Microphase Morphology Research Articles

Development of boosted microphase separation exploiting highly rigid poly(phenyl-alkane)s anion exchange membranes for excellent performance fuel cells

The advancement of the ionic conductivity and dimensional stability of anion exchange membranes (AEMs) while ensuring excellent alkali stability is the critical challenge in the development of AEM fuel cells. Construction of efficient ion transport channels through well-designed microphase morphology is considered to be an effective strategy to achieve this goal. Herein, we propose an ingenious design that a novel aryl ether-free poly(phenyl-alkane)s-based AEMs to optimize the conductivity and longevity of AEMs using rigid aryl units, i.e., 1,4-dimethoxybenzene and spirobisindane, as the main chains with connecting flexible alkyl chains. The rigid and non-rotatable aromatic structure can facilitate the formation of a well-defined microphase separation structure with long chain quaternary ammonium by reducing chain segment interactions, and can also ameliorate the dimensional stability of the membrane. Consequently, the as-prepared membrane exhibits an excellent hydroxide conductivity of 130 mS cm−1 at 80 °C and approaches a terrific conductivity retention rate of 90 % after immersion in 1 M NaOH solution at 80 °C for 1000 h. Furthermore, the as-prepared membrane achieves an excellent peak power density of 1.36 W cm−2 in the H2-O2 fuel cell and its initial voltage shows no signs of decreasing after running for 20 h under 0.2 A cm−2.

Effect of the Interplay between Polymer-Filler and Filler-Filler Interactions on the Conductivity of a Filled Diblock Copolymer System.

We investigate the relative roles of the involved interactions and micro-phase morphology in the formation of the conductive filler network in an insulating diblock copolymer (DBC) system. By incorporating the filler immersion energy obtained by means of the phase-field model of the DBC into the Monte Carlo simulation of the filler system, we determined the equilibrium distribution of fillers in the DBC that assumes the lamellar or cylindrical (hexagonal) morphology. Furthermore, we used the resistor network model to calculate the conductivity of the simulated filler system. The obtained results essentially depend on the complicated interplay of the following three factors: (i) Geometry of the DBC micro-phase, in which fillers are preferentially localized; (ii) difference between the affinities of fillers for dissimilar copolymer blocks; (iii) interaction between fillers. The localization of fillers in the cylindrical DBC micro-phase has been found to most effectively promote the conductivity of the composite. The effect of the repulsive and attractive interactions between fillers on the conductivity of the filled DBC has been studied in detail. It is quantitatively demonstrated that this effect has different significance in the cases when the fillers are preferentially localized in the majority and minority micro-phases of the cylindrical DBC morphology.

Nanostructures, Linear Rheological Responses, and Tunable Mechanical Properties of Microphase-Separated Cellulose-graft-Diblock Bottlebrush Copolymer Elastomers.

A series of cellulose-graft-diblock bottlebrush copolymer elastomers (cellulose-graft-poly(n-butyl acrylate)-block-poly(methyl methacrylate) (Cell-g-PBA-b-PMMA)) with short side chains were synthesized via successive atom transfer radical polymerization (ATRP) to study the influence of varying compositions and lengths of the graft diblock side chains on microphase morphologies and properties. The microphase-separated morphologies from misaligned spheres to cylinders were observed by atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) measurements. These bottlebrush copolymer elastomers possessed thermal stability and enhanced mechanical properties because the PMMA outer block could self-assemble into hard microdomains, which served as physical cross-links. The viscoelastic responses of these bottlebrush copolymers within the linear viscoelastic (LVE) regime were carried out by the oscillatory shear rheology. The time-temperature superposition (tTs) principle was applied to construct the master curves of the dynamic moduli, and the sequential relaxation of dense bottlebrush copolymers with different PMMA hard outer block lengths was analyzed. The rheological behaviors in this work could be utilized to build up the connection of microstructures and properties for the application of these bottlebrush copolymers as high-performance thermoplastic elastomers.

Molecular Architecture of Multiblock Copolymers Synthesized by the Chain Shuttling Technology

AbstractRecent advances in the characterization of ethylene/1‐octene‐based statistical multiblock copolymers (MBCs) synthesized via chain shuttling copolymerization are illustrated. The Perspective focuses on the peculiarity of MBC systems that consists in the nonuniform chain architecture of these intriguing systems due to compositional heterogeneity occurring at inter‐ and intra‐chain level. In the first part, the effect of dispersity on the phase behavior and properties of MBCs and block copolymers in general is discussed along with the consequences of crystallization of one of the blocks on microphase separation, domain spacing, and morphology. In the second part, the main results achieved in the elucidation of details of the chain microstructure in terms of average length of the blocks and block length distribution are presented. It is shown that solvent and thermal fractionation techniques, coupled with other techniques such as transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) represent powerful tools to elucidate the inter‐ and intra‐chain heterogeneous composition of the MBCs. Guidelines on how to establish structure/properties relationships for such polydisperse systems are also provided.

Fast-Tracking of the Segmental Orientation in Poly(ethylene oxide)-based Polyurethane Urea by Mechano-optical (Infrared Dichroism and Birefringence) Properties: Degree of the Soft-Segment Ordering Effect

The orientation behavior of segment-specific chemical groups of NH and CH was investigated for poly(ethylene oxide) (PEO)-based polyurethane urea (PUU) during uniaxial stretching using a uniaxial stretching system integrated with spectral birefringence and ultrafast IR spectrometers that capture two polarization states simultaneously. PUUs with 30% by-weight urethane-urea hard segment content were prepared using PEO oligomers with number average molecular weights of 2000, 4600, and 8000 g/mol. High-molecular weight PEO-based PUUs exhibited microphase morphologies with sharp interfaces between the PEO matrix and urethane-urea hard segments, while low-molecular weight PEO-2000 (2000 g/mol)-based PUU exhibited a gradient interphase. This is primarily due to substantial hydrogen-bonding interactions between the urea hard segments and ether groups of highly amorphous PEO-2000 compared with highly crystalline soft segments in PEO-4600 and PEO-8000, which lack significant hydrogen-bonding interactions with urea groups and hence a sharper interface and improved microphase separation. The segment-specific chemical group orientation study revealed that the relaxation and reorganization behaviors are closely dependent on the initial morphology. In microphase-separated PUU with a gradient interphase, responses of the hard and soft segments to deformation are similar even at lower strain levels. For the microphase-separated PUUs with a sharp interface, the low-strain level orientation is localized in the soft-segment regions until the connection with the hard segments drive the orientation in the chain axis toward the stretching direction. This network transition is also reflected in the mechano-optical behavior as a change from a high-strain optical constant to a lower-strain optical constant.

Controlling the microphase morphology and performance of cross-linked highly sulfonated polyimide membranes by varying the molecular structure and volume of the hydrophobic cross-linkable diamine monomers

Morphological control is essential for tuning the performance of polymer electrolyte membranes (PEMs). Block copolymerization is an effective but complicated way to control the morphology of PEMs. It is urgent to explore a simple alternative method to achieve this target. Herein, the molecular engineering strategy that changes the molecular structure and volume of hydrophobic cross-linkable diamine and introduces a hydrophobic network structure was used to optimize the microphase morphology of sulfonated polyimides (SPIs). Three diamine monomers containing tetrafluorostyrol pendant groups have been synthesized (4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene-1,3-diamine (TFVPDM), 1,3-bis(2-trifluoromethyl-4-amino-phenoxy)-5-(2,3,5,6-tetrafluoro-4-vinylphenoxy)benzene (6FTFPB), 2,2-bis(3-amino-4-(2,3,5,6-tetrafluoro-4-vinylphenoxy)phenyl)hexafluoropropane (6FATFVP)). Based on these monomers, 4,4′-diaminostilbene-2,2′-disulfonic acid (DASDSA) and 1,4,5,8-naphthalenetetracarboxylicdianhydride (NTDA), three cross-linked SPIs (CSPIs: CSPI-T-10, CSPI-TP-10, CSPI-AP-10) with similar ion-exchange capacity (IEC) value of 2.29–2.46 meq. g−1 but different main-chain structures were prepared through polycondensation and thermal cross-linking process. The introduced hydrophobic cross-linked structure improves the oxidative stability and methanol resistance of CSPI membranes. The CSPI membranes prepared from cross-linkable hydrophobic diamine with larger molecular volume and containing hydrophobic structural units in the main chain exhibit more pronounced phase separation morphology and higher proton conductivity. Moreover, the methanol resistance of CSPI membranes is dependent on the combined effect of IEC, degree of crosslinking (DC), and main-chain structure. The higher DC and main-chain containing hydrophobic structure are beneficial for enhancing the methanol resistance. The CSPI-AP-10, which was prepared from the 6FATFVP with the largest molecular volume, more hydrophobic cross-linkable pendant groups and hydrophobic linkages, exhibits the best performance. The CSPI-AP-10 membranes showed high proton conductivity and excellent methanol resistance. The direct methanol fuel cells (DMFCs) assembled from CSPI-AP-10 have a high max power density (PDmax) of 106.2 mW cm−2 in 2 M methanol and 75.1 mW cm−2 in 10 M methanol. The results indicated that the CSPI-AP-10 was a promising candidate as a PEM in DMFC application.

Immiscible Polymer Blends Compatibilized through Noncovalent Forces: Construction of a “Quasi-Block/Graft Copolymer” by Interfacial Stereocomplex Crystallites

Interfacial compatibilization is acknowledged to be the most effective approach to improve interfacial strength between the thermodynamically immiscible components of polymer blends. However, the compatibilizer, mainly achieved by graft or block copolymers, necessarily connected by covalent bonds, can rarely be satisfied presently. Herein, we propose a concept of “quasi-block/graft copolymer” to compatibilize the immiscible polyolefin elastomer (POE) and poly(styrene-acrylonitrile-glycidyl methacrylate) (SAG) blends. The quasi-block/graft copolymer was achieved by the stereocomplex crystals (SC) of poly-l-lactic acid (PLLA) and poly-d-lactic acid (PDLA) moieties that reactively grafted on the main chains of the components. By taking advantage of the interfacial compatibilization through noncovalent forces, the microphase morphology of the blend can be adjusted and the mechanical properties can be improved: firstly, the curvature of the phase interface decreases significantly, facilitating co-continuous morphology on account of the “rigid” interfacial layers; secondly, the tensile strength and modulus of the blend are obviously improved; thirdly, the original phase structure of the blend can be well maintained during long-term annealing due to the high melting point of the interfacial SC. This strategy of compatibilizing immiscible blends by using the hydrogen bonding force of the stereocomplex opens up an idea for interfacial compatibilization.

Effect of Fluorocarbon Side Chain on the Microphase Morphology and Rheological Behavior of Thermoplastic Polyurethanes

Effect of Fluorocarbon Side Chain on the Microphase Morphology and Rheological Behavior of Thermoplastic Polyurethanes

Pyrrolidinium-Based Hyperbranched Anion Exchange Membranes with Controllable Microphase Separated Morphology for Alkaline Fuel Cells.

It is well acknowledged that the microphase-separated morphology of anion exchange membranes (AEMs) is of vital importance for membrane properties utilized in alkaline fuel cells. Herein, a rigid macromolecule poly(methyldiallylamine) (PMDA) is incorporated to regulate the microphase morphology of hyperbranched AEMs. As expected, the hyperbranched poly(vinylbenzyl chloride) (HB-PVBC) is guided to distribute along PMDA chains, and longer PMDA cha leads to a more distinct microphase morphology with interconnected ionic channels. Consequently, high chloride conductivity of 10.49 mS cm-1 at 30 °C and suppressed water swelling ratio lower than 30% at 80 °C are obtained. Furthermore, the β-H of pyrrolidinium cations in the non-antiperiplanar position increases the energy barrier of β-H elimination, leading to conformationally disfavored Hofmann elimination and increased alkaline stability. This strategy is anticipated to provide a feasible way for preparing hyperbranched AEMs with clear microphase morphology and good overall properties for alkaline fuel cells.

High clarity polyurethane laminating adhesives based on poly (propylene glycol). Effect of hard segment on microphase morphology, haze and adhesion

Within this publication, the performance of high clarity polyurethane adhesives based on a poly(propylene glycol) soft-phase within a polycarbonate or ethanolamine surface-treated polycarbonate laminate, is described. A series of polyurethanes were prepared, with poly(propylene glycol) used as soft-phase due to the high clarity of this polyol and absence of carbonyl functionality, which allows for hard-phase architecture to be resolved with greater resolution. In total, eight adhesives were synthesised, each contained a different chain-extender formulation to gauge what influence hard-phase architecture had on laminate haze and peel strength. This was investigated using either 4,4-methylene diphenyl diisocyanate or isophorone diisocyanate as hard-phase with trimethylolpropane as the only chain-extender or by including one of the following sterically hindered diols: 2,2-diethyl-1,3-propane diol, 1,3-butane diol or 1,2-proane diol. DSC analysis showed that microphase morphology was strongly influenced by the diisocyanate present, as shown by the degree of phase mixing being greater in methylene diphenyl diisocyanate based formulations when compared with isophorone diisocyanate based. ATR complements this observed difference in microphase morphology, with isophorone diisocyanate based formulations having a greater composition of hydrogen-bonded urethane and urea functionality present within the hard-phase which displays a more phase separated composition. Interestingly, differences in microphase mixing did not have a consistent influence on the peel strength obtained, with only 31% of laminate combinations tested recording a peel strength of <3 N mm −1 after 18 months. Diol chain-extended formulations based on methylene diphenyl diisocyanate accounted for 25% of these lower values and was a consequence of their poorer process-ability during lamination. This resulted in higher haze values being encountered for both polycarbonate and ethanolamine surface-treated polycarbonate laminates which contained methylene diphenyl diisocyanate based formulations when compared to isophorone diisocyanate based formulations, where all values were <1.5%.

Superhigh strength polyurethane materials with oriented microdomains produced through mechanical deformation

Self-reinforcement is a preferred strategy to achieve high tensile strength polymer materials. Sparse work has been reported in this aspect on thermoplastic polyurethanes (TPUs). Three commercial TPUs, two polytetramethylene ether glycol (PTMG)-based TPUs (coded as MDIPTMG and TDIPTMG) and one polycaprolactone (PCL)-based TPU (MDIPCL) were chosen to study the dependences of mechanical tensile properties on the microstructures. Fourier transform infrared spectroscopy, thermogravimetric analysis and atomic force microscopy were used to characterize the chemical compositions, thermal stabilities and microphase morphologies. The mechanical properties such as tensile strength and the Young's modulus of the three TPUs were greatly improved through step-cycle tensile deformation, especially for MDIPTMG and MDIPCL. The true stress-true strain curves indicated that point A (the end of the Hooke range) and point B (the yield point) located at about same strains, whilst point C (the formation of oriented microdomains) for MDIPTMG and MDIPCL located at a much lower strain than that for TDIPTMG. In-situ small-angle X-ray scattering further revealed that the hard microdomains of MDIPTMG and MDIPCL could transform to oriented microstructures at the strains above 200%, consistent with the critical strains at point C . The oriented microstructures could be preserved, which played a significant role to achieve high strength TPUs, with a potential to widen their practical applications. • Superior TPUs with super high tensile strength were produced. • The oriented microdomains played a crucial role for TPUs. • Simple tensile deformation processing is applicable to TPUs.

Insights into permeability of rejuvenator in old asphalt based on permeation theory: Permeation behaviors and micro characteristics

Aiming to analyze the permeation behaviors and micro characteristics of rejuvenator in old asphalt, the rejuvenation fusion layer (RFL) of rejuvenator and old asphalt was first fabricated by permeation test. Then, the viscosity of RFLs was analyzed and its several influencing factors were explored via conducting the rotational viscosity test. On this basis, coupled with Fick’s law and composite material theory, the permeability coefficient (D) of rejuvenator in old asphalt was calculated and the influencing factors were investigated. Lastly, the micro-phase morphology, mechanical and chemical characteristics of RFL were analyzed via the AFM and FTIR tests. Results showed that the permeability of rejuvenator in old asphalt depended on permeation temperature, permeation time, rejuvenator type and asphalt layer thickness. The higher permeation temperature or longer time contributed to the permeation effect of rejuvenator in old asphalt. Moreover, based on the results, the mixing temperature should not be less than 150 °C and the mixing time should be about 12 s ∼ 18 s for the uniform mixing of RAP and rejuvenator in actual thermal rejuvenation engineering. The permeability of mineral oil rejuvenator in aged asphalt was stronger than that of bio-rejuvenator, and thinner aged asphalt layer made the rejuvenator more easily permeate. Further, the sampling layer exhibited the most remarkable influence on the permeability of rejuvenator in old asphalt, followed by rejuvenator type, permeation time and permeation temperature. The AFM test confirmed that the permeation effect of mineral oil rejuvenator in aged asphalt was superior to that of bio-rejuvenator from the micro perspective, and that under the permeation conditions of 130 °C and 6 h, the mineral oil rejuvenator can fully fuse with aged asphalt and show similar morphological characteristics (“bee” size and quantity) at different layers of RFLs. Further, the mineral oil rejuvenator greatly enhanced the micro mechanical properties of aged asphalt, demonstrating a favorable rejuvenation effect. FTIR test manifested that the functional group composition of the L-type rejuvenator was similar to that of the original asphalt, and that the L-type rejuvenator contained lower carbonyl contents compared to B-type and H-type rejuvenators and exhibited better permeability and rejuvenation effect.

Synthesis of well-defined PMMA-b-PDMS-b-PMMA triblock copolymer and study of its self-assembly behaviors in epoxy resin

PMMA- b -PDMS- b -PMMA block copolymers can mediate different reaction-induced microphase separation mechanism with different curing agents and formed ordered nanospheres. • A mild condition to conduct chain extension of Br-PDMS-Br with MMA via effective SARA ATRP was demonstrated and obtained a well-defined PMMA- b -PDMS- b -PMMA tBCP. • Then the tBCP shows its good compatibility with respect to epoxy resin, owing to the presence of compatible PMMA segments. • Through in-situ SAXS measurements, we found the tBCP underwent reaction-induced microphase separation (RIMPS) mechanism cured by 4,4′-methylenedianiline (MD) but self-assembly (SA) mechanism cured by phenol novolacs (PN). • We inspected the interesting mechanism variations, compatibility, and microphase morphology by using FT-IR, DSC, TGA, TEM, and SAXS of the obtaining MD- and PN-cured composites, mainly including nanospheres morphology in approximately 30 nm. With the evolutions of reversible deactivation radical polymerizations (RDRPs), including atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), one technique can be noted that supplemental activator and reducing agent (SARA) ATRP can conduct controlled/living radical polymerization fashion with a ppm level of catalyst. In addition, polydimethylsiloxane (PDMS) has wide ranges of applications in surfactants, sealants, and impact-relief materials. In this study, we first prepared a well-defined PDMS ended with α,ω-isobutyryl bromide (i.e., Br-PDMS-Br) macroinitiator (MI). Then chain extension of Br-PDMS-Br with methyl methacrylate (MMA) via SARA ATRP was conducted. Mild chain extension conditions were demonstrated and we successfully achieved controlled/living radical polymerization. A well-defined PMMA- b -PDMS- b -PMMA tBCP (named as ABA: M n, GPC = 49770; PDI = 1.44) comprising two external epoxy-philic blocks and a middle soft block was thus acquired. The ABA was further blended with diglycidyl ether of bisphenol-A (DGEBA) epoxy monomer and two crosslinkers of 4,4′-methylenedianiline (MD)/phenol novolacs (PN) to construct nanostructures driven by curing reactions. The cured epoxy thermoset (ET)/ABA composites showed good thermal properties and well-compatible behaviors (i.e, T g = ca. 100 °C and T (5 wt% loss) = ca. 270–335 °C) characterized by the measurements of differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). We further analyzed the two composite systems by utilizing Fourier transform infrared spectroscopy (FT-IR), (in-situ) small-angle X-ray scattering (SAXS), and transmission electron microscope (TEM). With different curing agent, interestingly, we observed a reaction-induced microphase separation (RIMPS) mechanism in MD-cured system but a self-assembly (SA) mechanism in PN-cured system. Furthermore, the PN-cured composites can create ordered nanospheres in a range of 27–41 nm.

(Invited) Poly(aryl-co-aryl piperidinium) Copolymers for High-Performance Anion Exchange Membrane Fuel Cells

Poly(aryl piperidinium)s (PAPs) have attracted great attention as durable anion exchange membrane (AEMs) and ionomers for AEM fuel cells (AEMFCs). However, most of PAP AEMs display poor microphase morphology, and ionomer research on PAPs is still lacking to date. Here, we report a series of high-performance poly(aryl-co-aryl piperidinium) copolymers (c-PAPs) for AEMs and ionomers, along with improving AEMFC performance (Figure 1). Compared with PAPs, c-PAP AEMs possess higher ion conductivity (>200 mS cm-1), enhanced mechanical properties (tensile strength>80 MPa), lower hydrogen permeability (<10 Barrer) and optimized microphase morphology. On the other hand, c-PAP ionomers display lower ionomer adsorption on platinum-group-metal (PGM) catalysts and higher electrochemical performance than PAP ionomers. Based on poly(diphenyl-co-terphenyl piperidinium) AEMs (PDTP) and poly(fluorenyl-co-biphenyl piperidinium) (PFBP) ionomers, the peak power density (PPD) of presented AEMFCs reaches 2.67 W cm-2 in H2-O2 and 1.38 W cm-2 in H2-air (CO2 free) at 80 oC based on optimized c-PAP AEMs and ionomers. Moreover, c-PAP based AEMFCs reach >1000 h in-situ durability under 1 A cm-2 current density in H2-O2 at 60oC. The presented works provide insight into c-PAP AEMs and ionomers. Figure 1. Chemical structure of c-PAP AEMs and ionomers, along with high PPDs of AEMFCs over 2.6 W cm-2. Reference [1] N. J. Chen and Y. M. Lee. Progress in Polymer Science. 2021, 113, 101345.[2] N. J. Chen, C. Hu, Y. M. Lee, et al. Angew. Chem. Int. Ed. 2021, 60, 7710-7718.[3] N. J. Chen, H. H. Wang, Y. M. Lee, et al. Nat. Commun. 2021. DOI. Figure 1

Effect of multi-armed chain extender on microphase morphology, stress-strain behavior and electromechanical properties of polyurethane elastomers

High dielectric constant and low modulus of thermoplastic polyurethane elastomers (PUEs) are required for various applications in actuators, sensors and energy harvestings. In this work, we controlled the microphase separated morphology of PUEs by regulation of the content of hydroxyl-terminated four-armed polycaprolactone (4amPCL) chain extender to achieve J-shaped stress-strain curve with low modulus and high electromechanical properties. Our results showed that the hydrogen bonding between hard segments (HSs) and crystallization of soft segment (SS) are significantly impeded by long-chain branched structure when added lower molar fraction (<20% of chain extenders) of 4amPCL as chain extender, whereas the branched long-chains are embedded in microphase separated hard and soft domains (HD and SD) to form strip shaped interconnected hard domain (HD) rich regions when added higher molar fraction (>20% of chain extenders) of 4amPCL as chain extender. The PUE with 29% of 4amPCL (PU-4amPCL-0.29) showed lower modulus (1.5 MPa), higher tensile strength (17.5 MPa) at 1048% of elongation, and 3.9% of actuation strain at 20 kV/mm, and higher contribution (48.1%) of Maxwell stress on actuation strain at 20 kV/mm. We found that the microphase separation of branched long-chains induced semi-interpenetration polymer network like structure of PUEs played an important role in exhibiting J-shaped stress-strain behavior. Our results can provide new insight on fabrication of high electromechanical performance of dielectric polyurethane elastomers.

Triple shape memory effect of ethylene-vinyl acetate copolymer/poly(propylene carbonate) blends with broad composite ratios and phase morphologies

In this work, a triple-shape memory polymer (SMP) was prepared by chemically crosslinking melting blending from ethylene-vinyl acetate copolymer (EVA) and poly(propylene carbonate) (PPC). The EVA/PPC blends combine the glass transition of PPC (~25.6 °C) and melting transition of EVA (~72.2 °C) to function as the shape memory mechanisms. The triple-shape memory effect (triple-SME) and its dependence on composite ratios and micro-phase morphologies were systematically investigated. The results show that EVA/PPC blends with different composite ratios and morphologies all exhibit excellent triple-SMEs, with shape fixing ratio over 90% and shape recovery ratio close to 90%. The key to realize such triple SME is the certain matching of the modulus of the two components. Specifically, the modulus of glassy PPC is much higher than the modulus of semi-crystalline EVA, whereas the modulus of viscoelastic PPC is lower than the modulus of semi-crystalline and elastic EVA. This work provides a comparatively simple and efficient method to design and prepare high-performance triple-SMP.

Dynamic Bonds Mediate π-π Interaction via Phase Locking Effect for Enhanced Heat Resistant Thermoplastic Polyurethane

Stimulus-responsive polymers containing dynamic bonds enable fascinating properties of self-healing, recycling and reprocessing due to enhanced relaxation of polymer chain/network with labile linkages. Here, we study the structure and properties of a new type of thermoplastic polyurethanes (TPUs) with trapped dynamic covalent bonds in the hard-phase domain and report the frustrated relaxation of TPUs containing weak dynamic bond and π-π interaction in hard segments. As detected by rheometry, the aromatic TPUs with alkyl disulfide in the hard segments possess the maximum network relaxation time in contrast to those without dynamic bonds and alicyclic TPUs. In situ FTIR and small-angle scattering results reveal that the alkyl disulfide facilitates stronger intermolecular interaction and more stable micro-phase morphology in π-π interaction based aromatic TPUs. Molecular dynamics simulation for pure hard segments of model molecules verify that the presence of disulfide bonds leads to stronger π-π stacking of aromatic rings due to both enhanced assembling thermodynamics and kinetics. The enhanced π-π packing and micro-phase structure in TPUs further kinetically immobilize the dynamic bond. This kinetically interlocking between the weak dynamic bonds and strong molecular interaction in hard segments leads to much slower network relaxation of TPU. This work provides a new insight in tuning the network relaxation and heat resistance as well as molecular self-assembly in stimulus-responsive dynamic polymers by both molecular design and micro-phase control toward the functional applications of advanced materials.

Hydrophilic/hydrophobic-bi-comb-shaped amphoteric membrane for vanadium redox flow battery

A novel hydrophilic/hydrophobic bi-comb-shaped amphoteric membrane was for the first time designed by the one-pot reactions of PBI with bromohexane and 1,3-propanesultone. The sulfonic acid chain promotes the formation of amphoteric ion clusters, while the alkyl side chain enhances the packing of hydrophobic segments. This unique structure design optimizes the segregated microphase morphology of the membrane, which is proved by TEM. Compared to the membrane without alkyl side chain, the bi-comb-shaped membrane shows a lowered area resistance (0.58 vs. 0.96 Ω cm2) as well as a reduced swelling ratio (11.7% vs. 14.3%). As a result, the cell with the bi-comb-shaped membrane exhibits improved voltage efficiency, thus achieving increased energy efficiency. In addition, the membrane of this structure occupies excellent cycle stability. The cell efficiencies maintain almost stable for 250 cycles, and the chemical structure has no change after immersing in the electrolyte solution for 28 days.

Blends of highly branched and linear poly(arylene ether sulfone)s: Multiscale effect of the degree of branching on the morphology and mechanical properties

This study reports the synthesis of highly branched poly(arylene ether sulfone)s (HBPAES) and their incorporation into linear poly(arylene ether sulfone) (LPAES) to investigate the effect of branched topology on the morphological and mechanical properties of final polymer blends. The A2 + B3 polymerization was utilized to synthesize HBPAESs with varying distance between branch points by reacting monomeric 4,4′-dichlorodiphenyl sulfone (DCDPS) or pre-synthesized chlorine terminated linear oligomers with various degrees of polymerization as the A₂ species with 1,1,1-tris(4-hydroxyphenyl)ethane (THPE) as the B₃ monomer. The chemical structure and the degree of branching of synthesized HBPAESs were characterized by 1H Nuclear Magnetic Resonance (NMR) spectroscopy, while Size Exclusion Chromatography (SEC) and Differential Scanning Calorimetry (DSC) were used for the determination of their molecular weight and glass transition temperatures. Polymer blends of HBPAES and LPAES (10/90 w/w) were solution cast into free-standing, dry films and characterized by tensile tests, Dynamic Mechanical Analysis (DMA), Atomic Force (AFM) and Scanning Electron (SEM) Microscopies. Complementary to experimental studies, these blends were modeled with dissipative particle dynamics (DPD) simulations to explain their microphase behavior, miscibility, and morphology. The experimental and computational studies together revealed that understanding the effect of the degree of branching on the intermolecular interactions of highly branched polymers with their linear analogues is critical to obtain final polymer blends with tunable mechanical properties and enhanced fracture behavior.

Direct modification of polyketone resin for anion exchange membrane of alkaline fuel cells

A kind of side-chain type anion exchange membranes (AEMs) with high ionic conductivity and good comprehensive stability was prepared via direct modification of commercial engineering plastic polyketone with diamines through Paal-Knorr reaction and quaternization reaction. It was found that the amount of diamine can effectively tune the microphase morphology and properties of the prepared quaternized functionalized-polyketone anion exchange membranes (QAFPK-AEMs). The tensile strength was increased from 18.6 MPa to 38.6 MPa, and the ion exchange capacity (IEC) was increased from 1.11 mmol/g to 2.71 mmol/g depending on the amount of added diamine. The QAFPK-1-6-AEM with the IEC of 1.43 mmol/g showed the highest hydroxide conductivity of 65 mS/cm at 25 °C and 96.8 mS/cm at 80 °C. The high ionic conductivity was achieved through the establishment of effective ionic channels, and it maintained 70% of the initial ionic conductivity after the 192 h treatment in 2 mol/L KOH (aq) at 80 °C. Moreover, a peak power density of 129 mW/cm2 was achieved when the assembled single cell with QAFPK-1-6-AEM was operated at 50 °C. Thus, the prepared QAFPK-AEMs showed great potential applications for the anion exchange membrane fuel cells (AEMFCs).