Toward a Better Understanding of the Parameters that Lead to the Formation of Nonspherical Polystyrene Particles via RAFT-Mediated One-Pot Aqueous Emulsion Polymerization

Peculiar Behavior of Methyl Methacrylate Emulsion Polymerization-Induced Self-Assembly Mediated by RAFT Using Poly(Methacrylic Acid) Macromolecular Chain Transfer Agent

Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of methyl methacrylate (MMA) is successfully performed in water in the presence of a poly(methacrylic acid) (PMAA) macromolecular chain transfer agent (macroCTA) leading to the formation of self-stabilized PMAA-b-PMMA amphiphilic block copolymer particles. At pH 3.7, the reactions are well-controlled with narrow molar mass distributions. Increasing the initial pH, particularly above 5.6, results in a partial loss of reactivity of the PMAA macroCTA. The effect of the degree of polymerization (DPn) of the PMMA block, the solids content, the nature of the hydrophobic segment, and the pH on the morphology of the obtained diblock copolymer particles is then investigated. Worm-like micelles are formed for a DPn of PMMA of 20 (PMMA20), while "onion-like" particles and spherical vesicles are obtained for PMMA30 and PMMA50, respectively. In contrast, spherical particles are obtained for the DPns higher than 150. This unusual evolution of particle morphologies upon increasing the DPn of the PMMA block seems to be related to hydrogen bonds between hydrophilic MAA and hydrophobic MMA units.

Shape-Shifting Thermoresponsive Block Copolymer Nano-Objects

In this Feature Article, we review our recent progress in the design of shape-shifting thermoresponsive diblock copolymer nano-objects, which are prepared using various hydroxyl-functional (meth)acrylic monomers (e.g. 2‑hydroxypropyl methacrylate, 4‑hydroxybutyl acrylate or hydroxybutyl methacrylate) to generate the thermoresponsive block. Unlike traditional thermoresponsive polymers such as poly(N-isopropylacrylamide), there is no transition between soluble and insoluble polymer chains in aqueous solution. Instead, thermally driven transitions between a series of copolymer morphologies (e.g. spheres, worms, vesicles or lamellae) occur on adjusting the aqueous solution temperature owing to a subtle change in the partial degree of hydration of the permanently insoluble thermoresponsive block. Such remarkable self-assembly behavior is unprecedented in colloid science: no other amphiphilic diblock copolymer or surfactant system undergoes such behavior at a fixed chemical composition and concentration. Such shape-shifting nano-objects are characterized by transmission electron microscopy, dynamic light scattering, small-angle X-ray scattering, rheology and variable temperature ¹H NMR spectroscopy. Potential applications for this fascinating new class of amphiphiles are briefly considered.

Morphology Control via RAFT Emulsion Polymerization-Induced Self-Assembly: Systematic Investigation of Core-Forming Blocks

Polymerization-induced self-assembly (PISA) is a useful formulation for readily obtaining nanoparticles from block copolymers in situ. Reversible addition-fragmentation chain-transfer (RAFT) emulsion polymerization is utilized as one of the PISA formulations. Various factors have so far been investigated for obtaining nonspherical particles via RAFT emulsion polymerization, such as the steric structure of the shell, the glass-transition temperature (T _g) of the core-forming block, and the water solubility of the core-forming monomer. This study focuses on core-forming blocks without changing the structure of the shell-forming block. In particular, we elucidate the balance between T _g for the core-forming block and the water solubility of the core monomer. A series of alkyl methacrylates, such as methyl methacrylate (MMA), ethyl methacrylate (EMA), and n-propyl methacrylate (PrMA), are emulsion-polymerized in the presence of a poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) macromolecular chain-transfer agent via the RAFT process. The resulting in situ morphology changes to form shapes such as spheres, worms (toroids), and vesicles are systematically investigated. The properties of the core that determine whether a morphological change occurs from spheres are (i) the solubility of the core-forming monomer in water, (ii) the relationship between T _g for the core-forming block and the polymerization temperature, and (iii) the hydrophobic core volume, which changes the packing parameter. These factors allow prediction of the block copolymer morphology produced during RAFT emulsion polymerization of other methacrylates such as n-butyl methacrylate (BuMA), tetrahydrofurfuryl methacrylate (THFMA) with physical properties of the homopolymer (poly(tetrahydrofurfuryl methacrylate) (PTHFMA)) between those for poly(MMA) (PMMA) and PBuMA, and 1-adamantyl methacrylate (ADMA) with low monomer solubility in water and high T _g of the homopolymer (PADMA).

Aldehyde-functional thermoresponsive diblock copolymer worm gels exhibit strong mucoadhesion

A series of thermoresponsive diblock copolymer worm gels is prepared via reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate using a water-soluble methacrylic precursor bearing pendent cis-diol groups. Selective oxidation using an aqueous solution of sodium periodate affords the corresponding aldehyde-functional worm gels. The aldehyde groups are located within the steric stabilizer chains and the aldehyde content can be adjusted by varying the periodate/cis-diol molar ratio. These aldehyde-functional worm gels are evaluated in terms of their mucoadhesion performance with the aid of a fluorescence microscopy-based assay. Using porcine urinary bladder mucosa as a model substrate, we demonstrate that these worm gels offer a comparable degree of mucoadhesion to that afforded by chitosan, which is widely regarded to be a ‘gold standard’ positive control in this context. The optimum degree of aldehyde functionality is approximately 30%: lower degrees of functionalization lead to weaker mucoadhesion, whereas higher values compromise the desirable thermoresponsive behavior of these worm gels.

Optimizing the aldehyde content of thermoresponsive diblock copolymer worm gels via periodate oxidation leads to mucoadhesion performance comparable to that of chitosan (a gold standard positive control) in a fluorescence assay using porcine mucosa.

Pyridine-functional diblock copolymer nanoparticles synthesized via RAFT-mediated polymerization-induced self-assembly: effect of solution pH

Polymerization-induced self-assembly (PISA) via reversible addition-fragmentation chain transfer (RAFT) polymerization has become widely recognized as a versatile and efficient strategy to prepare complex block copolymer nanoparticles with controlled morphology, size, and surface functionality. In this article, we report the preparation of cationic sterically-stabilized poly(2-vinylpyridine)-poly(benzyl methacrylate) (P2VP-PBzMA) diblock copolymer nanoparticles via RAFT-mediated PISA under aqueous emulsion polymerization conditions. It is demonstrated that the solution pH during PISA has a dramatic effect on the resulting P2VP-PBzMA nanoparticles, as judged by dynamic light scattering (DLS), disc centrifuge photosedimentometry (DCP) and transmission electron microscopy (TEM). Varying the solution pH results in the P2VP stabilizer having different solubilities due to protonation/deprotonation of the pyridine groups. This allows P2VP-PBzMA nanoparticles with tunable diameters to be prepared by altering the DP of the stabilizer (P2VP) and/or core-forming block (PBzMA), or simply by changing the solution pH for a fixed copolymer composition. For example, P2VP-PBzMA nanoparticles with larger diameters can be obtained at higher solution pH as the protonation degree of the P2VP stabilizer has a large effect on both the aggregation of polymer chains during the PISA process, and the resulting behavior of the diblock copolymer nanoparticles. Changing the dispersion pH post-polymerization has a relatively limited effect on particle diameter. Furthermore, aqueous electrophoresis studies indicate that these P2VP-PBzMA nanoparticles had good colloidal stability and high cationic charge (>30 mV) below pH 5 and can be dispersed readily over a wide pH range.

Synthesis of low glass transition temperature worms comprising a poly(styrene-stat-n-butyl acrylate) core segment via polymerization-induced self-assembly in RAFT aqueous emulsion polymerization

Synthesis of nanodimensional polymeric worms of low glass transition temperature using aqueous polymerization-induced self-assembly.

RAFT aqueous dispersion polymerization of 4-hydroxybutyl acrylate: effect of end-group ionization on the formation and colloidal stability of sterically-stabilized diblock copolymer nanoparticles

Poly(2-hydroxyethyl acrylate)-poly(4-hydroxybutyl acrylate) nano-objects are prepared by aqueous polymerization-induced self-assembly (PISA) using an ionic RAFT agent.

Morphological transitions of cationic PISA particles by salt, triflate ions and temperature; comparison of three polycations

Three strong polycation stabilizers, poly((vinylbenzyl) trimethylammonium chloride), PVBTMAC, poly((2-(methacryloyloxy)ethyl)trimethylammonium chloride), PMOTAC, and poly((3-acrylamidopropyl) trimethylammonium chloride), PAMPTMAC have been synthesized with reversible addition-fragmentation chain transfer, RAFT, reactions. Solubilities of the polycations...

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 Poly(methacrylic acid)-block-Polystyrene Diblock Copolymers at High Solid Contents via RAFT Emulsion Polymerization

The combination of polymerization-induced self-assembly (PISA) and reversible-addition fragmentation chain transfer (RAFT) emulsion polymerization offers a powerful technique to synthesize diblock copolymers and polymeric nanoparticles in a controlled manner. The RAFT emulsion diblock copolymerization of styrene and methacrylic acid (MAA) by using a trithiocarbonate as surfactant and RAFT agent was investigated. The Z-group of the RAFT agent was modified with a propyl-, butyl- and dodecyl- sidechain, increasing the hydrophobicity of the RAFT agent to offer well-controlled polymerization of poly(methacrylic acid)-block-polystyrene (PMAA-b-PS) diblock copolymers at high solid contents between 30-50 wt% in water. The kinetic data of the PMAA homopolymerization with the three different RAFT agents for various solvents was investigated as well as the RAFT emulsion polymerization of the diblock copolymers in pure water. While the polymerization of PMAA-b-PS with a propyl terminus as a Z-group suffered from slow polymerization rates at solid contents above 30 wt%, the polymerization with a dodecyl sidechain as a Z-group led to full conversion within 2 h, narrow molar mass distributions and all that at a remarkable solid content of up to 50 wt%.

Small-Angle X-Ray Scattering Studies of Block Copolymer Nano-Objects: Formation of Ordered Phases in Concentrated Solution During Polymerization-Induced Self-Assembly

We report that polymerization-induced self-assembly (PISA) can be used to prepare lyotropic phases comprising diblock copolymer nano-objects in non-polar media. RAFT dispersion polymerization of benzyl methacrylate (BzMA) at 90 °C using a trithiocarbonate-capped hydrogenated polybutadiene (PhBD) steric stabilizer block in n-dodecane produces either spheres or worms that exhibit long-range order at 40 % w/w solids. NMR studies enable calculation of instantaneous copolymer compositions for each phase during the BzMA polymerization. As the PBzMA chains grow longer when targeting PhBD80 -PBzMA40 , time-resolved small-angle X-ray scattering reveals intermediate body-centered cubic (BCC) and hexagonally close-packed (HCP) sphere phases prior to formation of a final hexagonal cylinder phase (HEX). The HEX phase is lost on serial dilution and the aligned cylinders eventually form disordered flexible worms. The HEX phase undergoes an order-disorder transition on heating to 150 °C and a pure HCP phase forms on cooling to 20 °C.

Synthesis of water-soluble europium-containing nanoprobes via polymerization-induced self-assembly and their cellular imaging applications

Lanthanide nanoprobes have attracted extensive attention for applications in cellular imaging and biological sensing. Herein, water-dispersible europium (III)-based (Eu(III)-based) nanoprobes were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA) of hydrophobic monomers (Eu(III)-containing monomer and methyl methacrylate (MMA)) using hydrophilic macro-chain transfer agent poly(PEGMA)-CTA. The resulted poly(PMEu) nanoprobes showed spherical in shape in good monodispersity with average diameters of around 210 nm. The poly(PMEu) nanoprobles excellent aqueous dispersity, high aqueous stability and good luminescence properties with quantum yields of 37.21% and fluorescence lifetime of 312.4 μs. Moreover, the poly(PMEu) nanoprobes exhibited good cellular biocompatibility with cell viabilities of 88.2% and high fluorescence intensity for in vitro cellular imaging. The present approach provides a facile strategy for fabrication of luminescent Eu(III)-based nanoprobes with great potential applications for biological imaging.

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.

Laponite®-based colloidal nanocomposites prepared by RAFT-mediated surfactant-free emulsion polymerization: the role of non-ionic and anionic macroRAFT polymers in stability and morphology control

The synthesis of Laponite®-based nanocomposite latexes by reversible addition-fragmentation chain transfer (RAFT)-mediated surfactant-free emulsion polymerization using different macroRAFT agents is described.

Synthesis of diblock copolymer spheres, worms and vesicles via RAFT aqueous emulsion polymerization of hydroxybutyl methacrylate

RAFT aqueous emulsion polymerization of hydroxybutyl methacrylate using a poly(glycerol monomethacrylate) precursor leads to diblock copolymer spheres, worms or vesicles. A pseudo-phase diagram is constructed and the vesicles are briefly evaluated as a Pickering emulsifier.

RAFT aqueous emulsion polymerization of methyl methacrylate: observation of unexpected constraints when employing a non-ionic steric stabilizer block

Using a non-ionic steric stabilizer for the RAFT aqueous emulsion polymerization of methyl methacrylate leads to flocculated nanoparticles when targeting DPs > 100; there is no such constraint when employing an anionic stabilizer block.

Pickering Emulsifiers Based on Block Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly

Block copolymer nanoparticles prepared via polymerization-induced self-assembly (PISA) represent an emerging class of organic Pickering emulsifiers. Such nanoparticles are readily prepared by chain-extending a soluble homopolymer precursor using a carefully selected second monomer that forms an insoluble block in the chosen solvent. As the second block grows, it undergoes phase separation that drives in situ self-assembly to form sterically stabilized nanoparticles. Conducting such PISA syntheses in aqueous solution leads to hydrophilic nanoparticles that enable the formation of oil-in-water emulsions. Alternatively, hydrophobic nanoparticles can be prepared in non-polar media (e.g., n-alkanes), which enables water-in-oil emulsions to be produced. In this review, the specific advantages of using PISA to prepare such bespoke Pickering emulsifiers are highlighted, which include fine control over particle size, copolymer morphology, and surface wettability. This has enabled various fundamental scientific questions regarding Pickering emulsions to be addressed. Moreover, block copolymer nanoparticles can be used to prepare Pickering emulsions over various length scales, with mean droplet diameters ranging from millimeters to less than 200 nm.

One polymer composition, various morphologies: the decisive influence of conditions on the polymerization-induced self-assembly (PISA) of N-acryloyl thiomorpholine

Polymerization-induced self-assembly (PISA) represents a powerful technique for the preparation of nanostructures comprising various morphologies. Herein, we demonstrate that the recently introduced monomer N-acryloylthiomorpholine (NAT) features a unique self-assembly behaviour during an aqueous PISA. The one-pot, aqueous RAFT dispersion polymerization starting from short poly(N-acryloylmorpholine) (PNAM) enables access to all common solution morphologies including spheres, worms, vesicles and lamellae, at very low molar masses (< 8 kDa). Moreover, all these structures can be obtained for the same polymer composition and size by the variation of the polymerization temperature and concentration of the monomer. This exceptional self-assembly behavior is associated with the combination of a high glass transition temperature, excellent water solubility of the monomer, and the early onset of aggregation during the polymerization, which stabilizes the morphology at different stages. This PISA system opens up new opportunities to reproducibly create versatile, functional nanostructures and enables an independent evaluation of morphology-property relationships, as it is exemplarily shown for the oxidative degradation of spherical and wormlike micelles, as well as vesicles.

Bilayer-Templated Two-Dimensional RAFT Polymerization for Directed Assembly of Polymer Nanostructures

Co-localization of monomers, crosslinkers, and chain-transfer agents (CTA) within self-assembled bilayers in an aqueous suspension enabled the successful directed assembly of nanocapsules using a reversible addition-fragmentation chain transfer (RAFT) process without compromising the polymerization kinetics. This study uncovered substantial influence of the organized medium on the course of the reaction, including differential reactivity based on placement and mobility of monomers, crosslinkers, and CTAs within the bilayer.

Synthesis of nano-capsules via aqueous emulsion RCMP-PISA and encapsulation

Synthesis of nano-capsules using aqueous RCMP-PISA and encapsulation of rhodamine-B (Rh-B).

Poly(ethylene glycol)-b-poly(vinyl acetate) block copolymer particles with various morphologies via RAFT/MADIX aqueous emulsion PISA

The polymerization-induced self-assembly (PISA) of amphiphilic diblock copolymers of poly(ethylene glycol)-b-poly(vinyl acetate) in water was achieved through macromolecular design via interchange of xanthate (MADIX) polymerization in emulsion.

Unravelling the formation of BAB block copolymer assemblies during PISA in water

BAB triblock copolymers prepared by PISA in water self-assemble into a transient network of bridged micelles. The slowdown of the exchange of B blocks between micelles during PISA is highlighted as well as the parameters affecting the polymerization.

Polymerization techniques in polymerization-induced self-assembly (PISA)

The development of controlled/“living” polymerization greatly stimulated the prosperity of the fabrication and application of block copolymer nano-objects.

RAFT dispersion polymerisation of lauryl methacrylate in ethanol–water binary mixtures: synthesis of diblock copolymer vesicles with deformable membranes

Diblock copolymer vesicles with deformable membranes are prepared via RAFT dispersion polymerisation of lauryl methacrylate in an 80 : 20 w/w ethanol–water mixture; visible light irradiation allows facile RAFT chain-end removal from these nano-objects.

Trending methods employed for polymerization induced self-assembly

Mother Nature produces a perfectly defined architecture that inspires researchers to make polymeric macromolecules for an array of functions. The present article describes recent development in the PISA to synthesize polymeric nano-objects.

Polymerization-induced self-assembly for the fabrication of polymeric nano-objects with enhanced structural stability by cross-linking

This review discusses the strategies of core-cross-linking in most of the PISA literatures (including post-polymerization cross-linking, photo-cross-linking and in situ cross-linking) and the applications of the cross-linked nano-objects.

Rational synthesis of epoxy-functional spheres, worms and vesicles by RAFT aqueous emulsion polymerisation of glycidyl methacrylate

The rational synthesis of epoxy-functional diblock copolymer nano-objects has been achieved by RAFT aqueous emulsion polymerisation of glycidyl methacrylate under mild conditions (50 °C, pH 7) to preserve the epoxy groups.

In Situ Small-Angle X-ray Scattering Studies During Reversible Addition-Fragmentation Chain Transfer Aqueous Emulsion Polymerization

Polymerization-induced self-assembly (PISA) is a powerful platform technology for the rational and efficient synthesis of a wide range of block copolymer nano-objects (e.g., spheres, worms or vesicles) in various media. In situ small-angle X-ray scattering (SAXS) studies of reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization have previously provided detailed structural information during self-assembly (see M. J. Derry et al., Chem. Sci. 2016 , 7 , 5078 - 5090 ). However, conducting the analogous in situ SAXS studies during RAFT aqueous emulsion polymerizations poses a formidable technical challenge because the inherently heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer droplets. In the present study, the RAFT aqueous emulsion polymerization of 2-methoxyethyl methacrylate (MOEMA) has been explored for the first time. Chain extension of a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precursor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the precise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproducibly targeted at copolymer concentrations ranging from 10 to 30% w/w solids. High MOEMA conversions are achieved within 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ SAXS studies using a new reaction cell. This bespoke cell enables efficient stirring and hence allows in situ monitoring during RAFT emulsion polymerization for the first time. For example, the onset of micellization and subsequent evolution in particle size can be studied when preparing PGMA29-PMOEMA30 spheres at 10% w/w solids. When targeting PGMA29-PMOEMA70 vesicles under the same conditions, both the micellar nucleation event and the subsequent evolution in the diblock copolymer morphology from spheres to worms to vesicles are observed. These new insights significantly enhance our understanding of the PISA mechanism during RAFT aqueous emulsion polymerization.

Tuning the membrane permeability of polymersome nanoreactors developed by aqueous emulsion polymerization-induced self-assembly

Polymeric vesicles (or polymersomes) are hollow bilayer structures consisting of an inner aqueous compartment enclosed by a hydrophobic membrane. Vesicular constructs are ubiquitous in nature and perform a variety of functions by compartmentalizing molecules into disparate environments. For polymer chemists, the synthesis of vesicles can be readily accomplished using polymerization-induced self-assembly (PISA), whereby pure vesicle morphologies can be easily accessed by tuning initial reaction parameters. Research into polymersomes is motivated primarily by the fact that hydrophilic cargo such as drug molecules, DNA, or enzymes can be encapsulated and protected from the often harsh conditions of the surrounding environment. A key factor governing the capability of vesicles to retain and protect their cargo is the permeability of their hydrophobic membrane. Herein, we demonstrate that membrane permeability of enzyme-loaded epoxy-functionalized polymersomes synthesized by aqueous emulsion PISA can be modulated via epoxide ring-opening with various diamine cross-linkers and hydrophobic primary amines. In general, membrane cross-linking or amine conjugation resulted in increased polymersome membrane thickness. Membrane modification was also found to decrease permeability in all cases, as measured by enzymatically-catalysed oxidation of an externally administered substrate. Functionalization with hydrophobic amines resulted in the largest reduction in enzyme activity, suggesting significant blocking of substrate diffusion into the central aqueous compartment. This procedurally facile strategy yields meaningful insight into how the chemical structure of the membrane influences permeability and thus could be generally applied to the formulation of polymeric vesicles for therapeutic applications.

A biomimetic magnetosome: formation of iron oxide within carboxylic acid terminated polymersomes

Bioinspired macromolecules can aid nucleation and crystallisation of minerals by mirroring processes observed in nature. Specifically, the iron oxide magnetite (Fe3O4) is produced in a dedicated liposome (called a magnetosome) within magnetic bacteria. This process is controlled by a suite of proteins embedded within the liposome membrane. In this study we look to synthetically mimic both the liposome and nucleation proteins embedded within it using preferential orientation polymer design. Amphiphilic block co-polymers self-assemble into vesicles (polymersomes) and have been used to successfully mimic liposomes. Carboxylic acid residue-rich motifs are common place in biomineralisation nucleating proteins and several magnetosome membrane specific (Mms) proteins (namely Mms6) have a specific carboxylic acid motifs that are found to bind both ferrous and ferric iron ions and nucleate the formation of magnetite. Here we use a combination of 2 diblock co-polymers: Both have the hydrophobic 2-hydroxypropyl methacrylate (PHPMA) block with either a poly(ethylene glycol) (PEG) block or a carboxylic acid terminated poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) block. These copolymers ((PEG113-PHPMA400) and (PMPC28-PHPMA400) respectively) self-assemble in situ to form polymersomes, with PEG113-PHPMA400 displaying favourably on the outer surface and PMPC28-PHPMA400 on the inner lumen, exposing numerous acidic iron binding carboxylates on the inner membrane. This is a polymersome mimic of a magnetosome (PMM28) containing interior nucleation sites. The resulting PMM28 were found to be 246 ± 137 nm in size. When the PMM28 were subjected to electroporation (5 pulses at 750 V) in an iron solution, iron ions were transported into the PMM28 polymersome core where magnetic iron-oxide was crystallised to fill the core; mimicking a magnetosome. Furthermore it has been shown that PMM28 magnetopolymersomes (PMM28Fe) exhibit a 6 °C temperature increase during in vitro magnetic hyperthermia yielding an intrinsic loss power (ILP) of 3.7 nHm2 kg-1. Such values are comparable to commercially available nanoparticles, but, offer the added potential for further tuning and functionalisation with respect to drug delivery.

Enzyme-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization: Precision polymer synthesis via enzymatic catalysis

Enzyme-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization provides a sustainable strategy for efficient production of well-defined polymers under mild conditions. Horseradish peroxidase (HRP), a heme-containing metalloenzyme, catalyzes oxidation of acetylacetone (ACAC) by hydrogen peroxide (H₂O₂) to generate ACAC radicals, initiating polymerization of vinyl monomers. This HRP/H₂O₂/ACAC ternary initiating system is applied to RAFT polymerization of different types of vinyl monomers. Furthermore, to overcome the inherent limitation of necessity for oxygen-free conditions, another enzyme, glucose oxidase (GOx) or pyranose 2-oxidase (P2Ox), with excellent deoxygenation capability, is introduced to consume oxygen by catalyzing oxidation of glucose to generate H₂O₂. The generated H₂O₂ is directly supplied to HRP catalysis for radical generation. Both GOx-HRP and P2Ox-HRP cascade catalysis afford RAFT polymerization with oxygen tolerance. In this chapter, we mainly focus on detailed synthetic protocols of RAFT polymerizations initiated by HRP/H₂O₂/ACAC ternary initiating system and P2Ox-HRP cascade catalysis. The general characterization and analytical methods used in these enzyme-initiated RAFT polymerizations are also included.