Multiblock Copolymers Research Articles

Olefin cross-metathesis of polynorbornene with polypentenamer: New norbornene–cyclopentene multiblock copolymers

Statistical multiblock copolymers of norbornene (NB) and cyclopentene (CP) with different compositions and average block lengths are synthesized via the metathesis of polynorbornene (PNB) with polypentenamer (PCP) mediated by Grubbs’ catalysts of the 1st (G1) and 2nd (G2) generations. Interest in the copolymerization of NB and CP is dictated by the attractive properties of their homopolymers, whereas its realization is hampered by the mismatch in their metathesis polymerization activities. This difficulty can be circumvented by starting from the homopolymers, which are well-known industrial products. Our study demonstrates that the interaction of PNB with PCP in dilute solutions at room temperature in the presence of G1 leads to the copolymers with short CP blocks of 1–3 units separating longer NB blocks. In situ 1H NMR monitoring of the process reveals nearly full depolymerization of PCP via the ring-closing intramolecular metathesis and the formation of NB–CP copolymers presumably via the interaction of CP with PNB. The depolymerization can be suppressed by increasing the concentration of reacting polymers and replacing G1 with more active G2. Under these conditions, the cross-metathesis of PNB with PCP results in the multiblock NB–CP copolymers with composition close to that of the initial homopolymer mixture, but short blocks of the both comonomers. A copolymer with longer blocks that can inherit properties of the parent homopolymers is obtained by decreasing the reaction temperature to 5 °C. Additional information about the structure of NB–CP copolymers is obtained via their hydrogenation followed by spectral and thermal characterization. Thus, the macromolecular cross-metathesis of unsaturated polymers appears to be a versatile method to synthesize copolymers with different backbone structures that are hard to reach by other methods.

Switchable Copolymerization of Maleic Anhydride/Epoxides/Lactide Mixtures: A Straightforward Approach to Block Copolymers with Unsaturated Polyester Sequences

AbstractSwitchable copolymerization of oxygenated heterocycle mixtures by a single catalytic system has been proved to be a promising approach to sequence‐controlled block copolymers. However, there are still big challenges in one‐step synthesis of multiblock copolymers containing unsaturated polyester blocks from maleic anhydride, epoxides, and lactone mixtures. Herein, a switchable pathway for polylactide‐b‐poly(MAH‐alt‐epoxide)‐b‐polylactide block copolymers is established. The excellent chemoselectivity in multicomponent copolymerization is achieved by bipyridine bisphenolate aluminum complexes that can induce an obvious kinetic differentiation between ring‐opening copolymerization of maleic anhydride/epoxides and ring‐opening polymerization of lactide. The scope of the epoxide for switchable copolymerization is explored and it is found that the steric hindrance of the substituents on epoxide significantly influences the formation of block copolymers. Block copolymers with various sequential and topological structures can be easily prepared by exquisite selection of different initiators. Furthermore, it is demonstrated that the conversion of cis‐maleate units in the block copolyester could be completely converted to trans‐fumarate units by isomerization without chain degradation, cross‐linking, and chain scrambling.

Characterization and Modeling of Free Volume and Ionic Conduction in Multiblock Copolymer Proton Exchange Membranes.

Free volume plays a key role on transport in proton exchange membranes (PEMs), including ionic conduction, species permeation, and diffusion. Positron annihilation lifetime spectroscopy and electrochemical impedance spectroscopy are used to characterize the pore size distribution and ionic conductivity of synthesized PEMs from polysulfone/polyphenylsulfone multiblock copolymers with different degrees of sulfonation (SPES). The experimental data are combined with a bundle-of-tubes model at the cluster-network scale to examine water uptake and proton conduction. The results show that the free pore size changes little with temperature in agreement with the good thermo-mechanical properties of SPES. However, the free volume is significantly lower than that of Nafion®, leading to lower ionic conductivity. This is explained by the reduction of the bulk space available for proton transfer where the activation free energy is lower, as well as an increase in the tortuosity of the ionic network.

Electrochemically Controlled Switchable Copolymerization of Lactide, Carbon Dioxide, and Epoxides.

Electrochemical redox-control is an emerging strategy for the regulation of polymerization process without the addition of external oxidants and reductants, which enables the control over composition, microstructure and properties of the polymer products. In this paper, based on the chemical selectivity of heterometallic Salen-Co-Mn complexes of different valences, an electrochemically switchable strategy was developed for the copolymerization of lactide (LA), CO2 and epoxides. The switchable redox reactions endowed this system with the capability to easily synthesize a multi-block copolymer of polylactide (PLA) and polycarbonate (PC). Moreover, the multi-block copolymer could be further modified by introducing various monomers with different microstructures and functional groups.

Multiblock copolymers type PDC - A family of multifunctional biomaterials for regenerative medicine1.

Multiblock copolymers type PDC are polyetheresterurethanes composed of poly(ɛ-caprolactone) and poly(p-dioxanone) segments. They were designed as degradadable shape-memory polymers for medical devices, which can be implanted minimally-invasively. While providing structural support in the initial phase after implantation, they are capable to modulate soft tissue regeneration while degradation. In this perspective, we elucidate cell-material interactions, compatibility both in-vitro and in-vivo and biofunctionality of PDC, which represents a promising candidate biomaterial family especially for cardiovascular applications.

Performance assessment of hybrid multiblock copolymers included with ionic liquid for fuel cell applications

To improve the proton conductivity and thermal stability of proton exchange membrane, hybrid poly (arylene ether) multiblock copolymers were synthesized by using 6F-bisphenol A monomer. The hydrophobic oligomers poly (arylene ether sulfone) containing 6F-bisphenol A with varying molecular weight were copolymerised with hydrophilic oligomer disulfonated poly (arylene ether ketone) containing pendant carboxylic acid group to prepare multiblock copolymers. For further enhancing the proton conductivity, ionic liquid is embedded into the synthesized multiblock copolymers to fabricate the hybrid multiblock membranes. The 1H NMR studies confirmed the synthesis of oligomers and multiblock copolymers whereas the FT-IR spectra revealed the interaction of ionic liquid with the multiblock copolymers. The proton conductivity of the membranes has also been examined at different temperatures and the activation energy required for the proton transport was calculated by using Arrhenius equation. At 30 °C, the maximum proton conductivity of 0.14 S/cm were shown by hybrid membrane (with 50% ionic liquid, 6FB1/I.L-50%), which is of 3.5 times greater than that of pristine 6FB1 membrane. Compared with pristine membranes, the hybrid membranes exhibit improved oxidative, thermal and mechanical stability. Moreover, the scanning electron microscopy (SEM) investigation depicts better phase separation in hybrid membranes than pristine membranes by forming ionic clusters. The membranes have been tested in H2/O2 fuel cell and their performance is compared with the state-of-art Nafion 117 membrane.

Expanding the Scope of RAFT Multiblock Copolymer Synthesis Using the Nanoreactor Concept: The Critical Importance of Initiator Hydrophobicity

Precise multiblock copolymer synthesis coupled with self-assembly offers morphology control on length scales ranging from a few nanometers to micrometer scale, providing enormous opportunities for future development of advanced materials and applications. The scope of multiblock copolymer synthesis via RAFT polymerization has recently been expanded by application of the nanoreactor concept for emulsion polymerization. This enabled use of slow propagating monomers, such as styrenes and methacrylates, in multiblock synthesis. However, severe limitations attributed to the high polymer glass transition temperature (Tg) of some polymers have hitherto remained. The use of monomers that give such high-Tg polymers effectively prevented penetration of aqueous-phase-generated radicals into the polymer particles wherein the RAFT functionality is located. We here demonstrate that these constraints can be relieved by judicious choice of the radical initiator. Multiblock homopolymers were synthesized by seeded RAFT emulsion polymerization using initiators that differ substantially in hydrophobicity. Ten sequential chain extensions using tert-butyl methacrylate (Tg of PtBMA = 118 °C) with targeted block DP = 100 were conducted at 80 °C for each initiator. Markedly narrower molecular weight distributions were obtained when more hydrophobic initiators were used. The same polymerizations targeting low -Tg polymers (PnBMA; Tg = 20 °C) resulted in only minor differences in control when the different initiators were used, supporting our hypothesis on the role of radical penetration. The present results are anticipated to significantly expand the scope of RAFT polymerization in aqueous emulsion by allowing access to a wider range of low-dispersity multiblock copolymers.

Ordered Nanostructures in Thin Films of Precise Ion-Containing Multiblock Copolymers.

We demonstrate that ionic functionality in a multiblock architecture produces highly ordered and sub-3 nm nanostructures in thin films, including bicontinuous double gyroids. At 40 °C, precise ion-containing multiblock copolymers of poly(ethylene-b-lithium sulfosuccinate ester)n (PESxLi, x = 12 or 18) exhibit layered ionic assemblies parallel to the substrate. These ionic layers are separated by crystalline polyethylene blocks with the polymer backbones perpendicular to the substrate. Notably, above the melting temperature (Tm) of the polyethylene blocks, layered PES18Li thin films transform into a highly oriented double-gyroid morphology with the (211) plane (d211 = 2.5 nm) aligned parallel to the substrate. The cubic lattice parameter (agyr) of the double gyroid is 6.1 nm. Upon heating further above Tm, the double-gyroid morphology in PES18Li transitions into hexagonally packed cylinders with cylinders parallel to the substrate. These layered, double-gyroid, and cylinder nanostructures form epitaxially and spontaneously without secondary treatment, such as interfacial layers and solvent vapor annealing. When the film thickness is less than ∼3agyr, double gyroids and cylinders coexist due to the increased confinement. For PES12Li above Tm, the layered ionic assemblies simply transform into disordered morphology. Given the chemical tunability of ion-functionalized multiblock copolymers, this study reveals a versatile pathway to fabricating ordered nanostructures in thin films.

Cover Picture

The cover picture displays two different copolymerizations of ε‐caprolactone (CL) with 1,3‐dioxolane (DO) catalyzed by rare earth triflates. The panda represents Janus polymerization which yields multiblock copolymers of CL and DO, while the red panda represents cationic copolymerization which yields random copolymers. Janus polymerization combines anionic and cationic polymerizations on the two ends of a single propagating chain, followed by a self‐triggered polycondensation of anionic and cationic centers. The mechanism of copolymerization is determined by the element of rare earth in catalyst and the presence or absence of an epoxide initiator. More details are given in the article by Ling et al. on page 705—712. image

Linear, Graft, and Beyond: Multiblock Copolymers as Next-Generation Compatibilizers.

Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technological breakthroughs on various fronts. Mechanical recycling of plastic waste into polymer blends is one method expected to contribute to a solution. Due to phase separation of individual components, mechanical recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance. However, when an appropriately designed compatibilizer is used, the recycled blend can have competitive properties to virgin materials. In its current state, polymer blend compatibilization is usually not cost-effective compared to traditional waste management, but further technical development and optimization will be essential for driving future cost competitiveness. Historically, effective compatibilizers have been diblock copolymers or in situ generated graft copolymers, but recent progress shows there is great potential for multiblock copolymer compatibilizers. In this perspective, we lay out recent advances in synthesis and understanding for two types of multiblock copolymers currently being developed as blend compatibilizers: linear and graft. Importantly, studies of appropriately designed copolymers have shown them to efficiently compatibilize model binary blends at concentrations as low as ∼0.2 wt %. These investigations pave the way for studies on more complex (ternary or higher) mixed waste streams that will require novel compatibilizer architectures. Given the progress outlined here, we believe that multiblock copolymers offer a practical and promising solution to help close the loop on plastic waste. While a complete discussion of the implementation of this technology would entail infrastructural, policy, and social developments, they are outside the scope of this perspective which instead focuses on material design considerations and the technical advancements of block copolymer compatibilizers.

Enhanced proton conductivity of poly(ether sulfone) multi-block copolymers grafted with densely pendant sulfoalkoxyl side chains for proton exchange membranes

A series of proton exchange membranes were prepared from poly(ether sulfone) multi-block copolymers grafted with densely pendent sulfoalkoxyl side chains for fuel cell applications. Each polymers contains four pendent sulfonic acids per unit. The chemical structures were confirmed by 1H NMR and FTIR spectroscopy, providing evidence of complete methoxy conversion and sulfobutylation. The introduction of densely grafted flexible pendent side chains to the block structure was effective to enhance phase separation and thus form broader hydrophilic channels. These membranes displayed considerably improved proton conductivities especially at low RH conditions. Furthermore, these membranes also showed promising fuel cell performance both at 20% and 80% RH conditions. In comparison to Nafion 212 membranes, the present membranes displayed enhanced swelling behavior, mechanical strength, proton conductivity, and fuel cell performance, demonstrating that they can be an alternative PEM to perfluorosulfonic acid polymers.

One-Pot Precision Synthesis of AB, ABA and ABC Block Copolymers via Switchable Catalysis.

The switchable catalysis using a commercial salenMn catalyst was firstly developed and applied in the one-pot selective copolymerization from anhydrides, epoxides, CO2 and ϵ-caprolactone (ϵ-CL) mixtures for the precise synthesis of AB, ABA and novel ABC block copolymers. The observed unique double switch process comprising three different polymerization cycles was rationalized by theoretical calculations. Surprisingly, the first block turned out to be an efficient macromolecular initiator for the consecutive introduction of carbonate linkages into copolymers, albeit with dominant cyclization with the catalyst alone. Further, through the selective reaction on different epoxides, the switchable copolymerization of up to five monomers was achieved yielding well-defined multi-block copolymers with structural diversity and functionality.

Olefin-Metathesis-Derived Norbornene-Ethylene-Vinyl Acetate/Vinyl Alcohol Multiblock Copolymers: Impact of the Copolymer Structure on the Gas Permeation Properties.

Commercial metathesis polynorbornene is used for the fabrication of high-damping coatings and bulk materials that dissipate vibration and impact energies. Functionalization of this non-polar polymer can improve its adhesive, gas barrier, and other properties, thereby potentially expanding its application area. With this aim, the post-modification of polynorbornene was carried out by inserting ethylene–vinyl acetate–vinyl alcohol blocks into its backbone via the cross-metathesis of polynorbornene with poly(5-acetoxy-1-octenylene) and subsequent deacetylation and hydrogenation of the obtained multiblock copolymers. For the first time, epoxy groups were introduced into the main chains of these copolymers, followed by the oxirane ring opening reaction. The influence of post-modification on the thermal, gas separation, and mechanical properties of the new copolymers was studied. It was shown that the gas permeability of the copolymer significantly depends on its composition, as well as on the amounts of hydroxyl and epoxy groups. The developed methods efficiently improve the barrier properties, reducing the oxygen permeability by 15–33 times in comparison with polynorbornene. The obtained results are promising for various applications and can be extended to a broader family of polydienes and other polymers containing backbone double bonds.

An exotic microstructured globular state formed by a single multiblock copolymer chain.

In this work, we studied the equilibrium structures formed by a single (AB)k multiblock copolymer chain. Within our model, the interactions between the A-type beads were repulsive and the B-type beads could form pairwise reversible bonds with each other (BB-bonds). Our goal was to investigate how the formation of pairwise reversible bonds between the A-type beads and the B-type beads (AB-bonds) affected the structure of the chain. We observed the formation of well-studied intramolecular micelles when the AB-bonds were absent; however, the chain folding changed dramatically when the formation of the AB-bonds was introduced. In this case, the multiblock copolymer formed a globule, which had a unique heterogeneous checkerboard-like distribution of the contact density. We discovered that contacts of beads of different types (i.e., AB-contacts) occurred much more frequently than contacts of beads of the same type (i.e., AA- and BB-contacts) in these structures. This effect can be explained by a simple model of chemical equilibrium in a two-component fluid of reversibly interacting particles, which can be solved exactly. This novel type of folding can serve as a basic model for any (AB)k multiblock copolymer chain with a non-vanishing attraction between A and B blocks.

Janus Polymerization: A One‐Shot Approach towards Amphiphilic Multiblock Poly(ester‐acetal)s Directly from 1,3‐Dioxolane with ε‐Caprolactone

Comprehensive SummaryJanus polymerization consists of anionic and cationic ring opening polymerizations (AROP and CROP) at the two ends of a single propagating polymer chain, followed by a self‐triggered chain extension generating multiblock copolymers (MBCPs) in one step. In the contribution, Janus polymerization by Tm(OTf)3 or Er(OTf)3 catalyst with an epoxy initiator is applied to synthesize MBCPs of semi‐crystalline poly(ε‐caprolactone) (PCL) blocks from coordinated AROP and poly(1,3‐dioxolane‐co‐ε‐caprolactone) (P(DO‐co‐CL)) blocks from CROP of DO with CL. Meanwhile, amorphous random copolymers [P(DO‐r‐CL)] are synthesized as control by employing other rare earth triflates [RE(OTf)3, RE = Y, Nd, Gd and Lu] as catalysts or in the absence of an initiator via CROP. On account of the distinguishable chemical structures and thermal properties between Janus MBCPs and cationic random copolymers, Janus features are confirmed including the CROP and AROP at a single propagating chain. The resultant amphiphilic copolymers self‐assemble to nanoparticles in aqueous solution with designable diameters with the corresponding ratios of hydrophilic and hydrophobic segments. MBCPs exhibit good shape memory properties with appropriate deformation temperature close to human body's, providing a prospect on the applications in biomedical devices.

Effects of polyimide sequence and monomer structures on CO2 permeation and mechanical properties of sulfonated polyimide/ionic liquid composite membranes

The effects of polymer structure on CO2 separation and mechanical properties of ion gel membranes composed of ionic liquids (ILs) and sulfonated polyimides (SPIs) were investigated. SPIs with different sequential distributions of ionic groups (multiblock and random) were synthesized. The multiblock copolymer exhibited higher IL uptake (∼80 wt.%) than the random copolymer, resulting in higher CO2 permeability (∼480 Barrer). The multiblock copolymer exhibited a clearer phase-separated structure than the random copolymer. However, the strain at the break of the multiblock copolymer was lower owing to the brittleness of the non-ionic phase. To improve the mechanical properties, an SPI containing fluorinated groups as a non-ionic part was also synthesized. Compared with the random SPI ion gel membranes, the multiblock SPI ion gel membranes containing fluorinated groups exhibited good CO2 permeability (∼500 Barrer) and simultaneously ductile properties with higher strain at the break due to the plasticization of the non-ionic phase, enabling a thin and tough membrane with excellent CO2 separation properties. These results indicate that the polyimide sequence in addition to the chemical structure of monomers affects CO2 permeation and mechanical properties of the sulfonated polyimide/ionic liquid composite membranes.

One-step synthesis of sequence-controlled multiblock polymers with up to 11 segments from monomer mixture

Switchable polymerization holds considerable potential for the synthesis of highly sequence-controlled multiblock. To date, this method has been limited to three-component systems, which enables the straightforward synthesis of multiblock polymers with less than five blocks. Herein, we report a self-switchable polymerization enabled by simple alkali metal carboxylate catalysts that directly polymerize six-component mixtures into multiblock polymers consisting of up to 11 blocks. Without an external trigger, the catalyst polymerization spontaneously connects five catalytic cycles in an orderly manner, involving four anhydride/epoxide ring-opening copolymerizations and one L-lactide ring-opening polymerization, creating a one-step synthetic pathway. Following this autotandem catalysis, reasonable combinations of different catalytic cycles allow the direct preparation of diverse, sequence-controlled, multiblock copolymers even containing various hyperbranched architectures. This method shows considerable promise in the synthesis of sequentially and architecturally complex polymers, with high monomer sequence control that provides the potential for designing materials.

Crystallization, thermal and mechanical properties of stereocomplexed poly(lactide) with flexible PLLA/PCL multiblock copolymer.

In this work, the synthesized PLLA/PCL multi-block copolymers with different compositions were introduced into a stereocomplexed poly(lactide) (sc-PLA) matrix to accelerate the stereocomplexation of PLA enantiomers and improve its inherent brittleness. The PLLA/PCL multi-block copolymers were in different compositions to adjust the molecular weight of the PLLA block. The structure, molecular weight, crystallization behavior, crystal structure and thermal stability of PLLA/PCL multi-block copolymers were investigated. The results indicated that PLLA/PCL multi-block copolymers with controllable structure and composition were successfully synthesized. On this basis, the blends of sc-PLA and PLLA/PCL multi-block copolymers were prepared by solution casting, and characterized. The results revealed that the introduction of PLLA/PCL multi-block copolymers promoted the stereocomplexation of the PLA enantiomers during the melting crystallization process to obtain a complete stereocomplexed material. But the presence of the PCL block leads to a decrease in the melting temperature of the stereocomplex and difficulty in homogeneous nucleation. Compared with sc-PLA, the elongation at break of the blends was significantly improved and their tensile strengths were only slightly reduced. And the thermal stability and mechanical properties of the blends could be adjusted by controlling the content and composition of PCL/PLLA multi-block copolymers. These results revealed that the degree of stereocomplexation and toughness of sc-PLA were improved, which may expand the application fields of PLA-based materials.

Dynamic Monte Carlo simulations of strain-induced crystallization in multiblock copolymers: effects of dilution.

Multiblock copolymers containing alternating semicrystalline and molten blocks are good thermoplastic elastomers. Their crystallization in the stretching process is however complicated by the dilution effects, prior microphase separation and contrast chain rigidity of the molten blocks. We designed our systematic investigation with three integrated steps, and herein, as the first step, we considered only the dilution effects without prior microphase separation and contrast chain rigidity. We compared two extreme situations of local dilution separately corresponding to parallel-posited and antiparallel-posited block copolymers upon strain-induced crystallization. Our dynamic Monte Carlo simulations of diblock and tetrablock copolymers demonstrated that the stretching introduces a constraint on the diffusion of locally posited crystallizable blocks along the stretching direction for crystallization and thus enhances the dilution effects to result in a higher diversity in crystal stabilities. We observed that the strain-induced crystallization of parallel-posited copolymers behaved like the melt crystallization of homopolymers; in contrast, the strain-induced crystallization of antiparallel-posited copolymers yielded crystallites near the block junction, which are relatively small and less stable due to their local dilution suppressing their melting points. Similar to the case of spider dragline silks, two contrasting stabilities of crystallites in semicrystalline multiblock copolymers explain their good toughness. Our modeling approach paves the way toward a better understanding of the structure-property relationship in the semicrystalline thermoplastic elastomers.

Multiblock Copolymers with Disulfonated Bis(Phenylsulfonylphenyl) Sulfone Group for Polymer Electrolyte Membrane Water Electrolysis

Multiblock Copolymers with Disulfonated Bis(Phenylsulfonylphenyl) Sulfone Group for Polymer Electrolyte Membrane Water Electrolysis