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

One-Step Radical-Induced Synthesis of Graft Copolymers for Effective Compatibilization of Polyethylene and Polypropylene

The synthesis of copolymers from high-density polyethylene (HDPE) and isotactic polypropylene (iPP) has gained increasing attention due to their ability to improve the recycling of incompatible mixed polyolefin waste feed streams. Herein, we report a new radical grafting process that yields HDPE-g-iPP copolymers from HDPE and iPP by using a commercially available peroxide. Tensile testing of brittle 70/30 HDPE/iPP mixtures with these graft copolymers added showed promising compatibilization, improving the elongation at break of the blends from 20% up to 1080%. Detailed kinetic studies coupled with thermal and rheological characterization revealed optimized conditions for HDPE and iPP macroradical coupling and a deeper understanding of the grafting reaction. This optimization yielded HDPE-g-iPP copolymers that compatibilize HDPE and iPP blends at loadings as low as 2.5 wt %. The versatility of this macroradical grafting reaction was demonstrated by preparing an effective compatibilizer from untreated postconsumer waste plastics.

PLA Block Polymers: Versatile Materials for a Sustainable Future

Block polymers present an almost endless realm of possibilities to develop functional materials for myriad applications. The established self-assembly of block polymers allows researchers to access properties that are inaccessible in homopolymers. However, there is a need to develop more sustainable options than the current commodity block polymers. Derived from renewable resources and industrially compostable, poly(lactide) (PLA) is at the forefront of technological advancements in sustainable block polymers. Its material properties including high stiffness, relatively high glass transition temperature, and semicrystallinity in isotactic versions lend themselves to many applications, and its ease of synthesis provides a well-established platform for developing high-performance materials. This Perspective highlights recent advancements associated with PLA-containing block polymers, including their syntheses, mesostructural considerations, and mechanical properties, from resilient elastomers to tough plastics. We also give our perspective on the subfield of PLA block polymers, our outlook on the future, and our assessment of exciting developments yet to come.

Tandem ADMET and CAMMP to Access Degradable Thermosets and Multiblock Copolymers

The development of degradable polymers and multiblock copolymeric (MBCP) compatibilizers represents an appealing strategy to address ever-growing concerns for treating waste plastics of traditional chemical degradation or mechanical recycling. Although recent advancements in cyclic-acyclic monomers metathesis polymerization (CAMMP) and tandem olefin metathesis polymerization (TOMP) have recently been reported to produce degradable polymers and MBCPs via copolymerization of cyclic monomers with acyclic diene comonomers, there have been no reports of preparing high-performance thermosetting materials and multiblock copolymers within the same polymerization system solely through the selection of cycloolefin monomers. To achieve this objective, a TOMP system has been designed that combines acyclic diene metathesis (ADMET) polymerization of diene comonomers followed by CAMMP with cyclic olefin monomers (dicyclopentadiene DCPD or cyclooctene COE). The selection of different cyclic olefin monomers provided access to degradable cross-linked thermosets and multiblock copolymers. Notably, this one-pot, two-step process is highly efficient and requires the addition of only one metathesis catalyst.

Tetragonally and Rectangularly Packed Hierarchical Cylinders from A1BA2C Tetrablock Terpolymer

Hierarchical cylindrical nanostructures with different diameters (or shapes) have received much attention because of potential applications to next-generation lithography or advanced optical devices. Herein, via small-angle X-ray scattering and transmission electron microscopy, tetragonally and rectangularly packed hierachical cylindrical nanostructures are observed by tailoring the volume fraction of polystyrene mid-block in polystyrene-b-polyisoprene-b-polystyrene-b-poly(2-vinylpyridine) tetrablock terpolymer (S1IS2V). P2VP becomes the main cylinder, while PI forms satellite cylinders surrounding the main P2VP cylinder. When the length of S2 block is relatively short, tetragonal arrangement of cylinders is observed. But, a rectangular arrangement of cylinders is formed for larger S2 block. The experimentally observed hierarchical cylindrical nanostructures are in good agreement with the prediction by the self-consistent field theory.

Linear Radical Additions-Coupling Polymerization (LRAsCP): Model, Experiment and Application

Exploring new polymerization strategies for currently available monomers is a challenge in polymer science. Herein, a bifunctional initiator (BFI) is introduced for the conventional radical polymerization of a vinyl monomer, resulting in linear radical additions-coupling polymerization (LRAsCP). In LRAsCP, the coupling reaction alongside the addition reaction of the radicals contributes to the construction of polymer chains, which leads to stepwise growth of the multiblock structure. Theoretical analysis of LRAsCP predicted variation of some structural parameters of the resulting multiblock polymer (MBP) with the extent of initiation of the BFI and the termination factor of the radicals. Simultaneous and cascade initiations of the BFI were compared. LRAsCP of styrene was conducted, and a kinetics study was carried out. The increment in Mn with polymerization time demonstrated the stepwise mechanism of the formation of the MBP. The variation of the structural parameters of MBP fitted well with the theoretical prediction. Two-step LRAsCP was conducted and multiblock copolymers (MBcP) were obtained either by in situ copolymerization of styrene and MMA or by a second copolymerization of styrene and BMA. The current results demonstrate that the introduction of a BFI to conventional radical polymerization generates a new polymerization strategy, leading to a new chain architecture, which can be extended to other radical polymerizable monomers.

Tunable and Degradable Dynamic Thermosets from Compatibilized Polyhydroxyalkanoate Blends

Polyhydroxyalkanoates (PHAs) are versatile, biobased polyesters that are often targeted for use as degradable thermoplastic replacements for polyolefins. Given the substantial chemical diversity of PHA, their potential as cross-linked polymers could also enable similar platforms for reversible, degradable thermosets. In this work, we genetically engineered Pseudomonas putida KT2440 to synthesize poly(3-hydroxybutyrate-co-3-hydroxyundecenoate) (PHBU), which contains both 3-hydroxybutyrate and unsaturated 3-hydroxyundecenoate components. To reduce the brittleness of this polymer, we physically blended PHBU with the soft copolymer poly(3-hydroxydecanonate-co-3-hydroxyundecenoate) in mass ratios of 1:3, 1:1, and 3:1. Upon observing varying degrees of immiscibility by scanning electron microscopy, we installed dynamic boronic ester cross-links via thiol-ene click chemistry, which resulted in compatibilized dynamic thermoset blends ranging in hard, medium, and soft rubber or elastomer thermomechanical profiles. These dynamic thermoset blends were subjected to controlled biological degradation experiments in freshwater conditions, achieving timely mass loss despite the cross-linked architectures. Overall, this work highlights a two-component platform for the production of degradable and reprocessable dynamic thermoset blends suitable for several classes of cross-linked polymer technologies from tailored, biological PHA copolymers.

Synthesis of highly effective polyester/polyacrylate compatibilizers using switchable polymerization

Multiblock copolymers (MBCPs) comprising polyester and polyacrylate segments offer an efficient strategy for enhancing the performance of polyester and polyolefin blends but synthesis and structural modification of these MBCPs remains challenging. Here, we propose a method for synthesizing MBCPs via the switchable polymerization of epoxides, cyclic anhydrides, and acrylates using a dinuclear Co-complex, wherein the anhydride acts as a switcher. Detailed studies on the copolymerization process reveal that the successful synthesis of MBCPs is achieved by intramolecular bimetallic synergistic catalysis, producing MBCPs with controlled molecular weights and narrow dispersities. Owing to the high compatibility of the monomers, this method allows for producing MBCPs with diverse structures and block numbers. Moreover, the resulting MBCPs effectively enhance the performance of the polyester and polyacrylate blends, improving the toughness of polyesters. Studies on microphase separation show that MBCPs can effectively compatibilize immiscible blends, highlighting their potential as compatibilizers.

Automated Ultra-Fast 13C NMR Analysis of Polyolefin Materials

Polyolefins are unique among synthetic polymers because their wide application envelope originates from a finely controlled microstructure of hydrocarbon chains, lacking any distinctive functional groups. This hampers the methods of automated sorting based on vibrational spectroscopies and calls for much more complex 13C NMR elucidations. High-temperature cryoprobes have dramatically shortened the acquisition time of 13C NMR spectra, and few minutes are now enough for polyolefin classification purposes; however, conventional data analysis remains labor and time-consuming. In this paper, we introduce an instrument for automated fast determinations of the 13C NMR microstructure on polyolefin materials, implemented by integrating High-Throughput Experimentation and Data Science tools and methods. From the scientific standpoint, the main interest of the approach is the solution proposed to address the general problem how to rapidly characterize statistically distributed analytes, of which synthetic polymers are a most important case. In practical terms, the instrument represents the first automated tool for microstructural polyolefin analysis: it is readily applicable to monomaterials, whereas extension to multimaterials, including postconsumer streams, is feasible but still requires some work.

Building Ultrastrong, Tough and Biodegradable Thermoplastic Elastomers from Multiblock Copolyesters Via a "Reserve-Release" Crystallization Strategy

Simultaneously attaining high strength and toughness has been a significant challenge in designing thermoplastic elastomers, especially biodegradable ones. In this context, we present a class of biodegradable elastomers based on multiblock copolyesters that afford extraordinary strength, toughness, and low-strain resilience despite expedient chemical synthesis and sample processing. With the incorporation of the semi-crystalline soft block and the judicious selection of block periodicity, the thermoplastic materials feature low quiescent crystallinity ("reserve") albeit with vast potential for strain-induced crystallization ("release"), resulting in their significantly enhanced ultimate strength and energy-dissipating capabilities. Moreover, a breadth of mechanical responses of the materials - from reinforced elastomers to shape-memory materials to toughened thermoplastics - can be achieved by orthogonal variation of segment lengths and ratios. This work and the "reserve-release" crystallization strategy herein highlight the double crystalline multiblock chain architecture as a potential avenue towards reconciling the strength-toughness trade-off in thermoplastic elastomers and can possibly be extended to other biodegradable building blocks to deliver functional materials with diverse mechanical performances.

Supramolecular Polymer Additives as Repairable Reinforcements for Dynamic Covalent Networks

Employing rigid (in)organic materials as reinforcement for dynamic covalent networks (DCNs) is an effective approach to develop high-performance materials. Yet, recycling of these materials after failure often necessitates inefficient chemical reprocessing or inevitably alters their performance due to unrepairable inert components. Here, a non-covalent reinforcement strategy is presented by introducing a supramolecular additive to a DCN that can reversibly depolymerize and reform on demand, therefore acting as an adaptive and repairable reinforcement. The strong hydrogen-bonding interactions in the supramolecular polymer of triazine-1,3,5-tribenzenecarboxamide (S-T) strengthen the DCN at room temperature, while its non-covalent nature allows for easy one-pot reprocessing at high temperatures. Depending on wether S-T is covalently bond to the DCN or not, it can play either the role of compatibilizer or filler, providing a synthetic tool to control the relaxation dynamics, reprocessability and mechanical properties. Moreover, the S-T reinforcement can be chemically recovered with high yield and purity, showcasing the recyclability of the composite. This conceptually novel supramolecular reinforcement strategy with temperature-controlled dynamics highlights the potential of supramolecular polymer additives to replace conventional unrepairable reinforcements.

Research Trends in the Development of Block Copolymer-Based Biosensing Platforms

Biosensing technology, which aims to measure and control the signals of biological substances, has recently been developed rapidly due to increasing concerns about health and the environment. Top-down technologies have been used mainly with a focus on reducing the size of biomaterials to the nano-level. However, bottom-up technologies such as self-assembly can provide more opportunities to molecular-level arrangements such as directionality and the shape of biomaterials. In particular, block copolymers (BCPs) and their self-assembly have been significantly explored as an effective means of bottom-up technologies to achieve recent advances in molecular-level fine control and imaging technology. BCPs have been widely used in various biosensing research fields because they can artificially control highly complex nano-scale structures in a directionally controlled manner, and future application research based on interactions with biomolecules according to the development and synthesis of new BCP structures is greatly anticipated. Here, we comprehensively discuss the basic principles of BCPs technology, the current status of their applications in biosensing technology, and their limitations and future prospects. Rather than discussing a specific field in depth, this study comprehensively covers the overall content of BCPs as a biosensing platform, and through this, we hope to increase researchers' understanding of adjacent research fields and provide research inspiration, thereby bringing about great advances in the relevant research fields.

Advances in Nonreactive Polymer Compatibilizers for Commodity Polyolefin Blends

Recycling mixed polyolefin plastics is a significant challenge due to the limitations in sorting and degraded mechanical properties of blends. Nonreactive compatibilization by adding a small amount of polymeric additive is a widespread approach to restoring the performance and value of recycled plastics. Over the past several decades, synthetic advances have enabled access to low-cost copolymers and precision architectures for deepening the understanding of compatibilization mechanisms in semicrystalline polyolefins. This review covers the design parameters of a polymeric compatibilizer, the testing of blends, the synthetic methods of producing economically viable additives, and surveys the literature of blends of compatibilized HDPE, LLDPE, LDPE, and iPP. From this, readers should gain a comprehension of the polymer mechanics, synthesis, and macromolecular engineering of processable polyolefin blends, along with the field's future directions.

Functional Upcycling of Polyurethane Thermosets into Value-Added Thermoplastics via Small-Molecule Carbamate-Assisted Decross-Linking Extrusion

The cross-linked structures of most commodity polyurethanes (PUs) hinder their recycling by common mechanical/chemical approaches. Catalyzed dynamic carbamate exchange emerges as a promising PU recycling strategy, which converts traditional static PU thermosets into reprocessable covalent adaptable networks (CANs). However, this approach has been limited to thermoset-to-thermoset reprocessing of PU CANs, accompanied by their well-preserved network structures and extremely high viscosities, which pose challenges to processing and certain applications. This study reports a catalytic decross-linking extrusion process aided by small-molecule carbamates, which can upcycle PU thermosets into easily processable and functional PU thermoplastics in a solvent-free and high-throughput manner. Key to this process is the employment of small-molecule carbamates as decross-linkers to simultaneously deconstruct cross-linked PUs and functionalize the decross-linked PU chains, through catalyzed carbamate exchange reactions in a twin-screw extruder. This strategy applies to both aromatic and aliphatic cross-linked PU films and foams, and the amount of small-molecule carbamates required to decross-link PU networks is determined through thermal, chemical, and structural analyses of the resulting extrudates. This approach is generalizable to small-molecule carbamates with various steric/electronic structures and chemical functionalities including methacrylate, anthracene, and stilbene groups. The chain-end functionalization is confirmed by analyzing the purified decross-linked extrudates after dialysis. This thermoset-to-thermoplastic extrusion process represents a powerful approach for upcycling postconsumer PU thermosets into a library of thermoplastic PUs with controlled molecular weights and chain-end functionalities for diverse applications, including adhesives, photoresins, and stimuli-responsive materials, as demonstrated herein. In the future, this strategy could be extended to upcycle many other step-growth networks capable of undergoing catalytic bond exchange reactions, such as cross-linked polyureas and polyesters, contributing to plastic waste management in general.

Biomolecular condensates as stress sensors and modulators of bacterial signaling

Microbes exhibit remarkable adaptability to environmental fluctuations. Signaling mechanisms, such as two-component systems and secondary messengers, have long been recognized as critical for sensing and responding to environmental cues. However, recent research has illuminated the potential of a physical adaptation mechanism in signaling-phase separation, which may represent a ubiquitous mechanism for compartmentalizing biochemistry within the cytoplasm in the context of bacteria that frequently lack membrane-bound organelles. This review considers the broader prospect that phase separation may play critical roles as rapid stress sensing and response mechanisms within pathogens. It is well established that weak multivalent interactions between disordered regions, coiled-coils, and other structured domains can form condensates via phase separation and be regulated by specific environmental parameters in some cases. The process of phase separation itself acts as a responsive sensor, influenced by changes in protein concentration, posttranslational modifications, temperature, salts, pH, and oxidative stresses. This environmentally triggered phase separation can, in turn, regulate the functions of recruited biomolecules, providing a rapid response to stressful conditions. As examples, we describe biochemical pathways organized by condensates that are essential for cell physiology and exhibit signaling features. These include proteins that organize and modify the chromosome (Dps, Hu, SSB), regulate the decay, and modification of RNA (RNase E, Hfq, Rho, RNA polymerase), those involved in signal transduction (PopZ, PodJ, and SpmX) and stress response (aggresomes and polyphosphate granules). We also summarize the potential of proteins within pathogens to function as condensates and the potential and challenges in targeting biomolecular condensates for next-generation antimicrobial therapeutics. Together, this review illuminates the emerging significance of biomolecular condensates in microbial signaling, stress responses, and regulation of cell physiology and provides a framework for microbiologists to consider the function of biomolecular condensates in microbial adaptation and response to diverse environmental conditions.

Stapler Strategies for Upcycling Mixed Plastics

Mechanical recycling is one of the simplest and most economical strategies to address ever-increasing plastic pollution, but it cannot be applied to immiscible mixed plastics and suffers from property deterioration after each cycle. By combining the amphiphilic block copolymer strategy and reactive compatibilization strategy, we designed a series of stapler strategies for compatibilizing/upcycling mixed plastics. First, various functionalized graft copolymers were accessed via different synthetic routes. Subsequently, the addition of a very small amount of stapler molecules induced a synergistic effect with the graft copolymers that improved the compatibility and mechanical properties of mixed plastics. These strategies were highly effective for various binary/ternary plastic systems and can be directly applied to postconsumer waste plastics, which can increase the toughness of mixed postconsumer waste plastics by 162 times. Most importantly, it also effectively improved the impact resistance, adhesion performance, and three-dimensional (3D) printing performance of mixed plastics, and permitted the recycling of plastic blends 20 times with minimal degradation in their mechanical properties.

Predicting compatibilized polymer blend toughness

Polymer blends can yield superior materials by merging the unique properties of their components. However, these mixtures often phase separate, leading to brittleness. While compatibilizers can toughen these blends, their vast design space makes optimization difficult. Here, we develop a model to predict the toughness of compatibilized glassy polymer mixtures. This theory reveals that compatibilizers increase blend toughness by creating molecular bridges that stitch the interface together. We validate this theory by directly comparing its predictions to extensive molecular dynamics simulations in which we vary polymer incompatibility, chain stiffness, compatibilizer areal density, and blockiness of copolymer compatibilizers. We then parameterize the model using self-consistent field theory and confirm its ability to make predictions for practical applications through comparison with simulations and experiments. These results suggest that the theory can optimize compatibilizer design for industrial glassy polymer blends in silico while providing microscopic insight, allowing for the development of next-generation mixtures.

Preparation and Characterization of H-Shaped Polylactide

An H-polymer has an architecture that consists of four branches symmetrically attached to the ends of a polymer backbone, similar in shape to the letter "H". Here, a renewable H-polymer efficiently synthesized using only ring-opening transesterification is demonstrated. The strategy relies on a tetrafunctional poly(±-lactide) macroinitiator, from which four poly(±-lactide) branches are grown simultaneously. 1H NMR spectroscopy, size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization (MALDI) spectrometry were used to verify the macroinitiator purity. Branch growth was probed using 1H NMR spectroscopy and SEC to reveal unique transesterification phenomena that can be controlled to yield architecturally pure or more complex materials. H-shaped PLA was prepared at the multigram scale with a weight-average molar mass Mw > 100 kg/mol and low dispersity Đ < 1.15. Purification involved routine precipitations steps, which yielded products that were architecturally relatively pure (∼93%). Small-amplitude oscillatory shear and extensional rheology measurements demonstrate the unique viscoelastic behavior associated with the H-shaped architecture.

Enhancing Polymer Blend Compatibility with Linear and Complex Star Copolymer Architectures: A Monte Carlo Simulation Study with the Bond Fluctuation Model

A Monte Carlo study of the compatibilization of A/B polymer blends has been performed using the bond fluctuation model. The considered compatibilizers are copolymer molecules composed of A and B blocks. Different types of copolymer structures have been included, namely, linear diblock and 4-block alternating copolymers, star block copolymers, miktoarm stars, and zipper stars. Zipper stars are composed of two arms of diblock copolymers arranged in alternate order (AB and BA) from the central unit, along with two homogeneous arms of A and B units. The compatibilization performance has been characterized by analyzing the equilibration of repulsion energy, the simulated scattering intensity obtained with opposite refractive indices for A and B, the profiles along a coordinate axis, the radial distribution functions, and the compatibilizer aggregation numbers. According to the results, linear alternate block copolymers, star block copolymers, and zipper stars exhibit significantly better compatibilization, with zipper stars showing slightly but consistently better performance.

Regioselective and controlled-density branching in amylose esters

Herein, we report creation of methodology for one-pot synthesis of 2,3-O-acetyl-6-bromo-6-deoxy (2,3Ac-6Br) amylose with controlled degree of substitution of bromide (DS(Br)) followed by quantitative azide substitution as a route to branched polysaccharide derivatives. This methodology affords complete control of "tine" location, and strong control of degree of branching of comb-structured polymers. In this way, we achieved bromination strictly at C6 and esterification at the other hydroxy groups, where the DS(Br) at C6 was well-controlled by bromination/acylation conditions in the one-pot process. Azide displacement of all C6 bromides followed by copper-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction with the small molecule tert-butyl propargyl ether (TBPE) demonstrated the potential to create such branched structures. This synthetic method has broad potential to generate well-defined polysaccharide-based comb-like structures, with a degree of structural control that is very unusual in polysaccharide chemistry.

A sustainable approach toward mechanical recycling unsortable post-consumer WEEE: Reactive and non-reactive compatibilization

While near-infrared (NIR) spectroscopy in post-consumer waste electrical and electronic equipment (WEEE) recycling accurately separates white or clear polymers, 40% containing dark plastics, termed 'unsortable WEEE,' are excluded from sorting lines and therefore incinerated or landfilled, causing environmental concerns. This study investigates the potential of using non-reactive and reactive copolymers as compatibilizers to enhance the performance of unsortable WEEE plastics free of brominated flame retardants. To the best of our knowledge, this is the first time that such copolymers have been explored as a solution for improving the compatibility of unsortable WEEE polymer blends. Initial trials with 4% of styrene-ethylene-butylene-styrene copolymer (SEBS-13) and SEBS-30-g-(maleic anhydride) copolymer (SEBS-30-g-MA MA) as compatibilizers showed insufficient results compared to virgin commercial polymers. However, the addition of higher concentrations of compatibilizers (i.e. up to 20 wt%) and the use of a SEBS having a higher styrene content (i.e. SEBS-30) improved the mechanical properties of the material, causing it to transition from brittle to ductile. This behavior was found more pronounced for the 20% non-reactive SEBS-30, for which the SEM analysis showed reduced phase segregation and revealed a more homogeneous fracture surface. This was further supported by Differential Scanning Calorimetry (DSC) analysis, which showed evidence of an interaction between one or more polymer phases. With a room temperature performance equivalent to that of virgin conventional polymers, the SEBS-30 compatibilization approach has made it possible to consider using unsortable WEEE streams as recycled materials in commercial applications.

Cyclic and Linear Tetrablock Copolymers Synthesized at Speed and Scale by Lewis Pair Polymerization of a One-Pot (Meth)acrylic Mixture and Characterized at Multiple Levels

Cyclic block copolymers (cBCP) are fundamentally intriguing materials, but their synthetic challenges that demand precision in controlling both the monomer sequence and polymer topology limit access to AB and ABC block architectures. Here, we show that cyclic ABAB tetra-BCPs (cABAB) and their linear counterpart (lABAB) can be readily obtained at a speed and scale from one-pot (meth)acrylic monomer mixtures, through coupling the Lewis pair polymerization's unique compounded-sequence control with its precision in topology control. This approach achieves fast (<15 min) and quantitative (>99%) conversion to tetra-BCPs of predesignated linear or cyclic topology at scale (40 g) in a one-pot procedure, precluding the needs for repeated chain extensions, stoichiometric addition steps, dilute conditions, and postsynthetic modifications, and/or postsynthetic ring-closure steps. The resulting lABAB and cABAB have essentially identical molecular weights (Mn = 165-168 kg mol-1) and block degrees/symmetry, allowing for direct behavioral comparisons in solution (hydrodynamic volume, intrinsic viscosity, elution time, and refractive indices), bulk (thermal transitions), and film (thermomechanical and rheometric properties and X-ray scattering patterns) states. To further the morphological characterizations, allylic side-chain functionality is exploited via the thiol-ene click chemistry to install crystalline octadecane side chains and promote phase separation between the A and B blocks, allowing visualization of microdomain formation.

Janus bottlebrush compatibilizers

Bottlebrush random copolymers (BRCPs), consisting of a random distribution of two homopolymer chains along a backbone, can segregate to the interface between two immiscible homopolymers. BRCPs undergo a reconfiguration, where each block segregates to one of the homopolymer phases, adopting a Janus-type structure, reducing the interfacial tension and promoting adhesion between the two homopolymers, thereby serving as a Janus bottlebrush copolymer (JBCP) compatibilizer. We synthesized a series of JBCPs by copolymerizing deuterated or hydrogenated polystyrene (DPS/PS) and poly(tert-butyl acrylate) (PtBA) macromonomers using ruthenium benzylidene-initiated ring-opening metathesis polymerization (ROMP). Subsequent acid-catalyzed hydrolysis converted the PtBA brushes to poly(acrylic acid) (PAA). The JBCPs were then placed at the interface between DPS/PS homopolymers and poly(2-vinyl pyridine) (P2VP) homopolymers, where the degree of polymerization of the backbone (NBB) and the grafting density (GD) of the JBCPs were varied. Neutron reflectivity (NR) was used to determine the interfacial width and segmental density distributions (including PS homopolymer, PS block, PAA block and P2VP homopolymer) across the polymer-polymer interface. Our findings indicate that the star-like JBCP with NBB = 6 produces the largest interfacial broadening. Increasing NBB to 100 (rod-like shape) and 250 (worm-like shape) reduced the interfacial broadening due to a decrease in the interactions between blocks and homopolymers by stretching of blocks. Decreasing the GD from 100% to 80% at NBB = 100 caused an increase the interfacial width, yet further decreasing the GD to 50% and 20% reduced the interfacial width, as 80% of GD may efficiently increase the flexibility of blocks and promote interactions between homopolymers, while maintaining relatively high number of blocks attached to one molecule. The interfacial conformation of JBCPs was further translated into compatibilization efficiency. Thin film morphology studies showed that only the lower NBB values (NBB = 6 and NBB = 24) and the 80% GD of NBB = 100 had bicontinuous morphologies, due to a sufficient binding energy that arrested phase separation, supported by mechanical testing using asymmetric double cantilever beam (ADCB) tests. These provide fundamental insights into the assembly behavior of JBCPs compatibilizers at homopolymer interfaces, opening strategies for the design of new BCP compatibilizers.

Polymeric surfactants at liquid-liquid interfaces: Dependence of structural and thermodynamic properties on copolymer architecture

Polymeric surfactants are amphiphilic molecules with two or more different types of monomers. If one type of monomer interacts favorably with a liquid, and another type of monomer interacts favorably with another, immiscible liquid, then polymeric surfactants adsorb at the interface between the two liquids and reduce the interfacial tension. The effects of polymer architecture on the structural and thermodynamic properties of the liquid-liquid interface are studied using molecular simulations. The interface is modeled with a non-additive binary Lennard-Jones fluid in the two-phase region of the phase diagram. Block and gradient copolymer surfactants are represented with coarse-grained, bead-spring models, where each component of the polymer favors one or the other liquid. Gradient copolymers have a greater concentration at the interface than do block copolymers because the gradient copolymers adopt conformations partially aligned with the interface. The interfacial tension is determined as a function of the surface excess of polymeric surfactant. Gradient copolymers are more potent surfactants than block copolymers because the gradient copolymers cross the dividing surface multiple times, effectively acting as multiple individual surfactants. For a given surface excess, the interfacial tension decreases monotonically when changing from a block to a gradient architecture. The coarse-grained simulations are complemented by all-atom simulations of acrylic-acid/styrene copolymers at the chloroform-water interface, which have been studied in experiments. The agreement between the simulations (both coarse-grained and atomistic) and experiments is shown to be excellent, and the molecular-scale structures identified in the simulations help explain the variation of surfactancy with copolymer architecture.

Polymer Multi-Block and Multi-Block+ Strategies for the Upcycling of Mixed Polyolefins and Other Plastics

Due to a continued rise in the production and use of plastic products, their end-of-life pollution has become a pressing global issue. One of the biggest challenges in plastics recycling is the separation of different polymers. Multi-block copolymers (MBCPs) represent an efficient strategy for the upcycling of mixed plastics via induced compatibilization, but this approach is limited by difficulties associated with synthesis and structural modification. In this contribution, several synthetic strategies are explored to prepare MBCPs with tunable microstructures, which were then used as compatibilizer additives to upcycle mixtures of polyolefins with other plastics. A multi-block+ strategy based on a reactive telechelic block copolymer platform was introduced, which enabled block extension during the in situ melt blending of mixed plastics, leading to better compatibilizing properties as well as better 3D printing capability. This strategy was also applicable to more complex ternary plastic blends. The polymer multi-block strategy enabled by versatile MBCPs synthesis and the multi-block+ strategy enabled by in situ block extension show exciting opportunities for the upcycling of mixed plastics.

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.

Advancing Plastic Recycling: Challenges and Opportunities in the Integration of 3D Printing and Distributed Recycling for a Circular Economy

The concept of the circular economy has emerged as a promising solution to address the mounting concerns surrounding plastic waste and the urgent need for sustainable resource management. While conventional centralized recycling remains a common practice for plastic waste, centralized facilities may prove inadequate in handling the ever-increasing volumes of plastic waste generated globally. Consequently, exploring alternative recycling methods, such as distributed recycling by additive manufacturing, becomes paramount. This innovative approach encompasses actively involving communities in recycling practices and promotes a circular economy. This comprehensive review paper aims to explore the critical aspects necessary to realize the potential of distributed recycling by additive manufacturing. In this paper, our focus lies on proposing schemes that leverage existing literature to harness the potential of distributed recycling by additive manufacturing as an effective approach to plastic waste management. We explore the intricacies of the recycling process, optimize 3D printing parameters, address potential challenges, and evaluate the mechanical properties of recycled materials. Our investigation draws heavily from the literature of the last five years, as we conduct a thorough critical assessment of DRAM implementation and its influence on the properties of 3D printing structures. Through comprehensive analysis, we reveal the potential of recycled materials in delivering functional components, with insights into their performance, strengths, and weaknesses. This review serves as a comprehensive guide for those interested in embracing distributed recycling by additive manufacturing as a transformative approach to plastic recycling. By fostering community engagement, optimizing 3D printing processes, and incorporating suitable additives, it is possible to collectively contribute to a more sustainable future while combatting the plastic waste crisis. As progress is made, it becomes essential to further delve into the complexities of material behavior, recycling techniques, and the long-term durability of recycled 3D printed components. By addressing these challenges head-on, it is feasible to refine and advance distributed recycling by additive manufacturing as a viable pathway to minimize plastic waste, fostering a circular economy and cultivating a cleaner planet for generations to come.

Threading-the-Needle: Compatibilization of HDPE/iPP blends with butadiene-derived polyolefin block copolymers

Management of the plastic industry is a momentous challenge, one that pits enormous societal benefits against an accumulating reservoir of nearly indestructible waste. A promising strategy for recycling polyethylene (PE) and isotactic polypropylene (iPP), constituting roughly half the plastic produced annually worldwide, is melt blending for reformulation into useful products. Unfortunately, such blends are generally brittle and useless due to phase separation and mechanically weak domain interfaces. Recent studies have shown that addition of small amounts of semicrystalline PE-iPP block copolymers (ca. 1 wt%) to mixtures of these polyolefins results in ductility comparable to the pure materials. However, current methods for producing such additives rely on expensive reagents, prohibitively impacting the cost of recycling these inexpensive commodity plastics. Here, we describe an alternative strategy that exploits anionic polymerization of butadiene into block copolymers, with subsequent catalytic hydrogenation, yielding E and X blocks that are individually melt miscible with PE and iPP, where E and X are poly(ethylene-ran-ethylethylene) random copolymers with 6 wt% and 90 wt% ethylethylene repeat units, respectively. Cooling melt blended mixtures of PE and iPP containing 1 wt% of the triblock copolymer EXE of appropriate molecular weight, results in mechanical properties competitive with the component plastics. Blend toughness is obtained through interfacial topological entanglements of the amorphous X polymer and semicrystalline iPP, along with anchoring of the E blocks through cocrystallization with the PE homopolymer. Significantly, EXE can be inexpensively produced using currently practiced industrial scale polymerization methods, offering a practical approach to recycling the world's top two plastics.

Ionic-Nanophase Hybridization of Nafion by Supramolecular Patching for Enhanced Proton Selectivity in Redox Flow Batteries

Nafion, as the mostly used proton exchange membrane material in vanadium redox flow batteries (VRFBs), encounters serious vanadium permeation problems due to the large size difference between its anionic nanophase (3-5 nm) and cationic vanadium ions (∼0.6 nm). Bulk hybridization usually suppresses the vanadium permeation at the expense of proton conductivity since conventional additives tend to randomly agglomerate and damage the nanophase continuity from unsuitable sizes and intrinsic incompatibility. Here, we report the ionic-nanophase hybridization strategy of Nafion membranes by using fluorinated block copolymers (FBCs) and polyoxometalates (POMs) as supramolecular patching additives. The cooperative noncovalent interactions among Nafion, interfacial-active FBCs, and POMs can construct a 1 nm-shrunk ionic nanophase with abundant proton transport sites, preserved continuity, and efficient vanadium screeners, which leads to a comprehensive enhancement in proton conductivity, selectivity, and VRFB performance. These results demonstrate the intriguing potential of the supramolecular patching strategy in precisely tuning nanostructured electrolyte membranes for improved performance.

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.

Fused Deposition Modeling of Single-Use Plastic Alloy

Packaging plastics are called ‘single-use plastics’ because of short lifetime. Among which, the three plastics of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) take more than 70%. Due to incompatibility, few research has been done on the alloy of the three plastics. The aim of this study is to investigate the possibility of single-use plastic alloy (SUPA) of ternary PE, PP, and PET as the 3D printing material. Tensile and bending tests are carried out to investigate the mechanical properties, photographs of scanning electron microscope (SEM) are taken for morphology analysis, and differential scanning calorimetry (DSC) are used to study the crystallization behavior of the alloys. The results show that there is an optimal ratio for all the components to obtain the best mechanical performances, i.e., the ratio of $\text{PP}/\text{PE}=40/60$ with 20 wt% PET, 2 wt% maleic anhydride grafted polypropylene (PP-g-MAH) and 2 wt% organic modified montmorillonite (OMMT). This SUPA has a tensile strength of 14.48 MPa, a tensile modulus of 586.42 MPa, a flexural strength of 15.85 MPa, and a flexural modulus of 544.67 MPa. Due to the function of compatibilizer and nanoclay (NC) will be affected by redundancy, the potential primary fibrosis while collecting the feeding filaments and the secondary fibrosis at the nozzle of 3D printing might be responsible for the variation of the mechanical performances.

Dihydroxy Polyethylene Additives for Compatibilization and Mechanical Recycling of Polyethylene Terephthalate/Polyethylene Mixed Plastic Waste

Polymer blend compatibilization is an attractive solution for mechanical recycling of mixed plastic waste because it can result in tough blends. In this work, hydroxy-telechelic polyethylene (HOPEOH) reactive additives were used to compatibilize blends of polyethylene terephthalate (PET) and linear low-density polyethylene (LLDPE). HOPEOH additives were synthesized with molar masses of 1-20 kg/mol by ring-opening metathesis polymerization of cyclooctene followed by catalytic hydrogenation. Melt-compounded blends containing 0.5 wt % HOPEOH displayed reduced dispersed phase LLDPE particle sizes with ductilities comparable to virgin PET and almost seven times greater than neat blends, regardless of additive molar mass. In contrast, analogous blends containing monohydroxy PE additives of comparable molar masses did not result in compatibilization even at 2 wt % loading. The results strongly suggest that both hydroxy ends of HOPEOH undergo transesterification reactions during melt mixing with PET to form predominantly PET-PE-PET triblock copolymers at the interface of the dispersed and matrix phases. We hypothesize that the triblock copolymer compatibilizers localized at the interface form trapped entanglements of the PE midblocks with nearby LLDPE homopolymer chains by a hook-and-clasp mechanism. Finally, HOPEOH compounds were able to efficiently compatibilize blends derived solely from postconsumer PET and PE bottles and film, suggesting their industrial applicability.

The synthesis and properties research of functionalized polyolefins

This work demonstrated a tandem ROMP/hydrogenation approach for the preparation of functionalized polyolefins and their properties were investigated.