IPN(I), but is a poor monomer for preparing IPN(II). At optimum conditions for the synthesis, both the (polyether-castor oil)PU/PAN IPNs and the (polybutadiene-castor oil)PU/polystyrene (PSt) IPNs possess permanent set about 10%, tensile strength over 13 and 11 MPa and ultimate elongation over 240% and 270%, respectively, thus behaving as elastomers. TEM micrograph of a (polybutadiene-castor oil)PU/PSt IPN showed a microphase separation in the IPN.     

Custom-made sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) nanocomposite membranes for vanadium redox flow battery applications

Sulfonated poly (vinylidene fluoride-co-hexafluoropropylene) (SPVDF-co-HFP) based nanocomposite proton exchange membranes (PEM) are fabricated by simple solution casting method using polydopamine coated exfoliated molybdenum disulfide (PDA-MoS₂) nanosheets as an alternative for Nafion® in vanadium redox flow batteries (VRFBs). PDA-MoS₂ is synthesized by the etching of exfoliated MoS₂ nanosheets with dopamine molecule by self-polymerization method. Various characteristic results clearly demonstrated that the incorporated PDA-MoS₂ nanosheets homogeneously distributed into the SPVDF-co-HFP matrix and the presence of NH/NH₂ group electrostatically interacts with SPVDF-co-HFP to form a strong acid-base pair and thus enhances the proton transport via Grotthuss type mechanism. Besides, the improvement in surface hydrophilicity provides the vehicle type conduction also. As a result, SPVDF-co-HFP/PM nanocomposite membranes showed higher proton conductivity in comparison with the pristine membrane. Especially SPVDF-co-HFP/PM-1 membrane demonstrated the excellent proton conductivity of 5.24 × 10⁻³ Scm⁻¹ at 25 °C, lower vanadium-ion permeability of 1.05 × 10⁻⁸ cm²min⁻¹ and highest membrane selectivity of 49.9 × 10⁴ Scm⁻³min. On the other hand, vanadium-ion stability of the membrane increased by adding the PD-MoS₂ content is attributed to their strong electrostatic attraction towards the polymer matrix. Overall results suggested that the SPVDF-co-HFP/PM-1 nanocomposite membrane is found to be a better alternative for commercially costly Nafion in VRFB applications.     

Polyurethane elastomers based on amphiphilic poly(caprolactone)‐b‐poly(butadiene)‐b‐poly(caprolactone) triblockcopolyols

Hydroxyl‐terminated poly(butadiene) (HTPB; M_n = 2100 g mol⁻¹) was capped with 30 and 60 wt % of ɛ‐caprolactone to reach amphiphilic triblock copolymers in form of capped poly(butadiene) CPB. The former (CPB30; M_n = 3300 g/mol) is amorphous with a glass temperature of −56 °C. CPB60 (M_n = 4000 g mol⁻¹) is semi‐crystalline with a melting point of 50 °C and a glass transition at −47 °C. The CPBs, HTPB and polycaprolactone diol (M_n = 2000 g mol⁻¹) were used as soft segment components in the preparation of polyurethane elastomers (PUE), using a 1/1 mixture of an MDI prepolymer and uretonimine modified MDI, and hard phase components in form of 1,3‐propane diol, 1,4‐butane diol, and 1,5‐pentane diol. CPB‐based elastomers with 1,4 butane diol (8 wt %) show hard domains as fringed aggregates with a better connection to the continuous phase than the HTPB‐based PUE. The soft segment glass transition temperature (T_g) is at −28 °C for HTPB‐based PUE and at −43 °C for those of CPB. The tensile strength of the CPB30&60‐based PUE is found between 20 and 30 MPa at an elongation at break of 400% and 550%, respectively. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1162–1172     

The swelling behaviour of siloxane elastomers in relation to their microscopic structure

Swelling experiments have been performed in order to characterize elastomer networks. The value of the interaction parameter χ of the Flory‐Rehner equation has been evaluated. We were particularly interested in equilibrium swelling and the kinetics of swelling when the solvent was of the same nature as the network polymer; a siloxane fluid in a siloxane elastomer. Now, the swelling capacity of elastomers can easily be predicted and this is of particular importance in relation to their formulation. The swelling experiments also revealed a more complex kinetics than expected. We relate this kinetics to the self‐bleeding process and give an interpretation based on the network microstructure. Finally, some data from electron microscopy in relation to light and neutron scattering and also results of a thermoporometry study of the elastomers are discussed.     

AN EPOXY/(METHYL METHACRYLATE)INTERPENETRATING POLYMER NETWORK FOR NONLINEAR OPTICS*

An interpenetrating polymer networks (IPN) consisting of an epoxy-based polymer network and apolymethyl methacrylate network were synthesized and characterized. The IPN showed only one T_g, andhence a homogeneous-phase morphology was suggested. The second-order nonlinear optical coefficient (d_(33))of the IPN was measured to be 1.72×10~(-7) esu. The study of NLO temporal stability at room temperature andelevated temperature (100℃) indicated that the IPN exhibits a high stability in the dipole orientation due tothe permanent entanglements of two component networks in the IPN system. Long-term stability of secondharmonic coefficients was observed at room temperature for more than 1000 h.