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The impact of the chemical structure on ion transport, nanoscale morphology, and dynamics in polymerized imidazolium-based ionic liquids is investigated by broadband dielectric spectroscopy and X-ray scattering, complemented with atomistic molecular dynamics simulations. Anion volume is found to correlate strongly with Tg-independent ionic conductivities spanning more than 3 orders of magnitude. In addition, a systematic increase in alkyl side chain length results in about one decade decrease in Tg-independent ionic conductivity correlating with an increase in the characteristic backbone-to-backbone distances found from scattering and simulations. The quantitative comparison between ion sizes, morphology, and ionic conductivity underscores the need for polymerized ionic liquids with small counterions and short alkyl side chain length in order to obtain polymer electrolytes with higher ionic conductivity.

The design of biocomposite membranes based on microcrystalline cellulose (MCC) extracted from sugarcane bagasse added into matrices of poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) was fabricated by the phase inversion method. The pore formation of biocomposite membranes was prepared by the phase inversion method, and the obtained biocomposite membranes showed a tunable microstructure formed in the membranes that was investigated by field-emission scanning electron microscope. Due to the high porosity and hydrophilic properties of MCC, the biocomposite membranes demonstrated excellent electrolyte wettability, large electrolyte uptake (up to 138%), and smaller interfacial resistance leading to enhancement of the ionic conductivity. Furthermore, the effects of MCC on the thermal properties of biocomposite membranes were evaluated by differential scanning calorimetry and the thermal shrinkage test. The addition of 5 wt% MCC showed the outstanding thermal stability of the biocomposite membranes. After thermal treatment at 135 °C for 1 h, this biocomposite membrane exhibited shrinkage of only 32% from the original shape while the PLA/PBS membrane showed shrinkage of 81%, which verifies that the introduction of MCC improves the thermal stabilities of biocomposite membranes. Promisingly, the biocomposite membranes represent candidate alternatives for future battery applications.

Polymerized ionic liquids (PILs) are single-ion conductors in which one of the ionic species is tethered to the polymer chain while the other is free to be transported. The ionic species can either be directly incorporated into the polymeric backbone (backbone PILs) or placed as pendant groups to the chain (pendant PILs). Here, we examined the morphology, conductivity, and rheology of imidazolium-based pendant and backbone PILs. We found that pendant PILs yielded higher ionic conductivity when scaled to Tg, but backbone PILs exhibited higher ionic conductivity on an absolute temperature scale, likely because of differences in the Tgs of the two systems. We also found that ion transport for backbone PILs was coupled to the segmental dynamics below Tg, where the decoupling of ionic conductivity from segmental relaxation was observed for pendant PILs. The results of this study will help the community to better understand the role of the PIL structure on conductivity to work toward the ultimate goal of designing high-performance solid polymer electrolytes.

Sulfonated cellulose (SC) was successfully derived from microcrystalline cellulose (MCC) extracted from sugarcane bagasse, which is a type of agricultural waste. The obtained MCC was first modified by oxidation using sodium periodate in order to cleave the carbon-carbon bonds at the C2 and C3 of the pyranose ring to form 2,3-dialdehyde cellulose. These activated aldehyde groups significantly facilitated the sulfonation carried out using potassium metabisulfite. The sulfonic acid group contents, surface morphology, and water solubility of the obtained products were characterized by titration, field-emission scanning electron microscopy, UV–vis spectroscopy, and zeta potential. High sulfonic acid group content was achieved for the obtained SC samples (i.e., 305–689 μmol/g). The increase in the sulfonic acid group content resulted in the gradual change in the surface morphology and water solubility of the SC samples. The obtained results imply that sugarcane bagasse is a promising raw material for the production of SC with good water solubility.

This paper represents the first comprehensive report of the molecular weight dependence of the dynamics of polyfarnesene (PF), utilizing oscillatory shear rheology and broadband dielectric spectroscopy. Extended PF chain conformations arising from tightly packed C11/C13 pendant groups reduce the probability of chain entanglements and lead to Rouse-like melt dynamics up to a critical molecular weight ∼105 g/mol. At higher molecular weights, PF behaves as an entangled polymer melt. Dielectric spectroscopy measurements establish PF as a type-A polymer, whose normal mode relaxation is strongly dependent on molecular weight, providing a compliment to melt rheology for the exploration of PF global chain dynamics.

Recent observations of the high-velocity impact response in poly (urethane urea), PUU, elastomers has inspired a new inquiry on whether enabling molecular mechanisms could benefit dynamic impedance optimization at the interface of a glass/polymer bilayer, particularly at the moment of impulse interaction. In this work, we investigate the molecular influence on dynamic impedance using microballistic measurements on two bulk elastomers, a PUU and a polyurea, PU. Upon impact at strain rates ∼108/s, PUU exhibits a moderate improvement in resistance against penetration than PU, that is more pronounced at higher speeds. The variation in dynamic stiffening corroborates well with the corresponding segmental dynamics data determined via broadband dielectric relaxation. Meanwhile, we calculate the shock impedance from the shock velocity data derived from the respective shock Hugoniot to discern the efficacy of dynamic impedance optimization between PUU and glass. New insight on molecular attributes will guide glass/polymer interface designs.

Polymerized ionic liquids (PILs) are believed to be ideal solid-state polymer electrolytes, and hence experimental and computational studies have been widely undertaken to understand the relationship between the chemical structure and mechanical/dielectric properties and the ionic conductivity of PILs. However, it is still a challenge to understand the effect of counterion ionic volume on the material properties of PILs. Herein, we demonstrate the effect of the ionic volume ratio of counteranions to side-chain cations on linear viscoelastic response using three imidazolium-based PILs with different counteranions. We show that the elastic modulus is significantly enhanced at temperatures higher than glass transition temperature once the ionic volume of the counteranion exceeds that of the side-chain cation. Our results provide an additional strategy to improve mechanical properties of PILs, while maintaining relatively high ionic conductivity.

A model semicrystalline polymer, poly(ethylene naphthalate) (PEN), was used to examine how morphological factors inhibit chain segment relaxations that contribute to dielectric loss. This was achieved by manipulating the extent of crystallization and the crystalline microstructure through a combination of annealing and uniaxial drawing and investigating the effects on dielectric performance. Varying crystallization conditions influenced the dynamic Tg and extent of rigid amorphous fraction formation but had only a moderate effect on loss magnitude. Film orientation, however, greatly reduced loss through strain-induced crystallization and the development of oriented amorphous mesophasic regions. Postdrawing annealing conditions were capable of further refining the crystal microstructure and, in turn, the dielectric properties. These findings demonstrate that the semicrystalline polymer morphology can have a very significant influence on amorphous chain relaxations that contribute to dielectric loss, and un...

In the present investigation, we explore the influence of uniaxial orientation and subsequent thermal annealing on semi-crystalline poly(ethylene-tetrafluoroethylene) (ETFE) microstructure and dynamics, and the connection to dielectric breakdown strength. Understanding the influence of crystalline microstructure on dynamics and breakdown, and in turn how processing influences microstructure, is critical for establishing rational design of polymer dielectrics. When drawn below the glass transition temperature (Tg), the Weibull breakdown strength decreases compared to that of the undrawn precursor film, but increases on thermal annealing near or above Tg. This behavior is associated with the formation and elimination of drawing-induced microvoids, respectively. When drawn above Tg, the breakdown strength increases to ∼870 MV/cm, dominated by orientation of amorphous segments, and decreases on thermal annealing above Tg to near that of the undrawn film.

It is a great challenge in dielectric polymers to achieve a high dielectric constant while maintaining low dielectric loss and high operating temperatures. Here we report that by blending two glassy state dipolar polymers i.e., poly(arylene ether urea) (PEEU, K=4.7) and an aromatic polythiourea (ArPTU, K=4.4) to form a nanomixture, the resulting blend exhibits a very high dielectric constant, K=7.5, while maintaining low dielectric loss (

In order to increase the dielectric constants of polymer-based dielectrics, composite approaches, in which inorganic fillers with much higher dielectric constants are added to the polar polymer matrix, have been investigated. However, high dielectric constant fillers cause high local electric fields in the polymer, resulting in a large reduction of the electric breakdown strength. We show that a significant increase in the dielectric constant can be achieved in polyetherimide nanocomposites with nanofillers whose dielectric constant can be similar to that of the matrix. The presence of nanofillers reduces the constraints on the dipole response to the applied electric field, thus enhancing the dielectric constant. Our results demonstrate that through nanostructure engineering, the dielectric constant of nanocomposites can be enhanced markedly without using high dielectric constant nanofillers.

Fully bio-based polyamide 1010 (PA1010) was successfully melt-blended with poly (vinyl alcohol) (PVA03, PVA05, PVA08 and PVA14) to prepare PA1010xPVAzy blends. The PA1010xPVA03y, PA1010xPVA05y, PA1010xPVA08y and PA1010xPVA14y films demonstrated the lowest oxygen transmission rates (OTR), free volume fraction (Fv), mean volume of the free volume holes (Vf) and mean number of free volume holes per unit volume (I3) values, when the PVA concentration in each PA1010xPVAzy series reached a corresponding critical value of 22.5, 20, 17.5 and 12.5 wt%, respectively. OTR, Fv, Vf and I3 values obtained for the best PA101087.5PVA1412.5, PA101082.5PVA0817.5, PA101080PVA0520 and PA101077.5PVA032.25 films reduced gradually as the degree of polymerization of PVA reduced. The results of dynamical mechanical and other experimental characterizations demonstrated that PA1010 and PVA are compatible to some extent, when the PVA are ≤ the corresponding critical concentration. The significantly enhanced oxygen permeation resistance and free volume characteristics for optimal PA1010xPVAzy films is at least partly due to the improved hydrogen-bonded molecular interactions between PA1010 C=O groups and PVA O-H groups.

Interface effects in a new class of nanocomposites generate superior energy storage performance over broad temperatures., Although many polymers exhibit excellent dielectric performance including high energy density with high efficiency at room temperature, their electric and dielectric performance deteriorates at high temperatures (~150°C). Here, we show that nanofillers at very low volume content in a high-temperature (high–glass transition temperature) semicrystalline dipolar polymer, poly(arylene ether urea), can generate local structural changes, leading to a marked increase in both dielectric constant and breakdown field, and substantially reduce conduction losses at high electric fields and over a broad temperature range. Consequently, the polymer with a low nanofiller loading (0.2 volume %) generates a high discharged energy density of ca. 5 J/cm3 with high efficiency at 150°C. The experimental data reveal microstructure changes in the nanocomposites, which, at 0.2 volume % nanofiller loading, reduce constraints on dipole motions locally in the glassy state of the polymer, reduce the mean free path for the mobile charges, and enhance the deep trap level.

Synthetic polymer leaflets in prosthetic cardiac valves hold the potential to reduce calcification and thrombus, while improving blood flow, durability, and device economics. A recently developed siloxane poly(urethane‐urea) (LifePolymer™, LP) exhibits properties essential for heart valve leaflets, including low dynamic modulus, high tensile strength, minimal creep, and excellent biostability. LP properties result from carefully designed “linked co‐macrodiol” chemistry that maximizes silicone content and virtual crosslinks between soft and hard phases. Characterization of multiple commercial batches demonstrates a robust synthesis process with minimal variation. Extensive ISO 10993‐based biocompatibility testing resulted in no observable toxicity or other adverse reactions. An ex vivo AV shunt thrombogenicity investigation revealed nearly undetectable levels of platelet attachment and thrombus formation on LP surfaces. Chronic ovine implantation of prototype heart valves with LP leaflets showed no differences in thrombogenicity or systemic tissue response when compared to a clinically standard tissue‐based valve. Toxicological risk assessment, based on extractables and leachables analysis of LP‐based heart valves, confirmed minimal toxicological risk. Lastly, 24‐week, strain‐accelerated in vivo LP biostability testing confirmed previous favorable in vitro biostability findings. These studies demonstrate that this newly developed elastomer exhibits ideal biomaterial properties for the flexible leaflets of a totally synthetic heart valve replacement.

This paper presents an investigation of semi-crystalline poly[tetrafluoroethylene -co-(perfluoropropylvinylether)] (PFA) films uniaxially drawn at two temperatures. The extent of crystal unit cell orientation increased significantly with drawing at both draw temperatures as expected, but crystallinity was found to increase with draw ratio only at the lower draw temperature, remaining unchanged at the higher temperature. Considering the evolution of small-angle X-ray scattering patterns as a function of deformation, a model for the changes in PFA lamellar microstructure on drawing was developed. The observed mechanical α and γ relaxations of PFA were assigned to relaxation of rigid and mobile amorphous segments, respectively. Drawing at 200 °C to a draw ratio of 7 leads to a ∼40 °C increase in the α transition temperature compared to the unoriented film, and the findings support the key role of molecular orientation in suppressing the cooperative motions of non-crystalline segments in drawn polymers.

Fluorinated semi-crystalline polymers are attractive for dielectric film applications due to their chemical inertness and high thermal stability. In the present investigation we explore the influence of orientation induced by uniaxial drawing on the crystalline microstructure and relaxation processes of poly(ethylene-tetrafluoroethylene) (ETFE), in order to ascertain how morphological control can benefit polymer dielectric design. When drawn below or near the Tg, the crystallinity of the drawn films is unchanged, and oriented amorphous structures and crystalline microfibrils form at high draw ratios. This orientation slows segmental relaxation, reflected by an increase in the dynamic Tg. When drawing above Tg, the films undergo strain-induced crystallization at high draw ratios. For these films, an increase in dynamic Tg is also observed, in addition to a second segmental relaxation process, appearing as a shoulder on the primary process. We propose that this represents a contribution from a rigid amorphous fraction, having slowed chain dynamics.

Environmental stress cracking (ESC) was replicated in vitro on Optim™ (OPT) insulation, a polydimethylsiloxane-based polyurethane utilized clinically in cardiac leads, using a Zhao-type oxidation model. OPT performance was compared to that of two industry standard polyether urethanes: Pellethane® 80A (P80A), and Pellethane® 55D (P55D). Clinically relevant specimen configurations and strain states were utilized: low-voltage cardiac lead segments were held in a U-shape by placing them inside of vials. To study whether aging conditions impacted ESC formation, half of the samples were subjected to a pretreatment in human plasma for 7 days at 37°C; all samples were then aged in oxidative solutions containing 0.9% NaCl, 20% H2 O2 , and either 0 or 0.1M CoCl2 , with or without glass wool for 72 days at 37°C. Visual and SEM inspection revealed significant surface cracking consistent with ESC on all P80A and P55D samples. Sixteen of twenty P80A and 10/20 P55D samples also exhibited breaches. Seven of 20 OPT samples exhibited shallow surface cracking consistent with ESC. ATR-FTIR confirmed surface changes consistent with oxidation for all materials. The number average molecular weight decreased an average of 31% for OPT, 86% for P80A, and 56% for P55D samples. OPT outperformed P80A and P55D in this Zhao-type in vitro ESC model. An aging solution of 0.9% NaCl, 20% H2 O2 , and 0.1M CoCl2 , with glass wool provided the best combination of ESC replication and ease of use. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1544-1558, 2017.

Dielectric relaxation spectroscopy is employed to investigate charge transport properties of two polyester ether ionomers in the bulk state and when confined in unidirectional nanoporous membranes (average pore diameter = 7.5 nm). Under nanometric confinement in nonsilanized pores, the macroscopic transport quantities (dc conductivity and characteristic frequency rate) are lower by about 1.4 decades compared to the bulk. The remarkable decrease of transport quantities in nonsilanized nanoporous membranes can be quantitatively explained by considering the temperature dependence of the interfacial layer between the ionomer and the silica membrane surfaces. On the other hand, an enhancement of dc conductivity is observed when the surfaces of the pores are treated with a nonpolar organosilane. This effect becomes more pronounced at lower temperatures and is attributed to slight changes in molecular packing density caused by the two-dimensional geometrical constraint.

The dielectric response of seven nonionic ethylene oxide-containing polymers are investigated. Four different backbone chemistries are considered, including polymethacrylate, polyester ether, polyphosphazene, and polysiloxane. The chemistry of the backbone and the linking chemistry to incorporate ether oxygen (EO) groups dramatically affect polymer segmental dynamics. The Tg of the inorganic backbone polymers is ∼15 °C lower than that of the PEO homopolymer. Polysiloxanes exhibit the lowest Tg of −86 °C when attached with pendent −(CH2–CH2–O)4–CH3 groups. The strength of the alpha relaxation is the same for the hydrocarbon backbone polymers (Δe = 10), whereas the dielectric constants of inorganic polymers with short pendent groups is lower (Δe = 3). The difference in relaxation strengths is due to restricted motion of ether oxygens close to the backbone. This effect diminishes as the relative backbone concentration is decreased by increasing the pendent EO length. As pendent EO chain length is increased, ...

Dielectric relaxation spectroscopy was used to investigate the segmental dynamics of a series of siloxane-based polar copolymers combining pendant cyclic carbonates and short poly(ethylene oxide) (PEO) chains. The homopolymer with cyclic carbonate as the only side chain exhibits higher glass transition temperature T(g) and dielectric constant ε(s) than the one with only PEO side chains. For their copolymers the observed T(g) (agreeing well with the predicted values from the Fox equation) and ε(s) decrease with increasing PEO side chain content. These polar polymers exhibit a glassy β relaxation with Arrhenius character, attributed to local chain motions of side groups attached to the main chain, and a segmental α relaxation, associated with the glass transition with a Vogel temperature dependence. As PEO side chain content increases, narrowing of the local glassy β relaxation was observed in the copolymers. The segmental α dynamics were observed to be faster, with an increase in breadth and decrease in strength with increasing PEO side chain content. Owing to the trade-off between T(g) and ε(s), copolymers of intermediate composition result in the highest ionic conductivity when these copolymers are used to plasticize Li single-ion conducting ionomers.

This paper describes sodium hexametaphosphate (SHMP)‐modified thermoplastic starch (TPS) resins (scCO₂TPS₁₀₀SHMPₓ) gelatinized and/or modified with the aid of supercritical carbon dioxide (scCO₂). TPS and scCO₂TPS₁₀₀SHMPₓ exhibit considerably higher melt flow rates, moisture resistance, and initial and retention tensile strength values than TPS and TPS₁₀₀SHMPₓ prepared using conventional atmospheric pressure. Only Vₕ‐type crystals are found in conditioned scCO₂TPS₁₀₀SHMPₓ, which show significantly lower melting temperatures (≈19 °C) than the corresponding conditioned TPS₁₀₀SHMPₓ. Relative to TPS₁₀₀SHMPₓ, conditioned scCO₂TPS₁₀₀SHMPₓ show a weaker hydrogen bonding network among the hydroxyl groups in the amylopectin chains and considerably less retrogradation. The loosely hydrogen‐bonded hydroxyl groups found in conditioned scCO₂TPS₁₀₀SHMPₓ can be replaced with stronger hydrogen bonds involving the phosphate groups of SHMP through the proper modification of scCO₂TPS₁₀₀SHMPₓ.

This paper represents the first report of polyvinyl alcohol (PVA) modified TPS resins (scCO2TPSxPVA05y), gelatinized and/or modified with the aid of supercritical carbon dioxide (scCO2). The melt flow rate, initial and retention values of tensile strength (σf) of scCO2TPSxPVA05y prepared with the aid of both scCO2 and PVA05 were considerably higher than those of the corresponding scCO2TPS prepared using scCO2 fluid and/or TPSxPVA05y materials prepared in the conventional way. The moisture contents of conditioned scCO2TPSxPVA05y were considerably lower than those of the corresponding scCO2TPS and TPSxPVA05y aged for the same amounts of time. Conditioned scCO2TPSxPVA05y exhibited only Vh-type crystals with melting temperatures ∼ 40 °C and ∼ 20 °C lower than those of corresponding conditioned TPS and TPSxPVA05y, respectively. In comparison to TPS and TPSxPVA05y, more dissociated amylopectin chains with loosely hydrogen-bonded −OH groups and significantly less retrogradation was obtained for conditioned scCO2TPS and scCO2TPSxPVA05y, respectively.

Oxygen transmission rates and free volume properties (i.e. average volumes of free-volume-cavities (Vf), mean number of the free volume cavities per unit volume (I3) and fractional free volume (Fv)) values of bio-based polyamide 612 (PA612)/poly(vinyl alcohol) (PVA) (i.e. PA612xPVA03y, PA612xPVA05y, PA612xPVA08y and PA612xPVA14y) blend films were reduced to a minimum value, when their PVA content reached corresponding optimal values of 25, 20, 15 and 10 wt%, respectively. The minimum oxygen transmission rate, Vf, I3 and Fv value obtained for the best PA61290PVA1410, PA61285PVA0815, PA61280PVA0520 and PA61275PVA0325 bio-based blown films reduced considerably with decreasing PVA degrees of polymerization. As evidenced by the results of dynamical mechanical analysis, differential scanning calorimetry, wide angle X-ray diffraction and Fourier transform infrared spectroscopic experiments, PA612 and PVA are miscible to some extent at the molecular level when their PVA contents are ≤ the corresponding optimal values. The significantly improved oxygen barrier and free volume properties for the PA612xPVAzy blend films with optimized compositions is at least in part to the enhanced intermolecular interactions between PA612 carbonyl groups and PVA hydroxyl groups.

Random ionomers based on methacryl poly(ethylene oxide) with nine ethylene oxide units on the side chain and sodium sulfonated styrene (NaSS) are synthesized by reversible addition–fragmentation chain transfer polymerization. The glass transition temperature increases gradually as ions are incorporated at low ion content then more strongly as the ion content reaches 51 mol % NaSS comonomer (1:9 ion to ether oxygen (EO) ratio), exceeding the polarizability volume overlap for contact pairs at 35 mol % NaSS comonomer. Ionomers with 51 and 70 mol % NaSS comonomer show microphase separation, as determined by X-ray scattering, where ion-rich microphases have glass transition temperature Tg = 165 °C excluding many of the PEO side chains, which primarily reside in a dilute ion-pair microphase. Fourier transform infrared spectroscopy was used to characterize the fraction of sulfonates in three different association states that can be related to the static dielectric constant from dielectric relaxation spectroscopy...

The dependences of the glass transition temperature and the dielectric constant on molecular volume of the repeat unit for polymerized ionic liquids, the monomers they were polymerized from and simple ionic liquids, are reviewed and compared. The ionic conductivities of these materials and the frequencies at which ionic rearrangements occur are shown to be controlled by their glass transition temperatures. The ionic conductivity is proportional to the product of dielectric constant and ionic rearrangement frequency, with the proportionality constant determined by the molecular volume of the repeat unit.

The dielectric and high voltage performance of polymethylpentene (PMP) is investigated and compared with biaxially-oriented polypropylene (BOPP) for high power density and high temperature capacitor applications. PMP has a melting temperature that is around 60 °C higher than BOPP, while still maintaining low dielectric loss and high charge–discharge efficiency that are comparable to the latter. Furthermore, PMP is the lightest commercial thermoplastic polymer with density of 0.83 g/cm3, which is 8 % lower than BOPP (0.9 g/cm3). PMP is a promising semicrystalline dielectric material that may replace BOPP for high temperature pulsed power and power conditioning applications.

Accelerated in vitro biostability studies are useful for making relativistic comparisons between materials. However, no in vitro study can completely replicate the complex biochemical and biomechanical environment that a material experiences in the human body. To overcome this limitation, three insulation materials [Optim™ insulation (OPT), Pellethane® 55D (P55D), and silicone elastomer] from cardiac leads that were clinically implanted for up to five years were characterized using visual inspection, SEM, ATR-FTIR, GPC, and tensile testing. Surface cracking was not observed in OPT or silicone samples. Shallow cracking was observed in 17/41 (41%) explanted P55D samples. ATR-FTIR indicated minor surface oxidation in some OPT and P55D samples. OPT molecular weight decreased modestly (∼20%) at 2-3 years before stabilizing at 4-5 years. OPT tensile strength decreased modestly (∼25%) at 2-3 years before stabilizing at 4-5 years. OPT elongation at 4-5 years was unchanged from controls. P55D had no significant changes in molecular weight or tensile properties. Overall, results for OPT and P55D were consistent with and limited to cosmetic surface oxidation. Silicone demonstrated excellent biostability with no identifiable degradation. This study of explanted cardiac leads revealed that OPT, P55D, and silicone elastomer demonstrate similar and excellent biostability through five years of implantation in human patients.

Poly(ethylene glycol) plasticizer is blended with a PEO-based single-ion conductor to lower the glass transition temperature of the ionomer and solvate the lithium counterions. With increasing plasticizer content at room temperature, FTIR spectra indicate that the fraction of ions in isolated ion pairs increases relative to those in ionic aggregates, and X-ray scattering data indicate that the ionic aggregates are further apart than expected by dilution alone. Together these data show that the average size of ionic aggregates decreases as PEG plasticizer is added. The dissolution of aggregates into ion pairs promotes ion conduction. Coupled with faster segmental dynamics and ion mobility from the depressed Tg, the ionic conductivity of plasticized ionomers improved by two orders of magnitude at room temperature. Resolving the alpha relaxation of these ionomer blends reveals that the mechanism for ion transport is segmentally-assisted ion motion.

To prepare a safe electrolyte for lithium ion batteries, two groups of novel low-volatility plasticizers combining pendant cyclic carbonates and short ethylene oxide chains have been successfully synthesized, as confirmed by 1H, 13C and 29Si NMR spectroscopy. The Fox equation describes the composition dependence of the glass transition temperature (Tg) very well for the random polysiloxane-based copolymer plasticizers (11 000 < M < 13 000) while the smaller oligomer plasticizers have Tg as much as 20 K lower than the Fox equation prediction because of their lower molecular weight (450 < M < 700). The Landau–Lifshitz mixing rule describes the dielectric constant of the random polysiloxane-based copolymer plasticizers at all temperatures above Tg. Mixing with 20 wt% polysiloxane tetraphenyl borate – Li ionomer (14 mol% borate and 86 mol% cyclic carbonate) increases conductivity relative to the neat ionomer by lowering Tg, increasing dielectric constant and providing better solvation of Li+. The best oligomeric plasticizer only has Tg 10 K lower than the Fox prediction but has dielectric constant 30% larger than expected by the Landau–Lifshitz mixing rule, owing to a surprisingly low viscosity, resulting in ambient conductivity 2 × 10−5 S cm−1. For both groups of plasticizers, the fraction of cyclic carbonates relative to ethylene oxide governs the magnitude and temperature dependence of the ionic conductivity.

Anion conducting polyphosphazene ionomer analogues of poly[bis(methoxyethoxyethoxy)phosphazene] (MEEP) were synthesized and their iodide transport properties studied. Polymer bound cations were quaternized with either short alkyl or short ether oxygen chains. X-ray scattering reveals a low q peak near 4 nm–1 arising from the backbone–backbone spacing between polyphosphazene chains, an ion-related peak at 8 nm–1, and a peak at 15 nm–1 corresponding primarily to the amorphous halo of the PEO side chains. Because of the short spacing of the intermediate q peak, the ions are proposed to exist mostly in isolated ion pairs or small aggregates. First-principles calculations combined with dielectric spectroscopy suggest that less than 10% of the ions are in isolated pairs while the remainder participate in quadrupoles or other small aggregates. These ionomers display high values for the high frequency dielectric constant, e∞ (highest value e∞ = 11), due to atomic polarization of the iodide anion. These MEEP-based...

Polysiloxane phosphonium single-ion conductors grafted with oligomeric PEO and with ion contents ranging from 5 to 22 mol % were synthesized via hydrosilylation reaction. The parent Br– anion was exchanged to F– or bis(trifluoromethanesulfonyl)imide (TFSI–). X-ray scattering data suggest ion aggregation is absent in these phosphonium ionomers, which contributes to low glass transition temperatures (below −70 °C) with only a weak dependence on both ion content and counteranion type. Conductivities weakly increase with ion content but exhibit a strong dependence on anion type. The highest conductivity at 30 °C is 20 μS/cm for dry neat ionomer, with the TFSI– anion, consistent with its relatively delocalized negative charge and large size that weaken interactions between TFSI– and the phosphonium cation.

Fourier transform infrared spectroscopy (FTIR) and linear viscoelasticity (LVE) were used to characterize amorphous copolyester ionomers synthesized via condensation of sulfonated phthalates with m...

Polyurethane biostability has been the subject of intense research since the failure of polyether polyurethane pacemaker leads in the 1980s. Accelerated in vitro testing has been used to isolate degradation mechanisms and predict clinical performance of biomaterials. However, validation that in vitro methods reproduce in vivo degradation is critical to the selection of appropriate tests. High temperature has been proposed as a method to accelerate degradation. However, correlation of such data to in vivo performance is poor for polyurethanes due to the impact of temperature on microstructure. In this study, we characterize the lack of correlation between hydrolytic degradation predicted using a high temperature aging model of a polydimethylsiloxane-based polyurethane and its in vivo performance. Most notably, the predicted molecular weight and tensile property changes from the accelerated aging study did not correlate with clinical explants subjected to human biological stresses in real time through 5 years. Further, DMTA, ATR-FTIR, and SAXS experiments on samples aged for 2 weeks in PBS indicated greater phase separation in samples aged at 85°C compared to those aged at 37°C and unaged controls. These results confirm that microstructural changes occur at high temperatures that do not occur at in vivo temperatures. In addition, water absorption studies demonstrated that water saturation levels increased significantly with temperature. This study highlights that the multiphase morphology of polyurethane precludes the use of temperature accelerated biodegradation for the prediction of clinical performance and provides critical information in designing appropriate in vitro tests for this class of materials.

Lithium ion conduction is investigated for a polysiloxane-based single-ion conductor containing weak-binding borates and cyclic carbonate side chains, plasticized with poly(ethylene glycol) (PEG). The addition of PEG increases the conductivity by up to 3 orders of magnitude compared to the host ionomer. A physical model of electrode polarization is used to separate ionic conductivity of the ionomers into number density of simultaneously conducting ions and their mobility. A reduction in Tg with increasing PEG content boosts ion mobility owing to an increase in polymer chain flexibility. Further, the PEG ether oxygens lower the activation energy of simultaneously conducting ions (from 14 to 8 kJ/mol), significantly increasing conducting ion content by 100X, suggesting that ion aggregates observed in the host ionomer are solvated by PEG. This directly reflects the disappearance of an ion aggregation peak observed in X-ray scattering, and an initial large increase in static dielectric constant (es), upon add...

This paper describes the influence of mixed poly(tetramethylene oxide) (PTMO) soft segments on microphase separation and morphology, hydrogen bonding, and polymer transitions for a series of alternating polyurea copolymers prepared from a single modified diphenylmethane diisocyanate. The fraction of two PTMO soft segments [with molecular weight = 1000 and 250 g/mol] was systematically varied and incorporated during bulk polymerization. ATR-FTIR spectroscopy confirmed that the intended polymers were synthesized and was used to determine the state of the local hydrogen bonding in these copolymers. Systematic changes in hard domain microstructure as a function of soft segment composition were clearly observed in AFM tapping mode phase images: the polyureas become progressively disordered with increasing content of the shorter PTMO. This was confirmed in a quantitative fashion using small-angle X-ray scattering. Results from dynamic mechanical analysis experiments reveal rather significant changes in dynamic segmental relaxations and storage moduli at 25 °C for this series of polyureas, which are in keeping with the findings from other experiments.

Three diisocyanates with different symmetry and planarity (2,6-TDI, 2,4-TDI and MDI) were used to synthesize polyureas with the same oligomeric polyetheramine having a molecular weight of ∼1000 g/mol. The influence of diisocyanate symmetry on the phase separated morphology, hydrogen bonding behavior, and molecular dynamics were investigated. Symmetric diisocyanate structures facilitated self-assembly of hard segments into ribbon-like domains, driven by strong bidentate hydrogen bonding. The hard domains for the 2,6-TDI polymer appear to be continuous in AFM images, while the persistence length of the hard domains in the 2,4-TDI and MDI polymers gradually decrease, and fewer hard domains are apparent with decreasing hard segment symmetry. The extent of hard/soft segment demixing, assessed from small-angle X-ray scattering, was very incomplete for all of the polyureas and is significantly influenced by hard segment structure. For the 2,4- and 2,6-TDI polyureas, two segmental relaxations were observed using dielectric relaxation spectroscopy; one arising from relatively unrestricted motion in the soft segment rich phase, and a slower process associated with segments in the soft phase constrained by their attachment to hard domains.

Some natural biopolymers such as spider silk exhibit superb mechanical properties, characterised by their great toughness. Synthetic polyurethane (PU) copolymers also endow great toughness but lack silk's stiffness and strength. The aim of this work was to elucidate the role of segment block architectural features that influence PU stiffness and strength after cold drawing. For this purpose PUs with varied soft segment character, crystalline versus rubbery, as well as with different hard segment chemistries, 4,4′-diphenylmethane diisocyanate/1,4-butanediol versus 1,6-hexamethylene diisocyanate/1,4-butanediol, were synthesised by a two-step polymerisation method. We found that the architecture of both block segments has a dramatic influence on drawn PU mechanical performance, in which PUs with crystallisable soft segments and crystalline hard segments are shown to have a greater impact on developing stiffer and stronger materials. © 2013 Society of Chemical Industry

A molecular-level understanding of dynamics in imidazolium-based ionomers with different counterions and side chain lengths was investigated using X-ray scattering, oscillatory shear, and dielectric relaxation spectroscopy (DRS). Variations of the counterion size and side chain length lead to changes in glass transition temperature (Tg), extent of ionic aggregation, and dielectric constant, with consequences for ion transport. A physical model of electrode polarization is used to determine the number density of simultaneously conducting ions and their mobility. Imidazolium-based ionomers with larger counterion and longer side chain have lower Tg, resulting in higher ionic conductivity and mobility. The ionic mobility is coupled to ion motions that are directly measured as a second segmental process in DRS, as these are observed to share the same Vogel temperature. Time–temperature superposition (tTS) was applied to create linear viscoelasticity master curves and to investigate the delay in chain motion re...

Porosity in polymers of intrinsic microporosity (PIMs) is closely related to free volume: it arises from a chain structure combining rigid segments with sites of contortion, producing a large concentration of interconnected pores smaller than 1 nm. Membranes of these polymers are subject to physical aging, which decreases their permeability and reduces their performance in gas separation. In this work, a robust interpretation of PIM X-ray scattering features is developed with support from molecular dynamics simulations. The sensitivity of scattering patterns to time, temperature and film thickness is shown to be qualitatively consistent with physical aging, demonstrating that these high-free-volume, porous polymeric glasses present a unique opportunity to study structural changes during physical aging using scattering methods. Quantitative modeling of PIM scattering patterns remains challenging, and the time resolution required to capture the initial aging stages of a single film is difficult to achieve with laboratory instruments. However, the spectrum of glassy states accessed by varying film thickness and aging temperature raises the possibility that there may be two distinct mechanisms of aging in PIMs.

Purpose – Polyurea is an elastomeric two-phase co-polymer consisting of nanometer-sized discrete hard (i.e. high glass transition temperature) domains distributed randomly within a soft (i.e. low glass transition temperature) matrix. A number of experimental investigations reported in the open literature clearly demonstrated that the use of polyurea external coatings and/or internal linings can significantly increase blast survivability and ballistic penetration resistance of target structures, such as vehicles, buildings and field/laboratory test-plates. When designing blast/ballistic-threat survivable polyurea-coated structures, advanced computational methods and tools are being increasingly utilized. A critical aspect of this computational approach is the availability of physically based, high-fidelity polyurea material models. The paper aims to discuss these issues. Design/methodology/approach – In the present work, an attempt is made to develop a material model for polyurea which will include the eff...

The role of thermal history on the nanoscale segregated structure of a bulk polymerized polyurea containing oligomeric poly(tetramethylene oxide) soft segments is investigated in the present study. Temperature-dependent unlike segment demixing was explored in two series of experiments: at constant heating (and cooling) rate and on annealing at selected elevated temperatures. Tapping mode atomic force microscopy on the as-polymerized polymer demonstrates that the polyurea hard segments self-assemble into a ribbon-like morphology that is generally preserved on annealing, although ribbon coarsening was observed at the highest annealing temperature. The results from the constant heating rate synchrotron X-ray scattering experiments demonstrate that the nanoscale structure begins to reorganize at temperatures as low as ∼70 °C, and the very significant changes in mean interdomain spacing observed at much higher temperatures are largely retained on returning to ambient conditions. Although there was surprisingly...

Dielectric relaxation spectroscopy was used to investigate the molecular dynamics of model segmented polyurethane copolymers having identical hard segments and hard segment weight fractions, but with four different soft segment chemistries of particular interest in biomedical devices. All soft segments have molecular weight ∼1000 g/mol and are composed of either tetramethylene oxide, hexamethylene oxide, aliphatic carbonate, or dimethylsiloxane (PDMS) segments. These microphase-separated materials exhibit rich dielectric relaxation behavior: up to two relaxations in the glassy state, a segmental α relaxation (two for the polymer with predominately PDMS soft segments), and three slower relaxations. The slowest process arises from interfacial (MWS) polarization, and its strength decreases significantly with increasing temperature (over a few tens of degrees) and disappears at a temperature similar to that at which the small-angle X-ray scattering from the phase-separated microstructure disappears.