Reversible Addition-fragmentation Chain Transfer Research Articles

Revealing into the formation mechanism of various nanostructures self-assembled from a bipyridine containing homopolymer

The control of the morphology and nanostructure of soft nanomaterials self-assembled from amphiphilic polymers has attracted significant attention. In this study, various nanostructures including bowl-shaped nanoparticles with controlled openings, round Yuanbao-shaped assemblies, nanowires and butterfly shaped twin nanosheets are formed by manipulating the self-assembly pathway of an amphiphilic homopolymer. The amphiphilic (poly(N-(2,2′-bipyridyl-4-acrylamide), PBPyAA) with bipyridine pendants is designed and synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization, which can self-assemble into bowl-shaped nanoparticles with controlled openings by solvent switch method at different initial concentrations. In addition, core–shell nanostructures are obtained taking advantage of the coordination between bipyridine and Fe2+. Upon annealing in ethanol, butterfly shaped twin nanosheets with thickness of about 10 nm are formed by controlling the cooling rate, while round Yuanbao-shaped assemblies are formed by naturally cooling. Revealing into the formation mechanism of the butterfly shaped twin nanosheets, a fusion induced assembly process of nanowires is observed. Overall, various nanostructures are obtained by manipulating the self-assembly pathways of a bipyridine containing amphiphilic homopolymer.

Synthesis and rheological analyzes of temperature and light sensitive gels comprising amphiphilic azobenzene polymers, chitosan and pluronic F127

AbstractThis study investigates the reinforcement of pluronic (PF127) based temperature responsive hydrogels with photosensitive functionalities to create smart and injectable materials. For this purpose, 4‐[4‐[(4‐phenyl)azo]phenoxy] methacrylate (PAzPMA) was synthesized and further polymerized via reversible addition‐fragmentation chain transfer (RAFT) polymerization. The structures of the copolymers were characterized by several techniques such as Fourier‐transform infrared (FT‐IR), nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The azobenzene‐functionalized copolymer was combined with P127 solid polymer in micelle form and with P127 micelles in solid form to obtain PF127‐AzoMx and PF127‐AzoPx gels, respectively. When the temperature profiles of the PF127‐AzoMx and PF127‐AzoPx systems were compared with PF127, sol–gel phase transition were shifted to lower temperatures due to stronger hydrophobic interactions. Additionally, different concentrations of N,N,N‐trimethyl chitosan (f‐chitosan) were added to the gel systems and their rheological properties were investigated by exposing them to UV light. It has been observed that the presence and concentration of f‐chitosan are important for the variation of the interactions' strength between the micelles. The study highlights the potential of multifunctional hydrogels for specific biomedical applications that combine sensitivity to both thermal and optical stimuli for controlled drug delivery and tissue engineering purposes.

Synthesis and Performance of Polycarboxylate Ether Superplasticizers with Controlled Structure via RAFT Polymerization

Synthesis and Performance of Polycarboxylate Ether Superplasticizers with Controlled Structure via RAFT Polymerization

Microphase Separation and Gelation through Polymerization-Induced Self-Assembly Using Star Polyethylene Glycols.

Polymerization-induced self-assembly (PISA) during the synthesis of diblock copolymers has garnered considerable interest; however, architectures beyond diblock copolymers have scarcely been explored. Here, we studied PISA using 4- and 8-arm star polyethylene glycol (PEG), as well as 2-arm (linear) PEG, wherein each terminus of PEG was functionalized with a chain-transfer agent, holding a constant molar mass for each arm. Styrene was polymerized from each PEG terminus through reversible addition-fragmentation chain-transfer (RAFT) polymerization in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6]), with a total solute concentration of 40 wt %. While the styrene monomer is soluble in [BMIM][PF6], polystyrene is not; thus, self-assembly and cross-linking (gelation) occur. Structural analysis by small-angle X-ray scattering revealed that a relatively ordered microphase-separated structure for PISA was observed. Two-arm PEG-PS formed hexagonally packed cylinders, whereas 4- and 8-arm PEG-PS exhibited hexagonal close-packed spheres and disordered spheres. The dynamics, studied by oscillatory rheology, were also influenced by the number of arms; the 4-arm star block copolymers showed the highest plateau modulus. This study demonstrates that the topology is an important factor in controlling the microphase-separated structure and mechanical properties when preparing gels through PISA.

Self-Assembly of Hydrophobic Hyperbranched PLMA Homopolymer with -COOH End Groups as Effective Nanocarriers for Bioimaging Applications.

Nanomedicine is a discipline of medicine that applies all aspects of nanotechnology strategies and concepts for treatment and screening possibilities. Synthetic polymer nanostructures are among the many nanomedicine formulations frequently studied for their potential as vectors. Bioimaging is a valuable diagnostic tool, thus, there is always a demand for new excipients/nanocarriers. In this study, hydrophobic hyperbranched poly(lauryl methacrylate) (PLMA) homopolymers comprised of highly hydrophobic LMA moieties with -COOH polar end groups were synthesized by employing reversible addition-fragmentation chain transfer (RAFT) polymerization. Ethylene glycol dimethacrylate (EGDMA) was utilized as the branching agent. End groups are incorporated through the RAFT agent utilized. The resulting amphiphilic hyperbranched polymer was molecularly characterized by size exclusion chromatography (SEC), Fourier transformation infrared spectroscopy (FT-IR), and 1H-NMR spectroscopy. Pyrene, curcumin, and IR-1048 dye were hydrophobic payload molecules successfully encapsulated to show how adaptable these homopolymer nanoparticles (prepared by nanoprecipitation in water) are as dye nanocarriers. This study demonstrates a simple way of producing excipients by generating polymeric nanoparticles from an amphiphilic, hyperbranched, hydrophobic homopolymer, with a low fraction of polar end groups, for bioimaging purposes.

Aqueous RAFT Dispersion Polymerization Mediated by an ω,ω-Macromolecular Chain Transfer Monomer: An Efficient Approach for Amphiphilic Branched Block Copolymers and the Assemblies.

Herein, an ω,ω-macromolecular chain transfer monomer (macro-CTM) containing a RAFT (reversible addition-fragmentation chain transfer) group and a methacryloyl group was synthesized and used to mediate photoinitiated RAFT dispersion polymerization of hydroxypropyl methacrylate (HPMA) in water. The macro-CTM undergoes a self-condensing vinyl polymerization (SCVP) mechanism under RAFT dispersion polymerization conditions, leading to the formation of amphiphilic branched block copolymers and the assemblies. Compared with RAFT solution polymerization, it was found that the SCVP process was promoted under RAFT dispersion polymerization conditions. Morphologies of branched block copolymer assemblies could be controlled by varying the monomer concentration and the [HPMA]/[macro-CTM] ratio. The branched block copolymer vesicles could be used as seeds for seeded RAFT emulsion polymerization, and framboidal vesicles were successfully obtained. Finally, degrees of branching of branched block copolymers could be further controlled by using a binary mixture of the macro-CTM and a linear macro-RAFT agent or a small molecule CTM. We believe that this study not only provides a versatile strategy for the preparation of branched block copolymer assemblies but also offers important insights into polymer synthesis via heterogeneous RAFT polymerization.

Phage probe on RAFT polymer surface for rapid enumeration of E. coli K12

This study presents a simple, fast, and sensitive label-free sensing assay for the precise enumeration of modeled pathogenic Escherichia coli K12 (E. coli K12) bacteria for the first time. The method employs the covalent binding bacteriophage technique on the surface of a reversible addition-fragmentation chain transfer (RAFT) polymer film. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) identified the charge transfer resistance Rct was calculated from a suitable electrochemical circuit model through an evaluation of the relevant parameter after the immobilization of the bacteriophage and the binding of specific E. coli K12. The impedimetric biosensor reveals specific and reproducible detection with sensitivity in the linear working range of 104.2-107.0 CFU/mL, a limit of detection (LOD) of 101.3 CFU/mL, and a short response time of 15 min. The SERS response validates the surface roughness and interaction of the SERS-tag with E. coli K12-modified electrodes. Furthermore, the covalently immobilized active phage selectivity was proved against various non-targeting bacterial strains in the presence of targeted E.coli K12 with a result of 94 % specificity and 98 % sensitivity. Therefore, the developed phage-based electrode surface can be used as a disposable, label-free impedimetric biosensor for rapid and real-time monitoring of serum samples.

Synthesis of phosphorus fluorine containing polymers for flame-retardant, low surface energy and good dielectric performance epoxy resin electronic packaging materials

In order to satisfy the application of epoxy resin (EP) in high-end electronic packaging, phosphorus fluorine containing polymers were synthesized to simultaneously enhance the flame retardant, dielectric, and hydrophobic properties of EP. Through the reaction of 2-hydroxyethyl methacrylate and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a monomer named HEMA-P was synthesized. By copolymerizing (2,2,2-trifluoroethyl methacrylate and 1H, 1H, 7H-dodecafluoroheptyl methacrylate) with HEMA-P through the typical reversible addition-fragmentation chain transfer (RAFT) polymerization, two phosphorus fluorine containing polymer modifiers named 3FOP and 12FOP with different lengths of fluorine side chain were obtained. The flame-retardant level of FOP/EP composites reached V-1 level. The limited oxygen index (LOI) values of 3FOP/EP and 12FOP/EP composites (10 wt% additive amount) increased to 33.6 ± 0.5 % and 32.8 ± 0.3 %, respectively, with corresponding peak heat release rates (pHRR) decreased by 37.8 % and 33.2 % compared with neat EP, suggesting the FOP modified EP composites have good flame retardant and smoke suppression effects. The mechanical properties of the FOP/EP composites can also be improved. Notably, with the 10 wt% addition of 12FOPs, the water contact angle of 12FOP/EP composite reached 116.5°, which was 40.7 % higher than that of EP. Moreover, the dielectric constant decreased with the increasing fluorine content. The thermal stability and possible thermal degradation pathways of 3FOP and 12FOP were characterized by TG-IR, Py-GC/MS, and Raman spectroscopy. Based on experimental results, we innovatively revealed a phosphorus fluorine synergistic flame retardancy mechanism.

Boosting catalytic efficiency of lipase by regulating amphiphilic microenvironment through reversible addition-fragmentation chain transfer polymerized modifications on polyacrylonitrile fiber

Lipases are increasingly attracting attention in green and sustainable biodiesel production. Currently, the research emphasis lies in immobilizing unstable lipase onto carriers to enhance its performance. Polyacrylonitrile fiber (PANF) is considered to be a promising material for lipase immobilization due to its excellent properties. In this study, functional carriers with regulated surface hydrophobicity were obtained by loading functional groups on PANF via reversible addition-fragmentation chain transfer (RAFT) polymerized modification, and Candida rugosa lipase (CRL) was covalently immobilized on the carrier with glutaraldehyde as a linker. By employing this optimized biocatalyst PANF@BMA&2VImBr-NH2-CRL in the transesterification process, the yield of biodiesel derived from soybean oil reached an impressive 92.7 %. The outstanding performance can be attributed to the activation of lipase interface induced by hydrophobic microenvironment derived from alkyl ester on the carrier skeleton. Moreover, the stability and storage performance of immobilized lipase were significantly improved. The immobilized lipase exhibited facile recovery and maintained a consistent biodiesel yield of 80.9 % even after undergoing 5 cycles of reuse, thereby highlighting its potential for sustainable production. To sum up, our research demonstrates that the designed and prepared process of PANF-supported lipase offers a promising approach for enzyme immobilization, thereby presenting extensive potential applications in the field of biotechnology.

Terpyridine-Decorated Polymer Nanosphere Latex: Template Nanocarriers for the Synthesis of Cu-CeO2 Hollow Spheres.

Water-soluble polymers with the ability to complex metal ions through complexing ligands have attracted significant interest in diverse domains, such as optical or catalyst applications. In this paper, we successfully synthesized, through a one-pot process combining polymerization-induced self-assembly and reversible addition-fragmentation chain transfer polymerization, aqueous dispersions of terpyridine-decorated poly[poly(ethylene glycol)methyl ether methacrylate]-b-poly(methyl methacrylate) (tpy-PPEGMA-b-PMMA) amphiphilic block copolymers. The in-situ formation of well-defined amphiphilic block copolymers and their self-assembly led to nanosphere latex with the hydrodynamic diameters increasing from 17 to 52 nm and the length of the copolymers increasing from 21,000 to 51,000 g·mol-1. These aqueous dispersed tpy-PPEGMA-b-PMMA nanospheres effectively complex metal ions, such as Cu2+, in a stoichiometric ratio of 2:1. Subsequently, these metal-complexed nanospheres were employed as soft template nanocarriers to control, on the nanometer scale, the dispersion of metal on a nanostructured support. This is exemplified by the synthesis of copper supported on cerium oxide hollow spheres (Cu-CeO2) using Cu2+-tpy-PPEGMA-b-PMMA as template nanocarriers and CeO2 nanoparticles. This novel assembly engineering strategy for the preparation of atomically dispersed metal on a nanostructured support was highlighted through the utilization of Cu-CeO2 hollow spheres as an electrocatalyst for the nitrate reduction reaction (NO3RR) to NH3. These encouraging outcomes emphasize the potential of metal-metal oxide-nanostructured materials to treat contaminated water sources with nitrate while allowing the green production of ammonia.

Exploiting the Reversible Dimerization of N-Heterocyclic Carbenes to Access Dynamic Polymer Networks with an Organocatalytic Activity.

The capability of some N-heterocyclic carbenes (NHCs) to reversibly dimerize is exploited to access dynamic polymer networks. Benzimidazolium motifs serving as NHC precursors have thus been supported onto copolymer chains by reversible addition-fragmentation chain transfer (RAFT) copolymerization of styrene and up to 20 mol % of 4-vinylbenzyl-ethyl-benzimidazolium chloride. Molecular versions of 1,3-dialkyl benzimidazolium salts have been synthesized as models, the deprotonation of which with a strong base yields the NHC dimers in the form of tetraaminoalkenes. The crossover reaction between two distinct NHC homodimers, forming heterodimers, is then evidenced. Applying this deprotonation method to the RAFT-derived copolymers leads to polymer networks with cross-links consisting of labile dimerized NHC motifs. These networks can be subsequently decross-linked using two distinct triggers, namely, a monofunctional NHC precursor as competitor and carbon dioxide (CO2). In the latter case, regeneration of the network occurs by chemically fueling the linear copolymer bearing benzimidazolium motifs with tBuOK in the presence of trace amounts of water. The same networks can also be used as latent precursors of transient polyNHCs to catalyze the benzoin condensation upon heating. The polymer-supported organocatalysts can thus be used in successive catalytic cycles.

Harnessing Guanidinium and Imidazole Functional Groups: A Dual-Charged Polymer Strategy for Enhanced Gene Delivery.

Histidine and arginine are two amino acids that exhibit beneficial properties for gene delivery. In particular, the imidazole group of histidine facilitates endosomal release, while the guanidinium group of arginine promotes cellular entry. Consequently, a dual-charged copolymer library based on these amino acids was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The content of the N-acryloyl-l-histidine (His) monomer was systematically increased, while maintaining consistent levels of methyl N-acryloyl-l-argininate hydrochloride (ArgOMe) or N-(4-guanidinobutyl)acrylamide hydrochloride (GBAm). The resulting polymers formed stable, nanosized polyplexes when complexed with nucleic acids. Remarkably, candidates with increased His content exhibited reduced cytotoxicity profiles and enhanced transfection efficiency, particularly retaining this performance level at lower pDNA concentrations. Furthermore, endosomal release studies revealed that increased His content improved endosomal release, while ArgOMe improved cellular entry. These findings underscore the potential of customized dual-charged copolymers and the synergistic effects of His and ArgOMe/GBAm in enhancing gene delivery.

Nanosized Complexes of the Proteolytic Enzyme Serratiopeptidase with Cationic Block Copolymer Micelles Enhance the Proliferation and Migration of Human Cells.

In this study, we describe the preparation of the cationic block copolymer nanocarriers of the proteolytic enzyme serratiopeptidase (SER). Firstly, an amphiphilic poly(2-(dimethylamino)ethyl methacrylate)-b-poly(ε-caprolactone)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA9-b-PCL35-b-PDMAEMA9) triblock copolymer was synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. Then, cationic micellar nanocarriers consisting of a PCL hydrophobic core and a PDMAEMA hydrophilic shell were formed by the solvent evaporation method. SER was loaded into the polymeric micelles by electrostatic interaction between the positively charged micellar shell and the negatively charged enzyme molecules. The particle size, zeta potential, and colloid stability of complexes as a function of SER concentration were investigated by dynamic and electrophoretic light scattering. It was found that SER retained its proteolytic activity after immobilization in polymeric carriers. Moreover, the complexes have a concentration-dependent enhancing effect on the proliferation and migration of human keratinocyte HaCaT and gingival fibroblast HGF cells.

Surface Grafting of Magnetic Carbon Nanotubes and Their Vertical Alignment in PVDF Asymmetric Ultrafiltration Membranes for Fast Nanochannel Construction

The application of carbon nanotubes (CNTs) in water treatment membranes can increase the permeability and selectivity of the membranes. However, traditional CNTs are usually affected by van der Waals forces, which makes them prone to agglomerate in polymer membranes, and their non-directional arrangement in the membranes limits their transport efficiency as water channels in the membranes. In this paper, a reversible addition-fragmentation chain transfer (RAFT) polymerization method was used to synthesize propargyl methacrylate - random copolymerization - poly (ethylene glycol) methacrylate - block - polymethyl methacrylate [P(PgMA-r-PEGMA) -b-PMMA]. The P(PgMA-r-PEGMA)-b-PMMA grafting rate was 60.4% on the surface of magnetic sulfhydryl functionalized carbon nanotubes (mCNTs-SH) by click-reaction grafting. Poly (vinylidene fluoride) (PVDF)/CNTs composite ultrafiltration membranes were prepared using vapor-induced phase separation (VIPS) combined with magnetic field arraying. When the mCNTs-g-P(PgMA-r-PEGMA)-b-PMMA were vertically aligned in the PVDF membrane through a magnetic field, the effective construction of the vertical nanochannels was realized, and an increased purified water flux from 25.6 LMH to 35.8 LMH, with the composite ultrafiltration membranes was obtained. In addition, the membranes also showed excellent hydrophilicity, mechanical properties, and polyethylene glycol 1200 (PEG1200) rejection. The water contact angle was reduced from 105° to 79°, the rejection of PEG1200 was increased from 44% to 91% of the 0.5 g/L PEG aqueous solutions, and excellent mechanical properties (tensile strengthes up to 9.3 MPa) were achieved. By designing the interface structure of the CNTs and studying the orientation of the CNTs in PVDF membranes, this work provides a new research idea for the field of water treatment ultrafiltration membranes.

Polyoxometalate-Polymer Directed Macromolecular Architectonics of Silver Nanoparticles as Effective Antimicrobials.

A novel inorganic-organic-inorganic ternary bioactive material formulated on antimicrobial peptide-based polymer has been reported. Supramolecular approach has been employed to incorporate molecularly crowded tyrosine-based polymer stabilized silver nanoparticles into membrane bound vesicles exploiting polyoxometalate-triggered surface templating strategy. Utilizing the covalent reversible addition fragmentation chain transfer (RAFT) polymerization and exploiting templated supramolecular architectonics at biopolymer interface, the bioactive ternary polymeric nanohybrids have been designed against Shigellosis leveraging the antibacterial activities of silver nanoparticle, cationic amphiphilic tyrosine polymer and inorganic polyoxometalate. The detail investigation against Shigella flexneri 2a cell line demonstrates that the collaborative mechanism of the ternary hybrid composite enhances the bactericidal activity in comparison to only polyoxometalate and polymer stabilized silver nanoparticle with an altered mechanism of action which is established via detailed biological analysis.

Direct Functionalization of Polyethylene Surfaces with High-Density Polymer Brushes.

Introducing functionality onto PE surfaces is a longstanding challenge in polymer science, driven by the need for polymer materials with improved adhesion and antifouling properties. Herein, we report surface-initiated hydrogen atom transfer-reversible addition-fragmentation chain transfer (SI HAT-RAFT) as a robust method to grow high-density brush polymers from PE surfaces. We demonstrate that, under mild conditions, direct initiation from the C-H bonds of PE surfaces allows for the graft polymerization of a variety of (meth)acrylate monomers. The resulting polymer brushes reached several hundred nanometers in thickness with densities of ca. 0.62 chains/nm2, compared to the current standard of ∼0.28 chains/nm2. Finally, we show that our method is capable of dramatically improving the adhesive properties of PE surfaces. This work enables the preparation of PE with diverse surface functionalities for potential use in biomedical, industrial, and battery applications.

Strategies for preparation of chitosan based water-soluble fluorescent probes to detect Cr3+ and Cu2+ ions

The low solubility of chitosan (CS) imposes adverse effects on its application. In this work, one of the aims is to improve the water solubility of CS. By introducing water-soluble side chains to CS, this aim was achieved. Besides, fluorescent moieties were incorporated into the side chains, the fluorescent copolymers were endowed with Cr3+ and Cu2+ ions recognition ability. Firstly, a reversible addition-fragmentation chain transfer polymerization (RAFT) reagent with naphthalimide units and CC groups was prepared. Water-soluble monomer methyl acrylic acid (MAA) was employed in the RAFT polymerization. Thus, water-soluble polymer with fluorescent unit and -C ≡ C on both ends of the polymer was obtained. They were introduced into CS, and the CS-based fluorescent copolymers were obtained eventually. The amount of MAA introduced could be tuned to obtain three side chains of different lengths. It was found that the more MAA was introduced, the better the solubility of CS-TP was. The detection limits (LOD) of Cr3+ and Cu2+ were 44.6 nM and 54.5 nM, respectively. The detection of Cr3+ and Cu2+ ions is further combined with a mobile APP to realize real-time, portable, and visual detection. And the application in the logic gate, a new detection platform, is prepared.

Harnessing Cytosine for Tunable Nanoparticle Self-Assembly Behavior Using Orthogonal Stimuli.

Nucleobases control the assembly of DNA, RNA, etc. due to hydrogen bond complementarity. By combining these unique molecules with state-of-the-art synthetic polymers, it is possible to form nanoparticles whose self-assembly behavior could be altered under orthogonal stimuli (pH and temperature). Herein, we report the synthesis of cytosine-containing nanoparticles via aqueous reversible addition-fragmentation chain transfer polymerization-induced self-assembly. A poly(N-acryloylmorpholine) macromolecular chain transfer agent (mCTA) was chain-extended with cytosine acrylamide, and a morphological phase diagram was constructed. By exploiting the ability of cytosine to form dimers via hydrogen bonding, the self-assembly behavior of cytosine-containing polymers was altered when performed under acidic conditions. Under these conditions, stable nanoparticles could be formed at longer polymer chain lengths. Furthermore, the resulting nanoparticles displayed different morphologies compared to those at pH 7. Additionally, particle stability post-assembly could be controlled by varying pH and temperature. Finally, small-angle X-ray scattering was performed to probe their dynamic behavior under thermal cycling.

Effect of Added Salt on the RAFT Polymerization of 2-Hydroxyethyl Methacrylate in Aqueous Media.

We report the effect of added salt on the reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-hydroxyethyl methacrylate (HEMA) in aqueous media. More specifically, poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC26) was employed as a salt-tolerant water-soluble block for chain extension with HEMA targeting PHEMA DPs from 100 to 800 in the presence of NaCl. Increasing the salt concentration significantly reduces the aqueous solubility of both the HEMA monomer and the growing PHEMA chains. HEMA conversions of more than 99% could be achieved within 6 h at 70 °C regardless of the NaCl concentration when targeting PMPC26-PHEMA800 vesicles at 20% w/w solids. Significantly faster rates of polymerization were observed at higher salt concentration owing to the earlier onset of micellar nucleation. Transmission electron microscopy (TEM) was used to construct a pseudo-phase diagram for this polymerization-induced self-assembly (PISA) formulation. High-quality images required cross-linking of the PHEMA chains with glutaraldehyde prior to salt removal via dialysis. Block copolymer spheres, worms, or vesicles can be accessed at any salt concentration up to 2.5 M NaCl. However, only kinetically trapped spheres could be obtained in the presence of 3 M NaCl because the relatively low HEMA monomer solubility under such conditions leads to an aqueous emulsion polymerization rather than an aqueous dispersion polymerization. In this case, dynamic light scattering studies indicated a gradual increase in z-average diameter from 26 to 86 nm when adjusting the target PHEMA degree of polymerization from 200 to 800. When targeting PMPC26-PHEMA800 vesicles, increasing the salt content up to 2.5 M NaCl leads to a systematic reduction in the z-average diameter from 953 to 92 nm. Similarly, TEM analysis and dispersion viscosity measurements indicated a gradual reduction in worm contour length with increasing salt concentration for PMPC26-PHEMA600 worms. This new PISA formulation clearly illustrates the importance of added salt on aqueous monomer solubility and how this affects (i) the kinetics of polymerization, (ii) the morphology of the corresponding diblock copolymer nano-objects, and (iii) the mode of polymerization in aqueous media.

Sub-micron colloidosomes with tuneable cargo release prepared using epoxy-functional diblock copolymer nanoparticles

HypothesisPickering emulsions stabilized using epoxy-functional block copolymer nanoparticles should enable the formation of sub-micron colloidosomes that are stable with respect to Ostwald ripening and allow tuneable small-molecule cargo release. ExperimentsEpoxy-functional diblock copolymer nanoparticles of 24 ± 4 nm were prepared via reversible addition-fragmentation chain transfer (RAFT)-mediated dispersion polymerization of methyl methacrylate (MMA) in n-dodecane. Sub-micron water-in-n-dodecane Pickering emulsions were prepared by high-pressure microfluidization. The epoxy groups were then ring-opened using 3-aminopropyltriethoxysilane (APTES) to prepare cross-linked colloidosomes. The colloidosomes survived removal of the aqueous phase using excess solvent. The silica shell thickness could be adjusted from 11 to 23 nm by varying the APTES/GlyMA molar ratio. The long-term stability of the colloidosomes was compared to precursor Pickering emulsions. Finally, the permeability of the colloidosomes was examined by encapsulation and release of a small molecule. FindingsThe Pickering emulsion droplet diameter was reduced from 700 to 200 nm by increasing the salt concentration within the aqueous phase. In the absence of salt, emulsion droplets were unstable due to Ostwald ripening. However, emulsions prepared with 0.5 M NaCl are stable for at least one month. The cross-linked colloidosomes demonstrated much more stable than the precursor sub-micron emulsions prepared without salt. The precursor nanoemulsions exhibited complete release (>99 %) of an encapsulated dye, while higher APTES/GlyMA ratios resulted in much lower dye release, yielding nearly impermeable silica capsules that retained around 95 % of the dye.