Linear Multiblock Copolymers Research Articles

Deformation and failure of glassy polymer-polymer interfaces compatibilized by linear multiblock copolymers

Deformation and failure of glassy polymer-polymer interfaces compatibilized by linear multiblock copolymers

Polyhydroxyurethane and Poly(ethylene oxide) Multiblock Copolymer Networks: Crosslinking with Polysilsesquioxane, Reprocessing and Solid Polyelectrolyte Properties.

This contribution reports the synthesis of polyhydroxyurethane (PHU)-poly(ethylene oxide) (PEO) multiblock copolymer networks crosslinked with polysilsesquioxane (PSSQ). First, the linear PHU-PEO multiblock copolymers were synthesized via the step-growth polymerization of bis(6-membered cyclic carbonate) (B6CC) with α,ω-diamino-terminated PEOs with variable molecular weights. Thereafter, the PHU-PEO copolymers were allowed to react with 3-isocyanatopropyltriethoxysilane (IPTS) to afford the derivatives bearing triethoxysilane moieties, the hydrolysis and condensation of which afforded the PHU-PEO networks crosslinked with PSSQ. It was found that the PHU-PEO networks displayed excellent reprocessing properties in the presence of trifluoromethanesulfonate [Zn(OTf)2]. Compared to the PHU networks crosslinked via the reaction of difunctional cyclic carbonate with multifunctional amines, the organic-inorganic PHU networks displayed the decreased reprocessing temperature. The metathesis of silyl ether bonds is responsible for the improved reprocessing behavior. By adding lithium trifluoromethanesulfonate (LiOTf), the PHU-PEO networks were further transformed into the solid polymer electrolytes. It was found that the crystallization of PEO chains in the crosslinked networks was significantly suppressed. The solid polymer electrolytes had the ionic conductivity as high as 7.64 × 10-5 S × cm-1 at 300 K. More importantly, the solid polymer electrolytes were recyclable; the reprocessing did not affect the ionic conductivity.

Thermodynamics and morphology of linear multiblock copolymers at homopolymer interfaces.

Block copolymers at homopolymer interfaces are poised to play a critical role in the compatibilization of mixed plastic waste, an area of growing importance as the rate of plastic accumulation rapidly increases. Using molecular dynamics simulations of Kremer-Grest polymer chains, we have investigated how the number of blocks and block degree of polymerization in a linear multiblock copolymer impacts the interface thermodynamics of strongly segregated homopolymer blends, which is key to effective compatibilization. The second virial coefficient reveals that interface thermodynamics are more sensitive to block degree of polymerization than to the number of blocks. Moreover, we identify a strong correlation between surface pressure (reduction of interfacial tension) and the spatial uniformity of block junctions on the interface, yielding a morphological framework for interpreting the role of compatibilizer architecture (number of blocks) and block degree of polymerization. These results imply that, especially at high interfacial loading, the choice of architecture of a linear multiblock copolymer compatibilizing surfactant does not greatly affect the modification of interfacial tension.

Linear, Star, Comb, and Ring Crystallizable Multiblock Copolymers Investigated by Molecular Dynamics Simulations

Linear, Star, Comb, and Ring Crystallizable Multiblock Copolymers Investigated by Molecular Dynamics Simulations

Hierarchical double periodic structures formed by the linear multiblock copolymers A(BA)2C and (BA)3C with compositions of the A, B and C blocks in ratio 1:1:2

Hierarchical double periodic structures formed by the linear multiblock copolymers A(BA)2C and (BA)3C with compositions of the A, B and C blocks in ratio 1:1:2

Sulfonated Poly(arylene ether sulfone) Multi-Block Copolymers with Selectively Cross-Linked Domains for Proton Exchange Membranes

A facile design of sulfonated poly(arylene ether sulfone) multi-block copolymer membranes with selectively cross-linked hydrophobic domains is reported for proton exchange membranes. The cross-linkable linear multi-block copolymers are prepared via coupling telechelic hydrophilic disulfonated oligomers (BPS100) and telechelic hydrophobic oligomers (PPA0) containing cross-linkable allyl-derivatized phenolphthalein moieties. The cross-linked membranes are prepared through UV-initiated thiol-ene cross-linking reactions between allyl-functionalized hydrophobic blocks with pentaerythritol tetrakis(3-mercaptopropionate) as a cross-linker. With highly cross-linked hydrophobic blocks and flexible hydrophilic blocks, the selectively cross-linked multiblock copolymer membranes exhibit remarkably improved dimensional stability and proton conductivity compared to the cross-linked random copolymers. The cross-linked membrane with the longest hydrophilic block length shows a remarkable proton conductivity of 123 mS/cm with a suppressed volume swelling ratio of 25% at 25 °C. At the highest ion exchange capacity level (2.25 meq/g) and the longest block length, the cross-linked multi-block copolymer membrane outperforms Nafion over the full relative humidity range.

Synthesis and Phase Behavior of a Linear Amphiphilic Multiblock Copolymer.

Linear amphiphilic multiblock copolymer PPMPEs, obtained through a stepwise method, and linear amphiphilic random copolymer PPMPEs-1, obtained through a one-pot method, were synthesized using poly(propylene glycol) diglycidyl ether (PPGDGE), poly(ethylene glycol) diglycidyl ether (PEGDGE), and monoethanolamine (MEA) as the main raw materials. The structures of PPMPEs and PPMPEs-1 were characterized by FT-IR, 1H NMR, and gel permeation chromatography, which proved that the copolymers were synthesized with different components. Transmittance of the copolymer was tested by UV–vis. By changing the ratio of PEGDGE content and the concentration of the copolymer aqueous solution, the phase behaviors of PPMPEs and PPMPEs-1 were compared and studied in depth. It mainly highlighted the advantages of the stepwise method compared to the one-pot method. The transmittance of the polymer solutions could be improved by lowering the pH value in the acidic solution or increasing the pH value in the alkaline solution. Moreover, as the reaction degree of the PPMPEs hydrophobic chain segment increased, the transmittance decreased.

A simple route to prepare supramolecular block copolymers using telechelic polystyrene/polydimethylsiloxane pairs

AbstractWhile supramolecular block copolymer (BCP) self‐assembly has been widely studied over the past decades as an effective means to generate functional nanomaterials, most of these systems require multiple steps of synthesis and processing. In this report, we introduce a facile approach to form linear multiblock copolymers by directly blending telechelic homopolymer pairs, using di‐sulfonated polystyrene and commercially available, aminopropyl terminated polydimethylsiloxane. A series of model multiblock copolymers were prepared, in which proton transfers between polymer chain ends enable the formation of strong ionic associations. These ionic junctions not only significantly enhance thin film stability of polymer blends by forming higher molecular weight copolymers, but also improve the chemical incompatibility between different segments, resulting in ordered nanostructures upon self‐assembly. These include different morphologies such as lamellae and cylinders. We also demonstrate that feature size of these BCPs can be adjusted by varying the molecular weight of the homopolymers, with a smallest domain spacing of approximately 12.9 nm being obtained. Utilizing low‐cost and widely available polymers as building blocks, our simple and efficient supramolecular assembly strategy for forming multiblock copolymers may provide a promising platform for cost‐efficient nanomanufacturing of polymeric materials. © 2021 Society of Industrial Chemistry.

Network topology and stability of homologous multiblock copolymer physical gels.

The mechanical properties of physical gels generated by selectively swelling a homologous series of linear multiblock copolymers are investigated by quasistatic uniaxial tensile tests. We use the slip-tube network model to extract the contributions arising from network crosslinks and chain entanglements. The composition dependence of these contributions is established and considered in terms of simulations that identify the probabilities associated with chain conformations. Dynamic rheology provides additional insight into the characteristics and thermal stability of the molecular networks.

Copolymer Surfactant Poloxamer 188 Accelerates Post-axonotemetic Sciatic Nerve Regeneration

Trauma-mediated peripheral nerve axon injury invariably involves structural alteration of the axonal plasmalemma cell membrane. Increased axonal membrane permeability to electrolytes results in metabolic stress and axonal degeneration if the axon does not seal. Poloxamer 188 (P188) is a linear multiblock copolymer composed of a hydrophobic polyoxypropylene (POP) block in the middle with polyethylene glycol (PEG) blocks on both ends. The central POP block concentrates at sites of cell membrane disruption and catalyzes sealing of disrupted cellular membranes. We tested the hypothesis that intravenously administered P188 (9800 Da, 0.2 mM) can accelerate distal axon recovery after sciatic nerve crush injury using an established axonotemetic model. A crush injury was performed on the sciatic nerve of thirty female Sprague-Dawley rats. Rats were randomized to receive either 0.2 mM P188 or Dextran, administered 1 h after crush injury. Compound nerve action potentials (CNAP) and density of neurofilament distal to the point of injury were analyzed on post-crush day (PCD) 4, 14, and 21. A significant improvement in axonal conduction for animals treated with P188 was observed for PCD 4 and PCD 14 (p < 0.01). The segment of axon distal to the site of injury in the P188-treated group demonstrated significant increase in nerve fiber density on PCD4 (p < 0.01). Therefore, a single dose of intravenous P188 administered 1 h after crush injury to rat sciatic nerve resulted in more rapid structural and functional nerve recovery. Nerve injuries are common in day-to-day physical trauma. On a molecular level, nerve injury is precipitated by damage to the nerve’s cell membrane, which disrupts the delicate balance of the cellular environment and leads to cell death. There are molecules that can repair ruptured cell membranes by inserting themselves into it and effectively resealing the cell. Copolymer P188 is one such molecules which can be injected intravenously and selectively targets injured cell membranes. In this study, we tested the hypothesis that copolymer P188 injected intravenously into rats following peripheral nerve injury could facilitate the functional recovery of the nerve.

Adsorption of Linear and Cyclic Multiblock Copolymers from Selective Solvent. A Monte Carlo Study

AbstractA systematic study of the adsorption of linear and cyclic chains on a planar surface is carried out through extensive computer simulations. 3D homopolymer and multiblock copolymer chains are studied. No atomic details are taken into consideration and polymer chains are modeled as sequences of statistical segments on a cubic lattice. Adsorption of macromolecules on a homogenous flat surface is studied at different solvent conditions. Homopolymers are built of solvophobic segments while copolymers are formed of solvophilic and solvophobic blocks. A Monte Carlo simulation employing the Replica Exchange technique is used. The main question is how the chain sequence, the internal architecture, the strength of adsorption, and the solvent quality influence the macromolecular structure. It is also shown that the differences in size and in parameters of adsorption between cyclic and linear chains are relatively small. The increase in the number of solvophobic blocks has a significant impact on a chain size and coil‐to‐globule transition while the critical adsorption temperature is less sensitive in the sequence.

Synthesis and properties of long-chain-branched poly(aryl ether sulfone)-poly(tetrahydrofuran) multiblock copolymers

Long-chain-branched poly(aryl ether sulfone)-poly(tetrahydrofuran) multiblock copolymers (PES-BPTHF) composed of hard linear and soft branching segments were synthesized from bromo-terminated poly(tetrahydrofuran) and hydroxy-terminated poly(aryl ether sulfone). A study on the effect of concentration on polymerization behavior revealed that soluble powder was obtained at the optimized reaction concentration of 7 wt%. Gelation and intramolecular cyclization were observed at high and low concentrations, respectively. The microphase-separated morphology of PES-BPTHF was confirmed by atomic force microscopy, small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA) measurements. Fewer entangled poly(tetrahydrofuran) segments were detected in PES-BPTHF than in PES-PTHF by SAXS, DMA and tensile measurements. Rheological measurements suggested high chain entanglement of PES-BPTHF in its melt phase. It is interesting to note that the polymer chains in the soft domains become less entangled and more reminiscent of hyperbranched architectures, whereas the overall chain entanglements are increased due to the long-chain-branched structure. Long-chain-branched poly(aryl ether sulfone)-poly(tetrahydrofuran) multiblock copolymers composed of hard linear and soft branching segments were synthesized from bromo-terminated poly(tetrahydrofuran) and hydroxy-terminated poly(aryl ether sulfone). Optimization of the polymerization conditions afforded soluble powder at a reaction concentration of 7 wt%. Microphase-separated morphology was observed for the branched multiblock copolymers. Compared with the corresponding linear multiblock copolymer, the branched polymer chains in the soft domains become less entangled and more reminiscent of hyperbranched architectures, whereas the overall chain entanglements are increased due to the long-chain-branched structure.

Non-uniform spontaneous surface curvature gives limited shape control in simulated single-polymer micelles

Polymeric micelles are used in a variety of applications, with the micelle’s shape often playing an important role. Consequently, it is desirable to identify a simple set of control parameters having an easily understood effect on micelle shape. In a previous study, we showed that a model two-dimensional linear multiblock copolymer may be designed to exhibit a dimpled shape. Extending this study, this paper characterizes in greater detail how such a dimpled micelle’s shape can be controlled by adjusting the copolymer block lengths. Using basic physical principles governing amphiphilic polymer, we identify a few aspects of the multiblock composition that are expected to have a well-behaved effect on micelle shape. Starting from a reference micelle composition, itself already exhibiting a nonstandard shape having a moderately sized concave dimple, we alter these aspects of the multiblock composition and observe the response of two features of the micelle shape: the size of the dimple and the magnitude of shape fluctuations. We find the response of the shape is smooth and regular for small excursions from a base composition, but larger excursions gave rise to nonmonotonic effects on the shape, suggesting that sophisticated techniques may be required to aid in micelle design.

Highly selective multi-block poly(ether-urea-imide)s for CO2/N2 separation: Structure-morphology-properties relationships

Polyethylene oxide (PEO)-containing multi-block copolymers are good candidates for CO2 membrane separations because of their strong affinity for CO2 but PEO crystallization and weak mechanical properties are two limitations to be overcome at high PEO content. In this work, PEO block incorporation within new linear multi-block copolymers avoided PEO crystallization. The copolymers consisted in Jeffamine soft blocks (SB) and particularly stiff urea-imide hard blocks for improved physical cross-linking and excellent film-forming ability. Varying the SB content from 41 to 70 wt% led to different copolymer physical properties, morphology and CO2 permeation properties. The copolymer with the lowest SB content was a rigid glassy material with very weak phase separation. Its soft and hard blocks formed large interpenetrated domains, resulting in low CO2 permeability (2 Barrer) but extreme selectivity (αCO2/N2 = 207) for CO2/N2 separation at 2 bar and 35 °C. CO2 permeability greatly improved with the SB content due to strong phase separation. The copolymer with the highest SB content was a thermoplastic elastomer with soft blocks forming well-separated highly permeable percolating nano-domains. Its CO2 permeability (57 Barrer) and high selectivity (αCO2/N2 = 50) are among the best properties reported for PEO-containing multi-block copolymers for CO2 capture.

One-step synthesis of self-healable hydrogels by the spontaneous phase separation of linear multi-block copolymers during the emulsion copolymerization

Self-healable polyacrylamide-based hydrogels were prepared at room temperature via a one-step emulsion copolymerization of acrylamide (AM), dodecyl 2-methacrylate (DM), and 5-acetylaminopentyl acrylate (AAPA) using sodium dodecyl sulfonate (SDS) as the emulsifier and ammonium persulfate (APS) as the initiator. The produced linear multi-block copolymer chains are composed of randomly-linked hydrophilic polyacrylamide segments (PAM) and hydrophobic segments constituted by DM and AAPA units (P(DM-co-AAPA)). The P(DM-co-AAPA) segments will self-aggregate into hydrophobic microdomains during the polymerization process driven by the hydrophobic interactions, and finally separate from water phase, acting as the crosslinks and leading to the formation of strong hydrogels with a storage modulus as high as 400Pa. These hydrophobic microdomains will be dissolved in water when the temperature increases to 70°C, resulting in a temperature-responsive reversible sol-gel transition of the prepared hydrogels. Furthermore, the prepared hydrogels have excellent self-healing ability. The broken hydrogels can be automatically healed into a body with a same strength within 2-min’s contact. This work provides a new simple way to prepare reversible physical crosslinked hydrogel with high strength and self-healing efficiency.

Hierarchical Microstructures Self‐Assembled from Linear Multiblock Copolymers in Thin Films

Hierarchical lamellae self‐assembled from linear multiblock copolymers in thin films are investigated by self‐consistent field theory. The thin films are confined between two parallel substrates. The confinement strategy allows generating hierarchical microstructures with various numbers and different orientations of small‐length‐scale lamellae. Effects of film thickness and surface affinity on the structures are studied. It is found that not only the period of the large‐ and small‐length‐scale lamellae but also the orientation of small‐length‐scale lamellae relative to large‐length‐scale lamellae can be tuned by varying the film thickness. Moreover, the structures of the hierarchical lamellae can be tailored by changing the surface affinity. Through analyzing free energies of various lamellae, phase diagrams are mapped out. The present work could provide guidance for fabricating hierarchical microstructures in a controllable way.

Grafting of multi-block copolymers: A new strategy for improving membrane separation performance for ethyl tert-butyl (ETBE) bio-fuel purification by pervaporation

Ethyl tert-butyl ether (ETBE) is considered as one of the most promising bio-fuels in Europe. During its industrial synthesis, ethanol forms an azeotropic mixture with ETBE, which cannot be separated by simple distillation. We have formerly reported several selective linear multi-block copolymer membranes for this separation by pervaporation. These multi-block copolymers offered good film forming ability and processability but their transport properties were limited by the permeability/selectivity trade-off. In this work, a new grafting strategy of multi-block copolymers is investigated, aiming at increasing membrane permeability strongly while maintaining a very high selectivity for ETBE purification. The grafted multi-block copolymers were obtained by a synthesis scheme involving step-growth polymerization, polymer functionalization and grafting by “click” chemistry. The membrane properties are discussed in terms of structure–morphology–property relationships for the sorption and pervaporation of the targeted mixture. By hindering the diffusion of the bulky ETBE molecules and ensuring high permeability for ethanol molecules, the particular morphology of the grafted multi-block copolymer membranes led to outstanding membrane separation performance for ETBE purification.

Collapse transitions in thermosensitive multi-block copolymers: a Monte Carlo study.

Monte Carlo simulations are performed on a simple cubic lattice to investigate the behavior of a single linear multiblock copolymer chain of various lengths N. The chain of type (AnBn)m consists of alternating A and B blocks, where A are solvophilic and B are solvophobic and N = 2nm. The conformations are classified in five cases of globule formation by the solvophobic blocks of the chain. The dependence of globule characteristics on the molecular weight and on the number of blocks, which participate in their formation, is examined. The focus is on relative high molecular weight blocks (i.e., N in the range of 500-5000 units) and very differing energetic conditions for the two blocks (very good-almost athermal solvent for A and bad solvent for B). A rich phase behavior is observed as a result of the alternating architecture of the multiblock copolymer chain. We trust that thermodynamic equilibrium has been reached for chains of N up to 2000 units; however, for longer chains kinetic entrapments are observed. The comparison among equivalent globules consisting of different number of B-blocks shows that the more the solvophobic blocks constituting the globule the bigger its radius of gyration and the looser its structure. Comparisons between globules formed by the solvophobic blocks of the multiblock copolymer chain and their homopolymer analogs highlight the important role of the solvophilic A-blocks.

Interplay between the Phase Transitions at Different Length Scales in the Supramolecular Comb–Coil Block Copolymers Bearing (AB)n Multiblock Architecture

We introduced the concept of comb–coil supramolecule into linear (AB)n-type multiblock copolymer and investigated the self-assembly behavior of the copolymers as a function of the unit number n. Linear (polystyrene-block-poly(2-vinylpyridine))n (denoted as (PS-b-P2VP)n, where n = 1, 2, 3) was complexed with a surfactant, dodecylbenzenesulfonic acid (DBSA), to yield the comb–coil multiblock copolymers, in which DBSA bound stoichiometrically with P2VP block via physical bonds. All three comb–coil block copolymers, including diblock (n = 1), tetrablock (n = 2), and hexablock (n = 3), self-organized to form cylinder-within-lamellae morphology at the lower temperature, where the cylindrical microdomains formed by the PS block embedded in the matrix composed of the lamellar mesophase organized by the P2VP(DBSA) comb block. The disordering of the smaller-scale lamellar mesophase formed by the comb block occurred upon heating; at the same time, the larger-scale cylindrical domains transformed to body-centered cubic-packed spheres in the diblock complex and to another hexagonally packed cylinder structure with smaller domain spacing in tetrablock and hexablock complexes, indicating that the order–disorder transition (ODT) of the smaller-scale structure drove an order–order transition (OOT) of the larger-scale structure irrespective of n. The transition temperatures were found to increase with increasing n due to the introduction of more interfacial area in the microphase-separated state of the multiblock with larger unit number.

Self-assembly of linear rod-coil multiblock copolymers

The self-assembly of the linear rod-coil multiblock copolymers is studied by applying self-consistent-field lattice techniques in a three-dimensional (3D) space. Compared to the copolymer with one rod, the copolymer with more rods (m rod ≥ 2) exhibits rich order-order phase transitions with increasing temperature, where the ordered morphology changes from strips to perforated lamellae and finally to lamellae. In addition, taking the copolymer with m rod = 2 as a representative, we further study the effects of the volume fractions of the rods, the spacer coils and the end coils on the phase behaviors respectively, by which the detailed self-assembled mechanism of the linear rod-coil multiblock copolymers is revealed. Our results are expected to provide guidance for the design of the rod-coil materials.