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

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.

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.