The Nanoreactor Concept: Kinetic Features of Compartmentalization in Dispersed Phase Polymerization

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.

Recycled PMMA prepared directly from crude MMA obtained from thermal depolymerization of mixed PMMA waste

Recycled PMMA was prepared by directly polymerizing crude pyrolysis oils from lab-scale pyrolysis of collected industrial waste PMMA. The pyrolysis oils consisted mainly of methyl methacrylate (MMA, >85%), while the type and number of by-products from the thermal process were assigned through GC-MS analysis showing a clear correlation to the pyrolysis temperature. By-products can be removed by distillation; however, directly employing the crude oils to prepare PMMA through solution, suspension, emulsion, or casting polymerization was investigated to assess the potential for omitting this costly step. It was found that the crude pyrolysis oils could be polymerized efficiently via solution, emulsion, and casting polymerization to produce a polymer similar to the PMMA prepared from a pristine monomer. The impurities in the PMMAs prepared from the crude mixtures were investigated by extraction analyses followed by screening by GC-MS. In the case of casting polymerization, the GC-MS analysis, as expected, revealed various residual by-products, while solution and emulsion polymerization showed only very few impurities, mainly originating from the polymerization and not the feed material. Additional purification of the crude pyrolysis oils would be required for applications in casting polymerization. In contrast, direct polymerization by emulsion or solution polymerization is considered applicable for producing pristine PMMA from crude waste PMMA pyrolysis oil.

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.

Polymer Colloids: Current Challenges, Emerging Applications, and New Developments

Polymer colloids are complex materials that have the potential to be used in a vast array of applications. One of the main reasons for their continued growth in commercial use is the water-based emulsion polymerization process through which they are generally synthesized. This technique is not only highly efficient from an industrial point of view but also extremely versatile and permits the large-scale production of colloidal particles with controllable properties. In this perspective, we seek to highlight the central challenges in the synthesis and use of polymer colloids, with respect to both existing and emerging applications. We first address the challenges in the current production and application of polymer colloids, with a particular focus on the transition toward sustainable feedstocks and reduced environmental impact in their primary commercial applications. Later, we highlight the features that allow novel polymer colloids to be designed and applied in emerging application areas. Finally, we present recent approaches that have used the unique colloidal nature in unconventional processing techniques.

Electrochemically-Initiated RAFT Synthesis of Low Dispersity Multiblock Copolymers by Seeded Emulsion Polymerization

We describe electrochemically initiated emulsion polymerization with reversible addition-fragmentation chain transfer (eRAFT) to form well-defined multiblock copolymers with low molar mass dispersity. We demonstrate the utility of our emulsion eRAFT process with the synthesis of low dispersity multiblock copolymers by seeded RAFT emulsion polymerization at ambient temperature (∼30 °C). Thus, a triblock, poly(butyl methacrylate)-block-polystyrene-block-poly(4-methylstyrene) [PBMA-b-PSt-b-PMS], and a tetrablock, poly(butyl methacrylate)-block-polystyrene-block-poly(styrene-stat-butyl acrylate)-block-polystyrene [PBMA-b-PSt-b-P(BA-stat-St)-b-PSt], were synthesized as free-flowing, colloidally stable latexes commencing with a surfactant-free poly(butyl methacrylate) macroRAFT agent seed latex. A straightforward sequential addition strategy with no intermediate purification steps was able to be employed due to the high monomer conversions achieved in each step. The method takes full advantage of compartmentalization phenomena and the nanoreactor concept described in previous work to achieve the predicted molar mass, low molar mass dispersity (Đ ∼ 1.1-1.2), incrementing particle size (Z_av = 100-115 nm), and low particle size dispersity (PDI ∼ 0.02) for each generation of the multiblocks.

Nanoreactor for cascade reaction between SOD and CAT and its tissue regeneration effect

Nanoreactors for scavenging reactive oxygen species (ROS), a major factor in inflammatory diseases, can reduce overproduced ROS, and thus can prevent further progress of the diseases or facilitate the regeneration of damaged inflamed tissues. Herein, we designed a pluronic-based nanocarrier loaded with dual antioxidant enzymes present in vivo (superoxide dismutase (SOD) and catalase (CAT)) as a nanoreactor system for the regeneration of inflammatory tissue. The catalytic activity of each enzyme was enhanced by loading it into the nanocarrier. More importantly, the nanocarrier could enhance the cascade reaction between SOD and CAT, which converts the superoxide anion to oxygen. The synergistic anti-inflammatory effect of the nanoreactor based on the cascade reaction was verified in vitro. Furthermore, in an inflammatory bowel disease (IBD) mouse model, the dual enzyme (SOD/CAT)-loaded nanocarrier could result in significantly enhanced tissue regeneration and notably alleviated inflammation activities upon intravenous administration of them compared to other control groups, including single enzyme (SOD or CAT)-loaded nanocarrier and the free mixture of both enzymes without the nanocarrier. Thus, the efficacy of the nanoreactor for the cascade reaction on tissue regeneration in vivo was proved. Accordingly, the nanoreactor could be applied for tissue regeneration therapy against various inflammatory diseases.

Simulation of the RAFT polymerization in 3D: steric restrictions and incompatibility between species

In this work we developed a RAFT polymerization model taking into account the main reactions of the experimental RAFT process and implemented that model in dissipative particle dynamics (DPD). With...

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.

Dispersion Polymerization versus Emulsifier-Free Emulsion Polymerization for Nano-Object Fabrication: A Comprehensive Comparison

Although the preparation of nano-objects by emulsifier-free controlled/living radical emulsion polymerization has drawn much attention, the morphologies of these formed objects are difficult to predict and to reproduce because of the much more complex nucleation mechanisms of emulsion polymerization compared to only one self-assembling nucleation mechanism of controlled radical dispersion polymerization. The present study compares dispersion polymerization with emulsifier-free emulsion polymerization in terms of nucleation mechanism, polymerization kinetics, and disappearance behavior of the macrochain transfer agent, gel permeation chromatograms curves of the obtained block copolymer as well as the structural and morphological differences between the produced nano-objects on the basis of published data. Moreover, the effects of the inherently heterogeneous nature of emulsion polymerization on the mechanism of reversible addition-fragmentation transfer polymerization and the nano-object morphology are examined, and efficient agitation and adequate solubility of the core-forming monomer in water are identified as the most crucial factors for the fabrication of nonspherical nano-objects.

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.

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.

RAFT miniemulsion polymerisation of benzyl methacrylate using non-ionic surfactant

RAFT miniemulsion polymerisation of benzyl methacrylate using a non-ionic surfactant affords latexes with controllable molar mass, narrow molar mass distributions and tuneable particle diameter.

Multisegmented polymers via step-growth and RAFT miniemulsion polymerization

We report a method to efficiently prepare multisegmented polymers via a combination of step-growth (SG) and reversible addition-fragmentation chain transfer (RAFT) polymerization.

Progress and Perspectives Beyond Traditional RAFT Polymerization

The development of advanced materials based on well-defined polymeric architectures is proving to be a highly prosperous research direction across both industry and academia. Controlled radical polymerization techniques are receiving unprecedented attention, with reversible-deactivation chain growth procedures now routinely leveraged to prepare exquisitely precise polymer products. Reversible addition-fragmentation chain transfer (RAFT) polymerization is a powerful protocol within this domain, where the unique chemistry of thiocarbonylthio (TCT) compounds can be harnessed to control radical chain growth of vinyl polymers. With the intense recent focus on RAFT, new strategies for initiation and external control have emerged that are paving the way for preparing well-defined polymers for demanding applications. In this work, the cutting-edge innovations in RAFT that are opening up this technique to a broader suite of materials researchers are explored. Emerging strategies for activating TCTs are surveyed, which are providing access into traditionally challenging environments for reversible-deactivation radical polymerization. The latest advances and future perspectives in applying RAFT-derived polymers are also shared, with the goal to convey the rich potential of RAFT for an ever-expanding range of high-performance applications.

Redox-Initiated Reversible Addition-Fragmentation Chain Transfer (RAFT) Miniemulsion Polymerization of Styrene using PPEGMA-Based Macro-RAFT Agent

Redox-initiated reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerizations are successfully conducted with an employment of trithiocarbonate-based macro-RAFT agents and surfactant. Two macro-RAFT agents-hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA₂₇ ) and amphiphilic poly(poly(ethylene glycol) methyl ether methacrylate)-b-polystyrene (PPEGMA₂₇ -b-PS₃₃ )- are examined for the miniemulsion polymerization of styrene. The use of PPEGMA₂₇ (in the presence of sodium dodecyl sulfate (SDS)) results in a slow polymerization rate with a broad particle size. In the absence of SDS, the use of PPEGMA₂₇ -b-PS₃₃ results in a broad particle size distribution due to its inability to form uniform initial droplets whereas the same amphiphilic block copolymer in the presence of SDS yields resulting products with a uniform particle size distribution. The latter exhibits a fashion of controlled polymerization with a high consumption of monomer (98% in 100 min) and a narrow molecular weight distribution throughout the polymerization. This is attributed to the formation of uniform droplets facilitated by SDS in a miniemulsion. The amphiphilic macro-RAFT agent is able to anchor efficiently on the monomer droplet or particle/water interface and form stabilized particles of well-defined PPEGMA₂₇ -b-PS block copolymer, confirmed using dynamic light scattering and transmission electron micrographs.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

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.