Synthesis of Reactive Comb Polymers and Their Applications as a Highly Efficient Compatibilizer in Immiscible Polymer Blends

Compatibilization of Immiscible Polypropylene/Poly(methyl methacrylate) Blends by Silica Particles with Janus and Random Component-Selective Grafts

Introducing component-selective polymer chains onto the surface of a particle is an effective approach to improve the compatibilization efficiency of a particle-based compatibilizer. In this study, two particles with different kinds of component-selective polymer chains that have the same length and similar density but different graft locations were synthesized and their compatibilization effects were comparatively investigated. It was found that compared with the particle with homogeneous PMMA and PP grafts (R-P), the particle with a hemisphere of poly(methyl methacrylate) (PMMA) grafts and other hemisphere of polypropylene (PP) chains (J-P) showed a better compatibilization effect under equal loadings, although both particles exhibited high efficiency. The better compatibilization effect of particles with Janus grafts may be attributed to the stronger entanglements between grafted polymer chains and selective individual components. This work suggests that optimizing the graft location of a particle is an effective strategy for improving its compatibilization efficiency and helpful for the design of advanced particle compatibilizers.

Crystalline lamellar films with honeycomb structure from comb-like polymers of poly(2-long-alkyl-2-oxazoline)s

Comb-like copolymers are usually structured by grafting polymeric side chains onto main polymer chain. There are few reports of comb-on-comb polymers in which dense secondary side chains are grafted onto primary side chain. In this work, we synthesized comb polymers with grafted-on-graft side chains (c-PEI-g-Acyl) via an effective acylation reaction of comb polymers possessing polyethyleneimine (PEI) side chain with long-alkyl acyl chlorides. For comparison, we also synthesized homopolymers l-PEI-g-Acyls via reaction of linear PEI with long-alkyl acyl chlorides. Then, we investigated their crystalline feature in the film formation by XRD, DSC and SEM, and found that the polymers tend to form hexagonal lamella structures with bilayer alkyl spacing. The comb polymers c-PEI-g-Acyls and linear polymers l-PEI-g-Acyls were used in preparation of honeycomb film by the "breath-figure" process by dropping chloroform solution of the polymers on substrate. Different to many honeycomb polymeric films which are supported by amorphous phase, interestingly, our polymers easily afford honeycomb films which are supported by crystalline lamellae frames under higher humidity condition. It was found that the comb polymers of c-PEI-g-Acyls with longer PEI primary side chain and long alkyl secondary side chain have advantages in producing honeycomb film than linear polymers of l-PEI-g-Acys.

Accelerating copolymer inverse design using monte carlo tree search

There exists a broad class of sequencing problems in soft materials such as proteins and polymers that can be formulated as a heuristic search that involves decision making akin to a computer game. AI gaming algorithms such as Monte Carlo tree search (MCTS) gained prominence after their exemplary performance in the computer Go game and are decision trees aimed at identifying the path (moves) that should be taken by the policy to reach the final winning or optimal solution. Major challenges in inverse sequencing problems are that the materials search space is extremely vast and property evaluation for each sequence is computationally demanding. Reaching an optimal solution by minimizing the total number of evaluations in a given design cycle is therefore highly desirable. We demonstrate that one can adopt this approach for solving the sequencing problem by developing and growing a decision tree, where each node in the tree is a candidate sequence whose fitness is directly evaluated by molecular simulations. We interface MCTS with MD simulations and use a representative example of designing a copolymer compatibilizer, where the goal is to identify sequence specific copolymers that lead to zero interfacial energy between two immiscible homopolymers. We apply the MCTS algorithm to polymer chain lengths varying from 10-mer to 30-mer, wherein the overall search space varies from 210 (1024) to 230 (∼1 billion). In each case, we identify a target sequence that leads to zero interfacial energy within a few hundred evaluations demonstrating the scalability and efficiency of MCTS in exploring practical materials design problems with exceedingly vast chemical/material search space. Our MCTS-MD framework can be easily extended to several other polymer and protein inverse design problems, in particular, for cases where sequence-property data is either unavailable and/or is resource intensive.

Improvement of PLLA Ductility by Blending with PVDF: Localization of Compatibilizers at Interface and Its Glycidyl Methacrylate Content Dependency

In this work, the localization of reactive compatibilizer (RC, containing poly(methyl methacrylate) (PMMA) backbone with randomly distributed glycidyl methacrylate (GMA) on it) at the polyvinylidene fluoride/poly(l-lactic acid) (PVDF/PLLA) interface has been manipulated by means of GMA contents. At the very beginning of mixing, RC tends to stay in the PVDF phase due to the miscibility between PVDF and PMMA. Upon further shearing, more and more PLLA chains have been grafted on PMMA backbone, producing PLLA-g-PMMA copolymer. The balanced stress on two sides accounts for the localization of compatibilizers at the PVDF/PLLA interface. Finally, the stress of the PLLA side has been enhanced remarkably due to the higher graft density of PLLA, resulting in the enrichment of the copolymer in the PLLA matrix. The migration of RC from the PVDF phase to the immiscible interface and PLLA matrix can be accelerated by employing RC with higher GMA content. Furthermore, the compatibilizer localization produces a significant influence on the morphology and ductility of the PVDF/PLLA blend. Only when the compatibilizers precisely localize at the interface, the blend exhibits the smallest domain and highest elongation at break. Our results are of great significance for not only the fabrication of PLLA with high ductility, but also the precise localization of compatibilizers at the interface of the immiscible blend.

Reactive Comb Polymer Compatibilized Immiscible PVDF/PLLA Blends: Effects of the Main Chain Structure of Compatibilizer

The compatibilizer with double comb structure has a superior compatibilizing effect for immiscible polymer blends due to the symmetrical structure on both sides of main chains. Extensive study related to the architectural effects of compatibilizer on the compatibilization has mainly focused on the side chains. We investigated the influence of the compatibilizer-main-chain structure on the compatibilizing effect for immiscible poly(vinylidene fluoride)/poly(L-lactic acid) (PVDF/PLLA) blends. Two reactive-comb compatibilizers with polystyrene (PS) and polymethylmethacrylate (PMMA) as main chains and PMMA as the side chains have been synthesized. PS is immiscible with both PLLA and PVDF, while PMMA is miscible with PVDF. It was found that both compatibilizers can improve the compatibility between the PLLA and PVDF, with different compatibilization effects. In the PVDF/PLLA (50/50) blends, 1 wt.% poly(styrene-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (RC-SG) tuned the morphology from the droplet-in-matrix structure to the co-continuous structure, while the blends with poly(methyl methacrylate-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (RC-MMG) kept the sea-island structure with even 3 wt.% loading. Moreover, RC-SG induces a wider co-continuous interval range than RC-MMG. The co-continuous structure obtained by RC-SG was also more stable than that by RC-MMG. It was further found that RC-SG-compatibilized PVDF/PLLA blends exhibit higher mechanical properties than the RC-MMG-compatibilized blends.

Effects of blending sequences and molecular structures of the compatibilizers on the morphology and properties of PLLA/ABS blends

The effects of molecular structures of the compatibilizers and blending sequences on the morphology and properties of the immiscible poly(l-lactide)/acrylonitrile-butadiene-styrene (PLLA/ABS) blend are investigated herein. The comb-like polymers (RC), which are constituted by a poly(methyl methacrylate) (PMMA) backbone and side chains and a few epoxy groups distributed randomly along the backbone, are found to be better compatibilizers for improving the morphology and mechanical properties of the PLLA/ABS blend, compared to linear polymers (RL) constituted by a PMMA backbone and epoxy groups along the backbone. In addition, the blending sequence, which dictates the extent of grafting reaction between carboxyl end groups of PLLA and epoxy groups in the RL and RC compatibilizers, is found to influence the diffusion and location of the in situ formed RL-g-PLLA and RC-g-PLLA polymers in the blend system. By blending RL or RC polymers with ABS phase firstly, the epoxy groups are diluted by ABS phase; thus, during the second step, blending with PLLA phase, lightly grafted polymers are formed. This method is found to be the best sequence to compatibilize the PLLA/ABS system. When the PLLA phase is mixed with the compatibilizers firstly, the highly grafted polymers are prone to be trapped in the PLLA phase, because the PMMA segments are shielded by the densely grafted PLLA segments from interacting efficiently with the ABS phase, and thus the morphology and mechanical properties of the blend deteriorate accordingly.

The morphology and properties of compatibilized PLLA/ABS blends can be optimized by using appropriate compatibilizers and blending sequences.

Reactive Compatibilization: Formation of Double-Grafted Copolymers by In Situ Binary Grafting and Their Compatibilization Effect

Reactive compatibilizers are usually used to enhance the compatibility of immiscible polymer blends. However, reactive linear compatibilizers containing reactive groups on the main chains form graft copolymers during reactive blending, and such graft copolymers with an asymmetric molecular structure are often "pulled in" or "pulled out" under mechanical shear. Double-grafted compatibilizers have a symmetric structure, and they usually exhibit higher compatibilizing efficiency. In this work, we propose a binary grafting strategy during melt blending to form compatibilizers located at the interface of an immiscible polymer blend. Specifically, poly(methyl methacrylate) (PMMA) oligomer with carboxylic end groups (PMMA-COOH) and poly(styrene-co-glycidyl methacrylate) (SG) copolymer were simultaneously incorporated into immiscible poly(vinylidene fluoride)/poly(l-lactic acid) (PVDF/PLLA) blends. The carboxylic acid groups of both the PMMA oligomer and PLLA can react with the epoxide groups on the SG main chains. Therefore, novel compatibilizing polymers with both PMMA and PLLA chains grafted onto the SG main chains form in situ. The grafted PMMA chains can entangle with PVDF, and the grafted PLLA chains are embedded in the PLLA phase, so the double-grafted copolymers act as effective compatibilizers for the PVDF/PLLA blends. Moreover, the effects of the PMMA molecular weight and PMMA loading (number of grafted PMMA side chains) on the compatibilization efficiency were investigated. The compatibilizing efficiency increases with increasing molecular weight and number of side chains in the ranges considered in this study. This one-pot synthesis of double-grafted compatibilizers by in situ grafting provides a new and simple method to prepare double-comb compatibilizers, and it offers the possibility of high-efficiency compatibilization.

Making a Supertough Flame-Retardant Polylactide Composite through Reactive Blending with Ethylene-Acrylic Ester-Glycidyl Methacrylate Terpolymer and Addition of Aluminum Hypophosphite

Biocompatible and biodegradable polylactide (PLA) composites with supertough mechanical property and sufficient flame retardancy were fabricated by employing a facile approach involving reactive blending of PLA and ethylene-acrylic ester-glycidyl methacrylate terpolymer (EGMA), with the addition of aluminum hypophosphite (AHP) as an effective flame retardant. In consideration of the balance between mechanical property and flame retardancy, the optimal formula was taking a PLA/EGMA 80/20 blend (supertough STPLA) as the matrix and adding 20 wt % of AHP (relative to the mass of STPLA) as the flame retardant, coded as STPLA/20AHP. The mechanical property test showed that for STPLA/20AHP the elongation at break was increased by about 22 times and the notched Izod impact strength was enhanced by approximately 11 times as compared to those for neat PLA. The flame-retardant property test showed that for STPLA/20AHP the limiting oxygen index value reached 26.6% and the UL-94 V0 rating test was passed. Thermogravimetric analysis, microscale combustion calorimetry, and cone calorimeter were further applied to reveal the thermal stability and combustion behaviors of STPLA/xAHP, respectively, where x indicated the mass content of AHP in percentage. The phase separation morphology, dispersion of AHP particles in STPLA matrix, and fracture surfaces and char residues after flame burning were examined by phase contrast optical microscopy and scanning electron microscopy, respectively, which helped comprehend the results obtained from the mechanical property and flame retardancy tests. The supertough STPLA/xAHP, with sufficient flame retardancy as prepared in this work, could have a potential for engineering applications.

Reactive Nanoparticles Compatibilized Immiscible Polymer Blends: Synthesis of Reactive SiO2 with Long Poly(methyl methacrylate) Chains and the in Situ Formation of Janus SiO2 Nanoparticles Anchored Exclusively at the Interface

The exclusive location of compatibilizers at the interface of immiscible binary polymer blends to bridge the neighboring phases is the most important issue for fabricating desirable materials with synergistic properties. However, the positional stability of the compatibilizers at the interface remains a challenge in both scientific and technical points of view due to the intrinsic flexibility of compatibilizer molecules against aggressive processing conditions. Herein, taking the typical immiscible poly vinylidene fluoride (PVDF)/polylactic acid (PLLA) blend as an example, we demonstrate a novel approach, termed as the interfacial nanoparticle compatibilization (IPC) mechanism, to overcome the challenges by packing nanoparticles thermodynamically at the interface through melt reactive blending. Specifically, we have first synthesized nanosilica with both reactive epoxide groups and long poly(methyl methacrylate) (PMMA) tails, called reactive PMMA-graft-SiO₂ (Epoxy-MSiO₂), and then incorporated the Epoxy-MSiO₂ into the PVDF/PLLA (50/50, w/w) blends by melt blending. PLLA was in situ grafted onto SiO₂ by the reaction of the carboxylic acid groups with epoxide groups on the surface of SiO₂. Therefore, the reacted SiO₂ particles were exclusively located at the interface by the formation of the Janus-faced silica hybrid nanoparticles (JSNp) with pregrafted PMMA tails entangled with PVDF molecular chains in the PVDF phase and the in situ grafted PLLA chains embedded in the PLLA phase. Such JSNp with a distinct hemisphere, functioning as compatibilizer, can not only suppress coalescence of PVDF domains by its steric repulsion but also enhance interfacial adhesion via the selective interactions with the corresponding miscible phase. The interfacial location of JSNp is very stable even under the severe shear field and annealing in the melt. This IPC mechanism paves a new possibility to use the various types of nanoparticles as both effective compatibilizers and functional fillers for immiscible polymer blends.

Neural-Network-Biased Genetic Algorithms for Materials Design: Evolutionary Algorithms That Learn

Machine learning has the potential to dramatically accelerate high-throughput approaches to materials design, as demonstrated by successes in biomolecular design and hard materials design. However, in the search for new soft materials exhibiting properties and performance beyond those previously achieved, machine learning approaches are frequently limited by two shortcomings. First, because they are intrinsically interpolative, they are better suited to the optimization of properties within the known range of accessible behavior than to the discovery of new materials with extremal behavior. Second, they require large pre-existing data sets, which are frequently unavailable and prohibitively expensive to produce. Here we describe a new strategy, the neural-network-biased genetic algorithm (NBGA), for combining genetic algorithms, machine learning, and high-throughput computation or experiment to discover materials with extremal properties in the absence of pre-existing data. Within this strategy, predictions from a progressively constructed artificial neural network are employed to bias the evolution of a genetic algorithm, with fitness evaluations performed via direct simulation or experiment. In effect, this strategy gives the evolutionary algorithm the ability to "learn" and draw inferences from its experience to accelerate the evolutionary process. We test this algorithm against several standard optimization problems and polymer design problems and demonstrate that it matches and typically exceeds the efficiency and reproducibility of standard approaches including a direct-evaluation genetic algorithm and a neural-network-evaluated genetic algorithm. The success of this algorithm in a range of test problems indicates that the NBGA provides a robust strategy for employing informatics-accelerated high-throughput methods to accelerate materials design in the absence of pre-existing data.

Polymeric Quaternary Ammonium-Containing Coatings with Potential Dual Contact-Based and Release-Based Antimicrobial Activity

In the present work, reactive blending of copolymers with complementary functional groups was applied to control their antimicrobial activity and antifouling action in real conditions. For this purpose, two series of copolymers, poly(4-vinylbenzyl chloride-co-acrylic acid), P(VBC-co-AAx), and poly(sodium 4-styrenesulfonate-co-glycidyl methacrylate), P(SSNa-co-GMAx), were synthesized via free radical copolymerization and further modified by the incorporation of biocidal units either covalently (4-vinyl benzyl dimethylhexadecylammonium chloride, VBCHAM) or electrostatically bound (cetyltrimethylammonium 4-styrenesulfonate, SSAmC₁₆). The cross-linking reaction of the carboxylic group of acrylic acid (AA) with the epoxide group of glycidyl methacrylate (GMA) of these two series of reactive antimicrobial copolymers was explored in blends obtained through solution casting after curing at various temperatures. The combined results from the ATR-FTIR characterization of the membranes, solubility tests, turbidimetry, and TEM suggest that the reaction occurs already at 80 °C, leading mostly to graft samples, while at higher curing temperatures (120 or 150 °C) insoluble cross-linked samples are usually obtained. Controlled release experiments of selected membranes were performed in pure water and aqueous 1 M NaCl solutions for a period of two months. The released material was followed through gravimetry and TOC/TN measurements, while the evolution of the integrity and the morphology of the membranes were followed visually and through SEM, respectively. Antimicrobial tests also revealed that the cross-linked membranes presented strong antimicrobial activity against S. aureus and P. aeruginosa. Finally, a specific blend combination was applied on aquaculture nets and cured at 80 °C. The modified nets, emerged in the sea for 15 and 35 days, exhibited high antifouling action as compared to blank nets.

Compatibilization of Immiscible Polymer Blends Using in Situ Formed Janus Nanomicelles by Reactive Blending

Block or graft copolymers located at polymer-polymer interfaces have been considered as ideal compatibilizers for immiscible polymer blends. Herein, we report a novel compatibilization mechanism using Janus nanomicelles (JNMs) formed in situ at the polymer-polymer interface in immiscible polyvinylidene fluoride (PVDF)/polylactic acid (PLLA) blends. A small amount of a reactive graft copolymer, poly(styrene-co-glycidyl methacrylate)-graft-poly(methyl methacrylate) (P((S-co-GMA)-g-MMA)), is incorporated into the PLLA/PVDF blends by simple melt mixing. The in situ grafting of PLLA chains onto P((S-co-GMA)-g-MMA) during melt mixing leads to the formation of numerous JNMs with a shell structure consisting of PLLA and PMMA hemispheres. These JNMs are located at the PLLA/PVDF interface, where they behave as effective compatibilizers for the immiscible PLLA/PVDF blends. This interfacial micelle compatibilization (IMC) mechanism opens new opportunities to exploit interfacial emulsification using JNMs and should be of great significance in the compatibilization of polymer alloys.