Rubbery Block Research Articles

Functionalization of rubbery domains in SBS triblock copolymers for anion exchange membrane applications with enhanced robustness

A series of anion exchange membranes (AEMs) based on hydrogenated poly (styrene-b-butadiene-b-styrene) (h-SBS) triblock copolymers were prepared via thiol-ene click reaction of the mid-block polybutadiene with 6-mercapto-1-hexanol, followed by hydrogenation of the remaining double bonds, direct bromination of the pendant alcohol group, and substitution of with trimethylamine (TMA). The thiol-ene click reaction provided a facile and effective control of degree of functionalization up to 50 mol% of total CC bonds in the polymer. Membrane properties of the TMA-functionalized h-SBS for AEM applications were investigated by measuring ion exchange capacity (IEC), water uptake, and ion conductivity. h-SBS-TMA-1.83 with 24% degree of functionalization of polybutadiene block exhibited an IEC of 1.83 mequiv./g and the highest hydroxide ion conductivity of 93 mS/cm at 80 °C. IEC and hydroxide ion conductivity of all h-SBS AEMs were preserved after treatment with aq. 1 M NaOH solution at 80 °C for 4 weeks, demonstrating good alkaline stability. The h-SBS AEMs with quaternary ammonium groups tethered to the rubbery polybutadiene block of SBS showed better mechanical properties, lower water uptake, less water swelling under humidified conditions, and higher and more stable hydroxide conductivity at 80 °C than the ones tethered to the rigid polystyrene block of hydrogenated SBS AEMs. These results suggest that ionic group functionalization at the rubbery block of SBS provides mechanically more robust AEMs and is better AEM material design than that of glassy block functionalized AEM.

Understanding Interfacial Block Copolymer Structure and Dynamics

Block copolymer (BCP) structure and dynamics were studied using small-angle neutron scattering (SANS), neutron spin echo (NSE) spectroscopy, and molecular dynamics (MD) simulations to obtain a fundamental understanding of the impact of an interfacial block on chain dynamics. A glassy block acted as the interface, and the dynamics of a rubbery block was studied. The rubbery block was protonated near the interface in one sample and near the chain end in another sample to observe the interfacial effect on the rubbery polymer. Analysis of the structure and dynamics revealed that the interfacial rubbery block was confined in layered morphologies and exhibited much slower dynamics than the chain-end rubbery block that was dispersed in the rubbery matrix. The interfacial rubbery block showed weaker dynamical relaxation than that at the chain end, and it also had critically important length scale dependence. Dynamical slowing was only observed at length scales significantly larger than the characteristic segmental length, and the disparity between interfacial and chain-end dynamics increased with increasing length.

Optimization of the elastic properties of block copolymers using coarse-grained simulation and an artificial neural network

Block copolymers consisting of immiscible glassy and rubbery blocks have microphase-separated structures that result in various elastic properties depending on the polymer structures. However, because the complete simulation approach to surveying a wide variety of polymer and microphase-separated structures is time-consuming, a more efficient approach is required for the design of materials with desired properties. In the present study, we used coarse-grained molecular dynamics (CGMD) simulations and an artificial neural network (ANN) to design polymer structures with the desired stress–strain properties. CGMD simulations were conducted to obtain stress–strain curves of linear diblock and triblock copolymers of various chain lengths, block volume fractions, and asymmetricities. We trained the ANN for regression between the polymer structures and the stress–strain curves. Then, using the trained ANN, we performed Bayesian optimization to obtain a polymer structure with an arbitrary target stress–strain curve. CGMD simulations of the optimized polymer structure produced a stress–strain curve that agreed with the curve predicted by the ANN. Therefore, simulation and use of an ANN are potentially useful strategies for the design of polymer structures with desired properties.

Gas Permeation Properties of Multiwalled Carbon Nanotubes on Polyether Block Amide (Pebax-1657)/Polyethersulfone(PES) Blend Mixed Matrix Membrane for CO<sub>2</sub>/CH<sub>4</sub> Separation

Mixed matrix membrane (MMM), a developing research area, is a membrane formed by incorporating fillers in the polymeric membrane to enhance gas separation performance. In this study, MMMs comprised of blend rubbery block copolymers of polyether block amide (Pebax-1657) with a glassy polyethersulfone (PES) polymer and multi-walled carbon nanotubes (MWCNTs) were synthesized by dry phase inversion method and explored further by gas permeability test. Pebax-1657/PES/MWCNTs membrane resulted in an increased permeability as well as CO2/CH4 selectivity. The Pebax-1657/PES polymer blend MMM with 10wt% of MWCNTs has shown the most superior performance of CO2 permeability, CH4 permeability and CO2/CH4 selectivity in comparison with the pure Pebax-1657 resulted in 66.3% and 11.6% difference respectively.

Fully biobased thermoplastic elastomers: Synthesis of highly branched linear comb poly(β-myrcene)-graft-poly(l-lactide) copolymers with tunable mechanical properties

Biobased thermoplastic elastomers are of interest for their merits, especially renewability and sustainability. In this work, a series of fully biobased linear comb poly(β-myrcene)-graft-poly(l-lactide) (PM-g-PLLA) copolymers consisting of interior rubbery block and exterior semicrystalline block were synthesized via ring-opening polymerization of l-lactide using hydroxylated poly(β-myrcene) as macroinitiator. To evaluate the effects of branch length and graft density of poly(β-myrcene) on the performances of these obtained copolymers, the chemical compositions and molecular weights, crystal structures and spherulite morphologies, phase morphologies, thermal and mechanical properties were systematically analyzed by various techniques. Analysis of NMR and GPC indicated that graft copolymers were successfully obtained as designed. Two distinct glass transitions corresponding to the two building blocks observed from both DMA and DSC measurements suggested the occurrence of microphase separation, which was further confirmed by SAXS and AFM morphological characterizations. Results of DSC, WAXD, and POM showed that the crystallization behavior of the graft copolymers depends on graft density and branch length. Tensile test suggested that the mechanical properties of graft copolymers depend on PM/PLLA composition, particularly graft density and branch length, which could be readily tailorable to different applications.

Tough polymers from renewable sources

Polymers Three renewable sources have been combined to create a tough thermoplastic. Zhang et al. used hydroxypropyl methylcellulose (HPMC) as a semirigid backbone and grafted on rubbery poly(β-methyl-δ-valerolactone) (PMVL) blocks that were then terminated with hard poly-l-lactide (PLLA) blocks. The rubbery block allowed the PLLA blocks to crystallize. These materials were easily processed in the molten state and showed exceptional toughness: They could be strained up to 600% and yet remained transparent up to the point of pulling apart. ACS Macro Lett. 5 , 407 (2016).

Thermoplastic Elastomers via Combined Crystallization and Vitrification from Homogeneous Melts

Block copolymers with crystalline, glassy, and rubbery blocks were synthesized by anionic polymerization of butadiene, styrene, and isoprene followed by chlorosilane coupling and hydrogenation. The performance of two pentablock copolymers, with the block sequence crystalline–glassy–rubbery–glassy–crystalline, as thermoplastic elastomers (TPEs) was evaluated against triblock copolymers having either crystalline or glassy end blocks. Judicious choices of block lengths yielded homogeneous melts for both pentablocks; consequently, the low-shear-rate viscosities of the pentablocks were more than 2 orders of magnitude lower than that of the glassy–rubbery–glassy triblock, which remained microphase-separated in the melt. In the pentablocks, physical cross-linking was achieved by crystallization of the end blocks followed by vitrification of the adjacent glassy blocks, forming composite crystalline–glassy hard domains. All of the polymers studied exhibited desirable mechanical behavior for TPEs, including low You...

Highly Permeable and Robust Responsive Nanoporous Membranes by Selective Swelling of Triblock Terpolymers with a Rubbery Block

The selective swelling of amphiphilic block copolymers has been demonstrated to be extremely facile and efficient in producing nanoporous membranes. However, all previous works are limited to diblock copolymers composed of two glassy blocks, suffering from inherent mechanical weakness. Here we elucidate the selective swelling-induced pore generation of triblock terpolymers with a rubbery polyisoprene (PIP) block, polyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (PIP-b-PS-b-P2VP). A short exposure to ethanol turns the initially dense films to nanoporous membranes with well-defined interconnected porosity. We fabricate composite membranes with the nanoporous terpolymer thin films as the selective layers deposited on macroporous substrates. Using PS-b-P2VP diblock copolymer without a rubbery third block for comparison, we identify the role of the rubbery PIP blocks in determining the mechanical properties as well as the swelling behaviors of the terpolymer. The rubbery PIP blocks enhance the mechan...

Toughening Polylactide with Phase‐Separating Complex Copolymer Architectures

Polylactide (PLA) is a commercially produced potentially sustainable plastic that holds promise to replace petroleum‐sourced materials. Unfortunately, the brittle nature of PLA limits its current utility to disposable packaging. Melt blends of PLA and a rubbery material can rubber toughen the plastic, but often require the addition of a compatibilizer and generate opaque materials. Current efforts explore using block and graft copolymers with a majority PLA block and minority rubbery block that phase separate on the nanometer length scale to rubber toughen PLA. With these complex architectures, the polymer matrix, the minor rubbery component, and the compatibilizer are present in one molecule. Many block and graft copolymers rely on non‐sustainable rubbery blocks, which limits the sustainability of these materials. Recent work has utilized polyisoprene (PI) as the sustainable backbone for PLA graft copolymers. Post‐polymerization functionalization and copolymerization of PI provides a method to create fully sustainable PLA/PI graft copolymers that phase separate on the nanometer‐scale to make potentially tough, sustainable plastics. image

Effect of graft density and molecular weight on mechanical properties of rubbery block copolymer grafted SiO2 nanoparticle toughened epoxy

15 nm diameter SiO2 nanoparticles with a grafted block copolymer consisting of a 5–20 nm rubbery polyhexylmethacrylate (PHMA) inner block and a 30 nm outer block of matrix compatible polyglycidylmethacrylate (PGMA) were synthesized to toughen an epoxy. A systematic study of the effect of block copolymer graft density (from 0.07 to 0.7 chains/nm2) and block molecular weight (from 20 to 80 kg/mol) on the tensile behavior, fracture toughness, and fatigue properties was conducted. It was found that the copolymer grafted SiO2 nanoparticles enhanced the ductility (maximum 60% improvement), fracture toughness (maximum 300% improvement) and fatigue crack growth resistance of the epoxy matrix while maintaining the modulus at loadings of less than 2 vol% of silica core. The PHMA block induced plastic void growth and shear banding. At lower graft density and larger molecular weight of the PHMA block, the nanocomposites exhibited simultaneous improvements in fracture toughness and tensile modulus. The PGMA epoxy compatible block also contributed to the improved fracture energy of the nanocomposites.

Influence of Tie and Loop Molecules on the Mechanical Properties of Lamellar Block Copolymers

We use coarse-grained molecular dynamics simulation to study the influence of molecular architecture and conformations on the mechanical response of lamellar nanostructured polymers. For this purpose, a recently developed generation method (radical like polymerization method) has been optimized to generate lamellar triblock copolymer samples with alternate glassy and rubbery stacks. Several systems, with various rate of loop (both ends of the chain are in the same glassy block), cilia (cut triblock, effectively a diblock chain) and tie molecules (TMs) (chain that bridges two subsequent glassy blocks through the intermediate rubbery block) were generated. Uniaxial tensile tests were performed, the tensile strain being applied in the normal direction of the lamellae. This situation can be understood as a simple way of mimicking the deformation of the equatorial stack in semicrystalline polymers, with the “hard” phase being the glassy (rather than crystalline) one. The resulting constitutive laws reveal the ...

Tough and Elastic Thermoplastic Organogels and Elastomers Made of Semicrystalline Polyolefin-Based Block Copolymers

Development of stereo- and regioselective living alkene polymerization catalysts has led to the capability to produce multiblock copolymers with semicrystalline syndiotactic polypropylene blocks and poly(ethylene-co-propylene) rubbery blocks that have excellent elastomeric properties, both undiluted and as gels with as little as 8 wt % copolymer in mineral oil. During step cycle mechanical processing, the crystals can plastically deform and partially transform from lamellae into rod-like fibrils, which align along the tensile direction, giving rise to very large tangent moduli at large strains. The dimensions of these aligned fibrils can be established from small-angle X-ray scattering and used to construct models of the large strain elasticity, as well as its evolution with plastic strain, based on short fiber composite theory. Wide angle X-ray scattering experiments as well as FTIR measurements suggest that the oriented fibrils have the transplanar (form III) crystal structure. The large toughness of the dilute gels can be attributed to the plastic deformation of the crystalline component, which not only evens out the forces on the rubbery chains running from crystal to crystal but also provides a mechanical hysteresis that is effective in absorbing energy at the tip of a growing crack.

The Mechanical Properties of Epoxy Composites Filled with Rubbery Copolymer Grafted SiO2

This study demonstrated a method for toughening a highly crosslinked anhydride cured DGEBA epoxy using rubbery block copolymer grafted SiO2 nanoparticles. The particles were synthesized by a sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The inner rubbery block poly(n-hexyl methacrylate) (PHMA) had a glass transition temperature below room temperature. The outer block poly(glycidyl methacrylate) (PGMA) was matrix compatible. A rubbery interlayer thickness of 100% and 200% of the particle core radius was achieved by grafting a 20 kg/mol and a 40 kg/mol PHMA at a graft density of 0.7 chains/nm2 from the SiO2 surface. The 20 kg/mol rubbery interlayer transferred load more efficiently to the SiO2 cores than the 40 kg/mol rubbery interlayer and maintained the epoxy modulus up to a loading of 10 vol% of the rubbery interlayer. Both systems enabled cavitation or plastic dilatation. Improvement of the strain-to-break and the tensile toughness was found in both systems. We hypothesize that plastic void growth in the matrix is the primary mechanism causing the improvement of the ductility.

Quantification of surface forces of thermoplastic elastomeric nanocomposites based on poly(styrene‐ethylene‐co‐butylene‐styrene) and clay by atomic force microscopy

AbstractAtomic force microscopy was used for qualitative phase morphological mapping as well as quantitative investigation of surface forces measured at constituting blocks and clay regions of a thermoplastic elastomeric nanocomposite based on triblock copolymer: poly(styrene‐ethylene‐co‐butylene‐styrene) (SEBS) and organically modified nano‐clay. The roughness and power spectral density analyses of surface topography provided the increment in random roughness of the nanocomposite surface compared to pristine SEBS surface. The same surfaces were examined by means of single point force‐distance, and force‐volume measurements. Large adhesive force of 25 nN and contact force of 260 nN were found in soft polyethylene (PEB) segments and higher cantilever deflection of 210 nm was found for clay regions of SEBS‐clay nanocomposite. Mapping of elastic modulus of the glassy and rubbery blocks and clay regions was probed by employing Hertzian and JKR model from respective approaching and retracting parts of force‐distance curves. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

All acrylic block copolymers based on poly (methyl methacrylate) and poly (butyl acrylate). A link between the physico-chemical properties and the mechanical behaviour on impact tests

Adding an elastomeric phase in a glassy matrix is extensively used to enhance impact resistance for common commercial polymers (high impact polystyrene or polymethylmethacrylate for example). The domain size of this elastomeric phase can vary in a large range from 100 microns upwards according to the expected optical properties. In contrast to the standard route, block copolymers can present morphology at the nanoscale which can be determined from their phase diagram. All acrylic block copolymers comprising rigid and rubbery blocks tethered together were prepared by a recently developed Controlled Radical Polymerization process, mediated by SG1 nitroxide. In this work, we studied four block copolymers (two diblock and two triblock copolymers) of roughly the same weight average Molecular Weight and the same composition of PolyMethylmethacrylate and PolyButylacrylate. The behaviour during impact tests is linked to the processing conditions: injection moulding or solvent-casting. We show that the nanoscale order, characterised here by the lamellar period size and obtained by solvent-casting, strongly influences the impact resistance.

Electrochemical Characterization of Vanadium Oxide Nanostructured Electrode

Films consisting of a vanadium pentoxide (i.e., ) phase formed within a rubbery block copolymer were developed for their potential use as nanocomposite cathodes in lithium rechargeable batteries. Films were prepared by sol-gel synthesis from vanadyl triisopropoxide precursor in poly(oligooxyethylene methacrylate)-block-poly(butyl methacrylate), incorporating and carbon black as conductivity additives. The morphology of the films was examined using electron microscopy, and their electrochemical performance was assessed by galvanostatic cycling. An all-solid-state battery comprising a polymer-based cathode and a block copolymer electrolyte was cycled repeatedly. The capacity was measured to be and found to be limited by the conductivity of the polymer electrolyte. A comparison between a nanocomposite cathode and a control cathode with the same carbon:vanadium oxide ratio demonstrated higher rate capability for the nanocomposite sample when paired with a liquid electrolyte. This study demonstrates the potential utility of block copolymers in the fabrication of high-surface-area cathodes for lithium batteries.

Toughness Properties of Lightly Crosslinked Epoxies Using Block Copolymers

AbstractSummary: In this work is discussed an alternative approach to the toughening of epoxy networks by the addition of acrylic block copolymers, composed of rigid and rubbery blocks. Once the reaction is completed, the initial self‐assembly of block copolymers in epoxy thermoset precursors produces rubbery domains: depending on the block copolymer structure and composition, these domains are of the micrometer or the nanometer size. Nanostructures are obtained when the rigid block is a random copolymer of methylmethacrylate and N,N‐dimethylacrylamide. The rubbery domains prevent rapid crack propagation and the highest toughness is obtained with filament‐like microparticles or wormlike micelles.

Crystallization Kinetics of Homogeneous and Melt Segregated PE Containing Diblock Copolymers

AbstractThe crystallization behavior of four types of polyethylene (PE) containing diblock copolymers with an approximate 50/50 composition has been investigated and compared with their respective PE homopolymers. A glassy block of polystyrene (PS), a rubbery block of poly (D,L‐lactide) (PDLA), a semicrystalline block of poly (L‐lactide) (PLLA) and a miscible block of (poly(ethylene‐alt‐propylene) (PEP) were used to asses the influence of the degree of confinement and miscibility on the crystallization kinetics of PE. PEP had the largest effect on the crystallization kinetics of the PE block in view of its miscibility. For the strongly segregated systems larger restrictions were imposed by vitreous PS due to hard confinement as compared with the soft confinement of the rubbery PDLA block. A nucleation effect of previously crystallized PLLA on the PE block was detected which offset its depression of the crystallization kinetics of PE.

Sol−Gel Synthesis of Vanadium Oxide within a Block Copolymer Matrix

Films consisting of a vanadium pentoxide (i.e., V2O5) phase formed within a rubbery block copolymer were developed for their potential use as nanocomposite cathodes in lithium rechargeable batteries. Nanocomposite films were prepared by sol−gel synthesis from vanadyl triisopropoxide precursor in poly(oligooxyethylene methacrylate)-block-poly(butyl methacrylate), POEM-b-PBMA. The in situ growth of amorphous V2O5 was confirmed by wide-angle X-ray scattering (WAXS), X-ray photoelectron spectroscopy (XPS), and small-angle X-ray scattering (SAXS). Scanning transmission electron microscopy (STEM) and differential scanning calorimetry (DSC) demonstrated the selective incorporation of vanadium oxide within the ion-conducting POEM domains, while the oxide morphology was revealed by TEM to be a filamentous network. Cyclic voltammetry and impedance spectroscopy confirmed the preservation of the redox properties of the vanadium oxide and the ion-conductive properties of the polymer in hybrid films. Co-assembled nanocomposite films incorporating up to 34 wt % (13 vol %) vanadium oxide were flexible and semi-transparent.

Barrier films made with various lamellar block copolymers

The permeabilities of helium, nitrogen, and oxygen across lamellar block copolymers can be accurately estimated from the properties of the glassy and rubbery blocks. The copolymers tested include poly(styrene-b-isoprene-b-styrene), poly(styrene-b-butadience-b-styrene), and poly(lactide-b-isoprene-b-lactide). The results show improvements in barrier properties that tend to be larger than those expected from the resistances of lamellae in series. These increases are not as large as those achieved with impermeable fillers like mica and clay. The changes in film elastic modulus caused by glassy lamellae are also discussed.