Streamlining the Generation of Advanced Polymer Materials Through the Marriage of Automation and Multiblock Copolymer Synthesis in Emulsion

Synthetic polymers are of paramount importance in modern life - an incredibly wide range of polymeric materials possessing an impressive variety of properties have been developed to date. The recent emergence of artificial intelligence and automation presents a great opportunity to significantly speed up discovery and development of the next generation of advanced polymeric materials. We have focused on the high-throughput automated synthesis of multiblock copolymers that comprise three or more distinct polymer segments of different monomer composition bonded in linear sequence. The present work has exploited automation to prepare high molar mass multiblock copolymers (typically>100,000 g mol-1) using reversible addition-fragmentation chain transfer (RAFT) polymerization in aqueous emulsion. A variety of original multiblock copolymers have been synthesised via a Chemspeed robot, exemplified by a multiblock copolymer comprising thirteen constituent blocks. Moreover, libraries of copolymers of randomized monomer compositions (acrylates, acrylamides, methacrylates, and styrenes), block orders, and block lengths were also generated, thereby demonstrating the robustness of our synthetic approach. One multiblock copolymer contained all four monomer families listed in the pool, which is unprecedented in the literature. The present work demonstrates that automation has the power to render complex and laborious syntheses of such unprecedented materials not just possible, but facile and straightforward, thus representing the way forward to the next generation of complex macromolecular architectures.

Robust Miniemulsion PhotoATRP Driven by Red and Near-Infrared Light

Photoinduced polymerization techniques have gathered significant attention due to their mild conditions, spatiotemporal control, and simple setup. In addition to homogeneous media, efforts have been made to implement photopolymerization in emulsions as a practical and greener process. However, previous photoinduced reversible deactivation radical polymerization (RDRP) in heterogeneous media has relied on short-wavelength lights, which have limited penetration depth, resulting in slow polymerization and relatively poor control. In this study, we demonstrate the first example of a highly efficient photoinduced miniemulsion ATRP in the open air driven by red or near-infrared (NIR) light. This was facilitated by the utilization of a water-soluble photocatalyst, methylene blue (MB+). Irradiation by red/NIR light allowed for efficient excitation of MB+ and subsequent photoreduction of the ATRP deactivator in the presence of water-soluble electron donors to initiate and mediate the polymerization process. The NIR light-driven miniemulsion photoATRP provided a successful synthesis of polymers with low dispersity (1.09 ≤ Đ ≤ 1.29) and quantitative conversion within an hour. This study further explored the impact of light penetration on polymerization kinetics in reactors of varying sizes and a large-scale reaction (250 mL), highlighting the advantages of longer-wavelength light, particularly NIR light, for large-scale polymerization in dispersed media owing to its superior penetration. This work opens new avenues for robust emulsion photopolymerization techniques, offering a greener and more practical approach with improved control and efficiency.

Synthesis and Characterization of All-Acrylic Tetrablock Copolymer Nanoparticles: Waterborne Thermoplastic Elastomers via One-Pot RAFT Aqueous Emulsion Polymerization

Reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization is used to prepare well-defined ABCB tetrablock copolymer nanoparticles via sequential monomer addition at 30 °C. The A block comprises water-soluble poly(2-(N-acryloyloxy)ethyl pyrrolidone) (PNAEP), while the B and C blocks comprise poly(t-butyl acrylate) (PtBA) and poly(n-butyl acrylate) (PnBA), respectively. High conversions are achieved at each stage, and the final sterically stabilized spherical nanoparticles can be obtained at 20% w/w solids at pH 3 and at up to 40% w/w solids at pH 7. A relatively long PnBA block is targeted to ensure that the final tetrablock copolymer nanoparticles form highly transparent films on drying such aqueous dispersions at ambient temperature. The kinetics of polymerization and particle growth are studied using 1H nuclear magnetic resonance spectroscopy, dynamic light scattering, and transmission electron microscopy, while gel permeation chromatography analysis confirmed a high blocking efficiency for each stage of the polymerization. Differential scanning calorimetry and small-angle X-ray scattering studies confirm microphase separation between the hard PtBA and soft PnBA blocks, and preliminary mechanical property measurements indicate that such tetrablock copolymer films exhibit promising thermoplastic elastomeric behavior. Finally, it is emphasized that targeting an overall degree of polymerization of more than 1000 for such tetrablock copolymers mitigates the cost, color, and malodor conferred by the RAFT agent.

Multiblock copolymer synthesis via RAFT emulsion polymerization

A multiblock copolymer is a polymer of a specific structure that consists of multiple covalently linked segments, each comprising a different monomer type. The control of the monomer sequence has often been described as the "holy grail" of synthetic polymer chemistry, with the ultimate goal being synthetic access to polymers of a "perfect" structure, where each monomeric building block is placed at a desired position along the polymer chain. Given that polymer properties are intimately linked to the microstructure and monomer distribution along the constituent chains, it goes without saying that there exist seemingly endless opportunities in terms of fine-tuning the properties of such materials by careful consideration of the length of each block, the number and order of blocks, and the inclusion of monomers with specific functional groups. The area of multiblock copolymer synthesis remains relatively unexplored, in particular with regard to structure-property relationships, and there are currently significant opportunities for the design and synthesis of advanced materials. The present review focuses on the synthesis of multiblock copolymers via reversible addition-fragmentation chain transfer (RAFT) polymerization implemented as aqueous emulsion polymerization. RAFT emulsion polymerization offers intriguing opportunities not only for the advanced synthesis of multiblock copolymers, but also provides access to polymeric nanoparticles of specific morphologies. Precise multiblock copolymer synthesis coupled with self-assembly offers material morphology control on length scales ranging from a few nanometers to a micrometer. It is imperative that polymer chemists interact with physicists and material scientists to maximize the impact of these materials of the future.

The effect of surface-active statistical copolymers in low-energy miniemulsion and RAFT polymerization

Study of the composition, lenght and chemical structure of surface-active statistical copolymers in low-energy miniemulsions.

Nanoconfinement in miniemulsion increases reaction rates of thiol–ene photopolymerization and yields high molecular weight polymers

Photoinitiated thiol–ene polymerization was performed in bulk and miniemulsion. We show that the compartmentalization of the reaction inside nanodroplets led to faster reaction kinetics and yielded polymers with higher molecular weight.

Multiblock copolymer synthesis via aqueous RAFT polymerization-induced self-assembly (PISA)

Employing RAFT PISA emulsion polymerization to synthesize high molecular weight hexablock multiblock copolymers.

Shape-Controlled Nanoparticles from a Low-Energy Nanoemulsion

Nanoemulsion technology enables the production of uniform nanoparticles for a wide range of applications. However, existing nanoemulsion strategies are limited to the production of spherical nanoparticles. Here, we describe a low-energy nanoemulsion method to produce nanoparticles with various morphologies. By selecting a macro-RAFT agent (poly(di(ethylene glycol) ethyl ether methacrylate-co-N-(2-hydroxypropyl) methacrylamide) (P(DEGMA-co-HPMA))) that dramatically lowers the interfacial tension between monomer droplets and water, we can easily produce nanoemulsions at room temperature by manual shaking for a few seconds. With the addition of a common ionic surfactant (SDS), these nanoscale droplets are robustly stabilized at both the formation and elevated temperatures. Upon polymerization, we produce well-defined block copolymers forming nanoparticles with a wide range of controlled morphologies, including spheres, worm balls, worms, and vesicles. Our nanoemulsion polymerization is robust and well-controlled even without stirring or external deoxygenation. This method significantly expands the toolbox and availability of nanoemulsions and their tailor-made polymeric nanomaterials.

Synthesis of Multicompositional Onion-like Nanoparticles via RAFT Emulsion Polymerization

Synthesis of multicompositional polymeric nanoparticles of diameters 100-150 nm comprising well-defined multiblock copolymers reaching from the particle surface to the particle core was conducted using surfactant-free aqueous macroRAFT emulsion polymerization. The imposed constraints on chain mobility as well as chemical incompatibility between the blocks result in microphase separation, leading to formation of an onion-like multilayered particle morphology with individual layer thicknesses of approximately 20 nm. The approach provides considerable versatility in particle morphology design as the composition of individual layers as well as the number of layers can be tailored as desired, offering more complex particle design compared to approaches relying on self-assembly of preformed diblock copolymers within particles. Microphase separation can occur in these systems under conditions where the corresponding bulk system would not theoretically result in microphase separation.

Biomimetic controlled radical photopolymerization in a two-dimensional organized environment under visible light

Fast and well-controlled photoinduced atom transfer radical polymerization (photoATRP) in the organized medium of a bilayer activated by visible light under environmentally friendly mild aqueous conditions leads to polymers with predetermined molecular weight and low dispersity. The decisive parameter for photoATRP of monomers in the organized medium was their mobility and orientation with respect to the bilayer and the photoredox catalyst localized in the interstitial layer.

A Review on Recent Progress of Glycan-Based Surfactant Micelles as Nanoreactor Systems for Chemical Synthesis Applications

The nanoreactor concept and its application as a modality to carry out chemical reactions in confined and compartmentalized structures continues to receive increasing attention. Micelle-based nanoreactors derived from various classes of surfactant demonstrate outstanding potential for chemical synthesis. Polysaccharide (glycan-based) surfactants are an emerging class of biodegradable, non-toxic, and sustainable alternatives over conventional surfactant systems. The unique structure of glycan-based surfactants and their micellar structures provide a nanoenvironment that differs from that of the bulk solution, and supported by chemical reactions with uniquely different reaction rates and mechanisms. In this review, the aggregation of glycan-based surfactants to afford micelles and their utility for the synthesis of selected classes of reactions by the nanoreactor technique is discussed. Glycan-based surfactants are ecofriendly and promising surfactants over conventional synthetic analogues. This contribution aims to highlight recent developments in the field of glycan-based surfactants that are relevant to nanoreactors, along with future opportunities for research. In turn, coverage of research for glycan-based surfactants in nanoreactor assemblies with tailored volume and functionality is anticipated to motivate advanced research for the synthesis of diverse chemical species.

Elucidating preparation-structure relationships for the morphology evolution during the RAFT dispersion polymerization of N-acryloyl thiomorpholine

Depending on the conditions, nearly monodisperse spherical micelles or complex morphologies are formed during a polymerization induced self-assembly (PISA) process based on the water-soluble monomer N-acryloylthiomorpholine.

Hard confinement systems as effective nanoreactors for in situ photo-RAFT: towards control over molecular weight distribution and morphology

Herein an alternative strategy to tune polymer dispersity and morphology was developed for photoiniferter-mediated RAFT giving well-defined ionic and non-ionic nanomaterials.

Aqueous emulsion polymerizations of methacrylates and styrene via reversible complexation mediated polymerization (RCMP)

Aqueous emulsion polymerization via reversible complexation mediated living radical polymerization yielded low-dispersity poly(methyl methacrylate)s and polystyrenes.

Confined polymerisation of bis-thyminyl monomers within nanoreactors: towards molecular weight control

Controlling polymer molecular weight by topochemical polymerisation inside nanoreactors.

Miniemulsion polymerization of styrene using carboxylated graphene quantum dots as surfactant

Carboxylated graphene quantum dots (cGQDs) were synthesized from dextrose and sulfuric acid via a hydrothermal process, and subsequently used as sole surfactant in miniemulsion polymerization of styrene.

Miniemulsion polymerization using carboxylated graphene quantum dots as surfactants: effects of monomer and initiator type

The effectiveness of carboxylated graphene quantum dots (cGQDs) as sole surfactants have been investigated in miniemulsion polymerization of 8 different vinyl monomers, initiated by oil-soluble initiator AIBN and water-soluble initiator VA-044.

Exploitation of the Nanoreactor Concept for Efficient Synthesis of Multiblock Copolymers via MacroRAFT-Mediated Emulsion Polymerization

Multiblock copolymers are a class of polymeric materials with a range of potential applications. We report here a strategy for the synthesis of multiblock copolymers based on methacrylates. Reversible addition-fragmentation chain transfer (RAFT) polymerization is implemented as an emulsion polymerization to generate seed particles as nanoreactors, which can subsequently be employed in sequential RAFT emulsion polymerizations. The segregation effect allowed the synthesis of a high molar mass (>100,000 g·mol^-1) decablock homopolymer at a high polymerization rate to an extent not previously achieved. A heptablock copolymer containing seven different 100 unit blocks was also successfully prepared, demonstrating how the strategy can be employed to precisely control the polymer composition at a level hitherto not accessible in environmentally friendly aqueous emulsion polymerization. Importantly, the methodology is a batch process without any intermediate purification steps, thus, rendering industrial scale up more feasible.

Modeling of Miniemulsion Polymerization of Styrene with Macro-RAFT Agents to Theoretically Compare Slow Fragmentation, Ideal Exchange and Cross-Termination Cases

A 5-dimensional Smith-Ewart based model is developed to understand differences for reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization with theoretical agents mimicking cases of slow fragmentation, cross-termination, and ideal exchange while accounting for chain length and monomer conversion dependencies due to diffusional limitations. The focus is on styrene as a monomer, a water soluble initiator, and a macro-RAFT agent to avoid exit/entry of the RAFT leaving group radical. It is shown that with a too low RAFT fragmentation rate coefficient it is generally not afforded to consider zero-one kinetics (for the related intermediate radical type) and that with significant RAFT cross-termination the dead polymer product is dominantly originating from the RAFT intermediate radical. To allow the identification of the nature of the RAFT retardation it is recommended to experimentally investigate in the future the impact of the average particle size (dp) on both the monomer conversion profile and the average polymer properties for a sufficiently broad dp range, ideally including the bulk limit. With decreasing particle size both a slow RAFT fragmentation and a fast RAFT cross-termination result in a stronger segregation and thus rate acceleration. The particle size dependency is different, allowing further differentiation based on the variation of the dispersity and end-group functionality. Significant RAFT cross-termination is specifically associated with a strong dispersity increase at higher average particle sizes. Only with an ideal exchange it is afforded in the modeling to avoid the explicit calculation of the RAFT intermediate concentration evolution.

The emulsion polymerization induced self-assembly of a thermoresponsive polymer poly(N-vinylcaprolactam)

A thermoresponsive polymer, poly(N-vinylcaprolactam) (PNVCL), was synthesized in an emulsion above its thermal transition temperature to produce particles via polymerization induced self-assembly (PISA).

Coupled stochastic simulation of the chain length and particle size distribution in miniemulsion radical copolymerization of styrene and N-vinylcaprolactam

Kinetic Monte Carlo modeling is applied for the coupled simulation of the chain length and particle size distribution in isothermal batch miniemulsion copolymerization of styrene and N-vinylcaprolactam.

Facile Synthesis of Chiral Polymers with Defined Architecture via Cooperative Assembly of Confined Templates

Herein is presented the synergistically self-assembled system as biomimetic polymerization media. This approach allows the facile synthesis of chiral amino acid-based polymers with high molecular weight and low dispersity inside of the bilayer of catanionic vesicles by using a conventional radical polymerization under moderate conditions.

Repurposing Biocatalysts to Control Radical Polymerizations

Reversible-deactivation radical polymerizations (controlled radical polymerizations) have revolutionized and revitalized the field of polymer synthesis. While enzymes and other biologically derived catalysts have long been known to initiate free radical polymerizations, the ability of peroxidases, hemoglobin, laccases, enzyme-mimetics, chlorophylls, heme, red blood cells, bacteria, and other biocatalysts to control or initiate reversible-deactivation radical polymerizations has only been described recently. Here, the scope of biocatalytic atom transfer radical polymerizations (bioATRP), enzyme-initiated reversible addition-fragmentation chain transfer radical polymerizations (bioRAFT), biocatalytic organometallic-mediated radical polymerizations (bioOMRP), and biocatalytic reversible complexation mediated polymerizations (bioRCMP) is critically reviewed, and the potential of these reactions for the environmentally friendly synthesis of precision polymers, for the preparation of functional nanostructures, for the modification of surfaces, and for biosensing is discussed.

Photoinduced Miniemulsion Atom Transfer Radical Polymerization

Photomediated atom transfer radical polymerization (photoATRP) of (meth)acrylic monomers was conducted in miniemulsion media. The polymerization procedures took advantage of an ion-pair catalyst formed by interaction of Cu/TPMA² (TPMA = tris(2-pyridylmethyl)amine) and an anionic surfactant, sodium dodecyl sulfate (SDS). The ion-pair catalyst was efficient in controlling ATRP reactions with catalyst loadings as low as 100 ppm. The effect of different polymerization parameters, such as the size of the reaction vial, amount of surfactant, and solids content influencing the photoATRP in miniemulsion, was studied. The polymerization was conducted with solids content ranging from 5 to 50 vol % under a moderate surfactant loading (<5 wt % relative to monomer). Excellent temporal control was achieved upon switching the UV light on and off multiple times, and the polymer was successfully chain extended, indicating high retention of chain-end fidelity.

Micellar polymerization: Computer simulations by dissipative particle dynamics

Nowadays, micellar polymerization is widely used in different fields of industry and research, including modern living polymerization technique. However, this process has many variables and there is no comprehensive model to describe all features. This research presents simulation methodology which describes key properties of such reactions to take a guide through a variety of their modifications. Dissipative particle dynamics is used in addition to Monte Carlo scheme to simulate initiation, propagation, and termination events. Influence of initiation probability and different termination processes on final conversion and molecular-weight distribution are presented. We demonstrate that prolonged initiation leads to increasing in polymer average molecular weight, and surface termination events play major role in conversion limitation, in comparison with recombination. © 2018 Wiley Periodicals, Inc.