Showing papers in "Macromolecules in 2016"
TL;DR: A critical appraisal of the various advantages offered by polymerization-induced self-assembly, while also pointing out some of its current drawbacks is provided.
Abstract: Recently, polymerization-induced self-assembly (PISA) has become widely recognized as a robust and efficient route to produce block copolymer nanoparticles of controlled size, morphology, and surface chemistry. Several reviews of this field have been published since 2012, but a substantial number of new papers have been published in the last three years. In this Perspective, we provide a critical appraisal of the various advantages offered by this approach, while also pointing out some of its current drawbacks. Promising future research directions as well as remaining technical challenges and unresolved problems are briefly highlighted.
655 citations
TL;DR: In this paper, the authors summarize the most widely used definitions of free volume and illustrate the differences between them, including the important distinction between total free volumes and excess free volumes, and discuss the implications when alternative estimates for free volume are inserted into relationships that connect experimentally measured properties (e.g., the viscosity) to free volume, such as those proposed by Doolittle, Fox and Flory.
Abstract: In this Perspective we summarize the most widely used definitions of free volume and illustrate the differences between them, including the important distinction between total free volume and excess free volume We discuss the implications when alternative estimates for free volume are inserted into relationships that connect experimentally measured properties (eg, the viscosity) to free volume, such as those proposed by Doolittle, Fox and Flory, Simha and Boyer, Cohen and Turnbull, and Williams, Landel, and Ferry Turning to the results of our own locally correlated lattice (LCL) model, we demonstrate, by analyzing data for a set of over 50 polymers, that our calculations for total percent free volume not only lead to a predictive relationship with experimental glass transition temperatures but also allow us to place the different definitions of free volume within a physical picture of what the proposed contributions represent We find that melts go glassy upon reaching a “boundary” of minimum (total)
302 citations
TL;DR: In this paper, a systematic study of poly(2,6-dimethyl-1,4-phenylene oxide)-based anion exchange membrane fuel cells with multiple cations per side chain site was conducted.
Abstract: Anion exchange membrane fuel cells (AEMFCs) have been developed as promising energy conversion devices for stationary and mobile applications due to their potentially low cost. To realize high-performance AEMFCs, new polymeric membranes are needed that are highly conductive and chemically stable. Here we report a systematic study of anion exchange membranes (AEMs) with multiple cations per side chain site to demonstrate how this motif can boost both the conductivity and stability of poly(2,6-dimethyl-1,4-phenylene oxide)-based AEMs. The highest conductivity, up to 99 mS/cm at room temperature, was observed for a triple-cation side chain AEM with 5 or 6 methylene groups between cations. This conductivity was considerably higher than AEM samples based on benzyltrimethylammonium or benzyldimethylhexylammonium groups with only one cation per side chain site. In addition to high conductivity, the multication side chain AEMs showed good alkaline and dimensional stabilities. High retention of ion exchange capaci...
292 citations
TL;DR: In this article, it was shown that poly(ethylene glycol) bis(3-aminopropyl) with 1,3,5-triformylbenzene with an equal molar ratio of amine and aldehyde functionalities in organic solvents with varying polarity and in neat condition exhibits malleability and self-healing characteristics.
Abstract: Covalent polymeric networks composed of imine cross-linkages have been prepared by condensation polymerization of poly(ethylene glycol) bis(3-aminopropyl) with 1,3,5-triformylbenzene with an equal molar ratio of amine and aldehyde functionalities in organic solvents with varying polarity and in neat condition. The polymer networks exhibit malleability and self-healing characteristics. Rheological measurements revealed that longer reaction time is required to reach the gel point (i.e., crossover of G′ and G″) in polar solvents than in nonpolar solvents. The malleability of the solvent-swelled polymer network is also strongly dependent on the solvent polarity. Polymer gels in polar solvents are more malleable than those in nonpolar solvents, as supported by the dynamic mechanical analysis. These results are consistent with faster dynamic imine bond exchange in the polar solvents relative to the nonpolar solvents, thus requiring higher functionality conversion to form an elastic network in the polar solvent ...
278 citations
TL;DR: In this paper, a physical hydrogel of poly(acrylamide-co-acrylic acid) (P(AAm-Co-AAc)) cross-linked by carboxyl-Fe3+ coordination complexes is reported.
Abstract: It is challenging to develop hydrogels with a combination of excellent mechanical properties, versatile functions, and good processability. Here we report a physical hydrogel of poly(acrylamide-co-acrylic acid) (P(AAm-co-AAc)) cross-linked by carboxyl–Fe3+ coordination complexes that possesses high stiffness and toughness, fatigue resistance, and stimulation-triggered healing along with shape memory and processing abilities. The copolymers have randomly dispersed AAm and AAc repeat units, making the physical cross-links with different strength. The strong coordination bonds and their associations serve as permanent cross-links, imparting the elasticity, whereas the weak ones reversibly rupture and re-form, dissipating the energy. Furthermore, a stick–slip instability is observed during the tearing test, which should be associated with the specific nature of metal-coordination bonds that are strong yet fragile. Because of the dynamic nature of coordination bonds, both tensile and tearing mechanical propert...
275 citations
TL;DR: In this article, the authors present detailed evidence of highly efficient and reversible iodine capture in hexaphenylbenzene-based conjugated microporous polymers (HCMPs), synthesized via Buchwald-Hartwig (BH) cross-coupling of a hexakis(4-bromophenyl) benzene (HBB) core and aryl diamine linkers, present moderate surface areas up to 430 m2 g-1, with narrow pore size distribution and uniform ultramicropore sizes of less than 1 nm
Abstract: The effective and safe capture and storage of radioactive iodine (129I or 131I) is of significant importance during nuclear waste storage and nuclear energy generation. Here we present detailed evidence of highly efficient and reversible iodine capture in hexaphenylbenzene-based conjugated microporous polymers (HCMPs), synthesized via Buchwald–Hartwig (BH) cross-coupling of a hexakis(4-bromophenyl)benzene (HBB) core and aryl diamine linkers. The HCMPs present moderate surface areas up to 430 m2 g–1, with narrow pore size distribution and uniform ultramicropore sizes of less than 1 nm. Porous properties are controlled by the strut lengths and rigidities of linkers, while porosity and uptake properties can be tuned by changing the oxidation state of the HCMPs. The presence of a high number of amine functional groups combined with microporosity provides the HCMPs with extremely high iodine affinity with uptake capacities up to 336 wt %, which is to the best of our knowledge the highest reported to date. Two ...
265 citations
TL;DR: In this paper, a systematic study was conducted for the analysis of polymer backbone chemical stability in alkaline media, including poly(arylene ethers, poly(biphenyl alkylene)s, and polystyrene block copolymers.
Abstract: Anion exchange membranes are an important component in alkaline electrochemical energy conversion and storage devices, and their alkaline stability plays a crucial role for the long-term use of these devices. Herein, a systematic study was conducted for the analysis of polymer backbone chemical stability in alkaline media. Nine representative polymer structures including poly(arylene ether)s, poly(biphenyl alkylene)s, and polystyrene block copolymers were investigated for their alkaline stability. Polymers with aryl ether bonds in their repeating unit showed poor chemical stability when treated with KOH and NaOCH3 solutions, whereas polymers without aryl ether bonds [e.g., poly(biphenyl alkylene)s and polystyrene block copolymers] remained stable. Additional NMR studies and density functional theory (DFT) calculations of small molecule model compounds that mimic the chemical structures of poly(arylene ether)s confirmed that electron-withdrawing groups near to the aryl ether bonds in the repeating unit acc...
261 citations
TL;DR: In this paper, a bioinspired design of high-performance and macroscopically responsive diene-rubber by engineering sacrificial metal-ligand motifs into a chemically cross-linked architecture network is presented.
Abstract: Reinforcing rubbers and expanding their application galleries are two important issues in material science and engineering. In this work, we demonstrate a bioinspired design of high-performance and macroscopically responsive diene-rubber by engineering sacrificial metal–ligand motifs into a chemically cross-linked architecture network. The metal–ligand bonds are formed through the coordination reaction between the pyridine groups in butadiene–styrene–vinylpyridine rubber (VPR) and metal ions. Under external load, the metal–ligand bonds serve as sacrificial bonds that preferentially rupture prior to the covalent network, which dissipates energy and facilitates rubber chain orientation. Based on the function mechanisms, the modulus, tensile strength, and toughness of the samples are simultaneously improved without sacrificing the extensibility, and these properties can be conveniently tuned by varying the structure parameters of the covalently cross-linked network and metal–ligand bonds. Moreover, the disso...
214 citations
TL;DR: Interest in this field continues to grow partially due to the variety of potential applications of SCNP including catalysis, sensors, nanoreactors, and nanomedicine.
Abstract: With the increasing appeal of nanotechnology, there is a demand for development of synthetic techniques for the fabrication of nano-sized objects that allow for precise size control and tailored functionalization. To this end, the collapse or folding of single polymer chains into architecturally defined nanostructures is a rapidly growing research topic in polymer science. Many synthetic approaches have been developed for the formation of single-chain nanoparticles (SCNP), and a variety of characterization methods and computational efforts have been utilized to detail their formation and probe their morphological characteristics. Interest in this field continues to grow partially due to the variety of potential applications of SCNP including catalysis, sensors, nanoreactors, and nanomedicine. While numerous developments have been made, the field is continuing to evolve, and there are still many unanswered questions regarding synthesis and characterization of SCNP. This Perspective serves to identify recen...
210 citations
TL;DR: In this article, a series of α-diimine ligands and corresponding palladium catalysts bearing both the dibenzhydryl moiety and with systematically varied ligand sterics were described.
Abstract: In the Brookhart type α-diimine palladium catalyst system, it is highly challenging to tune the polymer branching densities through ligand modifications or polymerization conditions. In this contribution, we describe the synthesis and characterization of a series of α-diimine ligands and the corresponding palladium catalysts bearing both the dibenzhydryl moiety and with systematically varied ligand sterics. In ethylene polymerization, it is possible to tune the catalytic activities ((0.77–8.85) × 105 g/(mol Pd·h)), polymer molecular weights (Mn: (0.2–164.7) × 104), branching densities (25–116/1000C), and polymer melting temperatures (amorphous to 98 °C) over a very wide range. In ethylene–methyl acrylate (E–MA) copolymerization, it is possible to tune the catalytic activities ((0.3–8.8) × 103 g/(mol Pd·h)), copolymer molecular weights (1.1 × 103–79.8 × 103), branching densities (30–119/1000C), and MA incorporation ratio (0.4–13.8%) over a very wide range. The molecular weights and branching densities coul...
204 citations
TL;DR: In this article, a review of the state of the art of block copolymer membranes and perspectives on pore morphology tuning are discussed. But, the main focus is on the pore tuning.
Abstract: Block copolymers are known for their intricate morphology. We review the state of the art of block copolymer membranes and discuss perspectives in this field. The main focus is on pore morphology tuning with a short introduction on nonporous membranes. The two main strategies for pore formation in block copolymer membranes are (i) film casting and selective block sacrifice and (ii) self-assembly and nonsolvent-induced phase separation (SNIPS). Different fundamental aspects involved in the manufacture of block copolymer membranes are considered, including factors affecting the equilibrium morphology in solid films, self-assembly of copolymer in solutions, and macrophase separation by solvent–nonsolvent exchange. Different mechanisms are proposed for different depths of the SNIPS membrane. Block copolymer membranes can be prepared with much narrower pore size distribution than homopolymer membranes. Open questions and indications of what we consider the next development steps are finally discussed. They inc...
TL;DR: In this article, the authors used time-domain thermoreflectance (TDTR) and the generation and detection of longitudinal and surface acoustic waves, to study the thermal conductivity, heat capacity, and elastic properties of thin films of poly(vinyl alcohol) (PVA), poly(acrylic acid)(PAA), polyacrylamide (PAM), polyvinylpyrrolidone), methyl cellulose (MC), poly4-styrenesulfonic acid) (PSS), polyN-acryloylpiperidine
Abstract: We use time-domain thermoreflectance (TDTR), and the generation and detection of longitudinal and surface acoustic waves, to study the thermal conductivity, heat capacity, and elastic properties of thin films of poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), polyacrylamide (PAM), poly(vinylpyrrolidone) (PVP), methyl cellulose (MC), poly(4-styrenesulfonic acid) (PSS), poly(N-acryloylpiperidine) (PAP), poly(methyl methacrylate) (PMMA), and a polymer blend of PVA/PAA. The thermal conductivity of six water-soluble polymers in the dry state varies by a factor of ≈2, from 0.21 to 0.38 W m–1 K–1, where the largest values appear among polymers with a high concentration of hydrogen bonding (PAA, PAM, PSS). The longitudinal elastic constants range from 7.4 to 24.5 GPa and scale linearly with the shear elastic constants, suggesting a narrow distribution of Possion’s ratio 0.35 < ν < 0.40. The thermal conductivity increases with the average sound velocity, as expected based on the model of the minimum thermal c...
TL;DR: In this paper, dual physically cross-linked (DPC) hydrogels are developed, which are triggered by clay nanosheets and iron ions (Fe3+) as cross-linkers.
Abstract: The applications of hydrogels are severely limited by their weak mechanical properties. Despite recent significant progress in fabricating tough hydrogels, it is still a challenge to realize high stretchability, toughness, and recoverability at the same time in a hydrogel. Herein, we develop a novel class of dual physically cross-linked (DPC) hydrogels, which are triggered by clay nanosheets and iron ions (Fe3+) as cross-linkers. First, clay nanosheets induce the formation of the first cross-linking points through the interaction of hydrogen bonds with poly(acrylamide-co-acrylic acid) (PAm-co-Ac) chains. Then the secondary cross-linking points are introduced by ionic coordinates between Fe3+ and −COO– groups of PAm-co-Ac polymer chains. The mechanical properties of DPC hydrogels can be tuned readily by varying preparation parameters such as clay concentration, Fe3+ concentration, and molar ratio of Ac/Am. More importantly, the optimal DPC hydrogels possess high tensile strength (ca. 3.5 MPa), large elonga...
TL;DR: In this article, the authors examined the impact of n-alkyl substituents on the polymerization thermodynamics and kinetics of substituted δ-valerolactone monomers and developed guiding design principles based on critical structure-property relationships.
Abstract: Aliphatic polyester block polymers constitute a highly useful and amazingly versatile class of self-assembled materials. Analogous to styrenic block polymers in both design and function, the property profiles of these degradable materials can be precisely tailored by altering the chemical structure of the components. Driven by this ideal, we have examined the impact of n-alkyl substituents on the polymerization thermodynamics and kinetics of substituted δ-valerolactone monomers and developed guiding design principles based on critical structure–property relationships in the resulting aliphatic polyesters. Under bulk room temperature conditions the polymerization rate depends strongly on substituent position and exhibits a more modest dependence on alkyl length (from −CH3 to −(CH2)8CH3). The enthalpy and entropy of polymerization are significantly influenced by substituent position, but both are largely insensitive to n-alkyl length. However, the physical properties of the resulting aliphatic polyesters de...
TL;DR: In this article, the effects of healing temperature and chemistry of polyampholyte hydrogels (chemical cross-linker density and chemical structure of the monomers) on the healing kinetics and healing efficiency were studied.
Abstract: Recently, polyampolytes have been discovered to form hydrogels that possess high toughness, full resilience, and self-healing between two cut surfaces. The self-healing of this class of hydrogels is based on the re-forming of the multiple ionic bonds at the fractured surfaces, in which the mobility of the polymer segments and strength of the ionic bonds play an important role. In this work, we study the effects of healing temperature and chemistry of the polyampholyte hydrogels (chemical cross-linker density and chemical structure of the monomers) on the healing kinetics and healing efficiency. The high healing temperature substantially accelerates the self-healing kinetics. Chemical cross-linking reduces the self-healing efficiency. Monomers with more hydrophobic feature give a low self-healing efficiency. For polyampholyte physical hydrogels with a softening temperature below the room temperature, excellent healing efficiency (∼84% on average and maximum 99%) was observed without any external stimuli. W...
TL;DR: In this article, the authors discuss some recent modifications and improvements on early coarse-grained approaches like the coil-stretch transition model for shish formation and the entropic reduction model for the enhancement of nucleation rate.
Abstract: Flow-induced crystallization (FIC) of polymers is a long-standing, industrial relevant, nonequilibrium thermodynamic challenge. Thanks to the development of in situ time and spatial resolved techniques like rheology and synchrotron radiation X-ray scattering, substantial progress on the understanding of FIC has been achieved in past 20 years. In this Perspective, we first discuss some recent modifications and improvements on early coarse-grained approaches like the coil–stretch transition model for shish formation and the entropic reduction model for the enhancement of nucleation rate. Then breaking out the two-phase model of classical nucleation theory, flow-induced coil–helix transition, density fluctuation or phase separation, and isotropic–nematic transition are considered as intermediate orders in FIC. Establishing flow morphology and phase diagrams is essential for revealing the nonequilibrium nature of FIC, which will serve as structural roadmap for the processing of high performance polymer products.
TL;DR: In this paper, fully bio-and CO2-sourced non-isocyanate polyurethanes (NIPUs) were synthesized by reaction of carbonated soybean oil (CSBO) either with biobased short diamines or amino-telechelic oligoamides derived from fatty acids to achieve respectively thermoset or thermoplastic NIPUs.
Abstract: Fully bio- and CO2-sourced non-isocyanate polyurethanes (NIPUs) were synthesized by reaction of carbonated soybean oil (CSBO) either with biobased short diamines or amino-telechelic oligoamides derived from fatty acids to achieve respectively thermoset or thermoplastic NIPUs. Biobased carbonated vegetable oils were first obtained by metal-free coupling reactions of CO2 with epoxidized soybean oils under supercritical conditions (120 °C, 100 bar) before complete characterization by FTIR, 1H NMR, and electrospray ionization mass spectroscopy (ESI-MS). In a second step, biobased NIPUs were produced by melt-blending of the so-produced cyclocarbonated oil with the biobased aminated derivatives. The thermal and mechanical properties of resulting polymers were found to be depending on the cyclocarbonated vegetable oil/amine ratio. More precisely, short diamines and CSBO led to the formation of cross-linked NIPUs, and the resulting tensile and thermal properties were poor. In contrast, elastomeric NIPUs derived f...
TL;DR: In this paper, a range of acrylate and acrylamide polymers were produced using the PET-RAFT polymerization technique with zinc tetraphenylporphyrin (ZnTPP) as photoredox catalyst.
Abstract: The production of a range of acrylate and acrylamide polymers in completely open reaction vessels has been achieved utilizing the PET-RAFT polymerization technique with zinc tetraphenylporphyrin (ZnTPP) as photoredox catalyst. Polymerization was conducted under extremely mild reaction conditions; low-intensity yellow light, ambient temperatures, and dimethyl sulfoxide (DMSO) as solvent were used. The resulting polymers display characteristics typical of RAFT polymerization, with narrow molecular weight distributions (typically, Đ < 1.10) and controlled molecular weights. One of the advantages of performing PET-RAFT using ZnTPP is the possibility to polymerize monomer in open vessels (i.e., in the presence of oxygen). Oxygen tolerance in DMSO was investigated and attributed to energy transfer from ZnTPP to oxygen to generate singlet oxygen. The effect of changing catalyst concentration and light intensity in these systems has been investigated. Extension of this polymerization technique to a flow system ha...
TL;DR: In this article, reinforced silica-epoxy vitrimer nanocomposites have been made in a solvent-free, easily processable, and economical way with filler contents up to 40 wt %.
Abstract: Reinforced silica–epoxy vitrimer nanocomposites have been made in a solvent-free, easily processable, and economical way with filler contents up to 40 wt %. Increasing silica content leads to higher modulus materials in both glassy and rubbery regions. These nanocomposites are insoluble like permanent cross-linked networks but can completely relax stresses by thermoactivated exchange reactions that rearrange the network topology. Furthermore, the surface functionalization of particles improves the dispersion of fillers and accelerates the relaxation process. Similar results were obtained with industrial precipitated silica, which would allow vitrimer nanocomposites to be produced on an industrial scale.
TL;DR: In this paper, the effects of EG content, temperature, and catalyst concentration on EG-assisted transesterification-type bond exchange reaction (BER) are investigated, and it is found that the amount of EG can be adjusted to tune the solution/solid transformation.
Abstract: Covalent adaptable networks (CANs; also known as dynamic covalent networks or vitrimers) are appealing for developing simple and efficient techniques for recycling thermosetting polymers. In this paper, ethylene glycol (EG) is used as a solvent to enable pressure-free surface welding, surface repair, and recycling of a malleable epoxy where the transesterification-type bond exchange reaction (BER) imparts a dynamic nature to the covalent network. At a high temperature, the EG molecules participate in the BER, leading to dissolution of the epoxy network. If the EG is allowed to evaporate, the dissolved epoxy can re-form into a solid. The effects of EG content, temperature, and catalyst concentration on EG-assisted BERs are investigated. It is found that the amount of EG can be adjusted to tune the solution/solid transformation: An excessive amount of EG is required to dissolve the epoxy; on the other hand, a shortage of EG can shift the reaction back to re-form the polymer. Furthermore, the catalyst concen...
TL;DR: In this article, the relationship between glass transition and ionic conductivity of an amorphous crosslinked polymer electrolyte membrane (PEM) was examined based on ion-dipole complexation between dissociated lithium cations and ether oxygen of poly(ethylene glycol diacrylate) and plasticization by succinonitrile (SCN).
Abstract: The relationship between glass transition (Tg) and ionic conductivity (σ) of an amorphous crosslinked polymer electrolyte membrane (PEM) was examined based on ion–dipole complexation between dissociated lithium cations and ether oxygen of poly(ethylene glycol diacrylate) and plasticization by succinonitrile (SCN). In a binary PEM consisting of a lithium salt/polymer network, Tg increased due to a strong ion–dipole interaction, whereas σ declined due to lower ion mobility coupled to reduced chain mobility. Above the threshold salt concentration of 7 mol %, dual loss tangent peaks were observed in dynamic mechanical studies, which may be ascribed to segmental relaxations of ion–dipole complexed networks and that of polymer chains surrounding the undissociated lithium salt acting like “fillers”. Upon SCN plasticization, these two peaks merged into one that was further suppressed below Tg of the pure network, whereas σ improved to the superionic conductor level. The role of plasticization on the ionic conduct...
TL;DR: This Perspective presents a pedagogical introduction to an improved version of the open-source Polymer Self-Consistent Field (PSCF) software package and of the underlying theory, and discusses methods for generating robust initial guesses for the fields that are computed in SCFT.
Abstract: Self-consistent field theory (SCFT) is a powerful tool for the design and interpretation of experiments on block polymer materials In this Perspective, we lower the barrier to entry to the use of SCFT by experimental groups by two means First, we present a pedagogical introduction to an improved version of the open-source Polymer Self-Consistent Field (PSCF) software package and of the underlying theory Second, we discuss methods for generating robust initial guesses for the fields that are computed in SCFT To demonstrate our approach, we present two case studies in which a typical desktop computer has been used to simulate the structure of (i) body-centered cubic, face-centered cubic, A15, and Frank–Kasper σ sphere-forming phases of a diblock copolymer melt and (ii) two core–shell morphologies of ABAC tetrablock terpolymers A companion Web site provides all of the relevant software and detailed instructions for reproducing all results contained herein
TL;DR: In this paper, a model system based on epoxidized natural rubber is presented which enables to differentiate and quantify the part of each process, including stress relaxation, swelling experiments, and adhesion measurements.
Abstract: To get intrinsic adhesion or healing properties in a cross-linked rubber, two levers are possible: the inherent relaxation in permanently but lightly cross-linked elastomers or the relaxation due to exchange reactions as recently reported in the case of vitrimers. The former is associated with dangling chain motion and cannot be controlled. Lightly cross-linked rubbers may show interesting adhesion and healing properties, but at the expense of mechanical properties: ultimate properties are limited, and materials are subjected to creep even at low temperature. Conversely, exchange reactions may be triggered by temperature, providing the healable materials with strong elastomeric properties in a wide temperature range. Here a model system based on epoxidized natural rubber is presented which enables to differentiate and quantify the part of each process. A comparative study including stress relaxation, swelling experiments, and adhesion measurements highlights the advantages of the vitrimer chemistry on inh...
TL;DR: In this paper, the authors propose a theoretical framework for dealing with a transient polymer network undergoing small deformations, based on the rate of breaking and reforming of network cross-links and the evolving elastic reference state.
Abstract: We propose a theoretical framework for dealing with a transient polymer network undergoing small deformations, based on the rate of breaking and reforming of network cross-links and the evolving elastic reference state. In this framework, the characteristics of the deformed transient network at microscopic and macroscopic scales are naturally unified. Microscopically, the breakage rate of the cross-links is affected by the local force acting on the chain. Macroscopically, we use the classical continuum model for rubber elasticity to describe the structure of the deformation energy, whose reference state is defined dynamically according to when cross-links are broken and formed. With this, the constitutive relation can be obtained. We study three applications of the theory in uniaxial stretching geometry: for the stress relaxation after an instantaneous step strain is imposed, for the stress overshoot and subsequent decay in the plastic regime when a strain ramp is applied, and for the cycle of stretching ...
TL;DR: In this paper, a quaternized chitosan (QCh) was homogeneously synthesized by homogeneous reaction with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in alkali/urea aqueous solution.
Abstract: Quaternized chitosan (QCh) was homogeneously synthesized by reacting chitosan with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in alkali/urea aqueous solution for the first time. The structure and solution properties of QCh were characterized by using element analysis, FT-IR, 13C NMR, SEC-LLS, rheology, viscometer, and ξ-potential measurements. Subsequently, polyelectrolyte complex (PEC) hydrogels were constructed by in situ polymerization of acrylic acid (AA) monomers in the concentrated QCh solution. The structure and mechanical behavior of the prepared hydrogels were systematic studied. Because of the high charge density and solubility of QCh, strong electrostatic interactions were formed in the hydrogels and endowed them tough with self-recovery properties. The mechanical behavior of the hydrogels was accurately tuned from stiff and viscoelastic to soft and elastic by changing the poly(acrylic acid) (PAA) content. The regulation mechanism relied on the remarkable difference in the chai...
TL;DR: In this article, a carboxylic acid functional trimer made from the reaction of isosorbide with maleic anhydride was used to cross-link epoxidized sucrose soyate (ESS), resulting in bio-based, degradable thermosets having a good combination of hardness and flexibility.
Abstract: A carboxylic acid functional trimer made from the reaction of isosorbide with maleic anhydride was used to cross-link epoxidized sucrose soyate (ESS), resulting in bio-based, degradable thermosets having a good combination of hardness and flexibility. This work addresses some critical needs for thermosets such as improving the sustainability of raw materials, enabling recycling, and achieving both good material hardness and flexibility/ductility simultaneously. In this paper, a dicarboxylic acid, MI, was synthesized from isosorbide and maleic anhydride and characterized in detail by FTIR and 1H NMR. It was utilized to cross-link ESS without using extra catalyst or toxic compounds except for ethanol and water. For comparison, a dicarboxylic acid from 1,3-propanediol and maleic anhydride (MP) was also synthesized and used to cross-link ESS. Because of the carbon–carbon double bond in conjugation with the carboxylic acid group, both MI and MP showed high reactivity toward ESS and could cross-link ESS with th...
TL;DR: In this article, a series of polymers with an insulating backbone and varying ratios of 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide as a pendant TADF unit are reported.
Abstract: Materials that display thermally activated delayed fluorescence (TADF) have recently been identified as the third generation emitters for organic light-emitting diodes (OLEDs). However, there are only a few reported examples of polymeric TADF materials. This study reports a series of polymers with an insulating backbone and varying ratios of 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide as a pendant TADF unit. Steady-state and time-resolved fluorescence spectroscopic data confirm the efficient TADF properties of the polymers. Styrene, as a comonomer, is shown to be a good dispersing unit for the TADF groups, by greatly suppressing the internal conversion and triplet–triplet annihilation. Increasing the styrene content within the copolymers results in relatively high triplet energy, small energy splitting between the singlet and triplet states (ΔEST), and a strong contribution from delayed fluorescence to the overall emission. Green emitting OLED devices employing these polymers as spin-coated emi...
TL;DR: In this article, a polythiophene derivative (PBDD4T) was used to increase the rotation barrier and stabilize its backbone conformation by introducing fluorine into the β- and β-position of the α-linked bithiophene segments.
Abstract: Here, taking a polythiophene derivative (PBDD4T) as a starting polymer, we tried to increase the rotation barrier and hence stabilize its backbone conformation by introducing fluorine into the β- and β′-position of the α-linked bithiophene segments and then synthesized a new polymer named as PBDD4T-2F. Our results demonstrate that the rotation barrier between the α-linked bithiophene significantly increases after the fluorination, so PBDD4T-2F has a more stable backbone conformation than PBDD4T. Compared to PBDD4T, PBDD4T-2F shows stronger aggregation effect in solution state and more compact π–π stacking in solid thin film and also possesses deeper HOMO level. These properties make PBDD4T-2F being an ideal donor material in PSCs. When blended with PC71BM, a fullerene acceptor, the PBDD4T-2F-based device showed a power conversion efficiency (PCE) of 9.04%, which is 38% higher than that of the PBDD4T-based device; when blended with ITIC, a non-fullerene acceptor, the PBDD4T-2F-based device showed a PCE of ...
TL;DR: In this article, a conjugated microporous polymer based on a BODIPY dye (CMPBDP) was designed and synthesized, which has shown excellent luminescence properties and an efficient heterogeneous photocatalytic activity.
Abstract: Here we report the design and synthesis of a new conjugated microporous polymer based on a BODIPY dye (CMPBDP) which has shown excellent luminescence properties and an efficient heterogeneous photocatalytic activity. CMPBDP shows high thermal stability and high surface area with microporous size and efficiently catalyzes the selective oxidation of thioanisole into the corresponding sulfoxide via singlet oxygen under visible light (up to 500 nm). The photocatalytic rate of the heterogeneous materials is 4-fold faster that the corresponding soluble (used as reference) under the same reaction conditions and can be reused several times.
TL;DR: The relationship between the morphology and ionic conductivity of block copolymer electrolytes over a wide range of salt concentrations for the system polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) was explored in this article.
Abstract: We explore the relationship between the morphology and ionic conductivity of block copolymer electrolytes over a wide range of salt concentrations for the system polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI). Two SEO polymers were studied, SEO(16–16) and SEO(4.9–5.5), over the salt concentration range r = 0.03–0.55. The numbers x and y in SEO(x–y) are the molecular weights of the blocks in kg mol–1, and the r value is the molar ratio of salt to ethylene oxide moieties. Small-angle X-ray scattering was used to characterize morphology and grain size at 120 °C, differential scanning calorimetry was used to study the crystallinity and the glass transition temperature of the PEO-rich microphase, and ac impedance spectroscopy was used to measure ionic conductivity as a function of temperature. The most surprising observation of our study is that ionic conductivity in the concentration regime 0.11 ≤ r ≤ 0.21 increases in SEO electrolyte...