Formation Of Block Copolymers Research Articles

Terpyridine-Decorated Polymer Nanosphere Latex: Template Nanocarriers for the Synthesis of Cu-CeO2 Hollow Spheres.

Water-soluble polymers with the ability to complex metal ions through complexing ligands have attracted significant interest in diverse domains, such as optical or catalyst applications. In this paper, we successfully synthesized, through a one-pot process combining polymerization-induced self-assembly and reversible addition-fragmentation chain transfer polymerization, aqueous dispersions of terpyridine-decorated poly[poly(ethylene glycol)methyl ether methacrylate]-b-poly(methyl methacrylate) (tpy-PPEGMA-b-PMMA) amphiphilic block copolymers. The in-situ formation of well-defined amphiphilic block copolymers and their self-assembly led to nanosphere latex with the hydrodynamic diameters increasing from 17 to 52 nm and the length of the copolymers increasing from 21,000 to 51,000 g·mol-1. These aqueous dispersed tpy-PPEGMA-b-PMMA nanospheres effectively complex metal ions, such as Cu2+, in a stoichiometric ratio of 2:1. Subsequently, these metal-complexed nanospheres were employed as soft template nanocarriers to control, on the nanometer scale, the dispersion of metal on a nanostructured support. This is exemplified by the synthesis of copper supported on cerium oxide hollow spheres (Cu-CeO2) using Cu2+-tpy-PPEGMA-b-PMMA as template nanocarriers and CeO2 nanoparticles. This novel assembly engineering strategy for the preparation of atomically dispersed metal on a nanostructured support was highlighted through the utilization of Cu-CeO2 hollow spheres as an electrocatalyst for the nitrate reduction reaction (NO3RR) to NH3. These encouraging outcomes emphasize the potential of metal-metal oxide-nanostructured materials to treat contaminated water sources with nitrate while allowing the green production of ammonia.

Enhancing poly(lactic acid)/maleated polypropylene blend with magnesium oxide catalyst: a reactive blending approach for improved mechanical properties

Some defects of polylactic acid (PLA), especially its poor mechanical properties, were modified using a minimum content of non-biodegradable maleated polypropylene (MAPP). To this end, first, the amount of MAPP was optimized, which was 20 wt.%. Second, MgO was used as a new catalyst to improve the exchange reactions between active groups in both polymers in a reactive blending process. Tensile and izod analyses showed that, compared to neat PLA, with a slight decrease in modulus and tensile strength, elongation at break, and impact resistance were improved in the presence of 20 and 0.1 wt.% of MAPP and MgO, respectively. This improvement in mechanical properties can be related to the exchange reactions between two polymers and the formation of PLA-MAPP block copolymers. MFI and WDCA analyses demonstrated the increase in melt flowability and surface hydrophilicity of the resulting blends, respectively. DSC analysis showed that the Tg values of both polymers approached each other in the presence of catalyst. Also, the elimination of cold crystallization of PLA and the decrease in the Tm and crystallinity of both polymers are clear reasons for the miscibility of the alloy. TEM displayed the proper dispersion of MgO nanoparticles within the polymer matrix, and in addition, the XRD test also proved the decrease in the crystallinity of both polymers and appropriate miscibility of the samples containing 20 and 0.1 wt.% of MAPP and MgO, respectively. These results can promise the design of a compound with the maximum amount of PLA for further use in various industries.

Modern Trends in Polymerization-Induced Self-Assembly.

Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for producing colloidal dispersions of block copolymer particles with desired morphologies. Currently, PISA can be carried out in various media, over a wide range of temperatures, and using different mechanisms. This method enables the production of biodegradable objects and particles with various functionalities and stimuli sensitivity. Consequently, PISA offers a broad spectrum of potential commercial applications. The aim of this review is to provide an overview of the current state of rational synthesis of block copolymer particles with diverse morphologies using various PISA techniques and mechanisms. The discussion begins with an examination of the main thermodynamic, kinetic, and structural aspects of block copolymer micellization, followed by an exploration of the key principles of PISA in the formation of gradient and block copolymers. The review also delves into the main mechanisms of PISA implementation and the principles governing particle morphology. Finally, the potential future developments in PISA are considered.

Polymerization/Depolymerization-Induced Self-Assembly under Coupled Equilibria of Polymerization with Self-Assembly.

Depolymerization breaks down polymer chains into monomers like unthreading beads, attracting more attention from a sustainability standpoint. When polymerization reaches equilibrium, polymerization and depolymerization can reversibly proceed by decreasing and increasing the temperature. Here, we demonstrate that such dynamic control of a growing polymer chain in a selective solvent can spontaneously modulate the self-assembly of block copolymer micellar nano-objects. Compared to polymerization-induced self-assembly (PISA), where irreversible growth of a solvophobic polymer block from the end of a solvophilic polymer causes micellization, polymerization/depolymerization-induced self-assembly presented in this study allows us to reversibly regulate the packing parameter of the forming block copolymer and thus induce reversible morphological transitions of the nano-objects by temperature swing. Under the coupled equilibria of polymerization with self-assembly, we found that demixing of the growing polymer block in a more selective solvent entropically facilitates depolymerization at a substantially lower temperature. Taking ring-opening polymerization of δ-valerolactone initiated from the hydroxyl-terminated poly(ethylene oxide) as a model system, we show that polymerization/depolymerization/repolymerization leads to reversible morphological transitions, such as rod-sphere-rod and fiber-rod-fiber, during the heating and cooling cycle and accompanied by changes in macroscopic properties such as viscosity, suggesting their potential as dynamic soft materials.

Influence of chain topology on gel formation and direct ink printing of model linear and star block copolymers with poly(ethylene oxide) and poly(ε-caprolactone) semi-crystalline blocks

In this work, a set of well-defined linear triblock copolymers and star block copolymers (3 and 4-arms) with semi-crystalline blocks consisting of poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL), synthesized by combining ring-opening polymerization and organic catalyst switch strategy, were studied as thermosensitive gel-forming biomaterials for applications in 3D extrusion printing. The hydrogels derived from linear copolymers underwent a temperature-dependent sol–gel–sol transition, behaving as a flowing sol at room temperature and transforming into a non-flowing gel upon heating. On the other hand, the hydrogels derived from 4-arm star block copolymers experienced a gel-sol transition and did not flow at room temperature. This behavior allowed them to be used as 3D printing inks at room temperature. 3D printing results revealed that the semi-crystalline hydrogels of the 4-arm star block copolymers could not only be extruded and printed with high shape fidelity, but they also exhibited a favorable dissolution profile for their use as sacrificial biomaterial inks. Additionally, we thoroughly investigated the crystalline organization of the PCL and the PEO blocks within the hydrogels through comparison with the results obtained in bulk. The results demonstrated evident structural ordering in the hydrogels associated with the crystallization of the PCL blocks. Unexpectedly, DSC results combined with SAXS experiments revealed the presence of PEO block crystals within the 30 % w/v hydrogels from 4-arm star block copolymers, in addition to the PCL block crystals. Hence, remarkable double crystalline hydrogels have been obtained for the first time.

Living Alternating Ring-Opening Metathesis Copolymerization of 2,3-Dihydrofuran to Provide Completely Degradable Polymers.

2,3-Dihydrofuran (DHF) has recently been gaining significant attention as a comonomer in metathesis polymerization, thanks to its ability to provide the resultant polymer backbones with stimuli-responsive degradability. In this report, we present living alternating copolymerization of DHF with less reactive endo-tricyclo[4.2.2.02,5 ]deca-3,9-dienes (TDs) and endo-oxonorbornenes (oxoNBs). By carefully controlling the reactivity of both the Ru initiators and the monomers, we have achieved outstanding A, B-alternation (up to 98 %) under near stoichiometric DHF loading conditions. Notably, we have also found that the use of a more sterically hindered Ru initiator helps to attain polymer backbones with higher DHF incorporation and superior A, B-alternation. While preserving the living characteristics of DHF copolymerization, as evidenced by controlled molecular weights (up to 73.9 kDa), narrow dispersities (down to 1.05), and block copolymer formation, our DHF copolymers could be broken down to a single repeat unit level under acidic conditions. 1 H NMR analysis of the model copolymer revealed that after 24 hours of degradation, up to 80 % of the initial polymer was transformed into a single small molecule product, and after purification, up to 66 % of the degradation product was retrieved. This study provides a versatile approach to improve the alternation and degradability of DHF copolymers.

Living Alternating Ring‐Opening Metathesis Copolymerization of 2,3‐Dihydrofuran to Provide Completely Degradable Polymers

Abstract2,3‐Dihydrofuran (DHF) has recently been gaining significant attention as a comonomer in metathesis polymerization, thanks to its ability to provide the resultant polymer backbones with stimuli‐responsive degradability. In this report, we present living alternating copolymerization of DHF with less reactive endo‐tricyclo[4.2.2.02,5]deca‐3,9‐dienes (TDs) and endo‐oxonorbornenes (oxoNBs). By carefully controlling the reactivity of both the Ru initiators and the monomers, we have achieved outstanding A, B‐alternation (up to 98 %) under near stoichiometric DHF loading conditions. Notably, we have also found that the use of a more sterically hindered Ru initiator helps to attain polymer backbones with higher DHF incorporation and superior A, B‐alternation. While preserving the living characteristics of DHF copolymerization, as evidenced by controlled molecular weights (up to 73.9 kDa), narrow dispersities (down to 1.05), and block copolymer formation, our DHF copolymers could be broken down to a single repeat unit level under acidic conditions. 1H NMR analysis of the model copolymer revealed that after 24 hours of degradation, up to 80 % of the initial polymer was transformed into a single small molecule product, and after purification, up to 66 % of the degradation product was retrieved. This study provides a versatile approach to improve the alternation and degradability of DHF copolymers.

Solution and Film Self-Assembly Behavior of a Block Copolymer Composed of a Poly(ionic Liquid) and a Stimuli-Responsive Weak Polyelectrolyte.

Cu(0)-mediated atom transfer radical polymerization was used to synthesize a poly(ionic liquid), poly[4-vinylbenzyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide] (PVBBImTf2N), a stimuli-responsive polyelectrolyte, poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA), and a novel block copolymer formed from these two polymers. The synthesis of the block copolymer, poly[2-(dimethylamino) ethyl methacrylate]-block-[poly(4-vinylbenzyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide] (PDMAEMA-b-PVBBImTf2N), was examined to evaluate the control of "livingness" polymerization, as indicated by molecular weight, characterizations of degree of polymerization, and 1HNMR spectroscopy. 2D DOSY NMR measurements revealed the successful formation of block copolymer and the connection between the two polymer blocks. PDMAEMA-b-PVBBImTf2N was further characterized for supramolecular interactions in both the bulk and solution states through FTIR and 1H NMR spectroscopies. While the block copolymer demonstrated similar intermolecular behavior to the PIL homopolymer in the bulk state as indicated by FTIR, hydrogen bonding and counterion interactions in solution were observed in polar organic solvent through 1H NMR measurements. The DLS characterization revealed that the PDMAEMA-b-PVBBImTf2N block copolymer forms a network-like aggregated structure due to a combination of hydrogen bonding between the PDMAEMA and PIL group and electrostatic repulsive interactions between PIL blocks. This structure was found to collapse upon the addition of KNO3 while still maintaining hydrogen bonding interactions. AFM-IR analysis demonstrated varied morphologies, with spherical PDMAEMA in PVBBImTf2N matrix morphology exhibited in the region approaching the film center. AFM-IR further revealed signals from silica nano-contaminates, which selectively interacted with the PDMAEMA spheres, demonstrating the potential for the PDMAEMA-b-PVBBImTf2N PIL block copolymer in polymer-inorganic nanoparticle composite applications.

Thermoplastic Toughening of a Semiaromatic Polyamide with an Amino-telechelic Polyethylene.

Semiaromatic polyamides are used for metal replacement in advanced engineering applications to reduce weight and improve efficiency, but their range of application is limited by their inherent lack of ductility and toughness. Here, we combined semiaromatic polyamide poly(hexamethylene terephthalamide-co-isophthalamide) (PA6TI) with up to 30 wt % amine-terminated polyethylene (PE(NH2)2) by high-temperature melt compounding, which was suggested to lead to the formation of PA-PE block copolymers at the interface between the PE(NH2)2 and the PA6TI. This resulted in PA6TI/PE(NH2)2 blends with smaller, more uniform particle sizes than in PA6TI blended with nonfunctional PE or the commercial impact modifier, maleic anhydride-functionalized styrene-ethylene-butylene-styrene (SEBS) under the same conditions. The PA6TI/PE(NH2)2 blends and the corresponding glass fiber-reinforced composites consequently showed significantly greater increases in room-temperature tensile ductility and fracture energy with respect to unmodified PA6TI, as well as maintained mechanical stability at high temperatures, and only modest decreases in stiffness and strength, even at high PE(NH2)2 contents. These improvements were attributed to the crystallinity of the PE(NH2)2 particles and to improved morphological stabilization and matrix-particle adhesion, consistent with the presence of PA-PE block copolymer at the matrix-particle interfaces.

The Process-Directed Self-Assembly of Block Copolymer Particles.

The kinetic paths of structural evolution and formation of block copolymer (BCP) particles are explored using dynamic self-consistent field theory (DSCFT). It is shown that the process-directed self-assembly of BCP immersed in a poor solvent leads to the formation of striped ellipsoids, onion-like particles and double-spiral lamellar particles. The theory predicts a reversible path of shape transition between onion-like particles and striped ellipsoidal ones by regulating the temperature (related to the Flory-Huggins parameter between the two components of BCP, χAB ) and the selectivity of solvent toward one of the two BCP components. Furthermore, a kinetic path of shape transition from onion-like particles to double-spiral lamellar particles, and then back to onion-like particles is demonstrated. By investigating the inner-structural evolution of a BCP particle, it is identified that changing the intermediate bi-continuous structure into a layered one is crucial for the formation of striped ellipsoidal particles. Another interesting finding is that the formation of onion-like particles is characterized by a two-stage microphase separation. The first is induced by the solvent preference, and the second is controlled by the thermodynamics. The findings lead to an effective way of tailoring nanostructure of BCP particles for various industrialapplications.

Bilayer-domain formation of thermoresponsive amphiphilic block copolymers in hybrid liposomes for synthetic molecular channels

Maltopentaose-b-PPO copolymer can be incorporated into phospholipid membranes and form bilayer-domains, where they act as synthetic molecular channels.

From monomer to micelle: a facile approach to the multi-step synthesis of block copolymers via inline purification.

A one-pass continuous flow strategy to form block copolymer nanoaggregates directly from monomers is presented. A key development towards such a sophisticated continuous flow setup is a significant improvement in continuous flow dialysis. Often impurities or solvent residues from polymerizations must be removed before block extensions or nanoaggregate formation can be carried out, typically disrupting the workflow. Hence, inline purification systems are required for fully continuous operation and eventual high throughput operation. An inline dialysis purification system is developed and exemplified for amphiphilic block copolymer synthesis from thermal and photoiniferter reversible addition fragmentation chain transfer (RAFT) polymerization. The inline dialysis system is found to be significantly faster than conventional batch dialysis and the kinetics are found to be very predictable with a diffusion velocity coefficient of 4.1 × 10-4 s-1. This is at least 4-5 times faster than conventional dialysis. Moreover, the newly developed setup uses only 57 mL of solvent for purification per gram of polymer, again reducing the required amount by almost an order of magnitude compared to conventional methods. Methyl methacrylate (MMA) or butyl acrylate (BA) was polymerized in a traditional flow reactor as the first block via RAFT polymerization, followed by a 'dialysis loop', which contains a custom-built inline dialysis device. Clearance of residual monomers is monitored via in-line NMR. The purified reaction mixture can then be chain extended in a second reactor stage to obtain block copolymers using poly(ethylene glycol) methyl ether acrylate (PEGMEA) as the second monomer. In the last step, nano-objects are created, again from flow processes. The process is highly tuneable, showing for the chosen model system a variation in nanoaggregate size from 34 nm to 188 nm.

Functionalization of Polylactide with Multiple Tetraphenyethane Inifer Groups to Form PLA Block Copolymers with Vinyl Monomers

In the present contribution, a new strategy for preparing block copolymers of polylactide (PLA), a bio-derived polymer of increasing importance, is described. The method should lead to multiblock copolymers of lactide with vinyl monomers (VM), i.e., monomers that polymerize according to different mechanisms, and is based on the introduction of multiple "inifer" (INItiator/transFER agent) groups into PLA's structure. As an "inifer" group, tetraphenylethane (TPE, known to easily thermally dissociate to radicals) was incorporated into PLA chains using diisocyanate. PLA that contained TPE groups (PLA-PU) was characterized, and its ability to form initiating radicals was demonstrated by ESR measurements. PLA-PU was used as a "macroinifer" for the polymerization of acrylonitrile and styrene upon moderate heating (85 °C) of the PLA-PU in the presence of monomers. The formation of block copolymers PLA/PVM was confirmed by 1H NMR, DOSY NMR, and FTIR spectroscopies and the SEC method. The prepared copolymers showed only one glass transition in DSC curves with Tg values higher than those of PLA-PU.

Catalytic Living Ring‐Opening Metathesis Polymerization Using Vinyl Ethers as Effective Chain‐Transfer Agents

AbstractA catalytic living ring‐opening metathesis copolymerization (ROMP) method is described that relies on a degenerative, reversible and regioselective exchange of propagating Fischer‐carbenes. All characteristics of a living polymerization such as narrow dispersity, excellent molar mass control and the ability to form block copolymers are achieved by this method. The method allows the use of up to 200 times less ruthenium complex than traditional living ROMP. We demonstrate the synthesis of ROMP‐ROMP diblock copolymers, ATRP from a ROMP macro‐initiator and living ROMP from a PEG‐based macro chain transfer agent. The cost‐effective, sustainable and environmentally friendly synthesis of degradable polymers and block copolymers enabled by this strategy will find various applications in biomedicine, materials science, and technology.

Catalytic Living Ring-Opening Metathesis Polymerization Using Vinyl Ethers as Effective Chain-Transfer Agents.

A catalytic living ring-opening metathesis copolymerization (ROMP) method is described that relies on a degenerative, reversible and regioselective exchange of propagating Fischer-carbenes. All characteristics of a living polymerization such as narrow dispersity, excellent molar mass control and the ability to form block copolymers are achieved by this method. The method allows the use of up to 200 times less ruthenium complex than traditional living ROMP. We demonstrate the synthesis of ROMP-ROMP diblock copolymers, ATRP from a ROMP macro-initiator and living ROMP from a PEG-based macro chain transfer agent. The cost-effective, sustainable and environmentally friendly synthesis of degradable polymers and block copolymers enabled by this strategy will find various applications in biomedicine, materials science, and technology.

Self-assembly and complex formation of amphiphilic star and bottle-brush block copolymers.

We use molecular dynamics computer simulations to investigate complexation and clustering of branched polymers. In this study, we focus on star and bottle-brush polymers. In our investigation, we identify key factors governing cluster formation of branched amphiphilic polymers and provide guidance for designing and preparing various types of polymer clusters for applications, e.g., in drug delivery or materials science. We observe different kinds of clustering in the polymer systems. Our star polymers consist of several arms of hydrophilic core particles with hydrophobic particles attached to the end of each star arm. We observe that amphiphilic star polymers generally tend to form spherical complexes. In contrast to this, bottle-brush polymers exhibit a larger variety of complex structures. With large grafting density and large side arms, we also observe spherical polymer clusters; however, for low grafting density and shorter side chains, distinct clusters connected by bridging particles are formed. Furthermore, we observe membrane-like clustering of bottle-brush polymers. We employ two different clustering algorithms for further analysis of the obtained structures with respect to shape factors, pair correlation functions, and radii of gyration. We find that the hydrophobic parts of polymers play a crucial role in the formation of the resulting structures during self-assembly. The hydrophilic core parts in star polymers along with steric hindrance lead to a screening effect for the hydrophobic parts of the polymers. With bottle-brush copolymers, the hydrophilic parts of the polymers exhibit a screening effect that is sensitive to the grafting density and side chain lengths along the backbone.

Raspberry-like Aggregate Formation of π-Stacked Block Copolymer of Dibenzofulvene and Methyl Methacrylate Synthesized by Atom-transfer Radical Polymerization

Block copolymerization of dibenzofulvene (DBF) forming a sequence having π-stacked conformation and methyl methacrylate (MMA) forming a flexible sequence was conducted by atom-transfer radical polymerization (ATRP) where MMA was polymerized first and DBF was then blocked. The block copolymer contained a fraction with number-averaged molar mass of 873400 (vs. polystyrene) which was found to be raspberry-like aggregates with sizes of hundreds of nanometers composed of smaller spherical particles with sizes of a few to low tens of nanometers. The aggregates are considered to have a core-shell structure where strong inter-chain interaction between poly(DBF) segments form the core and flexible poly(MMA) segments are the shell, and the formation appeared to be thermally driven. The aggregates having a rigid structure stabilized the π-stacked conformation of poly(DBF) segments both in the ground state and in excited states as found by NMR and fluorescence spectra, respectively, and restricted molecular motion of both the poly(DBF) segments and poly(MMA) segments.

Ionic Compatibilization of Polymers.

The small specific entropy of mixing of high molecular weight polymers implies that most blends of dissimilar polymers are immiscible with poor physical properties. Historically, a wide range of compatibilization strategies have been pursued, including the addition of copolymers or emulsifiers or installing complementary reactive groups that can promote the in situ formation of block or graft copolymers during blending operations. Typically, such reactive blending exploits reversible or irreversible covalent or hydrogen bonds to produce the desired copolymer, but there are other options. Here, we argue that ionic bonds and electrostatic correlations represent an underutilized tool for polymer compatibilization and in tailoring materials for applications ranging from sustainable polymer alloys to organic electronics and solid polymer electrolytes. The theoretical basis for ionic compatibilization is surveyed and placed in the context of existing experimental literature and emerging classes of functional polymer materials. We conclude with a perspective on how electrostatic interactions might be exploited in plastic waste upcycling.

Linear and Star Block Copolymer Nanoparticles Prepared by Heterogeneous RAFT Polymerization Using an ω,ω-Heterodifunctional Macro-RAFT Agent.

Herein, an ω,ω-heterodifunctional macromolecular reversible addition-fragmentation chain transfer (macro-RAFT) agent containing two different RAFT end groups was synthesized and employed to mediate aqueous photoinitiated RAFT dispersion polymerization of a methacrylic monomer. Because of the different RAFT controllability of two RAFT end groups toward methacrylic monomers, the RAFT end group with good controllability dominated the polymerization while the other RAFT end group with poor controllability was unreacted, leading to the formation of linear block copolymers. Because of the unique structure of the linear block copolymers, a diverse set of block copolymer nanoparticles with rich RAFT groups at the interface of the hydrophilic corona/the hydrophobic core were successfully prepared. Finally, μ-A(BC)C miktoarm star block copolymer nanoparticles were prepared by RAFT seeded emulsion polymerization of an acrylic monomer, which enables the further morphological control over polymer nanoparticles. We believe that the utilization of an ω,ω-heterodifunctional macro-RAFT agent in heterogeneous RAFT polymerization will offer considerable opportunities for the rational synthesis of well-defined molecular architectures and polymer nanoparticles.

Switchable Copolymerization of Maleic Anhydride/Epoxides/Lactide Mixtures: A Straightforward Approach to Block Copolymers with Unsaturated Polyester Sequences

AbstractSwitchable copolymerization of oxygenated heterocycle mixtures by a single catalytic system has been proved to be a promising approach to sequence‐controlled block copolymers. However, there are still big challenges in one‐step synthesis of multiblock copolymers containing unsaturated polyester blocks from maleic anhydride, epoxides, and lactone mixtures. Herein, a switchable pathway for polylactide‐b‐poly(MAH‐alt‐epoxide)‐b‐polylactide block copolymers is established. The excellent chemoselectivity in multicomponent copolymerization is achieved by bipyridine bisphenolate aluminum complexes that can induce an obvious kinetic differentiation between ring‐opening copolymerization of maleic anhydride/epoxides and ring‐opening polymerization of lactide. The scope of the epoxide for switchable copolymerization is explored and it is found that the steric hindrance of the substituents on epoxide significantly influences the formation of block copolymers. Block copolymers with various sequential and topological structures can be easily prepared by exquisite selection of different initiators. Furthermore, it is demonstrated that the conversion of cis‐maleate units in the block copolyester could be completely converted to trans‐fumarate units by isomerization without chain degradation, cross‐linking, and chain scrambling.