Search

Theoretical analysis of the kinetic scheme describing formation and randomization of a binary copolymer due to end‐group interchange reactions is presented. Compact analytical expressions are obtained for the transient and equilibrium values of the copolymer degree of blockiness and fractions of active end‐groups of different types. The resulting copolymer is described by the first‐order Markov statistics, which can be rather far from the Bernoullian one. Its structure is determined by the composition of the system and a single combination of the rate constants of four elementary reactions. The kinetics includes fast and slow stages with characteristic time periods independent of and proportional to the average polymerization degree, respectively. During the fast stage, the initial polymers disappear, whereas the copolymer degree of blockiness is still very low. The distribution of units in the copolymer is Markovian, only if the initial polymers possess the most probable molar mass distributions. At the slow stage copolymer randomization gradually progresses, whereas the distribution of end groups may change in the opposite direction compared to the fast stage. The results can be used to analyze the experimental data on the chain structure of condensation, metathesis, and dynamic covalent polymers, where interchange reactions play a significant role. [ABSTRACT FROM AUTHOR]

Droplet digital polymerase chain reaction (ddPCR) technology has attracted considerable attention in recent years. A multiblock surfactant based on perfluompolyethers (PFPE) has been widely used in droplet-based microfluidics and is known to provide high droplet stability and biocompatibility. We developed a multiblock copolymer surfactant synthesized by adjusting the proportions of the intermediates to enhance the stabilities of droplets at high temperatures. The surfactants were synthesized via amidation reactions that coupled the PFPE and diamine polyethylene glycol (PEG), and the introduction of triethylamine, as a catalyst, made the reaction more efficient. The assynthesized surfactants were used to generate water-in- fluorocarbon (W/F) droplets with a microfluidic device and a ddPCR device was used to evaluate the performance of the droplets. When the molar ratio (PFPE-PEG:PFPE-PEGPFPE) was 2:1 and the concentration reached 2 wt%, the droplets showed good thermal stability. Surfactant showed the best performance, lowering the interfacial tension to 2.5 mN/m, when it's critical micelle concentration (CMC) exceeded 50 mg/L. Furthermore, the use of an alkaline solution (pH = 9-10) as the washing buffer, improved the biocompatible of the surfactant. When applied to the detection of DNA, the limit of detection was 0.52 copies/µL. The as-synthesized surfactants showed promise in generating biocompatible and thermally stable droplets and providing a new surfactant option for future ddPCR technology. [ABSTRACT FROM AUTHOR]

The synthesis of polymers with high molecular weights, controlled sequence, and tunable dispersities remains a challenge. A simple and effective visible‐light controlled photoiniferter reversible addition‐fragmentation chain transfer (RAFT) polymerization is reported here to realize this goal. Key to this strategy is the use of switchable RAFT agents (SRAs) to tune polymerization activities coupled with the inherent highly living nature of photoiniferter RAFT polymerization. The polymerization activities of SRAs were in situ adjusted by the addition of acid. In addition to a switchable chain‐transfer coefficient, photolysis and polymerization kinetic studies revealed that neutral and protonated SRAs showed different photolysis and polymerization rates, which is unique to photoiniferter RAFT polymerization in terms of dispersity control. This strategy features no catalyst, no exogenous radical source, temporal regulation by visible light, and tunable dispersities in the unprecedented high molecular weight regime (up to 500 kg mol−1). Pentablock copolymers with three different dispersity combinations were also synthesized, highlighting that the highly living nature was maintained even for blocks with large dispersities. Tg was lowered for high‐dispersity polymers of similar MWs due to the existence of more low‐MW polymers. This strategy holds great potential for the synthesis of advanced materials with controlled molecular weight, dispersity and sequence. [ABSTRACT FROM AUTHOR]

Anion exchange membrane fuel cells (AEMFCs) and water electrolysis (AEMWE) show great application potential in the field of hydrogen energy conversion technology. However, scalable anion exchange membranes (AEMs) with desirable properties are still lacking, which greatly hampers the commercialization of this technology. Herein, we propose a series of novel multiblock AEMs based on ether‐free poly(biphenyl ammonium‐b‐biphenyl phenyl)s (PBPA‐b‐BPPs) that are suitable for use in high performance AEMFC and AEMWE systems because of their well‐formed microphase separation structures. The developed AEMs achieved outstanding OH− conductivity (162.2 mS cm−1 at 80 °C) with a low swelling ratio, good alkaline stability, and excellent mechanical durability (tensile strength >31 MPa and elongation at break >147 % after treatment in 2 M NaOH at 80 °C for 3750 h). A PBPA‐b‐BPP‐based AEMFC demonstrated a remarkable peak power density of 2.41 W cm−2 and in situ durability for 330 h under 0.6 A cm−2 at 70 °C. An AEMWE device showed a promising performance (6.25 A cm−2 at 2 V, 80 °C) and outstanding in situ durability for 3250 h with a low voltage decay rate (<28 μV h−1). The newly developed PBPA‐b‐BPP AEMs thus show great application prospects for energy conversion devices. [ABSTRACT FROM AUTHOR]

Multiblock copolymers are envisioned as promising materials with enhanced properties and functionality compared with their diblock/triblock counterparts. However, the current approaches can construct multiblock copolymers with a limited number of blocks but tedious procedures. Here, we report a thioester‐relayed in‐chain cascade copolymerization strategy for the easy preparation of multiblock copolymers with on‐demand blocks, in which thioester groups with on‐demand numbers are built in the polymer backbone by controlled/living polymerizations. These thioester groups further serve as the in‐chain initiating centers to trigger the acyl group transfer ring‐opening polymerization of episulfides independently and concurrently to extend the polymer backbone into multiblock structures. The compositions, number of blocks, and block degree of polymerization can be easily regulated. This strategy can offer easy access to a library of multiblock copolymers with ≈100 blocks in only 2 to 4 steps. [ABSTRACT FROM AUTHOR]

The present study describes the successful synthesis of –COOH functionalized carbon nanodots (f‐CNDs) via pyrolysis of citric acid and 4,4′‐bis(4‐hydroxyphenyl)valeric acid (DPA‐OH, Sigma Aldrich, St. Louis, Missouri, United States) based hydrophilic oligomer at 250 °C. The multiblock copolymers were prepared by a coupling reaction between phenoxide terminated valeric acid based poly(arylene ether ketone) (DPA‐OH) hydrophilic oligomer and decafluorobiphenyl (DFBP, Alfa Aesar, Haverhill, Massachusetts, United States) end‐capped poly(arylene ether sulfone) (BP‐X‐F) hydrophobic oligomers (where X is 6, 9 and 12). Multiblock poly(arylene ether ketone sulfone) copolymer crosslinked membranes were prepared using 6F‐bisphenol‐A based novolac epoxy resin (EFN) and –COOH functionalized multiwalled carbon nanotubes/functionalized carbon nanodots (f‐MWCNTs/f‐CNDs, Nanoshell company, Utah, U. S) were used for the preparation of acid doped composite membranes for fuel cell applications. From high resolution TEM images, the average size of the prepared f‐CNDs found to be ca 10–12 nm. The N1 multiblock copolymer membrane with loading of 0.9 wt% ratio of CNTs showed better proton exchange membrane related properties such as proton conductivity (0.136 S cm−1), ion exchange capacity (1.18 meq g−1) and selectivity ratio (0.17) compared to the prepared pristine, crosslinked and CND based composite membranes. The overall results revealed that the composite membranes with loading of 0.9 wt% of CNTs and CNDs exhibited a superior combination of fuel cell related properties such as higher proton conductivity, high dimensional and oxidative stability and low methanol permeability and also showed better fuel cell performance compared to the respective pristine and EFN crosslinked membranes. © 2022 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

Poly(diallyldimethylammonium chloride) (PDADMAC) is a useful material due to its high charge density and alkaline stability, but its hydrophilic nature limits applications to those where the dissolved polymer is appropriate. To make polymers suitable for applications as films and membranes containing the diallyldimethylammonium moiety, multiblock copolymers of polyaramides (PA) and polyimides (PI), materials known for their excellent physical properties and stabilities, were synthesized. Aminophenyl difunctionalized PDADMAC oligomers were synthesized using a disulfide iniferter then counterion exchanged to the hexafluorophosphate anion to produce telechelic oligomers with good solubility in polar aprotic solvents. The oligomers were reacted in situ with the proper difunctional monomers to produce PA, polyetheraramides, PI, and polyetherimides. All the classes of copolymers were synthesized over a range of compositions at high yield and material properties were demonstrated to be a result of both the backbone chemistry and the composition. Several of the synthesized copolymers formed films with good clarity, strength, and flexibility. The copolymers containing ether linkages had increased backbone flexibility and demonstrated better film‐forming properties. The multiblock copolyaramides and copolyimides demonstrate a method to produce materials with excellent thermal stability and good strength and flexibility, making them uniquely capable of serving as water insoluble, cationic films, and membranes. [ABSTRACT FROM AUTHOR]

Novel proton-conducting hybrid membranes consisting of sulfonated multiblock copolymer of polysulfone and polyphenylsulfone (SPES) reinforced with a HKUST-1 metal-organic framework (MOF) (5, 10, and 20 wt. %) were prepared and characterized for fuel cell applications. The presence of the MOF in the copolymer was confirmed by means of FE-SEM and EDS. The hybrid membranes show a lower contact angle value than the pure SPES, in agreement with the water uptake (WU%), i.e., by adding 5 wt. % of the MOF, this parameter increases by 20% and 40% at 30 °C and 60 °C, respectively. Additionally, the presence of the MOF increases the ion exchange capacity (IEC) from 1.62 to 1.93 mequivH+ g−1. Thermogravimetric analysis reveals that the hybrid membranes demonstrate high thermal stability in the fuel cell operation temperature range (<100 °C). The addition of the MOF maintains the mechanical stability of the membranes (TS > 85 MPa in the Na+ form). Proton conductivity was analyzed using EIS, achieving the highest value with a 5 wt. % load of the HKUST-1. This value is lower than that observed for the HKUST-1/Nafion system. However, polarization and power density curves show a remarkably better performance of the hybrid membranes in comparison to both the pure SPES and the pure Nafion membranes. [ABSTRACT FROM AUTHOR]

The effect of spatial dimension on the stability of hierarchical nanostructures with different mid‐thin layer k in A(BC)2B multi‐block copolymer are studied using self‐consistent field theory. For the 1D hierarchical lamellae (HL), larger χBC and smaller χAB favor the HL with less k. However, hierarchical cylinders (HC) with more mid‐thin layers are stable at larger χBC. A scaling theory based on the analysis of the single‐chain B/C interfacial energy suggests that the 2D HC phase with more k has a lower single‐chain interfacial energy due to the effect of spatial dimension. Furthermore, the 3D hierarchical gyroid (HG) phase shows the universal behavior based on the scaling analysis; larger χBC leads to the stability of HG with more mid‐thin layers. [ABSTRACT FROM AUTHOR]

Novel proton-conducting hybrid membranes consisting of sulfonated multiblock copolymer of polysulfone and polyphenylsulfone (SPES) reinforced with a HKUST-1 metal-organic framework (MOF) (5, 10, and 20 wt. %) were prepared and characterized for fuel cell applications. The presence of the MOF in the copolymer was confirmed by means of FE-SEM and EDS. The hybrid membranes show a lower contact angle value than the pure SPES, in agreement with the water uptake (WU%), i.e., by adding 5 wt. % of the MOF, this parameter increases by 20% and 40% at 30 °C and 60 °C, respectively. Additionally, the presence of the MOF increases the ion exchange capacity (IEC) from 1.62 to 1.93 mequivH+ g−1. Thermogravimetric analysis reveals that the hybrid membranes demonstrate high thermal stability in the fuel cell operation temperature range ( 85 MPa in the Na+ form). Proton conductivity was analyzed using EIS, achieving the highest value with a 5 wt. % load of the HKUST-1. This value is lower than that observed for the HKUST-1/Nafion system. However, polarization and power density curves show a remarkably better performance of the hybrid membranes in comparison to both the pure SPES and the pure Nafion membranes.

At selective liquid–liquid interface, amphiphilic homopolymers, having groups with different affinity for the liquids in each monomer unit, would demonstrate higher occupation of the interfacial layer than copolymers with various distributions of groups and be advantageous as interface stabilizers. By means of Langevin dynamics computer simulation, conformations of multiple chains of amphiphilic macromolecules adsorbed at the liquid–liquid interface were studied. Monomer units having different affinity for the liquids were distributed variously along the polymer chains. Homopolymers, amphiphilic at the level of an individual monomer unit, and copolymers with random, altermating and multiblock distribution of groups were considered. The surface coverage, structure of the layer, and spatial distribution of monomer units were investigated depending on the polymer concentration. Compared to copolymers with random, alternating and multiblock distributions of the groups, the interfacial layer concentration of amphiphilic homopolymer is about 1.5 times higher, the adsorbed layer is remarkably thinner, has membrane-like structure and is asymmetric with respect to interface boundary. Also, the adsorbed amphiphilic homopolymers form fewer loops and tails, most located on one side of the interface. This combination of properties is promising for practical application in modern self-assembling molecular devices. [ABSTRACT FROM AUTHOR]

Thermotropic liquid crystalline polymers (LCPs) have been of great interest for electronic packaging. Herein, we introduce a series of wholly aromatic, thermotropic LCPs from copoly(ester amide)s of 6-hydroxy-2-naphthalic acid, isophthalic acid, terephthalic acid, and 4-aminophenol, prepared by a convenient one-pot melt polycondensation. Almost synthesized copoly(ester amide)s exhibited good solubility in common organic solvents at room temperature. Furthermore, they possessed high thermal stability with 2% degradation temperatures (Tid) of 359–368 °C and the char yields (at 600 °C) of 50.3–55.6%. The synthesized copoly(ester amide)s had relatively low coefficient of thermal expansion (CTE) values, which were 35.85–41.21 ppm °C−1 in the temperature range of 50–200 °C. Furthermore, an annealing process could be employed to improve the thermomechanical properties of synthesized polymers. For instance, the CTE of sample LCP3 in range temperature of 275–315 °C was reduced by more than 90% after annealing at 320 °C for 1 h, implying the feasibility for electronic packaging. [ABSTRACT FROM AUTHOR]

A polymer chain usually contains two or more types of monomeric species from the perspective of polymer chemistry, which poses a challenge to the understanding of structure-property relationships. It is of course true in the field of polymer translocation. In the present work, I investigate the translocation dynamics of heterogeneous flexible polymers composed of two types of monomers labeled A and B through a nanopore assisted by binding particles (BPs) by using the coarse-grained Langevin dynamics simulations in two-dimensional domains. Specifically, multiblock copolymers with different block lengths and monomeric components are considered. I critically examine how the translocation dynamics responds to the variations in the block length and the monomeric content. Interestingly, it is found that the periodic structure of a multiblock copolymer causes an obvious fingerprint feature in the residence time of individual monomers in which the number of peaks is exactly equal to the number of blocks. These findings provide a basic understanding about the sequence-dynamics relationship for the BPs-assisted translocation of heterogeneous flexible polymers. [ABSTRACT FROM AUTHOR]

A poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO) alternating multiblock (AMB) copolymer with various molecular weights was prepared via precipitation fractionation from an acetone/nhexane mixture. The cloud point (Tc) of the aqueous solution of PEO-PPO AMB copolymer decreased as the number-average molecular weight of the sample increased. This phenomenon is generally observed for certain homopolymer systems having a lower critical solution temperature, such as PEO/water and poly(N,N-diethylacrylamide)/water systems. The relationship between the Tc of the solutions and the number of monomer units of the AMB copolymer suggests that the Shultz-Flory theory is applicable to this system. [ABSTRACT FROM AUTHOR]

A multiblock [poly(ethylene oxide)-b-spiro-polystyrene] ([(PEO-b-spiro-PS)]) copolymer with a topologically novel architecture was synthesized using thiol-ene step-growth polymerization reaction. Spiro-PS with dimercapto groups as the hard segment was synthesized in three main steps: (a) preparation of tetra-arm PS by atom transfer radical polymerization and the conversion of the chain-end group to azide functionality, (b) alkyne-azide click coupling reaction to synthesize a tricyclic PS, and (c) tactical ring opening of the tricyclic PS through disulfide/thiol redox reaction. The PEO soft segment was obtained as chain-ends modified with norbornene groups. Finally, the hydrothiolation of the highly reactive norbornene chain-ends of polyethylene glycol with the dimercapto groups of spiro-PS produced the multiblock ([(PEOb-spiro-PS)]) copolymer in quantitative yield. The multiblock copolymer was characterized using size-exclusion chromatography, proton nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

We investigate the structure–property relations of the multiblock copolymers of norbornene with cyclododecene synthesized via the macromolecular cross-metathesis reaction between amorphous polynorbornene and semicrystalline polydodecenamer in the presence of the first-generation Grubbs catalyst. By adjusting the reaction time, catalyst amount, and composition of the initial system, we obtain a set of statistical multiblock copolymers that differ in the composition and average length of norbornene and dodecenylene unit sequences. Structural, thermal, and mechanical characterization of the copolymers with NMR, XRD, DSC (including thermal fractionation by successive self-nucleation and annealing), and rotational rheology allows us to relate the reaction conditions to the average length of crystallizable unit sequences, thicknesses of corresponding lamellas, and temperatures of their melting. We demonstrate that isolated dodecenylene units can be incorporated into crystalline lamellas so that even nearly random copolymers should retain crystallinity. Weak high-temperature endotherms observed in the multiblock copolymers of norbornene with cyclododecene and other cycloolefins could indicate that the corresponding systems are microphase-separated in the melt state.

The thin‐film morphology of stereoregular syndiotactic poly(p‐methylstyrene)–(cis‐1,4‐polybutadiene) (sP(pMS–B)) multiblock copolymers has been investigated using tapping mode atomic force microscopy with variation of the polymer composition and monomer block lengths. The morphology of the thin films ranges from isolated circular domains of sP(pMS) embedded into a matrix of polybutadiene (PB) to isolated domains of PB embedded into a matrix of sP(pMS), passing through bicontinuous (jagged) lamellae when the pMS concentration is in the range 20–67 mol%. Multiple folding of the polymer segments, i.e. where reciprocal inclusions of polymer segments to each other phase are able to generate greater domain, has been postulated and validated by considerations on the polymer architecture and the thermal and crystalline behaviour. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

We propose to extend the well-known Doi–Edwards theory to model the viscosity divergence caused by shear-induced crystallization occurring upon startup flow experiments in segmented block copolymers (M w ¯ = 50 kg mo l − 1). Unlike models such as Convective Constraint Release in which the chain relaxation is accelerated by the shear, we propose to increase the final relaxation time of the polymer within the memory function to take into consideration the progressive association of the hard-segments. To this aim, we make use of the Avrami equation in which we parametrize the crystallization rate to depend on the shear rate in a linear way. In this context and contrary to what is generally proposed for supramolecular polymers, we consider the hard-segments aggregation as an irreversible process (infinite lifetime) due to the crystalline nature and the high-functionality of the resulting topological nodes. The exponential trend of the Avrami process is then validated by stress relaxation experiments performed at different levels of strain. Moreover, the growth mode parameter, usually assigned to the geometry of the crystallites, is found to be independent of the shear rate and in excellent agreement with a previous work in which we investigated the quiescent crystallization of the same system. We finally apply our model to fit data measured at different temperatures, well-confirming the development of hard-segments' crystallites from the very first stages of the isothermal shearing process. [ABSTRACT FROM AUTHOR]

To improve the chemical stability and acid doping levels of proton exchange membranes, a series of sulfonated polybenzimidazole multiblock copolymers containing pyridine rings (sPBI40-b-PyPBI5-b-PIx) was synthesized. All the copolymers exhibited excellent solubility. The proton exchange membranes were prepared using a solvent casting method. All the membranes were characterized by thermal stability, a tension test, chemical stability, dimensional stability, PA-doping ability, and proton conductivity. All of the membranes had good thermal stability, mechanical properties, and dimensional stability. The proton conductivity of sPBI40-b-PyPBI5-b-PI5 (ion exchange capacity, IEC = 1.83 mmol g−1) was 0.018 S cm−1 at 105 °C and 100% relative humidity. The proton conductivity of the sPBI40-b-PyPBI5-b-PI5 membrane with the highest PA uptake (199.8%) reached 0.23 S cm−1 at 180 °C. The high doping level and the proton conductivity were due to the pyridine group which increased the basicity of the copolymer. The chemical stability of the membranes, which was also a consequence of introducing the pyridine group, was better than that of sPBI-b-PI which does not have a pyridine group. This series of block copolymers have a promising application in proton exchange membranes. [ABSTRACT FROM AUTHOR]

Multiblock glycopolymers have gathered attention because of their potential use as effective ligands for sugar‐binding proteins. The authors report the quantitative preparation of multiblock glycopolymers by reversible addition‐fragmentation chain transfer polymerization. The optimized polymerization condition enabled the complete monomer incorporation into the elongating polymer chains at each polymerization step. The structure of the heptablock glycopolymer was well‐defined (polydispersity index <1.35), and their molecular recognition against lectins was evaluated. [ABSTRACT FROM AUTHOR]

Ecofriendly autoxidation is a reaction of air oxygen with unsaturated organic molecules at room temperature. Castor oil and ricinoleic acid were ecofriendly autoxidized for 5 months to obtain castor oil macroperoxide with a Mn of 1935 g mol−1 (Pcast5m) and the ricinoleic acid macroperoxide initiator (Prici5m) with a Mn of 1169 g mol−1. Peroxide groups thermally initiated the free radical polymerization of methyl methacrylate (MMA), n‐butyl methacrylate (nBMA), and styrene (S). Peroxide formation in the oxidized castor oil and ricinoleic acid was confirmed using iodometric analysis, elemental analysis, and differential scanning calorimetry technique. Peroxide decomposition in both macroperoxide initiators was observed at 166 °C for Prici5m and 170 °C for Pcast5m. Hydroxyl groups of Pcast5m were reacted with methacryloyl chloride to obtain methacrylated castor oil macroperoxide (PcastMA). The polymerization rates of the obtained macroinitiators were compared. The polymerization rate order is Pcast5m > Prici5m > PcastMA. Polymerization of styrene by PcastMA resulted in an increase in molar masses and an increase in the polymerization time while those of the styrene polymerization by Pcast5m and Prici5m remained constant. Carboxylic acid groups were reacted with amine‐terminated polyethylene glycol (PEG), polydimethyl siloxane (PDMS), and polytetrahydrofuran (PTHF) while the hydroxyl functionality initiated the ring‐opening polymerization of ε‐caprolactone (CL). Prici‐PEG‐PMMA, Prici‐PS‐PDMS, Prici‐PS‐PTHF, Pcast‐PS‐PCL, Pcast‐PCL‐PMMA, and Pcast‐PS‐PnBMA multiblock copolymers were prepared and characterized using spectrometric, thermal, and stress–strain measurement techniques. [ABSTRACT FROM AUTHOR]

The effect of relative humidity (RH) and degree of sulfonation (DS) on the ionic conductivity and water uptake of proton-exchange membranes based on sulfonated multiblock copolymers composed of polysulfone (PSU) and polyphenylsulfone (PPSU) is examined experimentally and numerically. Three membranes with a different DS and ion-exchange capacity are analyzed. The heterogeneous structure of the membranes shows a random distribution of sulfonated (hydrophilic) and non-sulfonated (hydrophobic) domains, whose proton conductivity is modeled based on percolation theory. The mesoscopic model solves simplified Nernst–Planck and charge conservation equations on a random cubic network. Good agreement is found between the measured ionic conductivity and water uptake and the model predictions. The ionic conductivity increases with RH due to both the growth of the hydrated volume available for conduction and the decrease of the tortuosity of ionic transport pathways. Moreover, the results show that the ionic conductivity increases nonlinearly with DS, experiencing a strong rise when the DS is varied from 0.45 to 0.70, even though the water uptake of the membranes remains nearly the same. In contrast, the increase of the ionic conductivity between DS=0.70 and DS=0.79 is significantly lower, but the water uptake increases sharply. This is explained by the lack of microphase separation of both copolymer blocks when the DS is exceedingly high. Encouragingly, the copolymer membranes demonstrate a similar performance to Nafion under well hydrated conditions, which can be further optimized by a combination of numerical modeling and experimental characterization to develop new-generation membranes with better properties.

Multiblock copolymers (MBCs) have garnered considerable interest in both industrial and fundamental polymer science. However, the phase structure and properties at a molecular level of MBCs remain largely unexplored. To address this, the effects of three structural factors (block number index α , interaction strength between hard segments ε H − H , and hard segment stiffness k H) on the phase structure, dynamic properties and mechanical properties of MBCs have been investigated using coarse-grained molecular dynamics (CGMD) simulations. The degree of phase separation, ψ , has been quantified based on the number of neighboring beads designated to measure the phase separation structure. Results indicate that a lower α (longer block chain length), stronger ε H − H , and weaker k H significantly reduce the contacts between soft and hard segments, leading to an increase in ψ. An examination of higher ψ (greater than 0.7) reveals two T g s that converge as ψ decreases and eventually merge into one. Mechanical properties are improved with increasing α at low strains, whilst they change non-monotonically at high strains, likely due to differing contributions of soft and hard segments to the stress. Systems with stronger ε H − H and k H exhibit superior mechanical properties due to their higher non-bonded energy increments and bond orientation. In general, the mode of the variation of phase separation structure, glass transition temperature and mechanical properties of MBCs at the molecular level, has been elucidated valuable insight for the design and synthesis of high-performance MBCs materials. [Display omitted] • Constructing block copolymer models with different block number indices. • A new parameter is defined to characterize the degree of phase separation. • Two glass transition temperatures are obtained for the phase separation system. • Investigating the change of mechanical properties and revealing the mechanism. [ABSTRACT FROM AUTHOR]

Hydrogen, a zero-emissions fuel, is increasingly being targeted as a source of renewable energy. However, hydrogen production by electrolysis is limited by the characteristics of the hydrogen-separating membrane. Here, a series of multiblock copolymers composed of a hydrophilic block based on disulfonated bis(phenyulfonylphenyl) sulfone groups, and a hydrophobic block based on bis(p -phenoxyphenyl) ether groups is developed for application as a proton exchange membrane for water electrolysis. The multiblock copolymers combining stiff hydrophilic block and flexible hydrophobic block are expected to have reduced water swelling and low hydrogen permeability even under full-wet and high-temperature conditions in water electrolysis. Microscopy and X-ray scattering analyses of the multiblock copolymer-based membranes reveal strong nanophase separation and well-developed ion transport channels. The as-synthesized membranes exhibit advantages including low swelling, high proton conductivity, good mechanical and thermal properties, high oxidative stability, and reduced hydrogen permeability. A membrane electrode assembly employing the multiblock copolymer membrane achieved a current density above 3 A cm−2 at 1.8 V, far surpassing that of Nafion 212, and a long-term operating stability exceeding 500 h, demonstrating the suitability of the membrane for practical water electrolysis. • The ion exchange capacity and molecular weights of multiblock copolymers are tuned. • Strong nanophase separation and well-developed ion transport channels are observed. • The membranes show high proton conductivity and low hydrogen permeability. • The inclusion of sulfone linkages contributes to enhanced stability. • The optimal membrane outperforms Nafion 212, operating stably for >500 h. [ABSTRACT FROM AUTHOR]

The cross-metathesis of polynorbornene and polyoctenamer in d-chloroform mediated by the 1st generation Grubbs’ catalyst Cl2(PCy3)2Ru=CHPh is studied by monitoring the kinetics of carbene transformation and evolution of the dyad composition of polymer chains with in situ 1H and ex situ 13C NMR spectroscopy. The results are interpreted in terms of a simple kinetic two-stage model. At the first stage of the reaction all Ru-benzylidene carbenes are transformed into Ru-polyoctenamers within an hour, while the polymer molar mass is considerably decreased. The second stage actually including interpolymeric reactions proceeds much slower and takes one day or more to achieve a random copolymer of norbornene and cyclooctene. Its rate is limited by the interaction of polyoctenamer-bound carbenes with polynorbornene units, which is hampered, presumably due to steric reasons. Polynorbornene-bound carbenes are detected in very low concentrations throughout the whole process thus indicating their higher reactivity, as compared with the polyoctenamer-bound ones. Macroscopic homogeneity of the reacting media is proved by dynamic light scattering from solutions containing the polymer mixture and its components. In general, the studied process can be considered as a new way to unsaturated multiblock statistical copolymers. Their structure can be controlled by the amount of catalyst, mixture composition, and reaction time. It is remarkable that this goal can be achieved with a catalyst that is not suitable for ring-opening metathesis copolymerization of norbornene and cis-cyclooctene because of their substantially different monomer reactivities.

A multiblock copolymer termed as PCL-PIBMD, consisting of crystallizable poly(ε-caprolactone) (PCL) segments and crystallizable poly(3S-isobutyl-morpholine-2,5-dione) (PIBMD) segments, has been reported as a material showing a thermally-induced shape-memory effect. While PIBMD crystalline domains act as netpoints to determine the permanent shape, both PCL crystalline domains and PIBMD amorphous domains, which have similar transition temperatures (Ttrans) can act as switching domains. In this work, the influence of the deformation temperature (Tdeform = 50 or 20°C), which was above or below Ttrans, on the structural changes of PCL-PIBMD during uniaxial deformation and the shapememory properties were investigated. Furthermore, the relative contribution of crystalline PCL and PIBMD amorphous phases to the fixation of the temporary shape were distinguished by a toluene vapor treatment approach. The results indicated that at 50°C, both PCL and PIBMD amorphous phases can be orientated during deformation, resulting in thermallyinduced crystals of PCL domains and joint contribution to the switching domains. In contrast at 20°C, the temporary shape was mainly fixed by PCL crystals generated via strain-induced crystallization.

The ability to control the micelle size of poly(lactic acid) and poly(ethylene glycol) (PLA–PEG) block copolymers is important for controlling their circulation in blood cell recognition, drug release and therapeutic effects. We successfully controlled the micelle size by changing the block number of copolymers (multiblock index). PLA–PEG multiblock copolymers with multiblock indexes ranging from 1.35 to 2.78 were synthesized by direct polycondensation with tin chloride/p-toluenesulfonic acid binary catalysts, using PEG with a molecular weight (Mw) of 3200 Da. The Mw of PLA–PEG copolymers increased with an increase in the multiblock index, while micelle size, measured by dynamic light scattering, decreased greatly from 349 to 28 nm. In addition, the X-ray diffraction peak of the PLA crystal disappeared when the multiblock index was increased. These results indicate that a multiblock structure is useful for controlling micelle size without changing the PLA/PEG composition or PEG molecular weight, which strongly influences other micelle features.

Abstract: The polyamide‐6 based poly(ether‐block‐amide) (PEBA) multiblock copolymers were reactively prepared in typical processing equipment, torque rheometer. The reactive processing conditions of PEBA were discussed in details on the base of the tensile strength as the main quantization parameter and the torque rheological curves. The optimized reaction temperature, reaction time, and rotational speed were 150°C, 10 min, and 40 rpm respectively. The chemical structure, tensile properties, thermal transition, thermal stability, water absorption, and solubility in organic solvents of PEBA prepared in optimized reaction conditions were characterized by Fourier transform infrared spectroscopy, tensile testing, differential scanning calorimetry, thermogravimetric analysis, and soaking testing in water and organic solvents. The tensile strength and elongation at break of PEBA are 35.9 MPa and 580% respectively. The glass transition temperature and melting temperature of soft segment of PEBA are −50 and 15°C, respectively; the glass transition temperature and melting temperature of hard segment of PEBA are 50 and 140°C respectively. Meanwhile, the PEBA has low water absorption, robust organic solvent resistance, and good thermal stability. The optimization process of PEBA will give the deep understanding of reactive processing of polymer materials. [ABSTRACT FROM AUTHOR]

We present here the application of in situ cascade polycondensation-coupling ring-opening polymerization (PROP) method for the facile synthesis of a series of three-component poly(butylene terephthalate)- block -poly(ethylene oxide)- block -poly(propylene oxide)- block -poly(ethylene oxide) multiblock terpolymers (PBT- b -PEO- b -PPO- b -PEO- b -PBT) n , using cyclic oligo(butylene terephthalate)s (COBTs) as monomers and dihydroxyl end-functional PEO- b -PPO- b -PEO (EPE) as macroinitiator. The structure details of these copolymers were characterized by 1 H- 1 H gCOSY and 1 H- 13 C gHSQC NMR spectra. With the assignment of multiblock chain ends, block segmental ends and corresponding groups for each segment, the number-average molecular weights for multiblock terpolymers and each block segment were estimated by the quantitative 1 H NMR spectra. Polymerization kinetics studies confirm the PROP mechanism. With crystalline PBT and PEO segments, the multiblock terpolymers are double-crystalline polymers, where the melting point and crystallinity of PBT and PEO segments increase with corresponding PBT and PEO content, respectively. The covalent linking of PBT segments with PEO segments leads to the confined crystallization environment for both blocks, where a strong depression on melting point of PEO crystals was observed, which becomes amorphous at an EPE triblock content of 50%. TEM and SAXS results show interesting lamella-like microphase separation morphologies in these multiblock terpolymers. [ABSTRACT FROM AUTHOR]