Showing papers in "Journal of Polymer Science Part B in 2017"

Liquid crystal elastomer actuators: Synthesis, alignment, and applications

Abstract: Liquid crystal elastomers (LCEs) are a unique class of materials which combine rubber elasticity with the orientational order of liquid crystals. This combination can lead to materials with unique properties such as thermal actuation, anisotropic swelling, and soft elasticity. As such, LCEs are a promising class of materials for applications requiring stimulus response. These unique features and the recent developments of the LCE chemistry and processing will be discussed in this review. First, we emphasize several different synthetic pathways in conjunction with the alignment techniques utilized to obtain monodomain LCEs. We then identify the synthesis and alignment techniques used to synthesis LCE-based composites. Finally, we discuss how these materials are used as actuators and sensors. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 395–411

Effect of (3-glycidyloxypropyl)trimethoxysilane (GOPS) on the electrical properties of PEDOT:PSS films

Abstract: Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) has been reported as a successful functional material in a broad variety of applications. One of the most important advantages of PEDOT:PSS is its water-solubility, which enables simple and environmental friendly manufacturing processes. Unfortunately, this also implies that pristine PEDOT:PSS films are unsuitable for applications in aqueous environments. To reach stability in polar solvents, (3-glycidyloxypropyl)trimethoxysilane (GOPS) is typically used to cross-link PEDOT:PSS. Although this strategy is widely used, its mechanism and effect on PEDOT:PSS performance have not been articulated yet. Here, we present a broad study that provides a better understanding of the effect of GOPS on the electrical and electronic properties of PEDOT:PSS. We show that the GOPS reacts with the sulfonic acid group of the excess PSS, causing a change in the PEDOT:PSS film morphology, while the oxidation level of PEDOT remains unaffected. This is at the origin of the observed conductivity changes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 814–820

Thiol-acrylate main-chain liquid-crystalline elastomers with tunable thermomechanical properties and actuation strain

Abstract: The purpose of this study was to investigate the influence of cross-linking on the thermomechanical behavior of liquid-crystalline elastomers (LCEs). Main-chain LCE networks were synthesized via a thiol-acrylate Michael addition reaction. The robust nature of this reaction allowed for tailoring of the behavior of the LCEs by varying the concentration and functionality of the cross-linker. The isotropic rubbery modulus, glass transition temperature, and strain-to-failure showed strong dependence on cross-linker concentration and ranged from 0.9 MPa, 3 °C, and 105% to 3.2 MPa, 25 °C, and 853%, respectively. The isotropic transition temperature (Ti) was shown to be influenced by the functionality of the cross-linker, ranging from 70 °C to 80 °C for tri- and tetra-functional cross-linkers. The magnitude of actuation can be tailored by controlling the amount of cross-linker and applied stress. Actuation increased with increased applied stress and decreased with greater amounts of cross-linking. The maximum strain actuation achieved was 296% under 100 kPa of bias stress, which resulted in work capacity of 296 kJ/m3 for the lowest cross-linked networks. Overall, the experimental results provide a fundamental insight linking thermomechanical properties and actuation to a homogenous polydomain nematic LCE networks with order parameters of 0.80 when stretched. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 157–168

The influence of grafted cellulose nanofibers and postextrusion annealing treatment on selected properties of poly(lactic acid) filaments for 3D printing

Abstract: l-lactide monomers were grafted onto cellulose nanofibers (CNFs) via ring-opening polymerization, forming poly(lactic acid) grafted cellulose nanofibers (PLA-g-CNFs). PLA-g-CNFs and pristine PLA were then blended in chloroform and dried to prepare a master batch. PLA-g-CNFs/PLA composite filaments targeted for 3D printing were produced by compounding the master batch in PLA matrix and melt extrusion. The as-extruded composite filaments were subsequently thermal annealed in a conventional oven, and their morphological, thermal, and mechanical properties were evaluated. PLA was successfully grafted on the surface of CNFs as demonstrated by elemental analysis, and the concentration of grafted PLA was estimated to be 33 wt %. The grafted PLA were highly crystallized, contributing to the growth of crystalline regions of PLA matrix. The incorporation of PLA-g-CNFs improved storage modulus of the composite filaments in both low temperature glassy state and high temperature rubbery state. Postextrusion annealing treatment led to 28 and 63% increases for tensile modulus and strength of the filaments, respectively. Simulated Young's moduli from the Halpin-Tsai and Krenchel models were found comparable with the experimental values. The formed composite filaments are suitable for use in 3D printing. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 847–855

Pinch‐off dynamics and extensional relaxation times of intrinsically semi‐dilute polymer solutions characterized by dripping‐onto‐substrate rheometry

Abstract: Stream-wise velocity-gradients associated with extensional flows arise in thinning liquid necks spontaneously formed during jetting, printing, coating, spraying, atomization, and microfluidic-based drop formation. In this contribution, we employ Dripping-onto-Substrate (DoS) rheometry protocols to measure the extensional rheology response of intrinsically semi-dilute polymer solutions by visualizing and analyzing capillary-driven thinning of a columnar neck formed between a nozzle and a sessile drop. We show that extensional viscosity that quantifies the resistance to stream-wise velocity gradients is orders of magnitude higher than the shear viscosity. Although shear flows only weakly perturb the chain dimensions, extensional flows can strongly stretch and orient the chains, thus influencing both intra- and inter-chain interactions. We find that the extensional relaxation times for intrinsically semi-dilute PEO solutions in a good solvent for five different molecular weights increase linearly with concentration, exhibiting a stronger concentration dependence than observed for dilute solutions, or anticipated by blob models, developed for relaxation of weakly perturbed chains in a good solvent. The observed distinction between the concentration-dependent relaxation dynamics of intrinsically dilute and semi-dilute solutions arises due the complex influence of stretching, conformational anisotropy, and polymer concentration on excluded volume and hydrodynamic interactions of flexible, highly extensible polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

An analysis of the role of nonreactive plasticizers in the crosslinking reactions of a rigid resin

Abstract: A uniform dispersion of reactants is necessary to achieve a complete reaction involving multiple components Using a combination of infrared spectroscopy, thermal analysis, and low field NMR, we have elucidated the role of a new class of nonreactive plasticizers on the crosslinking reaction between hexamethylenetetramine (HMTA) and phenol formaldehyde resin These two seemingly dissimilar reactants are responsible for the exceptionally high mechanical strength in a number of organic–inorganic composites The efficiency of the curing reaction is characterized by the changing functionality of HMTA Infrared active vibrations are used to characterize the changing molecular structures as a function of temperature The T1 spin-lattice relaxation time is used for the characterization of segmental dynamics of the chains in the formation of the crosslinked product The segmental mobility depends on the amount of crosslinking and the stiffness of the chain This study shows that this new class of nonreactive plasticizer can induce highly crosslinked structures without any of the environmental impact of the current technology An efficient crosslinking reaction in phenolic resin can be achieved by using methyl benzoate as a nonreacting plasticizer Low field NMR, in conjunction with infrared spectroscopy (mid and near) and DSC, clarified the crosslinking reaction mechanism and the ensuing structure © 2016 Wiley Periodicals, Inc J Polym Sci, Part B: Polym Phys 2016

Solubility characteristics of poly(3-hexylthiophene)

Abstract: Solubility data for poly(3-hexylthiophene) (P3HT) in 29 pure solvents are presented and discussed in detail. Functional solubility parameter (FSP) and convex solubility parameter (CSP) computations are performed and the CSP and FSP results are compared to previously reported Hansen solubility parameters (HSPs) and to the parameters calculated using additive functional group contribution methods. The empirical data reveals experimental solubility parameters with substantial polar (δP) and hydrogen-bonding (δH) components, which are not intrinsic to the structure of the P3HT polymer. Despite these apparent irregularities, it is shown that the predictor method based on the solubility function, f, does provide a reliable way to quantitatively evaluate the solubility of P3HT in other solvents in terms of a given set of empirical solubility data. The solubility behavior is further investigated using linear solvation energy relationship (LSER) modeling and COSMO-RS computations of the activity coefficients of P3HT. The LSER model reveals that (1) the cavity term, δT, is the dominant factor governing the solubility behavior of P3HT and (2) the solvent characteristics that dictate the structural order (crystallinity) of P3HT aggregates do not similarly influence the overall solubility behavior of the polymer. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Enhanced interfacial interaction by grafting carboxylated-macromolecular chains on nanodiamond surfaces for epoxy-based thermosets

Abstract: A novel core-shell-structured carboxylated-styrene butadiene rubber (XSBR)-functionalized nanodiamond (ND-XSBR) was synthesized and characterized. Epoxy (EP) nanocomposites toughened by pristine ND and ND-XSBR were investigated and compared. The ND-XSBR-reinforced nanocomposite exhibited mechanical properties superior to those of the one filled by pristine ND. At a low-filler loading, the ND-XSBR exhibited an impressive toughening effect. The maximum flexural strength was shown when the filler loading was as low as 0.1 wt % for the EP/ND-XSBR nanocomposite. Furthermore, enhanced fracture toughness and fracture energy were shown by surface functionalization, representing enhanced compatibility between the ND-XSBR and EP matrix. The glass transition temperature (Tg) and storage modulus of the nanocomposites were studied, and the EP/ND-XSBR0.1 nanocomposite exhibited the highest Tg owing to the stronger interfacial interaction. The EP/ND-XSBR0.2 exhibited higher storage modulus and Tg than the EP/ND0.2, because the higher interfacial interaction can restrict the molecular mobility of the EP by the functionalized ND-XSBR. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017.

Small-angle neutron scattering analysis of bottlebrush backbone and side chain flexibility

Abstract: Bottlebrush polymers have densely tethered side chains grafted to a linear polymer backbone, resulting in stretching of both the side chains and backbone. Prior studies have reported that the side chains are only weakly stretched while the backbone is highly elongated. Here, scaling laws for the bottlebrush backbone and side chains are determined through small-angle neutron scattering analysis of a systematic series of poly(lactic acid) bottlebrush polymers synthesized via a “grafting-through” ring-opening polymerization. Scattering profiles are modeled with the empirical Guinier–Porod, rigid cylinder, and flexible cylinder models. Side chains are found to be only weakly stretched, with an end-to-end distance proportional to N0.55, while the overall bottlebrush increases in size proportional to N0.77. These results demonstrate that the bottlebrush backbone is not fully extended and that both side chains and backbone have significant conformational flexibility in solution. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016

Thermocapillary approaches to the deliberate patterning of polymers

Abstract: The phenomenon of thermocapillarity, the response of fluids to thermal gradients due to thermal alteration of their surface tension, was first reported over a century ago. Since then, research has focused generally on either the fundamentals or mitigation of this effect during the processing of materials. Only in the past two decades has the deliberate use of thermocapillary forces for the patterning of polymers been actively pursued, either for the ordering of internal structure or the introduction of topographic features. This review seeks to highlight this work and to identify directions for further investigation. In particular, while thermocapillary forces are often inextricably bound to other mechanisms, there are emerging directions in the deliberate coupling of forces to improve the capabilities of each mechanism. Further, the applications of thermocapillary patterning to polymer-nanoparticle composites has recently provided another promising route to active architectures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Effects of additives and post‐treatment on the thermoelectric performance of vapor‐phase polymerized PEDOT films

Abstract: Vapor-phase polymerization (VPP) is an important method for the fabrication of high-quality conducting polymers, especially poly(3,4-ethylenedioxythiophene) (PEDOT). In this work, the effects of additives and post-treatment solvents on the thermoelectric (TE) performance of VPP-PEDOT films were systematically investigated. The use of 1-butyl-3-menthylinidazolium tetrafluoroborate ([BMIm][BF4], an ionic liquid) was shown to significantly enhance the electrical conductivity of VPP-PEDOT films compared with other additives. The VPP-PEDOT film post-treated with mixed ethylene glycol (EG)/[BMIm][BF4] solvent displayed the high power factor of 45.3 μW m−1 K−2 which is 122% higher than that prepared without any additive or post-treatment solvent, along with enhanced electrical conductivity and Seebeck coefficient. This work highlighted the superior effect of the [BMIm][BF4] additive and the EG/[BMIm][BF4] solvent post-treatment on the TE performance of the VPP-PEDOT film. These results should help with developing the VPP method to fabricate high-performance PEDOT films. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

The crystallization of polypropylene with reduced density of entanglements

Abstract: The crystallization of polypropylene with different density of macromolecular entanglements was studied in isothermal and non-isothermal conditions. The growth rate of spherulites increased with reduced concentration of entanglements. Reduction of entanglements shifted the temperature of transition between Regimes II and III, which means that more regular growth of crystals was possible at lower temperature. The range of temperatures at which polypropylene cavitated in regions of melt occluded by spherulites was limited to 137–139°C, with weak dependence on entanglements density. DSC studies showed that isothermal crystallization is faster in less entangled polymers, however the crystallinity degree and long period of structure (by SAXS) were similar for studied materials. When the crystallization was completed during fast cooling, the differences between individual samples were more significant. The partial disentangling, overcoming some limitation for movements of macromolecules, made possible easier crystallization, even at low temperature of Regime III. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 748–756

Effects of water on epoxy cure kinetics and glass transition temperature utilizing molecular dynamics simulations

Abstract: Effects of water on epoxy cure kinetics are investigated. Experimental tests show that absorbed water in an uncured bisphenol-F/diethyl-toluene-diamine epoxy system causes an increase in cure rate at low degrees of cure and a decrease in cure rate at high degrees of cure. Molecular simulations of the same epoxy system indicate that the initial increase in cure rate is due to an increase in molecular self-diffusion of the epoxy molecules in the presence of water. Effects of water on the glass transition temperature (Tg) of the crosslinked thermoset are also studied. Both experiments and simulations show that water decreases Tg. Both types of results indicate that Tg effects are small below 1% water by weight, but that Tg depression occurs much quickly with increasing water content above 1%. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

DABCO-functionalized polysulfones as anion-exchange membranes for fuel cell applications: Effect of crosslinking

Abstract: A series of DABCO-functionalized polysulfones were synthesized and characterized. The effect that crosslinking has on the membrane properties containing different degrees of functionalization was evaluated. These polymers showed good thermal stability below the fuel cell operation temperature, T < 100 °C, reflected by the TOD, TFD, and thermal durability. The water uptake increased as the percentage of DABCO groups increased and the crosslinked membranes showed lower capacity to absorb water than the non-crosslinked ones favoring thus the dimensional stability of the first ones. Membranes in the chloride form containing low degree of functionalization exhibited the highest tensile strength values. The ionic conductivity of non-crosslinked membranes varied as a function of the functionalization degree until a value of around 100% achieving a maximum value at 86%. However, the crosslinked ones showed satisfactory ionic conductivities for values higher than 100%. The behavior of these polymeric materials in alkaline solutions revealed a great alkaline stability necessary to be used as solid electrolytes in fuel cells. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1326–1336

Physically cross-linked networks of POSS-capped poly(acrylate amide)s: Synthesis, morphologies, and shape memory behavior

Abstract: In this work, we synthesized a novel organic–inorganic semitelechelic polymer from polyhedral oligomeric silsesquioxane (POSS) and poly(acrylate amide) (PAA) via reversible addition-fragmentation chain transfer (RAFT) polymerization. The organic–inorganic semitelechelic polymers have been characterized by means of nuclear magnetic resonance spectroscopy, thermal gravimetric analysis, and dynamic mechanical thermal analysis. It was found that capping POSS groups to the single ends of PAA chains caused a series of significant changes in the morphologies and thermomechanical properties of the polymer. The organic–inorganic semitelechelics were microphase-separated; the POSS microdomains were formed via the POSS–POSS interactions. In a selective solvent (e.g., methanol), the organic–inorganic semitelechelics can be self-assembled into the micelle-like nanoobjects. Compared to plain PAA, the POSS-capped PAAs significantly displayed improved surface hydrophobicity as evidenced by the measurements of static contact angles and surface atomic force microscopy. More importantly, the organic–inorganic semitelechelics displayed typical shape memory properties, which was in marked contrast to plain PAA. The shape memory behavior is attributable to the formation of the physically cross-linked networks from the combination of the POSS–POSS interactions with the intermolecular hydrogen-bonding interactions in the organic–inorganic semitelechelics. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Highly enhanced thermoelectric performance of WS2 nanosheets upon embedding PEDOT:PSS

Abstract: Two-dimensional (2D) WS2 nanosheets (NSs) as a promising thermoelectric (TE) material have gained great concern recently. The low electrical conductivity significantly limits its further development. Herein, we reported an effective method to enhance the TE performance of WS2 NSs by combining poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS). The restacked WS2 NSs thin film with 1T phase structure obtained by a common chemical lithium intercalation show a high Seebeck coefficient of 98 μV K−1 and a poor electrical conductivity of 12.5 S cm−1. The introduction of PEDOT:PSS with different contents obviously improve the electrical conductivity of WS2 NSs thin films. Although a declining Seebeck coefficient was observed, an optimized TE power factor of 45.2 μW m−1 k−1 was achieved for WS2/PEDOT:PSS composite thin film. Moreover, the as-prepared WS2/PEDOT:PSS thin film can be easily peeled off and transferred to other substrate leading to a more promising application. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 997–1004

Preparation of polypropylene microspheres for selective laser sintering via thermal‐induced phase separation: Roles of liquid–liquid phase separation and crystallization

Abstract: Although selective laser sintering (SLS) has been widely applied in many fields, more research work is needed to develop proper polymer microspheres for SLS. Thermal-induced phase separation (TIPS) is a facile way but rarely reported to prepare the polymer microspheres. The roles of liquid–liquid phase separation (LLPS) and crystallization in the TIPS process are not clear. In this study, proper polypropylene (PP) microspheres for SLS are successfully prepared via TIPS with xylene. The diameters and morphologies of these PP microspheres can be regulated easily by changing the PP concentration and the quench temperature. The large undercooling drives the solution into the metastable LLPS region and produces PP microspheres with smooth surfaces. The PP crystallization occurs both on the LLPS interface and inside the polymer-rich phase when the solution is quenched to a temperature near the binodal line, and the tiny bent lamellae are formed on the microsphere surface. At higher temperature only PP crystallization occurs, which results in the formation of PP particles consisting of packed lamellae. The PP microspheres prepared here are suitable for SLS and promote the development of SLS potentially. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016.

Influence of side chain linker length on ion-transport properties of polymeric ionic liquids

Abstract: We used atomistic molecular dynamics simulations to study the properties of polymerized 1-alkene-3-butylimidazolium-hexafluorophosphate, a polymerized ionic liquid electrolyte, and characterized the influence of the linear alkene length on the mobility of the hexafluorophosphate ions. Consistent with experimental observations, our simulations indicate that as the alkene length increases, the diffusivity of hexafluorophosphate anion monotonically increases. We demonstrate that such a trend arises from the influence of linker segments on the intermolecular ion hopping rates, which is in turn modulated by intermolecular cationic separation distances. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 00, 000–000

Mechanically Strong and Flexible Hydrolyzed Polymers of Intrinsic Microporosity (PIM‐1) Membranes

Abstract: A systematic strategy to molecularly design flexible tough hydrolyzed polymers of intrinsic microporosity (hPIM-1) films from the PIM-1 polymer is explored in this study. Flexible films can be fabricated from N-methyl-2-pyrrolidone (NMP) by appropriate hydrolysis conditions. The optimal weight ratio of NaOH/H2O/EtOH in the base-catalyzed reaction is 0.5/2/2. Because of the highly polar carboxylic acid groups, the resultant hPIM-1 has a lower water contact angle. The hPIM-1 has one-half fractional free volume compared to PIM-1 which is in good agreement with permeability. Moreover, hPIM-1 follows as the same dual-mode sorption model as PIM-1. To the best of our knowledge, this is the first ever reported flexible hPIM-1 film in the literature. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 344–354

Modulation of ionization and structural properties of weak polyelectrolytes due to 1D, 2D, and 3D confinement

Abstract: What is the impact of reducing the space available to molecules onto their properties is a fundamental question for capillary systems, molecular biology and transport, protein and material sciences. Possibly influenced by space restriction, ionization degree has rarely been studied for confined polyelectrolytes; Monte Carlo titrations and coarse-grained models are thus used to investigate structural and ionization changes induced on a single polyelectrolyte chain by confinement into slit (1D), cylindrical (2D), or spherical (3D) cavities. Four polyelectrolyte models differing in chain stiffness and the possible formation of charged hydrogen bonds (cHbonds) are studied. Low pH effective ionization constants (pKa) of confined chains are lower than for the free species if cHbonds can be formed. This is especially evident for 3D-confined stiff chains, a finding rationalized by the impact of global compression onto chain conformations. If no cHbonds are allowed, chain ionization is largely unaffected by 1D or 2D confinement, while it is depressed by 3D. Chain confinement Helmholtz energy (ΔAconf) was computed as a function of both pH and confining width (W) to gauge the impact of ionization-induced stiffening onto ΔAconf versus W behavior, the partition coefficient K(pH,W) governing absorption, and the average number of cHbond formed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017.

Highly thermal conductive benzoxazine-epoxy interpenetrating polymer networks containing liquid crystalline structures

Abstract: A diamine-based benzoxazine monomer (Bz) and a liquid crystalline epoxy monomer (LCE) are synthesized, respectively. Subsequently, a benzoxazine-epoxy interpenetrating polymer network (PBEI) containing liquid crystalline structures is obtained by sequential curing of the LCE and the Bz in the presence of imidazole. The results show that the preferential curing of LCE plays a key role in the formation mechanism of liquid crystalline phase. Due to the introduction of liquid crystalline structures, the thermal conductivity of PBEI increases with increasing content of LCE. When the content of LCE is 80 wt %, the thermal conductivity reaches 0.32 W m−1 K−1. Additionally, the heat-resistance of PBEI is superior to liquid crystalline epoxy resin. Among them, PBEI55 containing equal weight of Bz and LCE has better comprehensive performance. Its thermal conductivity, glass transition temperature, and the 5 % weight loss temperature are 0.28 W m−1 K−1, 160 °C, and 339 °C, respectively. By introducing boron nitride (BN) fillers into PBEI55, a composite of PBEI/BN with the highest thermal conductivity of 3.00 W m−1 K−1 is obtained. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1813–1821

Revisiting thermoplastic polyurethane, from composition to morphology and properties

Abstract: Thermoplastic polyurethanes (TPUs) are among the most versatile engineering polymers. The presence of hard and soft segments on their backbone and specific hydrogen bond interactions between the hard segments, provide TPUs with outstanding engineering properties while rendering them as very complex systems to study. Knowledge of morphology–property relationship is essential for TPUs since their thermal and mechanical behavior are directly dictated by their complicated morphology. In this research, TPU morphological features related to the hard segment content (HSC) were explored in tandem with system macroscopic properties. It was observed that TPUs display multiscale phase separated morphology with specific morphological features dependent on the HSC. At a certain critical HSC, an interconnected network of hard segments was formed which resulted in significant changes in TPU properties. This was explained in analogy with percolation phenomena in filler reinforced systems and considering the hard segments as reinforcing agent. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Thermoelectric properties of PEDOT films prepared by electrochemical polymerization

Abstract: Thermoelectric (TE) properties of flexible and free-standing poly(3,4-ethylenedioxythiophene) (PEDOT) films synthesized via galvanostatic polymerization of 3,4-ethylenedioxythiophene in propylene carbonate containing sulfated poly(β-hydroxyethers) (S-PHE) as polymer electrolyte were elaborately studied. Both electrical conductivities (σ) and Seebeck coefficients (S) of the PEDOT:S-PHE films were increased by decreasing the temperature (T) or by increasing the current density (J) during electrosynthesis. Possible reasons for the lack of a trade-off relation commonly observed between σ and S are discussed on the basis of SEM and oxidation-level measurements. Preparation of the PEDOT:S-PHE films was optimized with respect to T and J. In addition, the oxidation level of the PEDOT:S-PHE films was controlled by potential and the change of their TE performances was discussed in conjunction with the change of chemical species involved. The power factor (PF = σS2) of the PEDOT:S-PHE films reached 7.9 μW m−1 K−2, leading to a dimensionless TE figure-of-merit (ZT) of 0.013. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 524–531

Effects of polymer network on electrically induced reflection band broadening of cholesteric liquid crystals

Abstract: The reflection band of polymer stabilized cholesteric liquid crystals with negative dielectric anisotropy can be broadened by DC electric fields, which was ascribed to the pitch gradient caused by the motion of the structural chirality, that is, the polymer network. They systematically varied the mixture components, such as the photo-initiator concentration, the monomer functionality, and the chiral dopant, to explore their influences on the reflection band broadening behavior. They learned how to control the polymer network morphology and ion density, which in turn determined the reflection bandwidth. By optimizing the mixture, they have greatly enhanced the broadening effect and achieved large bandwidth at low voltages. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Deformation and failure kinetics of iPP polymorphs

Abstract: In this study, the mechanical performance of the different polymorphs of isotactic polypropylene, typically present in iPP crystallized under industrial processing conditions, is assessed. Different preparation strategies were used to obtain samples consisting of almost solely α, β, or γ crystals. X-Ray measurements were used to validate that the desired phase was obtained. The intrinsic true stress - true strain response of all individual phases was measured in uniaxial compression at several strain rates (deformation kinetics). Moreover, measurements were performed over a wide temperature range, covering the window in between the glass transition and the melting temperature. The relation between obtained yield stress and the strain rate is described with a modification of the Ree-Eyring model. Differences and similarities in the deformation kinetics of the different phases are presented and discussed. Furthermore, the presence of three deformation processes, acting in parallel, is revealed. The Ree-Eyring equation enables lifetime prediction for given thermal and mechanical conditions. These predictions were experimentally validated using constant load tests in uniaxial compression. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 729–747

Homoconjugation in poly(phenylene methylene)s: A case study of non-π-conjugated polymers with unexpected fluorescent properties

Abstract: Poly(phenylene methylene) (PPM) exhibits pronounced blue fluorescence in solutions as well as in the solid state despite its non-π-conjugated nature. Optical spectroscopy was used to explore the characteristics and the physical origin of its unexpected optical properties, namely absorption in the 350–450 nm and photoluminescence in the 400–600 nm spectral regions. It is shown that PPM possesses two discrete optically active species, and a relatively long photoluminescence lifetime (>8 ns) in the solid-state. Given the evidence reported herein, π-stacking and aggregation/crystallization, as well as the formation of anthracene-related impurities, are excluded as the probable origins of the optical properties. Instead there is sufficient evidence that PPM supports homoconjugation, that is: π-orbital overlap across adjacent repeat units enabled by particular chain conformation(s), which is confirmed by DFT calculations. Furthermore, poly(2-methylphenylene methylene) and poly(2,4,6-trimethylphenylene methylene) – two derivatives of PPM – were synthesized and found to exhibit comparable spectroscopic properties, confirming the generality of the findings reported for PPM. Cyclic voltammetry measurements revealed the HOMO–LUMO gap to be 3.2–3.3 eV for all three polymers. This study illustrates a new approach to the design of light-emitting polymers possessing hitherto unknown optical properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 707–720

Flexible conducting polymer transistors with supercapacitor function

Abstract: Planar organic electrochemical transistors (OECTs) using PEDOT:PSS as the channel material and nanostructured carbon (nsC) as the gate electrode material and poly(sodium 4-styrenesulfonate (PSSNa) gel as the electrolyte were fabricated on flexible polyethylene terephthalate (Mylar®) substrates. The nsC was deposited at room-temperature by supersonic cluster beam deposition (SCBD). Interestingly, the OECT acts as a hybrid supercapacitor (to give a device that we indicate as transcap). The energy storage ability of transcaps has been studied with two cell configurations: one featuring PEDOT:PSS as the positive electrode and nsC as the negative electrode and another configuration with reversed electrode polarity. Potentiostatic charge/discharge studies show that both supercapacitors show good performance in terms of voltage retention, in particular, when PEDOT:PSS is used as the positive electrode. Galvanostatic charge–discharge characteristics show typical symmetric triangular shape, indicating a nearly ideal capacitive behavior with a high columbic efficiency (close to 100%). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016

Effect of annealing temperature on interrelation between the microstructural evolution and plastic deformation in polymers

Abstract: The mechanical loading induced flow of glassy polymers is triggered by the nucleation of shear transformation units, and strongly depends on the initial microstructural state of the material. Therefore, investigation of the possible relationship between the microstructural state variables and plastic deformation is required for a better understanding of the macroscopic response of this class of materials during large deformation. In this study, free volume content is considered as a state variable and thermal treatment is selected as a process through which the accelerated and forced evolution of the free volume can be imposed. For two well-known glassy polymers, poly(methyl methacrylate) and polycarbonate, the free volume content alteration upon annealing is monitored via positron annihilation spectroscopy, and the changes of the micro- and macromechanical properties are also obtained by utilizing nanoindentation technique and employing the homogeneous amorphous flow theory. The correlation between the microstructural state variable, that is, free volume, and the micromechanical state variable, that is, shear activation volume, is then investigated. The results reveal opposite direction of alterations of free volume and shear activation volume with annealing temperature. Accordingly, the possibility of the existence of an interrelation between these two state variables is critically discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1286–1297

Polymer strategies in perovskite solar cells

Abstract: Since their emergence in 2013, perovskite solar cells have reached remarkable efficiencies exceeding 22%. Such rapid development of this technology has been possible, in part, due to the feed of ideas from previous research in organic photovoltaics (OPVs) and light emitting diodes (OLEDs). This comprehensive review discusses the various polymer strategies that have led to the success of perovskite devices: from hole and electron transporting materials to polymer templating agents. This review further covers how these strategies potentially serve to overcome the two major obstacles that stand in the way of global implementation of perovskite solar cells; stability and J-V curve hysteresis. Through reference and comparison of OPV, OLED, and perovskite technologies, we highlight the need for a unified approach to establish appropriate control systems and ageing protocols that are necessary to further research in this exciting direction. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 549–568.

Room temperature deformable shape memory composite with fine-tuned crystallization induced via nanoclay particles

Abstract: This work was supported by Consejo Nacional de Ciencia y Tecnologia (CONACYT) Mexico (Grant# 427049), Natural Sciences and Engineering Research Council of Canada (NSERC) (Grant# 459389) and Canada Research Chairs program (CRS) (Grant# 480255)