Multiblock Copolymers Research Articles

Simultaneously Enhanced Chain Flexibility, Three Dimensional Printability, and Reduction of Shrinkage Stress in Biodegradable and Photocurable Multiblock Copolymers

A library of biodegradable and photocurable poly(propylene fumarate)-co-poly(trimethylene carbonate) (PPF-co-PTMC) multiblock copolymers encompassing the entire composition range and various block lengths has been designed and synthesized. By combining experiments and atomistic molecular dynamics simulations, we reveal the effects of chain architectures such as composition and block lengths on the thermal, rheological, and printing properties of these copolymers. The introduction of flexible PTMC blocks, which are found to be highly miscible with PPF blocks, into the unentangled copolymer backbone dramatically expedites chain relaxation, lowers the activation energy, and enhances the solubility in toluene. The chain flexibility of the copolymers is positively correlated with the composition of PTMC, while the block length of either PPF or PTMC affects little. Thus, lower values in glass transition temperature Tg, zero-shear viscosity η0, printing speed, and shrinkage stress in photocuring are consistently seen at higher compositions of PTMC. Photocurable PPF-co-PTMCs can be printed into high-precision 3D objects. This study provides a series of novel biopolymers and also a guideline to design photocurable polymers used in biomedical implants.

Emergence and Stability of Hierarchical Structures under Cylindrical Confinement

Front Cover: In article number 2200076, Tiancheng Chen and Yuci Xu study the self-assembly of A(BC)2B multiblock copolymer in a nanopore using the self-consistent field theory. Obtain the hierarchical concentric ring (HCk), hierarchical perforated cylinder (HPk), hierarchical helix (HHk), and hierarchical disk (HDk) in research. Then discuss the stability of hierarchical structures by exploring the influence of pore size and χAB on k.

ONE-POT SYNTHESIS OF NORBORNENE-CYCLOOCTENE COPOLYMERS

The one-pot synthesis of random multiblock copolymers of norbornene and cyclooctene has been performed for the first time. It is shown that the first generation Grubbs Ru-carbene complex makes it possible to obtain these copolymers directly from monomers. In the course of one-pot synthesis, the metathesis polymerization of norbornene, which has a markedly higher ring strain, occurs first. Then, cyclooctene polymerizes and simultaneously an interchain cross-metathesis reaction takes place, during which the block structure of the copolymer is formed. Compared to the previously studied interaction of polynorbornene and polycyclooctene, the one-pot method makes it possible to obtain copolymers with a higher molar mass at a lower catalyst consumption.

Effect of Chain Structure on the Various Properties of the Copolymers of Fluorinated Norbornenes with Cyclooctene.

Fluorinated polymers are attractive due to their special thermal, surface, gas separation, and other properties. In this study, new diblock, multiblock, and random copolymers of cyclooctene with two fluorinated norbornenes, 5-perfluorobutyl-2-norbornene and N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide, are synthesized by ring-opening metathesis copolymerization and macromolecular cross-metathesis in the presence of the first- to third-generation Grubbs' Ru-catalysts. Their thermal, surface, bulk, and solution characteristics are investigated and compared using differential scanning calorimetry, water contact angle measurements, gas permeation, and light scattering, respectively. It is demonstrated that they are correlated with the chain structure of the copolymers. The properties of multiblock copolymers are generally closer to those of diblock copolymers than of random ones, which can be explained by the presence of long blocks capable of self-organization. In particular, diblock and multiblock fluorine-imide-containing copolymers show a tendency to form micelles in chloroform solutions well below the overlap concentration. The results obtained may be of interest to a wide range of researchers involved in the design of functional copolymers.

Nanocarbon-Based Mixed Matrix Pebax-1657 Flat Sheet Membranes for CO2/CH4 Separation.

In the present work, Pebax-1657, a commercial multiblock copolymer (poly(ether-block-amide)), consisting of 40% rigid amide (PA6) groups and 60% flexible ether (PEO) linkages, was selected as the base polymer for preparing dense flat sheet mixed matrix membranes (MMMs) using the solution casting method. Carbon nanofillers, specifically, raw and treated (plasma and oxidized) multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) were incorporated into the polymeric matrix in order to improve the gas-separation performance and polymer's structural properties. The developed membranes were characterized by means of SEM and FTIR, and their mechanical properties were also evaluated. Well-established models were employed in order to compare the experimental data with theoretical calculations concerning the tensile properties of MMMs. Most remarkably, the tensile strength of the mixed matrix membrane with oxidized GNPs was enhanced by 55.3% compared to the pure polymeric membrane, and its tensile modulus increased 3.2 times compared to the neat one. In addition, the effect of nanofiller type, structure and amount to real binary CO2/CH4 (10/90 vol.%) mixture separation performance was evaluated under elevated pressure conditions. A maximum CO2/CH4 separation factor of 21.9 was reached with CO2 permeability of 384 Barrer. Overall, MMMs exhibited enhanced gas permeabilities (up to fivefold values) without sacrificing gas selectivity compared to the corresponding pure polymeric membrane.

Dynamic crosslinking compatibilizes immiscible mixed plastics.

The global plastics problem is a trifecta, greatly affecting environment, energy and climate1-4. Many innovative closed/open-loop plastics recycling or upcycling strategies have been proposed or developed5-16, addressing various aspects of the issues underpinning the achievement of a circular economy17-19. In this context, reusing mixed-plastics waste presents a particular challenge with no current effective closed-loop solution20. This is because such mixed plastics, especially polar/apolar polymer mixtures, are typically incompatible and phase separate, leading to materials with substantially inferior properties. To address this key barrier, here we introduce a new compatibilization strategy that installs dynamic crosslinkers into several classes of binary, ternary and postconsumer immiscible polymer mixtures in situ. Our combined experimental and modelling studies show that specifically designed classes of dynamic crosslinker can reactivate mixed-plastics chains, represented here by apolar polyolefins and polar polyesters, by compatibilizing them via dynamic formation of graft multiblock copolymers. The resulting in-situ-generated dynamic thermosets exhibit intrinsic reprocessability and enhanced tensile strength and creep resistance relative to virgin plastics. This approach avoids the need for de/reconstruction and thus potentially provides an alternative, facile route towards the recovery of the endowed energy and materials value of individual plastics.

Biobased and Compostable Multiblock Copolymer of Poly(l-lactic acid) Containing 2,5-Furandicarboxylic Acid for Sustainable Food Packaging: The Role of Parent Homopolymers in the Composting Kinetics and Mechanism.

In the last years, the exponential growth in the demand of petroleum-based plastic materials, besides the extreme exploitation of nonrenewable resources, lead to the mismanagement of their disposal and to serious ecological issues related to their dispersion in the environment. Among the possible practical solutions, the design of biobased and biodegradable polymers represents one of the most innovative challenges. In such a context, the eco-design of an aromatic-aliphatic multiblock copolymer based on poly(lactic acid) and containing 2,5-furandicarboxylic acid was carried out with the aim of improving the properties of poly(l-lactic acid) for sustainable packaging applications. The synthetic method followed a novel top-down approach, starting from industrial high-molecular-weight poly(l-lactic acid) (PLLA), which was reacted with 1,5-pentanediol to get hydroxyl-terminated PLLA and then chain-extended with hydroxyl-terminated poly(pentamethylene furanoate) (PPeF-OH). The final copolymer, called P(LLA50PeF50)-CE, was subjected to molecular, structural, and thermal characterization. Tensile and gas permeability tests were also carried out. According to the results obtained, PLLA thermal stability was improved, being the range of processing temperatures widened, and its stiffness and brittleness were decreased, making the new material suitable for the realization of films for flexible packaging. The oxygen permeability of PLLA was decreased by 40% and a similar improvement was measured also for carbon dioxide. P(LLA50PeF50)-CE was found to be completely biodegraded within 60 days of composting treatment. In terms of mechanism, the blocks of PPeF and PLLA were demonstrated to undergo surface erosion and bulk hydrolysis, respectively. In terms of kinetics, PPeF blocks degraded slower than PLLA ones.

Reversible Thermo-Optical Response Nanocomposites Based on RAFT Symmetric Triblock Copolymers (ABA) of Acrylamide and N-Isopropylacrylamide and Gold Nanoparticles.

The development of composite materials with thermo-optical properties based on smart polymeric systems and nanostructures have been extensively studied. Due to the fact of its ability to self-assemble into a structure that generates a significant change in the refractive index, one of most attractive thermo-responsive polymers is poly(N-isopropylacrylamide) (PNIPAM), as well as its derivatives such as multiblock copolymers. In this work, symmetric triblock copolymers of polyacrylamide (PAM) and PNIPAM (PAMx-b-PNIPAMy-b-PAMx) with different block lengths were prepared by reversible addition-fragmentation chain-transfer polymerization (RAFT). The ABA sequence of these triblock copolymers was obtained in only two steps using a symmetrical trithiocarbonate as a transfer agent. The copolymers were combined with gold nanoparticles (AuNPs) to prepare nanocomposite materials with tunable optical properties. The results show that copolymers behave differently in solution due to the fact of variations in their composition. Therefore, they have a different impact on the nanoparticle formation process. Likewise, as expected, an increase in the length of the PNIPAM block promotes a better thermo-optical response.

Preparation and Fractionation of Poly(ethylene oxide)‐Poly(N‐tert‐butylacrylamide) Alternating Multiblock Copolymers

AbstractPreparation and fractionation of poly(ethylene oxide) (PEO)‐poly(N‐tert‐butylacrylamide) (PNtBAm) alternating multiblock (AMB) copolymers have been reported. A reversible addition‐fragmentation chain transfer (RAFT) polymerization is used for preparing α,ω‐dicarboxy PNtBAm. 1H NMR measurements reveal that the conversion of N‐tert‐butylacrylamide (NtBAm) becomes 78% at 30 min after the initiation, and then reaches plateau with ca. 88% at 60 min. The molecular weight distribution of α,ω‐dicarboxy PNtBAm is 1.1–1.2, indicating that the RAFT polymerization is successfully carried out. α,ω‐Dicarboxy PNtBAms with 10 and 19 of the polymerization degree have been used to prepare PEO‐PNtBAm AMB copolymers after the active esterification. The precipitation fractionation of PEO‐PNtBAm AMB copolymers is performed with an acetone/n‐hexane mixed solvent. The molecular weight of the fractionated samples decreases in the order of precipitation, while the PEO/PNtBAm ratio of the fractionated samples is almost identical. The precipitation fractionation of the PEO‐PNtBAm AMB copolymer can be carried out in the same manner for general homopolymers.

Multi-Block Copolymer Membranes Consisting of Sulfonated Poly(p-phenylene) and Naphthalene Containing Poly(arylene Ether Ketone) for Proton Exchange Membrane Water Electrolysis

Glassy hydrocarbon-based membranes are being researched as a replacement for perfluorosulfonic acid (PFSA) membranes in proton exchange membrane water electrolysis (PEMWE). Here, naphthalene containing Poly(arylene Ether Ketone) was introduced into the Poly(p-phenylene)-based multi-block copolymers through Ni(0)-catalyzed coupling reaction to enhance π-π interactions of the naphthalene units. It is discovered that there is an optimum input ratio of the hydrophilic monomer and NBP oligomer for the multi-block copolymers with high ion exchange capacity (IEC) and polymerization yield. With the optimum input ratio, the naphthalene containing copolymer exhibits good hydrogen gas barrier property, chemical stability, and mechanical toughness, even with its high IEC value over 2.4 meq g-1. The membrane shows 3.6 times higher proton selectivity to hydrogen gas than Nafion 212. The PEMWE single cells using the membrane performed better (5.5 A cm-2) than Nafion 212 (4.75 A cm-2) at 1.9 V and 80 °C. These findings suggest that naphthalene containing copolymer membranes are a promising replacement for PFSA membranes in PEMWE.

Janus Effect of Lewis Acid Enables One‐Step Block Copolymerization of Ethylene Oxide andN‐Sulfonyl Aziridine

AbstractOne‐step sequence‐selective block copolymerization requires stringent catalytic control of monomers relative activity and enchainment order. It has been especially rare for AnBm‐type block copolymers from simple binary monomer mixtures. Here, ethylene oxide (EO) andN‐sulfonyl aziridine (Az) compose a valid pair provided with a bicomponent metal‐free catalyst. Optimal Lewis acid/base ratio allows the two monomers to strictly block‐copolymerize in a reverse order (EO‐first) as compared with the conventional anionic route (Az‐first). Livingness of the copolymerization facilitates one‐pot synthesis of multiblock copolymers by addition of mixed monomers in batches. Calculation results reveal that a Janus effect of Lewis acid on the two monomers is key to enlarge the activity difference and reverse the enchainment order.

Janus Effect of Lewis Acid Enables One-Step Block Copolymerization of Ethylene Oxide and N-Sulfonyl Aziridine.

One-step sequence-selective block copolymerization requires stringent catalytic control of monomers relative activity and enchainment order. It has been especially rare for AnBm-type block copolymers from simple binary monomer mixtures. Here, ethylene oxide (EO) and N-sulfonyl aziridine (Az) compose a valid pair provided with a bicomponent metal-free catalyst. Optimal Lewis acid/base ratio allows the two monomers to strictly block-copolymerize in a reverse order (EO-first) as compared with the conventional anionic route (Az-first). Livingness of the copolymerization facilitates one-pot synthesis of multiblock copolymers by addition of mixed monomers in batches. Calculation results reveal that a Janus effect of Lewis acid on the two monomers is key to enlarge the activity difference and reverse the enchainment order.

Bisphenol-Derived Single-Ion Conducting Multiblock Copolymers as Lithium Battery Electrolytes: Impact of the Bisphenol Building Block

Bisphenol-Derived Single-Ion Conducting Multiblock Copolymers as Lithium Battery Electrolytes: Impact of the Bisphenol Building Block

Precise Synthesis of Sequence-Controlled Oxygen-Rich Multiblock Copolymers via Reversible Carboxylation of a Commercial Salen-Mn(III) Catalyst

Precise Synthesis of Sequence-Controlled Oxygen-Rich Multiblock Copolymers via Reversible Carboxylation of a Commercial Salen-Mn(III) Catalyst

Cell Spheroid Formation on the Surface of Multi-Block Copolymers Composed of Poly(2-methoxyethyl acrylate) and Polyethylene Glycol.

3D structured cells have great drug screening potential because they mimic in vivo tissues better than 2D cultured cells. In this study, multi-block copolymers composed of poly(2-methoxyethyl acrylate) (PMEA) and polyethylene glycol (PEG) are developed as a new kind of biocompatible polymers. PEG imparts non-cell adhesion while PMEA acts as an anchoring segment to prepare the polymer coating surface. The multi-block copolymers show higher stability in water than PMEA. A specific micro-sized swelling structure composed of a PEG chain is observed in the multi-block copolymer film in water. A single NIH3T3-3-4 spheroid is formed in 3h on the surface of the multi-block copolymers with 8.4 wt% PEG. However, at a PEG content of 0.7 wt%, spheroid formed after 4 days. The adenosine triphosphate (ATP) activity of cells and the internal necrotic state of the spheroid change depending on PEG loading in the multi-block copolymers. As the formation rate of cell spheroid on low-PEG-ratio multi-block copolymers is slow, internal necrosis of cell spheroid is less likely to occur. Consequently, the cell spheroid formation rate by changing the PEG chain content in multi-block copolymers is successfully controlled. These unique surfaces are suggested to be useful for 3D cell culture.

Emergence and Stability of Hierarchical Structures under Cylindrical Confinement

AbstractFocusing on the formation of hierarchical structure under cylindrical confinement, the self‐assembly of A(BC)2B multiblock copolymer of chain length N in a nanopore with size R is studied using the self‐consistent field theory. The hierarchical concentric ring (HCk), hierarchical perforated cylinder (HPk), hierarchical helix (HHk), and even hierarchical disk (HDk) is obtained with different number of mid‐thin layers k via a proposed design principle. The results show that large pore size and χAB favor the hierarchical structure with more k, while χBC prefers hierarchical structure with less k, consistent with the results of hierarchical structure in bulk. By investigating the effect of the volume fraction of the tail A block (fA), the phase transition sequence, HCk → HPk → HHk → HDk is explored, which shares the same transition of multiblock copolymer in bulk with Lk → Gk → Ck → Sk. Finally, the phase diagram with respect to the fA and R is explored, where the stability regime of these hierarchical structures is well understood. The results provide a compelling panacea for the fabrication of hierarchical 3D nanostructures under confinement.

Inverse Design of Complex Block Copolymers for Exotic Self-Assembled Structures Based on Bayesian Optimization.

Variable chain topologies of multiblock copolymers provide great opportunities for the formation of numerous self-assembled nanostructures with promising potential applications. However, the consequent large parameter space poses new challenges for searching the stable parameter region of desired novel structures. In this Letter, by combining Bayesian optimization (BO), fast Fourier transform-assisted 3D convolutional neural network (FFT-3DCNN), and self-consistent field theory (SCFT), we develop a data-driven and fully automated inverse design framework to search for the desired novel structures self-assembled by ABC-type multiblock copolymers. Stable phase regions of three exotic target structures are efficiently identified in high-dimensional parameter space. Our work advances the new research paradigm of inverse design in the field of block copolymers.

General weak segregation theory with an application to monodisperse semi-flexible diblock copolymers.

A general theory has been developed for a polydisperse semi-flexible multi-block copolymer melt. Using the Bawendi-Freed approach to model semi-flexible chains, an expression for the Landau free energy is derived in the weak segregation regime, which includes density and orientation order-parameters. The orientation order-parameter is described in the smectic phase and in more complicated structures, such as the hexagonal phase. The Landau free energy contains contributions of two kinds of interactions. The first kind is the Flory-Huggins interaction, which describes the incompatibility of chemically different blocks and may induce microphase separation. The second kind is the Maier-Saupe interaction, which may induce nematic ordering. In the framework of the weak segregation limit, the Landau theory allows us to predict phase structures in the melt as a function of the composition, persistence length, and the strength of the Flory-Huggins and Maier-Saupe interaction. The general theory is applied to a simple system of monodisperse semi-flexible diblock copolymers. In several phase diagrams, a number of possible phase structures are predicted, such as the bcc, hexagonal, smectic-A, smectic-C, and nematic phase. The influence of the Maier-Saupe interaction on the microphase structure is thoroughly discussed.

Phase behavior of medium-length hydrophobically associating PEO-PPO multiblock copolymers in aqueous media

HypothesisThe micellization of block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) is driven by the dehydration of PPO at elevated temperatures. At low concentrations, a viscous solution of isolated micelles is obtained, whereas at higher concentrations, crowding of micelles results in an elastic gel. Alternating PEO-PPO multiblock copolymers are expected to exhibit different phase behavior, with altered phase boundaries and thermodynamics, as compared to PEO-PPO-PEO triblock copolymers (Pluronics®) with equal hydrophobicity, thereby proving the pivotal role of copolymer architecture and molecular weight. ExperimentsMultiple characterization techniques were used to map the phase behavior as a function of temperature and concentration of PEO-PPO multiblock copolymers (ExpertGel®) in aqueous solution. These techniques include shear rheology, differential and adiabatic scanning calorimetry, isothermal titration calorimetry and light transmittance. The micellar size and topology were studied by dynamic light scattering. FindingsMultiblocks have lower transition temperatures and higher thermodynamic driving forces for micellization as compared to triblocks due to the presence of more than one PPO block per chain. With increasing concentration, the multiblock copolymers in solution gradually evolve into a viscoelastic network formed by soluble bridges in between micellar nodes, whereas hairy triblock micelles jam into liquid crystalline phases resembling an elastic colloidal crystal.

Easy Access to Diverse Multiblock Copolymers with On-Demand Blocks via Thioester-Relayed In-Chain Cascade Copolymerization.

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.