Structure Of Copolymers Research Articles

Closely Packed Core-Shell Micelle Structures of Double Hydrophilic Miktoarm Star Copolymers at the Air-Water Interface.

The aggregation behavior of amphiphilic block copolymers at the air-water interface has been extensively studied, but less attention was given to that of star copolymers. In this work, we studied the interfacial aggregation behavior of two double hydrophilic pH- and temperature-responsive miktoarm star copolymers of poly[di(ethylene glycol) methyl ether methacrylate]-poly[2-(dimethylamino)ethyl methacrylate] (PDEGMA3-PDMAEMA3 and PDEGMA4-PDMAEMA7, the subscripts denote arm numbers) with different molecular weights. The effects of subphase pH and temperature on the monolayer isotherms and hysteresis curves of the two star copolymers and the morphologies of their Langmuir-Blodgett (LB) films were studied by the Langmuir film balance technique and atomic force microscopy, respectively. At the air-water interface, the two star copolymers tend to form closely packed micelles. These micelles exhibit a core-shell structure, where the small hydrophobic core consists of cross-linker of ethylene glycol dimethacrylate (EGDMA) and the carbon backbones of PDEGMA and PDMAEMA arms and the short hydrophilic shell is composed of di(ethylene glycol) and tertiary amine side groups. With increasing subphase pH, the surface pressure versus molecular area isotherms shift toward larger mean molecular areas as a result of the enhanced interface adsorption of nonprotonated tertiary amine groups. The isotherm shift of PDEGMA3-PDMAEMA3 monolayers is primarily attributed to high density of tertiary amine groups in the shells, while that of PDEGMA4-PDMAEMA7 is mainly attributed to high density of di(ethylene glycol) groups in the shells. The hysteresis degrees in the monolayers of the two copolymers under alkaline and neutral conditions are greater than those under acidic conditions due to the decreased protonation degree of the tertiary amine groups. At 10 °C, the mobility of the shells is poor and the isotherms are located on the right. Above the lower critical solution temperature, di(ethylene glycol) groups contract, which causes a slight shift of the isotherms toward smaller mean molecular areas.

Lamellar Microphase Separation and Phase Transition of Hydrogen-Bonding/Crystalline Statistical Copolymers: Amide Functionalization at the Interface.

Microphase separation of random copolymers, as well as that of high χ-low N block copolymers, is promising to construct sub-10-nm structures into materials. Herein, we designed statistical copolymers consisting of 2-hydroxyethyl acrylate (HEA) and N-octadecylacrylamide (ODAAm) to produce crystallization and hydrogen bond-assisted lamellar structure materials. The copolymers not only formed a crystalline lamellar structure with 3-4 nm domain spacing but also maintained an amorphous lamellar structure via phase transition above the melting temperature up to approximately 100 °C. The key is to introduce hydrogen-bonding amide junctions between the octadecyl groups and the polymer backbones, by which the polymer chains are physically fixed at the interface of lamellar structures even above the melting temperature. The stabilization of the lamellar structure by the amide units is also supported by the fact that the lamellar structure of all-acrylate random copolymers bearing hydroxyethyl and crystalline octadecyl groups is disordered above the melting temperature. By spin-coating on a silicon substrate, the HEA/ODAAm copolymer formed a multilayered lamellar thin film consisting of a hydrophilic hydroxyethyl/main chain phase and a hydrophobic octadecyl phase. The structure and order-disorder transition were analyzed by neutron reflectivity.

The Macromolecular Design of Poly(styrene-isoprene-styrene) (SIS) Copolymers Defines their Performance in Flexible Electrothermal Composite Heaters.

Electric cars are desirable for their environmental and economic benefits yet face limitations in range in cold weather due to the increased energy demands for cabin heating. To provide efficient heating for vehicles, flexible composite electrothermal heaters offer a viable solution owing to their lightweight design, efficiency, and adaptability for use within and beyond vehicle interiors. The current study aims to improve electrothermal heater stability and performance by understanding the impact of the polymer structure on composite properties. We explore how the presence and molecular structure of olefinic bonds within the polyisoprene block of styrenic triblock copolymers affect thermal stability and performance. Composite electrothermal heaters were fabricated by dispersing carbon black (CB) as the heating material in three triblock copolymer matrices, poly(styrene-1,4-isoprene-styrene) (1,4-SIS), poly(styrene-3,4-isoprene-styrene) (3,4-SIS), and its hydrogenated version poly(styrene-ethylene-propylene-styrene) (SEPS). The chemical structure and thermal properties of each copolymer were linked to electrothermal performance measurements of composite heaters to establish structure-function relationships. Notably, 3,4-SIS with 28 wt % CB demonstrated the highest thermal and electrical conductivity, resulting in uniform heat distribution. The outcomes unambiguously demonstrate that the olefinic structure of SIS copolymers enhances the electric and thermal conductivity, leading to enhanced electrothermal performance of prototype heaters compared to that of the hydrogenated copolymer.

Polysaccharides as a Hydrophilic Building Block of Amphiphilic Block Copolymers for the Conception of Nanocarriers.

Polysaccharides are gaining increasing attention for their relevance in the production of sustainable materials. In the domain of biomaterials, polysaccharides play an important role as hydrophilic components in the design of amphiphilic block copolymers for the development of drug delivery systems, in particular nanocarriers due to their outstanding biocompatibility, biodegradability, and structural versatility. The presence of a reducing end in polysaccharide chains allows for the synthesis of polysaccharide-based block copolymers. Compared with polysaccharide-based graft copolymers, the structure of block copolymers can be more precisely controlled. In this review, the synthesis methods of polysaccharide-based amphiphilic block copolymers are discussed in detail, taking into consideration the structural characteristics of polysaccharides. Various synthetic approaches, including reductive amination, oxime ligation, and other chain-end modification reactions, are explored. This review also focuses on the advantages of polysaccharides as hydrophilic blocks in polymeric nanocarriers. The structure and unique properties of different polysaccharides such as cellulose, hyaluronic acid, chitosan, alginate, and dextran are described along with examples of their applications as hydrophilic segments in the synthesis of amphiphilic copolymers to construct nanocarriers for sustained drug delivery.

Thermophysical Properties of Composite Metal-Filled Copolymers of Polyvinylpyrrolidone

The effect of the presence of finely dispersed metal fillers of various natures (Zn, Co, Ni) on the thermophysical characteristics (Vick heat resistance, glass transition temperature) of polyvinylpyrrolidone block copolymers with 2-hydroxyethylmethacrylate was studied. It was found that the heat resistance of the obtained composites significantly exceeds the heat resistance of unfilled copolymers and is in the range of 360-395K, depending on the nature and content of the metal filler. The change in heat resistance correlates with the change in glass transition temperature, which was evaluated according to the results of thermomechanical and dynamic mechanical thermal analyses. The results of this work are an additional source to characterize the structure of metal-filled copolymers: they confirm the participation of metal filler particles in the formation of the nodes of the copolymer spatial network, and also prove the formation of a different polymer network structure in the interfacial layer on the surface of the metal particle and in the polymer volume.

Preparation of xyloglucan-grafted poly(N-hydroxyethyl acrylamide) copolymer by free-radical polymerization for in vitro evaluation of human dermal fibroblasts

Xyloglucan is a rigid polysaccharide that belongs to the carbohydrate family. This hemicellulose compound has been widely used in biomedical research because of its pseudoplastic, mucoadhesive, mucomimetic, and biocompatibility properties. Xyloglucan is a polyose with no amino groups in its structure, which also limits its range of applications. It is still unknown whether grafting hydrophilic monomers onto xyloglucan can produce derivatives that overcome these shortcomings. This work aimed to prepare the first copolymers in which N-hydroxyethyl acrylamide is grafted onto tamarind xyloglucan by free-radical polymerization. The biocompatibility of these structures in vitro was evaluated using human dermal fibroblasts. Gamma radiation-induced graft polymerization was employed as an initiator by varying the radiation dose from 5–25 kGy. The structure of the graft copolymer, Xy-g-poly(N-hydroxyethyl acrylamide), was verified by thermal analysis, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The findings indicate that the degree of grafting and the cytotoxicity/viability of the xyloglucan-based copolymer were independent of dose. Notably, the grafted galactoxyloglucan exhibited efficient support for human dermal fibroblasts, showing heightened proliferative capacity and superior migration capabilities compared to the unmodified polymer. This copolymer might have the potential to be used in skin tissue engineering.

Reactive melt‐grafting of maleic anhydride onto olefin block copolymer toward high‐performance polar polyolefin thermoplastic elastomer

AbstractThe block structure of olefin block copolymer (OBC) elastomer gives it good elasticity and heat resistance relative to other polyolefin elastomers. However, the non‐polar nature of OBC chains limits its comprehensive properties like dyeing and toughening for polar engineering plastics. In this work, maleic anhydride (MA) and dicumyl peroxide (DCP) were selected as a typical polar monomer and a radical initiator to modify the polarity of OBC elastomer. During the melt‐grafting process, the DCP content was tuned to optimize the grafting efficiency while the MA‐to‐OBC ratio was fixed at 5 wt%. It was found that all the melt‐grafting reactions show high efficiency and can be finished in 3 min at 170 °C. With the increase of DCP content, the estimated grafting degree of OBC‐g‐MA elastomer increases from 0.40% to 1.16% along with increased gel content from 4.27% to 22.44%. A suitable grafting process was obtained with a DCP content of 3.0 wt% by balancing grafting efficiency and final mechanical properties. The optimized OBC‐g‐MA elastomer with a grafting degree of 0.92% has a mechanical strength of 17.15 MPa, a Young's modulus of 26.35 MPa, elongation of 1564% and strain recovery of 59.73%. Additionally, the contact angle test shows that polar grafting can increase surface hydrophilicity while excessive crosslinking promotes hydrophobicity. Therefore, our work has demonstrated the feasibility of the reactive melt‐grafting method to prepare OBC‐g‐MA elastomer and can also provide a processing reference for other chemical functionalization of polyolefin thermoplastic elastomers. © 2024 Society of Industrial Chemistry.

Toughening mechanism of α/β core-shell structure for high toughness polypropylene random copolymer

Weak interfaces can impede crack propagation in rigid natural materials containing small amounts of organic compounds. Inspired from this, we start from the core-shell structured isotactic propylene (iPP)/polypropylene random copolymers (PPR) homocomposites and construct serval kinds of interfaces to study the toughening mechanisms by applying the crystallization epitaxies of PPR on iPP. Through molecular chain diffusion and crystallization epitaxy, derived models from microscopic core-shell structured crystals in the homocomposites to macroscopic layer-by-layer assemblies with different interfaces are established to magnify the role that each layer plays during crack initiation and propagation. As a result, the ductile β-PP interface can decrease crack tip strength so that a further step of crack initiation is triggered in the composite laminates with a fold of fracture energy consumption compared to the laminates with weak or rigid interfaces. At last, we come back to the core-shell structured homocomposites and toughen them with an improve in impact toughness from ∼10.8 to ∼18.2 kJ/m2 by manipulating the content of ductile interfaces. This work provides a novel research routine and a new toughening mechanism toward the toughening of PP and can be extended to study the fracture mechanisms of other toughening systems with core-shell structures.

Transient Interfacial Pattern Formation in Block Copolymer Thin Films via Sequential Thermal and Solvent Immersion Annealing.

A variety of structures encountered in nature only arise in materials under highly nonequilibrium conditions, suggesting to us that the scope for creating new functional block copolymer (BCP) structures might be significantly enlarged by embracing complex processing histories that allow for the fabrication of structures quite unlike those created under "near-equilibrium" conditions. The present work examines the creation of polymer film structures in which highly nonequilibrium processing conditions allow for the creation of entirely new types of transient BCP morphologies achieved by transitioning between different ordered states. Most previous studies of BCP materials have emphasized ordering them from their disordered state obtained from a solution film casting process, followed by a slow thermal annealing (TA) process at elevated temperatures normally well above room temperature. We have previously shown that achieving the equilibrium TA state can be accelerated by a direct solvent immersion annealing (DIA) preordering step that creates nascent ordered microstructures, followed by TA. In the present work, we examine the reverse nonequilibrium sequential processing in which we first thermally anneal the BCP film to different levels of partial (lamellar) order and then subject it to DIA to swell the lamellae. This sequential processing rapidly leads to a swelling-induced wrinkle pattern that initially grows with immersion time and can be quenched by solvent evaporation into its corresponding glassy state morphology. The article demonstrates the formation of wrinkling "defect" patterns in entangled BCP films by this sequential annealing that does not form under ordinary TA conditions. At long DIA times, these highly "defective" film structures evolve in favor of the equilibrium morphology of parallel lamellae observed with DIA alone. In conjunction with our previous study of sequential DIA + TA, the present TA + DIA study demonstrates that switching the order of these processing methods for block copolymer films gives the same final state morphology in the limit of long time as any one method alone, but with drastically different intermediate transient state morphologies. These transient morphologies could have many applications.

Spatially Amplified and Rigid Junction in Diblock Copolymers: Reduced Microphase Separation Size via Interface Expansion.

We introduce an approach in diblock copolymer design, where modifying the junction point with rigid bulky monomer expands the cross-sectional area of the interface and leads to a decrease in the repeat period. Using living anionic polymerization, we synthesized a series of dialkynyl midfunctionalized poly(styrene-b-methyl methacrylate) (PSM-DA) and functionalized them using the thiol-alkyne click reaction with specifically selected rigid bulky monomers: PSS-(3-mercapto)propyl-heptaisobutyl substituted (PSS) and 1-adamantanethiol (ADA). This modification, though involving only a single monomer unit within the diblock copolymer structure, brought about a significant reduction in domain size, with PSS and ADA reducing it by 18% and 15%, respectively. The results indicate a method for reducing the domain sizes of block copolymers, which could lead to advancements in lithography and various nanotechnological applications.

Effects of Copolymer Structure on Enzyme-Catalyzed Polyester Recycling

Effects of Copolymer Structure on Enzyme-Catalyzed Polyester Recycling

A mathematical model of thermoplastic elastomers for analysing the topology of microstructures and mechanical properties during elongation

In this study, a mathematical model based on graph theory is developed to analyse the deformed structures and mechanical properties of thermoplastic elastomers (TPEs) using ABA-type triblock copolymers. TPEs exhibit a network structure formed by bridge chains; deformation of this network structure causes stress. During the deformation of TPEs, domain breakage and coalescence occur, accompanied by topological changes in the chains, such as conformational transitions between the bridge and loop chains. By employing the mathematical concepts of harmonic realization of graphs in the physical space and the tension tensor to quantify the stress in the bridge-chain network structure, an effective method for analysing topologicalchanges in microstructures caused by elongation is proposed. As an application of this method, optimal geometric structures of block copolymers with desired functionalities can be determined.

Development of a deep-learning model for phase-separation structure of diblock copolymer based on self-consistent field analysis

Self-consistent field (SCF) analysis is an indispensable tool for predicting the microphase separation structures of polymer alloys. However, the computation of the phase-separated structures in the equilibrium state is computationally intensive, leading to high costs. To address this challenge, we propose a novel deep learning approach that leverages a generative adversarial network (GAN), a powerful deep generative model, to accelerate SCF analysis. Specifically, we trained the GAN using comprehensive data obtained from SCF analysis, enabling us to generate various images of feasible structures that are similar to the SCF analysis results. Our results demonstrate that the latent variables in the GAN are linked to the physical parameters and features of the phase-separation structures.

Synthesis, Properties, and Degradation of Poly(butylene succinate-co-sebacicate-co-salicylicate) Copolyesters

Since monomers in backbone of poly(butylene succinate-co-adipate) (PBSA) are not entirely derived from bio-based sources, limiting its application in the face of increasingly stringent environmental policies. In this study, a novel full bio-based biodegradable random copolyester poly(butylene succinate-co-sebacicate-co-salicylicate) was successfully synthesized. Detailed investigations were conducted on the structural, mechanical, and degradation characteristics resulting from the introduction of salicylicate and sebacicate units. Introduction of salicylicate units effectively enhanced the mechanical performance. In comparison to PBSA, the tensile modulus of copolymer increased by 20.2% with 10% salicylic acid. Introduction of sebacicate units significantly altered the crystalline structure of copolymer and promote the degradation efficiency. Considering both mechanical strength and degradation efficiency, the copolyester with 2% salicylic acid and 20% sebacic acid was found to meet practical application requirements. Relative to PBSA, this copolymer demonstrated a 13.7% increase in tensile modulus and a remarkable 143.1% improvement in degradation efficiency. Importantly, this study focused on the effect of the bio-based rigid monomer salicylic acid and the soft monomer sebacic acid on the degradability of biodegradable polymers. The insights gained provide valuable guidance for tailoring the synthesis of degradable plastics to meet diverse degradation cycle requirements.

Structural study of two polymer chains of poly(2-methoxyethyl glycidyl ether)-b-poly(2-ethoxyethyl glycidyl ether) thermoresponsive block copolymers using molecular dynamics simulations

Block copolymers are expected to be applied in a wide variety of fields due to the property of self-assembly. Our group has reported that poly(glycidyl ether) block copolymers exhibited complex temperature response in aqueous solution. In this study, we investigated the two chains of the block copolymer structure and configurations at different temperatures by using MD simulation. The results showed that at low temperatures, the polymer structure is linear and can form micelles, but above a certain temperature, the polymer structure changes to a U-shape and the micelle structure would be destroyed, which is responsible for the complex temperature response.

Relationship between molecular structure and corrugations in self-assembled polypeptoid nanosheets revealed by cryogenic electron microscopy

Designing conformationally dynamic molecules that self-assemble into predictable nanostructures remains an important unmet challenge. This paper describes how atomic-scale cryogenic transmission electron microscopy (cryo-TEM) can be used to explore the relationship between molecular structure and self-assembly of block copolymers. We examined sheetlike micelles formed in water using a series of diblock copolypeptoids with the same hydrophilic block and three distinct crystalline hydrophobic blocks. Our cryo-TEM images revealed all the structures share nansoscale features, but differ in their intermolecular packing geometries. Different molecular arrangements, parallel and antiparallel V-shaped crystal motifs, were revealed by two-dimensional atomic-scale through-plane images. However, images from tilted samples revealed an unexpected feature when the hydrophobic polypeptoid block comprised phenyl rings with substituted bromine atoms at the para position. The nanosheets contained atomic-scale corrugations that were absent in the other systems which comprised unsubstituted aliphatic and aromatic side chains. We hypothesize that these corrugations are due to the dipolar characteristics of the brominated phenyl group and interactions between this group and water molecules. Published by the American Physical Society 2024

Exploration of complex nanostructures in block copolymers

The exploration of nanoscale morphologies with three-dimensional spatial arrangements in block copolymers involves the manipulation of compositional fluctuations at interfaces, induction of conformational asymmetry, and design of complex architectures. Despite the abundance of triply periodic minimal surfaces identified to date, the experimental demonstration of thermodynamically stable complex nanostructures with high-packing frustration remains limited. This research update focuses on the importance of molecular interactions for stabilizing complex nanostructures and proposes the use of end-group chemistry as a versatile method for realizing thermodynamically stable network structures with high-packing frustration in simple linear diblock copolymers. The proposed approach substantially alters phase diagrams and reveals unprecedented network structures in block copolymers. Ongoing research has the potential to generate even more diverse and stable nanostructures, thereby advancing nanotechnology and expanding our understanding of polymers and materials science. Published by the American Physical Society 2024

Nonadditive Effective Interactions and Entropy-Driven Non-Close-Packed Self-Assembly Cluster of Nanoparticle in Ordered Block Copolymer Structure

Nonadditive Effective Interactions and Entropy-Driven Non-Close-Packed Self-Assembly Cluster of Nanoparticle in Ordered Block Copolymer Structure

The Effect of Colloidal Nanoparticles on Phase Separation of Block and Heteroarm Star Copolymers Confined between Polymer Brushes.

The effect of colloidal nanoparticles on the phase changes of the amphiphilic AB linear diblock, A1A2B, and A2B heteroarm star copolymers confined between two polymer brush substrates was investigated by using a real-space self-consistent field theory. By changing the concentrations of nanoparticles and polymer brushes, the phase structure of the amphiphilic AB copolymer transforms from lamellar to core-shell hexagonal phase to cylinder phase. The pattern of A2B heteroarm star copolymer changes from core-shell hexagonal phases to lamellar phases and the layer decreases when increasing the density of the polymer brushes. The results showed that the phase behavior of the system is strongly influenced by the polymer brush architecture and the colloidal nanoparticle numbers. The colloidal nanoparticles and the soft confined surface of polymer brushes make amphiphilic AB copolymers easier to form ordered structures. The dispersion of the nanoparticles was also investigated in detail. The soft surfaces of polymer brushes and the conformation of the block copolymers work together to force the nanoparticles to disperse evenly. It will give helpful guidance for making some new functional materials by nano etching technology, nano photoresist, and nanoprinting.

A novel anion exchange membrane comprised of three aromatic units for fuel cells

Anion exchange membrane fuel cell (AEMFC) has made great progress recently due to the continuous improvement of anion exchange membrane (AEM). Aryl ether bond-free membranes are considered to be promising for improving the overall performance of AEMs. Here, we present a copolymer consisting of m-terphenyl, diphenyl ethane and biphenyl (PMDBP) to further enhance the microphase separation structure by introducing a third structural unit, biphenyl. Meanwhile, the more compact biphenyl structure enhances the mechanical strength of AEMs. Specifically, PMDBP AEMs possess superior OH- conductivity (up to 113 mS cm−1) and excellent mechanical properties (tensile strength up to 42 MPa). Furthermore, the PMDBP has an outstanding single-cell performance with a peak power density (PPD) of up to 95 mW cm−2 with a platinum-carbon (Pt/C) catalyst at 80°C in H2-air. In addition, PMDBP is provided with excellent durability, including NMR spectral consistency and over 90% ion conductivity retention in 1 M NaOH at 60°C for 720 h. This study provided a copolymer structure suitable for anion exchange membrane that can provide excellent performance for fuel cells and electrolyzers.