Synthesis Of Well-defined Polymers Research Articles

Valorization of Lactate Esters and Amides into Value-Added Biobased (Meth)acrylic Polymers.

(Meth)acrylic polymers are massively produced due to their inherently attractive properties. However, the vast majority of these polymers are derived from fossil resources, which is not aligned with the tendency to reduce gas emissions. In this context, (meth)acrylic polymers derived from biomass (biobased polymers) are gaining momentum, as their application in different areas can not only stand the comparison but even surpass, in some cases, the performance of petroleum-derived ones. In this review, we highlight the design and synthesis of (meth)acrylic polymers derived from lactate esters (LEs) and lactate amides (LAs), both derived from lactic acid. While biobased polymers have been widely studied and reviewed, the poly(meth)acrylates with pendant LE and LA moieties evolved slowly until recently when significant achievements have been made. Hence, constraints and opportunities arising from previous research in this area are presented, focusing on the synthesis of well-defined polymers for the preparation of advanced materials.

Dl-Methionine-Mediated Reversible Deactivation Radical Polymerization of Styrene and Methyl Methacrylate.

Reversible deactivation radical polymerization (RDRP) is a facile and highly efficient technique for the synthesis of well-defined polymer with precise structure. dl-Methionine (Met) as a RDRP control agent is described and assessed for RDRP of styrene (St) and methyl methacrylate (MMA) with AIBN as radical initiator at 75°C, which enables excellent control of this polymerization. The addition of dl-Methionine significantly decreased the dispersity (Đ) of the polymers for both monomers and first-order linear kinetic plots of polymethyl methacrylate (PMMA) are observed in DMSO. Considering the heat resistance of dl-Methionine, kinetic studies indicate that polymerization develops at a faster rate at higher reaction temperature (100°C) with the same dl-Methionine content. Well-defined polymethyl methacrylate-block-polystyrene (PMMA-block-PSt) is successfully achieved by the chain extension reaction that demonstrates the high end fidelities of this polymerization approach. The system allows the use of dl-Methionine, a rich source and easily synthesized agent, to mediate RDRP strategy.

Synthesis of Cleavable Polymers via Oxidation of Thioether Moieties and Thiol Click Reactions: A Click-Declick Strategy.

In the past decades click chemistries including thiol chemistries have found wide applications in the synthesis of well-defined polymers. In this research, a click-declick strategy based on the oxidation of heteroaromatic thioethers and the substitution reactions between the oxidized groups and thiols, is proposed for the synthesis of the cleavable polymers. In proof-of-concept experiments, block copolymers (BCPs) and star-like polymers are synthesized by thiol-phenylsulfone substitution reactions, and heteroaromatic thioethers are produced at the junction points of the BCP chains or on the crosslinking sites of the star-like polymer. The thioethers can be oxidized to heteroaromatic sulfoxides or sulfones, depending on the oxidization condition. It is demonstrated that both sulfoxides or sulfones can have base catalyzed nucleophilic substitution reactions with thiols, leading to the cleavage of the polymers.

Monte Carlo simulation of photoinduced atom-transfer radical polymerization for dynamic microscopic properties

Atom-transfer radical polymerization (ATRP) is a powerful and versatile technique for the synthesis of well-defined polymers with precise control over the molecular weight and architecture. Photoinduced ATRP (photoATRP) is a variant of ATRP based on the transfer of radical polymers through a photochemical process, offering numerous benefits over traditional ATRP, including reduced environmental impact and improved polymer yields. Monte Carlo (MC) simulation is an attractive tool for simulating photoATRP, enabling one to predict microscopic properties of the polymers. In this work, a dynamic Monte Carlo (DMC) model is developed for the photoATRP processes at microscopic resolution. The dependency information of individual chains’ length on the radical, dormant, and dead polymers is captured. Furthermore, the polymerization process simulation of photoATRP systems based on the developed DMC method for temporal control over polymer growth is established. Several facets on the enhancement of temporal control are investigated under the condition of light intermittency.

Rapid Controlled Synthesis of Large Polymers by Frontal Ring-Opening Metathesis Polymerization

Tunable molecular weight and well-defined polydispersity are the hallmarks of a controlled polymerization. This process relies on vanishingly small termination rates, minimal chain transfer, and initiation rates faster than propagation rates. Ring-opening metathesis polymerization (ROMP) is a well-known controlled polymerization based on the opening of strained cyclic olefins. The exothermic nature of ROMP allows rapid conversion of neat monomers to polymers through frontal ROMP (FROMP). Unlike traditional ROMP, FROMP uses the exothermic heat from the opening of strained cyclic olefins to thermally activate the initiator that sustains the propagation of a cascading reaction front. Although the reaction mechanisms for ROMP and FROMP are the same, the reaction conditions differ greatly, especially in the temperature and monomer concentration. The ability to control the polymerization under FROMP conditions has yet to be investigated, as well as its potential in the synthesis of well-defined polymers without the use of solvents and with minimal energy input. Here, we show that FROMP rapidly transforms monomers into polymers of high-molecular weight (Mn) with good fidelity and low dispersity (Đ). Specifically, the synthesis of polymers with Mn up to 700 kg/mol and Đ of 1.5 was achieved with a rapid, solvent-free, and oxygen-tolerant frontal polymerization technique. Further control of the polymerization was possible with the addition of a phosphite ligand that lowered the Đ to 1.2. We anticipate that controlled FROMP will become a valuable macromolecular synthetic tool due to its reliability, speed, scalability, and simplicity.

Controlling Radical Polymerization with Biocatalysts

Reversible deactivation radical polymerization (RDRP) is a set of powerful and versatile methods for the synthesis of well-defined polymers. Over the past two decades, the engagement of biocatalysts, namely, enzymes and bacteria, has granted distinctive features to RDRP and propelled RDRP toward a more sustainable future. In this Perspective, we highlight the green conditions, oxygen tolerance, versatile function, and the ability to access difficult polymers in RDRP conducted by biocatalysis (bio-RDRP), discuss major considerations when conducting bio-RDRP, and point out the drawbacks and bottlenecks that limit its further development. The future of bio-RDRP may benefit from expanding the biocatalyst library, improving the redox potential of bacteria, enhancing the biocatalyst robustness, and in-depth mechanistic studies.

Biomimetic and Hydrophilic Vitamin B5 Analogous Methacrylamide Polymers Prevent Surface Fouling

This study reports the synthesis of well-defined polymers of vitamin B5 analogous methacrylamide (poly(B5AMA)) using the reversible addition fragmentation chain transfer polymerization method. The prepared telechelic poly(B5AMA) with a predicted molecular weight and narrow polydispersities are grafted onto silanized glass surfaces using a “grafting to” approach. The polymer-treated samples are characterized for the water contact angle and surface roughness properties, as a function of polymer size and density of the polymers grafted onto the glass slides. The antifouling behavior of poly(B5AMA)-grafted glass slides is then studied and compared with that of PEGylated glass slides, upon treatment with a variety of proteins and bacteria. The functionalized surfaces exhibit remarkable antifouling properties that are found to be dependent on both the density and the molecular weight of the grafted polymers.

Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis.

Photoinduced atom transfer radical polymerization (photo-ATRP) has risen to the forefront of modern polymer chemistry as a powerful tool giving access to well-defined materials with complex architecture. However, most photo-ATRP systems can only generate radicals under biocidal UV light and are oxygen-sensitive, hindering their practical use in the synthesis of polymer biohybrids. Herein, inspired by the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, we demonstrate a dual photoredox/copper catalysis that allows open-air ATRP under green light irradiation. Eosin Y was used as an organic photoredox catalyst (PC) in combination with a copper complex (X-CuII/L). The role of PC was to trigger and drive the polymerization, while X-CuII/L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X-CuII/L, generating CuI/L activator and PC˙+. The ATRP ligand (L) used in excess then reduced the PC˙+, closing the photocatalytic cycle. The continuous reduction of X-CuII/L back to CuI/L by excited PC provided high oxygen tolerance. As a result, a well-controlled and rapid ATRP could proceed even in an open vessel despite continuous oxygen diffusion. This method allowed the synthesis of polymers with narrow molecular weight distributions and controlled molecular weights using Cu catalyst and PC at ppm levels in both aqueous and organic media. A detailed comparison of photo-ATRP with PET-RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically relevant conditions. The kinetic studies and fluorescence measurements indicated that in the absence of the X-CuII/L complex, green light irradiation caused faster photobleaching of eosin Y, leading to inhibition of PET-RAFT polymerization. Importantly, PET-RAFT polymerizations showed significantly higher dispersity values (1.14 ≤ Đ ≤ 4.01) in contrast to photo-ATRP (1.15 ≤ Đ ≤ 1.22) under identical conditions.

Conjugated Cross-linked Phenothiazines as Green or Red Light Heterogeneous Photocatalysts for Copper-Catalyzed Atom Transfer Radical Polymerization.

Using the power of light to drive controlled radical polymerizations has provided significant advances in synthesis of well-defined polymers. Photoinduced atom transfer radical polymerization (ATRP) systems often employ UV light to regenerate copper activator species to mediate the polymerization. Taking full advantage of long-wavelength visible light for ATRP would require developing appropriate photocatalytic systems that engage in photoinduced electron transfer processes with the ATRP components to generate activating species. Herein, we developed conjugated microporous polymers (CMP) as heterogeneous photocatalysts to exploit the power of visible light in promoting copper-catalyzed ATRP. The photocatalyst was designed by cross-linking phenothiazine (PTZ) as a photoactive core in the presence of dimethoxybenzene as a cross-linker via the Friedel-Crafts reaction. The resulting PTZ-CMP network showed photoactivity in the visible region due to the extended conjugation throughout the network because of the aromatic groups connecting the PTZ units. Therefore, photoinduced copper-catalyzed ATRP was performed with CMPs that regenerated activator species under green or red light irradiation to start the ATRP process. This resulted in efficient polymerization of acrylate and methacrylate monomers with high conversion and well-controlled molecular weight. The heterogeneous nature of the photocatalyst enabled easy separation and efficient reusability in subsequent polymerizations.

PhotoATRP Approach to Poly(methyl methacrylate) with Aggregation-Induced Emission

In the past decades, polymeric fluorescent materials with aggregation-induced emission (AIE) properties play important roles in the fields of biomedical and analytical chemistry, and the synthesis of well-defined polymers under mild conditions is in demand. In this report, narrowly distributed poly(methyl methacrylate)s (PMMAs) with AIE properties were prepared in mild conditions using 4-(1,2,2-triphenylvinyl)benzyl 2-bromo-2-phenylacetate (TPE-BPA), a novel initiator with an AIE-based functional group. This approach resulted in PMMAs with a fluorescent tag at the chain end (TPE-PMMA). Specifically, a high efficiency of initiation was observed using a low amount of air-stable copper(II) bromide/tris(2-pyridylmethyl)amine (CuIIBr2/TPMA) as a photocatalyst under the irradiation of LED@405 nm. Moreover, the TPE presented in the system did not affect the polymerization kinetics of MMA and the temporal control. The dispersities of the obtained PMMAs were as low as 1.12. Interestingly, TPE-PMMA with narrow dispersity was also obtained (Mw/Mn < 1.25) in the presence of air. Regarding the fluorescent properties of TPE-PMMAs, it was observed that their AIE intensities increased with the molecular weights. Moreover, they could also be used to probe the increased viscosity of the solution, indicating their potential of synthesizing functional sensors. The approach proposed in this work is convenient to prepare poly(methacrylate)s with well-defined structures in the presence of AIE-based fluorescent tags, and it thus paves a new way for the rational design of AIE-functionalized polymeric materials.

Dendrons and Dendritic Terpolymers: Synthesis, Characterization and Self-Assembly Comparison.

To the best of our knowledge, this is the very first time that a thorough study of the synthetic procedures, molecular and thermal characterization, followed by structure/properties relationship for symmetric and non-symmetric second generation (2-G) dendritic terpolymers is reported. Actually, the synthesis of the non-symmetric materials is reported for the first time in the literature. Anionic polymerization enables the synthesis of well-defined polymers that, despite the architecture complexity, absolute control over the average molecular weight, as well as block composition, is achieved. The dendritic type macromolecular architecture affects the microphase separation, because different morphologies are obtained, which do not exhibit long range order, and various defects or dislocations are evident attributed to the increased number of junction points of the final material despite the satisfactory thermal annealing at temperatures above the highest glass transition temperature of all blocks. For comparison reasons, the initial dendrons (miktoarm star terpolymer precursors) which are connected to each other in order to synthesize the final dendritic terpolymers are characterized in solution and in bulk and their self-assembly is also studied. A major conclusion is that specific structures are adopted which depend on the type of the core connection between the ligand and the active sites of the dendrons.

RAFT Emulsion Polymerization: MacroRAFT Agent Self-Assembly Investigated Using a Solvachromatic Dye.

Polymerization-induced self-assembly (PISA) and amphiphilic-macroRAFT-mediated emulsion polymerization are commonly used approaches for synthesis of well-defined polymers and sophisticated particle morphologies. One aspect of these systems that remains relatively unexplored is the conformational state of macroRAFT agents in aqueous solution. To redress this deficiency, we have used fluorescence spectrometry experiments to conduct detailed investigations of the coil conformation across a wide range of pH values for a series of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) macroRAFT agents with different Z-groups (-S-(CH2)2-COOH, -S-(CH2)3-CH3, and -S-(CH2)11-CH3), as well as amphiphilic macroRAFT agents (PMAA-b-poly(methyl methacrylate)(PMMA) and PAA-b-polystyrene(PS)). The critical aggregate concentrations (CAC) or critical micelle concentrations (CMC) for all systems ranged from 7.48 × 10-7 to 2.57 × 10-3 mol L-1. Overall, an extensive library of CAC/CMC values has been compiled for PAA- and PMAA-based macroRAFT agents at different pH conditions, providing important information related to the mechanistic understanding and optimization of macroRAFT-assisted emulsion polymerization.

Glycopolymer Brushes by Reversible Deactivation Radical Polymerization: Preparation, Applications, and Future Challenges.

The cellular surface contains specific proteins, also known as lectins, that are carbohydrates receptors involved in different biological events, such as cell–cell adhesion, cell recognition and cell differentiation. The synthesis of well-defined polymers containing carbohydrate units, known as glycopolymers, by reversible deactivation radical polymerization (RDRP) methods allows the development of tailor-made materials with high affinity for lectins because of their multivalent interaction. These polymers are promising candidates for the biomedical field, namely as novel diagnostic disease markers, biosensors, or carriers for tumor-targeted therapy. Although linear glycopolymers are extensively studied for lectin recognition, branched glycopolymeric structures, such as polymer brushes can establish stronger interactions with lectins. This specific glycopolymer topology can be synthesized in a bottlebrush form or grafted to/from surfaces by using RDRP methods, allowing a precise control over molecular weight, grafting density, and brush thickness. Here, the preparation and application of glycopolymer brushes is critically discussed and future research directions on this topic are suggested.

High-Throughput Preparation of Antibacterial Polymers from Natural Product Derivatives via the Hantzsch Reaction.

SummaryThe Hantzsch and free-radical polymerization reactions were combined in a one-pot high-throughput (HTP) system to simultaneously prepare 30 unique polymers in parallel. Six aldehydes derived from natural products were used as the starting materials to rapidly prepare the library of 30 poly(1,4-dihydropyridines). From this library, HTP evaluation methods led to the identification of an antibacterial polymer. Mechanistic studies revealed that the dihydropyridine group in the polymer side-chain structure plays an important role in resisting bacterial attachment to the polymer surface, thus leading to the antibacterial function of this polymer. This research demonstrates the value of multicomponent reactions (MCRs) in interdisciplinary fields by discovering functional polymers for possible practical applications. It also provides insights to further developing new functional polymers using MCRs and HTP methods with important implications in organic chemistry, polymer chemistry, and materials science.

Utilization of 4-(trifluoromethyl)benzenesulfonates as Counter Ions Tunes the Initiator Efficiency of Sophisticated Initiators for the Preparation of Well-Defined poly(2-oxazoline)s.

During the last decades, poly(2-oxazoline)s (POx) have gained increased interest due to their versatility. In particular, cationic ring-opening polymerization (CROP) enables the synthesis of well-defined polymers bearing quantitative α- and ω-functionalities. In contrast to small initiating groups, the introduction of more sophisticated, respectively demanding groups remains challenging. To fulfill this challenge, the initiator should comply with one major requirement in order to yield well-defined polymers: a fast and complete initiation. The straight forward two-step synthesis of a novel initiator containing a 4-(trifluoromethyl)benzenesulfonate (fluorylate, TosCF3 ) counter-ion is herein presented to accomplish the introduction of a sophisticated functional 3-(2-(2-ethoxy)ethoxy)ethoxy)prop-1-ene (TEG) initiating group. Kinetic studies are conducted in acetonitrile and chlorobenzene using the hydrophilic 2-ethyl-2-oxazoline (EtOx) as well as the hydrophobic 2-octyl-2-oxazoline (OctOx) as monomers to examine the influences of the solvent as well as the different monomers. In particular, the initiator efficiency is determined by 1 H and 19 F nuclear magnetic resonance spectroscopy and compared to the corresponding tosylate (TEGTos) and triflate (TEGTf). It is shown that the fluorylate combines the stability of the tosylate and an enhanced propagation rate comparable to the triflate.

Enzyme-Deoxygenated Low Parts per Million Atom Transfer Radical Polymerization in Miniemulsion and Ab Initio Emulsion.

The development of robust oxygen-tolerant reversible deactivation radical polymerization (RDRP) systems can dramatically simplify synthesis of well-defined polymers without redundant deoxygenation procedures. Herein, we broaden the application of oxygen-tolerant RDRP from homogeneous aqueous and organic solutions to dispersed media. The glucose oxidase (GOx) degassed atom transfer radical polymerization (ATRP) was conducted in miniemulsion and ab initio emulsion systems using various catalyst regeneration methods: ARGET, ICAR, photo, and eATRP. All of these polymerization procedures led to polymers with predetermined molecular weight, low dispersity, and high chain-end functionality. Emulsion ATRP on a larger scale with preserved control was also successful. Circular dichroism (CD) studies demonstrated that the anionic surfactant, sodium dodecyl sulfate (SDS), did not damage the secondary structure of GOx. This confirms the versatility of the GOx system for various low ppm ATRP methods. GOx-assisted oxygen removal in the synthesis of hydrophobic polymers is reported for the first time. The low cost of deoxygenation reagents and the ability to scale up the procedure suggest the potential for industrial production, especially for emulsion polymerization.

Beyond Gene Transfection with Methacrylate-Based Polyplexes-The Influence of the Amino Substitution Pattern.

Methacrylate-based polymers represent promising nonviral gene delivery vectors, since they offer a large variety of polymer architectures and functionalities, which are beneficial for specific demands in gene delivery. In combination with controlled radical polymerization techniques, such as the reversible addition-fragmentation chain transfer polymerization, the synthesis of well-defined polymers is possible. In this study we prepared a library of defined linear polymers based on (2-aminoethyl)-methacrylate (AEMA), N-methyl-(2-aminoethyl)-methacrylate (MAEMA), and N,N-dimethyl-(2-aminoethyl)-methacrylate (DMAEMA) monomers, bearing pendant primary, secondary, and tertiary amino groups, and investigated the influence of the substitution pattern on their gene delivery capability. The polymers and the corresponding plasmid DNA complexes were investigated regarding their physicochemical characteristics, cytocompatibility, and transfection performance. The nonviral transfection by methacrylate-based polyplexes differs significantly from poly(ethylene imine)-based polyplexes, as a successful transfection is not affected by the buffer capacity. We observed that polyplexes containing a high content of primary amino groups (AEMA) offered the highest transfection efficiency, whereas polyplexes bearing tertiary amino groups (DMAEMA) exhibited the lowest transfection efficiency. Further insights into the uptake and release mechanisms could be identified by fluorescence and transmission electron microscopy, emphasizing the theory of membrane-pore formation for the time-efficient endosomal release of methacrylate-based vectors.

Open-to-Air RAFT Polymerization in Complex Solvents: From Whisky to Fermentation Broth.

We investigate the use of in situ enzyme degassing to facilitate the open-to-air reversible addition-fragmentation chain transfer (RAFT) polymerization of hydroxyethyl acrylate (HEA) in a wide range of complex aqueous solvents, including, beer, wine, liquor, and fermentation broth. This enzyme-assisted polymerization procedure is impressively robust, and poly(HEA) was attained with good control over molecular weight and a narrow dispersity in nearly all of the solvents tested. Kinetics experiments on HEA polymerization in whisky and spectroscopic analysis of the purified polymers suggest high end-group fidelity, as does the successful chain extension of a poly(HEA) macro chain transfer agent with narrow dispersity. These results suggest enzyme-assisted RAFT may be a powerful and underutilized tool for high-throughput screening and materials discovery and may simplify the synthesis of well-defined polymers in complex conditions.

Photoinduced Iron-Catalyzed Atom Transfer Radical Polymerization with ppm Levels of Iron Catalyst under Blue Light Irradiation

Photoinduced atom transfer radical polymerization (ATRP) has been mainly explored using copper-based catalytic systems. Recently developed iron-catalyzed photochemical ATRP employed high amounts of iron catalysts under high-energy UV light irradiation. Herein, a successful photoinduced iron-catalyzed ATRP mediated under blue light irradiation with ppm amounts (100–400 ppm) of iron(III) bromide/tetrabutylammonium bromide as the catalyst is reported. Several methacrylate monomers were polymerized with excellent control providing molecular weight in good agreement with theoretical values and low dispersity (Đ < 1.20). Near-quantitative monomer conversions (∼95%) enabled in situ chain extension and block copolymerization, indicating high retention of chain-end functionality. Notably, this system can tolerate oxygen, enabling synthesis of well-defined polymers with good chain-end functionality in the presence of air.

Automated Synthesis of Well-Defined Polymers and Biohybrids by Atom Transfer Radical Polymerization Using a DNA Synthesizer.

A DNA synthesizer was successfully employed for preparation of well-defined polymers by atom transfer radical polymerization (ATRP), in a technique termed AutoATRP. This method provides well-defined homopolymers, diblock copolymers, and biohybrids under automated photomediated ATRP conditions. PhotoATRP was selected over other ATRP methods because of mild reaction conditions, ambient temperature, tolerance to oxygen, and no need to introduce reducing agents or radical initiators. Both acrylate and methacrylate monomers were successfully polymerized with excellent control in the DNA synthesizer. Diblock copolymers were synthesized with different targeted degrees of polymerization and with high retention of chain-end functionality. Both hydrophobic and hydrophilic monomers were grafted from DNA. The DNA-polymer hybrids were characterized by SEC and DLS. The AutoATRP method provides an efficient route to prepare a range of different polymeric materials, especially polymer-biohybrids.