RAFT Dispersion PISA with Poly(methyl methacrylate) as Stabilizer Block in Alcohol/Water: Unconventional PISA Morphology Transitions.

Reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization-induced self-assembly (PISA) was conducted in the presence of poly(methyl methacrylate) (PMMA) stabilizer in ethanol/water mixture (80/20 by volume). Two different systems were explored by utilizing (i) 2-ethylhexyl methacrylate (EHMA) and (ii) n-butyl methacrylate (BMA). The morphology transitions of these systems were investigated by varying the polymerization conditions, i.e., the presence of the solvophilic comonomer MMA, the solids content, and the target degree of polymerization (DP). As observed in conventional PISA, the presence of solvophilic comonomer, increase in solids content and target DP promoted the formation of high-order morphology. However, unusual morphology transitions were observed whereby the morphology transformed from high-order morphologies to a mixture of spherical nanoparticles, worms, and vesicles and finally to vesicles with increasing target DP. This unusual evolution may be attributed to the limited solubility of PMMA in the ethanol/water solvent mixture, whereby PMMA is soluble at the polymerization temperature but insoluble at lower temperatures.

Quorum sensing inhibiting dihydropyrrol-2-ones embedded polymer/graphene oxide nanocomposite waterborne antimicrobial coatings.

With increasing antibiotic resistance and hospital acquired microbial infections, there has been a growing interest to explore alternate antimicrobial approaches. This is particularly challenging when aiming to protect surfaces over a large area to avoid contact mediated infection transmission. Quorum sensing (QS) inhibition has emerged as an alternate antimicrobial approach overcoming evolutionary stress driven resistance observed in antibiotic treatment. However, specific surface orientation requirements and limited work on delivery of small molecule QS inhibiting compounds have limited their widespread applicability certainly when it comes to coating large surfaces. Here, we report antimicrobial nanocomposite coatings overcoming the dependence on molecular orientation of QS inhibiting dihydropyrrol-2-ones (DHP) analogues and release small molecule analogues. In a systematic study, we developed poly(styrene-stat-n-butyl acrylate)/graphene oxide (GO)/DHP analogue nanocomposite antimicrobial coatings that can be easily applied to surfaces of any length scale and studied their efficacy against Staphylococcus aureus. The polymer nanocomposite was designed to undergo coating formation at ambient temperature. The antimicrobial coatings exhibited DHP dose dependent antimicrobial response both in the supernatant growth media with a ∼7-log10 reduction in cell growth and virtually a complete inhibition in cell adhesion on the surface in the best coating compared to controls. When compared, DHP-Br coatings outperformed other DHP analogues (-F and -Ph) both in limiting the cell growth in the media and cellular adhesion on the coating surface. This is the first example of nanocomposite coatings comprising QS inhibiting compounds, and their exceptional performance is expected to pave the way for further research in the field.

On-demand activatable peroxidase-mimicking enzymatic polymer nanocomposite films.

Nanozymes continue to attract considerable attention to minimise the dependence on expensive enzymes in bioassays, particularly in medical diagnostics. While there has been considerable effort directed towards developing different nanozymes, there has been limited progress in fabricating composite materials based on such nanozymes. One of the biggest gaps in the field is the control, tuneability, and on-demand catalytic response. Herein, a nanocomposite nanozymatic film that enables precise tuning of catalytic activity through stretching is demonstrated. In a systematic study, we developed poly(styrene-stat-n-butyl acrylate)/iron oxide-embedded porous silica nanoparticle (FeSiNP) nanocomposite films with controlled, highly tuneable, and on-demand activatable peroxidase-like activity. The polymer/FeSiNP nanocomposite was designed to undergo film formation at ambient temperature yielding a highly flexible and stretchable film, responsible for enabling precise control over the peroxidase-like activity. The fabricated nanocomposite films exhibited a prolonged FeSiNP dose-dependent catalytic response. Interestingly, the optimised composite films with 10 wt% FeSiNP exhibited a drastic change in the enzymatic activity upon stretching, which provides the nanocomposite films with an on-demand performance activation characteristic. This is the first report showing control over the nanozyme activity using a nanocomposite film, which is expected to pave the way for further research in the field leading to the development of system-embedded activatable sensors for diagnostic, food spoilage, and environmental applications.

Block Copolymer Self-assembly: Exploitation of Hydrogen Bonding for Nanoparticle Morphology Control via Incorporation of Triazine Based Comonomers by RAFT Polymerization.

Synthesis of polymeric nanoparticles of controlled non-spherical morphology is of profound interest for a wide variety of potential applications. Self-assembly of amphiphilic diblock copolymers is an attractive bottom-up approach to prepare such nanoparticles. In the present work, RAFT polymerization is employed to synthesize a variety of poly(N,N-dimethylacrylamide)-b-poly[butyl acrylate-stat-GCB] copolymers, where GCB represents vinyl monomer containing triazine based Janus guanine-cytosine nucleobase motifs featuring multiple hydrogen bonding arrays. Hydrogen bonding between the hydrophobic blocks exert significant influence on the morphology of the resulting nanoparticles self-assembled in water. The Janus feature of the GCB moieties makes it possible to use a single polymer type in self-assembly, unlike previous work exploiting, e.g., thymine-containing polymer and adenine-containing polymer. Moreover, the strength of the hydrogen bonding interactions enables use of a low molar fraction of GCB units, thereby rendering it possible to use the present approach for copolymers based on common vinyl monomers for the development of advanced nanomaterials.

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.

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.

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 (D ∼ 1.1-1.2), incrementing particle size (Zav = 100-115 nm), and low particle size dispersity (PDI ∼ 0.02) for each generation of the multiblocks.

Polymeric Nanofibers of Various Degrees of Cross-Linking as Fillers in Poly(styrene-stat-n-butyl acrylate) Nanocomposites: Overcoming the Trade-Off between Tensile Strength and Stretchability.

Synthesis of light polymer nanocomposites with high strength and toughness has been a significant interest for its potential applications in industry. Herein, the authors have synthesized polymerization-induced self-assembly (PISA) derived nanodimensional polymeric worm (fiber) reinforced polymer nanocomposites by a simple and environmentally friendly synthesis process without the addition of volatile organic compounds. PISA-derived worms with a core-forming block of low glass transition temperature (Tg  ≈ 27.1 °C) comprising poly(styrene-stat-n-butyl acrylate) have been employed as reinforcing filler. The influence of core-segment cross-linking on reinforcement efficiency has been explored by comparing noncross-linked worms, and worms cross-linked with a small amount of ethylene glycol diacrylate introduced at t = 0 h or t = 2 h of polymerization. Upon addition of 1 wt% of noncross-linked, t = 0 h cross-linked, and t = 2 h cross-linked worms, toughness of polymer nanocomposites can be enhanced by 62%, 114%, and 120%, respectively. The results suggest that the reinforcement efficiency of worms is significantly influenced by the cross-linking of core-segments regardless of cross-linking methods. This work broadens the understanding in application of PISA-derived worms as reinforcing filler by demonstrating the efficient reinforcement with low Tg worms.

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.

Influence of Anionic Surfactants on the Fundamental Properties of Polymer/Reduced Graphene Oxide Nanocomposite Films.

Surfactants are frequently employed in the fabrication of polymer/graphene-based nanocomposites via emulsion techniques. However, the impact of surfactants on the electrical and mechanical properties of such nanocomposite films remains to be explored. We have systematically studied the impact of two anionic surfactants [sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS)] on intrinsic properties of the nanocomposite films comprising reduced graphene oxide in a matrix of poly(styrene-stat-n-butyl acrylate). Using these ambient temperature film-forming systems, we fabricated films with different concentrations of the surfactants (1-7 wt %, relative to the organic phase). Significant differences in film properties were observed both as a function of amount and type of surfactant. Thermally reduced films exhibited concentration-dependent increases in surface roughness, electrical conductivity, and mechanical properties with increasing SDS content. When compared with SDBS, SDS films exhibited an order of magnitude higher electrical conductivity values at every concentration (highest value of ∼4.4 S m-1 for 7 wt % SDS) and superior mechanical properties at higher surfactant concentrations. The present results illustrate how the simple inclusion of a benzene ring in the SDS structure (as in SDBS) can cause a significant change in the electrical and mechanical properties of the nanocomposite. Overall, the present results demonstrate how nanocomposite properties can be judiciously manipulated by altering the concentration and/or type of surfactant.

Structural Complexity of Graphene Oxide: The Kirigami Model.

Investigation of highly oxidized graphene oxide (GO) by solid-state nuclear magnetic resonance (NMR) spectroscopy has revealed an exceptional level of hitherto undiscovered structural complexity. A number of chemical moieties were observed for the first time, such as terminal esters, furanic carbons, phenolic carbons, and three distinct aromatic and two distinct alkoxy carbon moieties. Quantitative one-dimensional (1D) and two-dimensional (2D) 13C{1H} NMR spectroscopy established the relative populations and connectivity of these different moieties to provide a consistent "local" chemical structure model. An inferred 2 nm GO sheet size from a very large (∼20%) edge carbon fraction by NMR analysis is at odds with the >20 nm sheet size determined from microscopy and dynamic light scattering. A proposed kirigami model where extensive internal cuts/tears in the basal plane provide the necessary edge sites is presented as a resolution to these divergent results. We expect this work to expand the fundamental understanding of this complex material and enable greater control of the GO structure.

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.

Synthesis of diamine functionalised graphene oxide and its application in the fabrication of electrically conducting reduced graphene oxide/polymer nanocomposite films.

The focus of research in diamine functionalised graphene oxide (GO) has been limited to the use of diamines either as crosslinker or to achieve simultaneous functionalisation, reduction and stitching of GO sheets, especially in the case of ethylene diamine (EDA). Controlling the extent of stitching and functionalisation has to date remained a challenge. In particular, synthesis of colloidally stable monofunctionalised GO-NH2 with dangling amine groups using diamines has remained elusive. This has been the limiting factor towards the utility of EDA functionalised GO (GO-NH2) in the field of polymer-based nanocomposites. We have synthesised colloidally stable GO-NH2 with dangling amine groups and subsequently demonstrated its utility as a surfactant to synthesize colloidally stable waterborne polymer nanoparticles with innate affinity to undergo film formation at room temperature. Thermally annealed dropcast polymer/GO-NH2 nanocomposite films exhibited low surface roughness (∼1 µm) due to the homogeneous distribution of functionalised GO sheets within the polymer matrix as observed from confocal laser scanning microscopy, scanning electron microscopy and transmission electron microscopy. The films exhibited considerable electrical conductivity (∼0.8 S m-1), demonstrating the potential of the GO-NH2/polymer nanocomposite for a wide range of applications.

Preparation of Methacrylate Polymer/Reduced Graphene Oxide Nanocomposite Particles Stabilized by Poly(ionic liquid) Block Copolymer via Miniemulsion Polymerization.

Poly(n-butyl methacrylate) (PnBMA)/reduced graphene oxide (rGO) nanocomposite films are prepared using two different routes. The first route involves preparation of PnBMA nanoparticles containing homogeneously dispersed rGO nanosheets by miniemulsion polymerization using a block copolymer of ionic liquid (IL) monomer and nBMA. The IL units act as adsorption sites for rGO whereas BMA units provide solubility in the BMA monomer droplets. Nanocomposite films obtained from miniemulsion polymerization exhibit higher tensile modulus in comparison with the films prepared by mixing a PnBMA emulsion and aqueous graphene oxide (GO) dispersion. The second route involves preparation of PnBMA particles armored with rGO nanosheets via miniemulsion polymerization using the same poly(ionic liquid) (PIL) block copolymer. An anionic exchange reaction is conducted to obtain more hydrophilic PIL units in the block copolymer, thus providing adsorption sites of GO nanosheets at the interface of the polymer particles. Subsequent chemical reduction of GO to rGO using hydrazine monohydrate results in formation of a PnBMA/rGO nanocomposite. The resulting nanocomposite film exhibits electrical conductivity (2.0 × 10-3 S m-1).

Ambient-Temperature Waterborne Polymer/rGO Nanocomposite Films: Effect of rGO Distribution on Electrical Conductivity.

Electrically conductive polymer/rGO (reduced graphene oxide) films based on styrene and n-butyl acrylate are prepared by a variety of aqueous latex based routes involving ambient temperature film formation. Techniques based on miniemulsion polymerization using GO as surfactant and "physical mixing" approaches (i.e., mixing an aqueous polymer latex with an aqueous GO dispersion) are employed, followed by heat treatment of the films to convert GO to rGO. The distribution of GO sheets and the electrical conductivity depend strongly on the preparation method, with electrical conductivities in the range 9 × 10-4 to 3.4 × 102 S/m. Higher electrical conductivities are obtained using physical mixing compared to miniemulsion polymerization, which is attributed to the former providing a higher level of self-alignment of rGO into larger linear domains. The present results illustrate how the distribution of GO sheets within these hybrid materials can to some extent be controlled by judicious choice of preparation method, thereby providing an attractive means of nanoengineering for specific potential applications.

Reversible Destabilization of UV-Responsive Polymer Particles (Latex) using a Photoresponsive Surfactant.

Production of aqueous dispersions of polymeric nanoparticles via heterogeneous radical polymerization in emulsion-type systems is of enormous commercial importance. The ability to reversibly destabilize such a latex is highly desirable, for example, to save transportation costs. Herein, a method for synthesis of photo-responsive polymer latexes that can be destabilized (leading to sedimentation) by only using UV irradiation (no addition of chemicals or change in the experimental conditions) and subsequently redispersed by stirring under visible light irradiation is described. The destabilization/redispersion mechanism relies on photoinduced trans-cis isomerization of the cationic diazene surfactant 2-(4-(4-butylphenyl)diazenylphenoxy)ethyltrimethylammonium bromide (C4AzoTAB) used in conjunction with the anionic surfactant sodium dodecyl sulfate. It is demonstrated that reversible destabilization can be achieved very rapidly (90 s residence time) employing continuous flow technology.

Enhanced Osteogenic Differentiation of Human Fetal Cartilage Rudiment Cells on Graphene Oxide-PLGA Hybrid Microparticles.

Poly(d,l-lactide-co-glycolide) (PLGA) has been extensively explored for bone regeneration applications; however, its clinical use is limited by low osteointegration. Therefore, approaches that incorporate osteoconductive molecules are of great interest. Graphene oxide (GO) is gaining popularity for biomedical applications due to its ability to bind biological molecules and present them for enhanced bioactivity. This study reports the preparation of PLGA microparticles via Pickering emulsification using GO as the sole surfactant, which resulted in hybrid microparticles in the size range of 1.1 to 2.4 µm based on the ratio of GO to PLGA in the reaction. Furthermore, this study demonstrated that the hybrid GO-PLGA microparticles were not cytotoxic to either primary human fetal cartilage rudiment cells or the human osteoblast-like cell line, Saos-2. Additionally, the GO-PLGA microparticles promoted the osteogenic differentiation of the human fetal cartilage rudiment cells in the absence of exogenous growth factors to a greater extent than PLGA alone. These findings demonstrate that GO-PLGA microparticles are cytocompatible, osteoinductive and have potential as substrates for bone tissue engineering.

Electrically conductive polymer/rGO nanocomposite films at ambient temperature via miniemulsion polymerization using GO as surfactant.

We have developed a facile and industrially scalable method to synthesize colloidally stable polymer nanoparticles decorated with graphene oxide (GO) sheets via miniemulsion polymerization, which in turn enables the preparation of electrically conductive films using a simple dropcasting method at ambient temperature. The resulting nanocomposite films exhibited high electrical conductivity with a wide range of potential applications as conductive coatings.

Polymerization of cubosome and hexosome templates to produce complex microparticle shapes.

Cubic and hexagonal liquid crystalline particles, or cubosomes and hexosomes, are used as templates to polymerize various monomers to produce particles with unique micron-scale geometric shapes. Emulsion droplets containing water, ethanol, and the lipid glyceryl monooleate are suspended in a yield stress fluid and used to produce shapes based on cubic and hexagonal symmetry by slow crystallization. The underlying liquid crystalline ordering of the aqueous lipid system drives symmetric shape formation, while its amphiphilicity allows incorporation of various organic monomers. Photopolymerization of monomers in the lipid templates creates polymeric particles shaped like polyhedra based on cubic symmetry as well as biconical cylinders based on hexagonal symmetry, and their shape is preserved after template removal. Product particle shapes are controlled by varying the structures and hydrophobicity of the monomers, as they control formation of different phases and microstructures. Monomer polarity determines whether the template can exhibit hexagonal phase, as when divinylbenzene is used, or cubic phase, when di(ethylene glycol) dimethacrylate is used. The monomers also control the microstructure of the final particles produced, forming rigid shapes composed of linked polymer nanospheres when divinylbenzene or di(ethylene glycol) dimethacrylate are used, and soft hydrogel particles when N,N'-methylenebisacrylamide is used.

Polymerization-Induced Self-Assembly under Compressed CO2 : Control of Morphology Using a CO2 -Responsive MacroRAFT Agent.

Polymerization-induced self-assembly of 2-hydroxypropyl methacrylate is conducted in water and water/MeOH using a CO2 -responsive macroRAFT agent in the form of a statistical copolymer comprising N,N-diethylaminoethyl methacrylate (DEAEMA) and poly(ethylene glycol) methyl ether methacrylate (M n  = 475 g mol-1 ). Pressurization with CO2 leads to protonation of DEAEMA units within the stabilizer block, thereby offering a means of adjusting the charge density of the coronal layer. It is demonstrated that a wide range of tunable particle morphologies are accessible by simply varying the CO2 pressure during polymerization in the range of 10-45 bar.