How Do Spherical Diblock Copolymer Nanoparticles Grow during RAFT Alcoholic Dispersion Polymerization?

Controlling Adsorption of Diblock Copolymer Nanoparticles onto an Aldehyde-Functionalized Hydrophilic Polymer Brush via pH Modulation

Sterically stabilized diblock copolymer nanoparticles with a well-defined spherical morphology and tunable diameter were prepared by RAFT aqueous emulsion polymerization of benzyl methacrylate at 70 °C. The steric stabilizer precursor used for these syntheses contained pendent cis-diol groups, which means that such nanoparticles can react with a suitable aldehyde-functional surface via acetal bond formation. This principle is examined herein by growing an aldehyde-functionalized polymer brush from a planar silicon wafer and studying the extent of nanoparticle adsorption onto this model substrate from aqueous solution at 25 °C using a quartz crystal microbalance (QCM). The adsorbed amount, Γ, depends on both the nanoparticle diameter and the solution pH, with minimal adsorption observed at pH 7 or 10 and substantial adsorption achieved at pH 4. Variable-temperature QCM studies provide strong evidence for chemical adsorption, while scanning electron microscopy images recorded for the nanoparticle-coated brush surface after drying indicate mean surface coverages of up to 62%. This fundamental study extends our understanding of the chemical adsorption of nanoparticles on soft substrates.

Determination of Reaction Kinetics by Time-Resolved Small-Angle X-ray Scattering during Polymerization-Induced Self-Assembly: Direct Evidence for Monomer-Swollen Nanoparticles

The kinetics of heterogeneous polymerization is determined directly using small-angle X-ray scattering (SAXS). This important advancement is exemplified for the synthesis of sterically-stabilized diblock copolymer nanoparticles by reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) in mineral oil at 90 °C. The principle of mass balance is invoked to derive a series of equations for the analysis of the resulting time-resolved SAXS patterns. Importantly, there is a continuous change in the X-ray scattering length density for the various components within the reaction mixture. This enables the volume fraction of unreacted BzMA monomer to be calculated at any given time point, which enables the polymerization kinetics to be monitored in situ directly without relying on supplementary characterization techniques. Moreover, SAXS enables the local concentration of both monomer and solvent within the growing swollen nanoparticles to be determined during the polymerization. Data analysis reveals that the instantaneous rate of BzMA polymerization is proportional to the local monomer concentration within the nanoparticles. In principle, this powerful new time-resolved SAXS approach can be applicable to other heterogeneous polymerization formulations.

Liquid Crystalline Nanoparticles via Polymerization-Induced Self-Assembly: Morphology Evolution and Function Regulation

Liquid crystalline nanoparticles (LC NPs) are a kind of polymer NPs with LC mesogens, which can form special anisotropic morphologies due to the influence of LC ordering. Owing to the stimuli-responsiveness of the LC blocks, LC NPs show abundant morphology evolution behaviors in response to external regulation. LC NPs have great application potential in nano-devices, drug delivery, special fibers and other fields. Polymerization-induced self-assembly (PISA) method can synthesize LC NPs at high solid content, reducing the harsh demand for reaction solvent of the LC polymers, being a better choice for large-scale production. In this review, we introduced recent research progress of PISA-LC NPs by dividing them into several parts according to the LC mesogen, and discussed the improvement of experimental conditions and the potential application of these polymers.

Continuous-Flow Laboratory SAXS for In Situ Determination of the Impact of Hydrophilic Block Length on Spherical Nano-Object Formation during Polymerization-Induced Self-Assembly

In situ small-angle X-ray scattering (SAXS) is a powerful technique for characterizing block-copolymer nano-object formation during polymerization-induced self-assembly. To work effectively in situ, it requires high intensity X-rays which enable the short acquisition times required for real-time measurements. However, routine access to synchrotron X-ray sources is expensive and highly competitive. Flow reactors provide an opportunity to obtain temporal resolution by operating at a consistent flow rate. Here, we equip a flow-reactor with an X-ray transparent flow-cell at the outlet which facilitates the use of a low-flux laboratory SAXS instrument for in situ monitoring. The formation and morphological evolution of spherical block copolymer nano-objects was characterized during reversible addition fragmentation chain transfer polymerization of diacetone acrylamide in the presence of a series of poly(dimethylacrylamide) (PDMAm) macromolecular chain transfer agents with varying degrees of polymerization. SAXS analysis indicated that during the polymerization, highly solvated, loosely defined aggregates form after approximately 100 s, followed by expulsion of solvent to form well-defined spherical particles with PDAAm cores and PDMAm stabilizer chains, which then grow as the polymerization proceeds. Analysis also indicates that the aggregation number (Nagg) increases during the reaction, likely due to collisions between swollen, growing nanoparticles. In situ SAXS conducted on PISA syntheses using different PDMAm DPs indicated a varying conformation of the chains in the particle cores, from collapsed chains for PDMAm47 to extended chains for PDMAm143. At high conversion, the final Nagg decreased as a function of increasing PDMAm DP, indicating increased steric stabilization afforded by the longer chains which is reflected by a decrease in both core diameter (from SAXS) and hydrodynamic diameter (from DLS) for a constant core DP of 400.

Preparation of Water-Soluble Polyion Complex (PIC) Micelles with Random Copolymers Containing Pendant Quaternary Ammonium and Sulfonate Groups

Cationic random copolymers (PCm) consisting of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC; P) with methacroylcholine chloride (MCC; C) and anionic random copolymers (PSn) consisting of MPC and potassium 3-(methacryloyloxy)propanesulfonate (MPS; S) were prepared via a reversible addition-fragmentation chain transfer method. "m" and "n" represent the compositions (mol %) of the MCC and MPS units in the copolymers, respectively. The degrees of polymerization for the copolymers were 93-99. Water-soluble MPC unit contains a pendant zwitterionic phosphorylcholine group whose charges are neutralized in pendant groups. MCC and MPS units contain the cationic quaternary ammonium and anionic sulfonate groups, respectively. The stoichiometrically charge-neutralized mixture of a matched pair of PCm and PSn aqueous solutions resulted in the spontaneous formation of water-soluble PCm/PSn polyion complex (PIC) micelles. These PIC micelles have the MPC-rich surface and MCC/MPS core. These PIC micelles were characterized using ¹H NMR, dynamic and static light scattering, and transmission electron microscopic measurements. The hydrodynamic radius of these PIC micelles depends on the mixing ratio of the oppositely charged random copolymers. The charge-neutralized mixture formed maximum-size PIC micelles.

Customizable nano-sized colloidal tetrahedrons by polymerization-induced particle self-assembly (PIPA)

Colloidal molecules (CMs) are colloidal clusters with molecule-like symmetry and architecture, generated from the self-assembly of nanoparticles with attractive patches. However, large-scale preparation of patchy nanoparticles remains challenging. Here, we...

Direct Access to Polysaccharide-Based Vesicles with a Tunable Membrane Thickness in a Large Concentration Window via Polymerization-Induced Self-Assembly

Polymersomes are multicompartmental vesicular nano-objects obtained by self-assembly of amphiphilic copolymers. When prepared in the aqueous phase, they are composed of a hydrophobic bilayer enclosing water. Although such fascinating polymeric nano-objects have been widely reported with synthetic block copolymers, their formation from polysaccharide-based copolymers remains a significant challenge. In the present study, the powerful platform technology known as polymerization-induced self-assembly was used to prepare in situ pure vesicles from a polysaccharide-grafted copolymer: dextran-g-poly(2-hydroxypropyl methacrylate) (Dex-g-PHPMA). The growth of the PHPMA grafts was performed with a dextran-based macromolecular chain transfer agent in water at 20 °C using photomediated reversible addition fragmentation chain transfer polymerization at 405 nm. Transmission electron microscopy, cryogenic electron microscopy, small-angle X-ray scattering, atomic force microscopy, and dynamic light scattering revealed that amphiphilic Dex-g-PHPMA_{X = 100-300} (X is the targeted average degree of polymerization, X_n̅, of each graft at full conversion) exhibit remarkable self-assembly behavior. On the one hand, vesicles were obtained over a wide range of solid concentrations (from 2.5% to 13.5% w/w), which can facilitate posterior targeting of such rare morphology. On the other hand, the extension of X_n̅ induces an increase in the vesicle membrane thickness, rather than a morphological evolution (spherical micelles to cylinders to vesicles).

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.

Boron-rich, cytocompatible block copolymer nanoparticles by polymerization-induced self-assembly

A new methacrylic boronate ester is synthesized and exploited to produce biocompatible nanoparticles with a boron-rich core by PISA.

Synthesis of well-defined diblock copolymer nano-objects by RAFT non-aqueous emulsion polymerization of N-(2-acryloyloxy)ethyl pyrrolidone in non-polar media

RAFT non-aqueous emulsion polymerization of N-(2-acryloyloxy)ethyl pyrrolidone in n-dodecane using a poly(stearyl methacrylate) precursor is used to prepare sterically-stabilized nanoparticles, which are evaluated as a putative Pickering emulsifier.

In situ SAXS studies of a prototypical RAFT aqueous dispersion polymerization formulation: monitoring the evolution in copolymer morphology during polymerization-induced self-assembly

Small-angle X-ray scattering (SAXS) is used to characterize the in situ formation of diblock copolymer spheres, worms and vesicles during reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate at 70 °C using a poly(glycerol monomethacrylate) steric stabilizer. 1H NMR spectroscopy indicates more than 99% HPMA conversion within 80 min, while transmission electron microscopy and dynamic light scattering studies are consistent with the final morphology being pure vesicles. Analysis of time-resolved SAXS patterns for this prototypical polymerization-induced self-assembly (PISA) formulation enables the evolution in copolymer morphology, particle diameter, mean aggregation number, solvent volume fraction, surface density of copolymer chains and their mean inter-chain separation distance at the nanoparticle surface to be monitored. Furthermore, the change in vesicle diameter and membrane thickness during the final stages of polymerization supports an 'inward growth' mechanism.

Drug-Directed Morphology Changes in Polymerization-Induced Self-Assembly (PISA) Influence the Biological Behavior of Nanoparticles

The effect of the hydrophobic block length on the morphologies of polymerization-induced self-assembled (PISA) nanoparticles is well understood. However, the influence of drug loading on the phase morphology of the nanoparticles during the PISA process, and the resulting biological function of PISA nanoparticles, has barely been investigated. In this work, we show that the addition of a drug, curcumin, during the PISA process shifts the phase diagram toward different morphologies. The PISA system was based on hydrophilic poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC), which was chain extended with hydrophobic methyl methacrylate (MMA) in various concentrations of curcumin. According to transmission electron microscopy, the presence of curcumin led to the transition of, for example, worms to polymersome and micelles to worms analysis. To understand the interaction between polymer particles and drug, small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), and fluorescence lifetime measurements were carried out. These measurements show that curcumin is predominantly located in the core in the case of micelles and worms while it is found in the shell of polymersomes. The change in morphology influences the cellular uptake by MCF-7 cells and the movement of the particles in multicellular cancer spheroids (3D model). With the increasing amount of drug, the cellular uptake of micelles and worms was enhanced with the increasing grafting density of MPC chains, which contrasts the decreasing cellular uptake in the higher drug-loaded polymersomes due to the lower shell hydration.

Time-resolved small-angle neutron scattering studies of the thermally-induced exchange of copolymer chains between spherical diblock copolymer nanoparticles prepared via polymerization-induced self-assembly

Sterically-stabilized diblock copolymer nanoparticles (a.k.a. micelles) are prepared directly in non-polar media via polymerization-induced self-assembly (PISA). More specifically, a poly(lauryl methacrylate) chain transfer agent is chain-extended via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of methyl methacrylate (MMA) to form sterically-stabilized spheres at 20% w/w solids in n-dodecane at 90 °C. Both fully hydrogenous (PLMA39-PMMA55 and PLMA39-PMMA94) and core-deuterated (PLMA39-d8PMMA57 and PLMA39-d8PMMA96) spherical nanoparticles with mean core diameters of approximately 20 nm were prepared using this protocol. After diluting each dispersion in turn to 1.0% w/w with n-dodecane, small-angle X-ray scattering studies confirmed essentially no change in spherical nanoparticle diameter after thermal annealing at 150 °C. Time-resolved small angle neutron scattering was used to examine whether copolymer chain exchange occurs between such nanoparticles at elevated temperatures. Copolymer chain exchange for a binary mixture of PLMA39-PMMA55 and PLMA39-d8PMMA57 nanoparticles produced hybrid (mixed) cores containing both PMMA55 and d8PMMA57 blocks within 3 min at 150 °C. In contrast, a binary mixture of PLMA39-PMMA94 and PLMA39-d8PMMA96 nanoparticles required 8 min at this temperature before no further reduction in neutron scattering intensity could be observed. These observations suggest that the rate of copolymer chain exchange depends on the degree of polymerization of the core-forming block. Relatively slow copolymer chain exchange was also observed at 80 °C, which is below the Tg of the core-forming PMMA block as determined by DSC studies. These observations confirm rapid exchange of individual copolymer chains between sterically-stabilized nanoparticles at elevated temperature. The implications of these findings are briefly discussed in the context of PISA, which is a powerful technique for the synthesis of sterically-stabilized nanoparticles.

A Neutron Scattering Study of the Structure of Poly(dimethylsiloxane)-Stabilized Poly(methyl methacrylate) (PDMS-PMMA) Latexes in Dodecane

Hard-sphere particles in nonpolar solvents are an essential tool for colloid scientists. Sterically stabilized poly(methyl methacrylate) (PMMA) particles have long been used as the exemplary hard-sphere system. However, neither the particles themselves nor the poly(12-hydroxystearic acid) (PHSA) stabilizer necessary to prevent aggregation in nonpolar solvents are commercially available. To counter this, several alternatives have been proposed. In recent years, there has been an increased interest in poly(dimethylsiloxane) (PDMS) stabilizers as a commercially available alternative to PHSA, yet the structure of particles made in this way is not as well understood as those produced using PHSA. In this work, we employ small-angle neutron scattering to determine the internal structure of PDMS-stabilized PMMA particles, synthesized with and without an additional crosslinking agent. We report data consistent with a homogeneous PMMA core with a linearly decaying PDMS shell. The thickness of the shell was in excess of 50 nm, thicker than the PHSA layer typically used to stabilize PMMA but consistent with reports of the layer thickness for similar molecular weight PDMS at planar surfaces. We also show that the amount of the hydrogenous material in the particle core of the crosslinked particles notably exceeds the amount of added ethylene glycol dimethacrylate crosslinker, suggesting some entrapment of the PDMS stabilizer in the PMMA matrix.

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.

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.

Self-assembly of amphiphilic copolymers containing polysaccharide: PISA versus nanoprecipitation, and the temperature effect

The self-assembly methods and the temperature have a considerable impact on the morphology of the resulting nanoobjects in the case of amphiphilic glycopolymers.

Investigating the influence of solvent quality on RAFT-mediated PISA of sulfonate-functional diblock copolymer nanoparticles

Solvent quality has a marked impact on the assembly of sulfonate-functional diblock copolymer nanoparticles prepared by PISA.

Unraveling the kinetics of the structural development during polymerization-induced self-assembly: decoupling the polymerization and the micelle structure

Upon extending a hydrophobic polymer chain from the end of a preceding hydrophilic chain in aqueous solutions, the resultant block copolymers may eventually undergo self-assembly.

Rigor and reproducibility in polymer nanoparticle synthesis and characterization

Standardized process improvement methods and tools were used to enhance the rigor and reproducibility of diblock copolymer nanoparticle (NP) synthesis and characterization. Models linking design parameters with NP characteristics boosted process control for NP synthesis, which may improve translation and commercialization of NP research.

Novel modeling and process control approaches provide useful insights to improve rigor and reproducibility in polymer nanoparticle synthesis and characterization.

pH-Responsive Polyion Complex Vesicle with Polyphosphobetaine Shells

When a bioactive molecule is taken into cells by endocytosis, it is sometimes unable to escape from the lysosomes, resulting in inefficient drug release. We prepared pH-responsive polyion complex (PIC) vesicles that collapse under acidic conditions such as those inside a lysosome. Furthermore, under acidic conditions, cationic polymer was released from the PIC vesicles to break the lysosome membranes. Diblock copolymers (P₂₀M₁₆₇ and P₂₀A₁₉₀) consisting of water-soluble zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) block and cationic or anionic blocks were synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. Poly(3-(methacrylamidopropyl) trimethylammonium chloride) (PMAPTAC) and poly(sodium 6-acrylamidohexanoate) (PAaH) were used as the cationic and anionic blocks, respectively. The pendant hexanoate groups in the PAaH block are ionized in basic water and in phosphate buffered saline (PBS), while the hexanoate groups are protonated in acidic water. In basic water, PIC vesicles were formed from a charge neutralized mixture of oppositely charged diblock copolymers. At the interface of PIC vesicle and water exists biocompatible PMPC shells. Under acidic conditions, the PIC vesicles collapsed, because the charge balance shifted due to protonation of the PAaH block. After collapse of the PIC vesicles, P₂₀A₁₉₀ formed micelles composed of protonated PAaH core and PMPC shells, while P₂₀M₁₆₇ was released as unimers. PIC vesicles can encapsulate hydrophilic nonionic guest molecules into their hollow core. Under acidic conditions, the PIC vesicles can release the guest molecules and P₂₀M₁₆₇. The cationic P₂₀M₁₆₇ can break the lysosome membrane to efficiently release the guest molecules from the lysosomes to the cytoplasm.

RAFT-photomediated PISA in dispersion: mechanism, optical properties and application in templated synthesis

Diblock copolymer nanoparticles were prepared by photomediated polymerization-induced self-assembly (“photo-PISA”) in dispersion.

RAFT dispersion polymerization of glycidyl methacrylate for the synthesis of epoxy-functional block copolymer nanoparticles in mineral oil

Epoxy-functional poly(stearyl methacrylate)-poly(glycidyl methacrylate) (PSMA-PGlyMA) diblock copolymer nanoparticles are synthesized via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of glycidyl methacrylate (GlyMA) in mineral oil at 70 °C.

Functionalization-Induced Self-Assembly of Block Copolymers for Nanoparticle Synthesis

Nanoparticle synthesis was demonstrated via functionalization-induced self-assembly (FISA) of block copolymers using Suzuki-Miyaura cross-coupling. In situ self-assembly was triggered in organic media by the progressive installation of solvophobic pendant groups onto an initially soluble diblock copolymer, rendering the reactive block insoluble and causing the formation of spherical polymeric micelles. Self-assembly was found to depend on the percent functionalization (f_%), where after a critical threshold micelles were accessible that increased in size with increasing f_% values. We found the chemical nature of the installed functional group to be crucial for conducting FISA and for controlling the solution morphology, with relatively solvophilic adducts remaining as unimers and increasingly solvophobic adducts trending toward larger micelles, from ca. 40 to 100 nm in diameter. The core and corona of the anticipated micellar structure were visualized using fluorine mapping through electron energy loss spectroscopy, in conjunction with FISA achieved through pendent trifluorophenyl functionality. This work establishes FISA as a new, versatile synthetic strategy to create nanoparticles having tunable morphologies with potential application as molecular payload delivery vehicles.

In Situ Spectroscopic Studies of Highly Transparent Nanoparticle Dispersions Enable Assessment of Trithiocarbonate Chain-End Fidelity during RAFT Dispersion Polymerization in Nonpolar Media

We report the synthesis of highly transparent poly(stearyl methacrylate)-poly(2,2,2-trifluoroethyl methacrylate) (PSMA-PTFEMA) diblock copolymer nanoparticles via polymerization-induced self-assembly (PISA) in nonpolar media at 70 °C. This was achieved by chain-extending a PSMA precursor block via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of TFEMA in n-tetradecane. This n-alkane has the same refractive index as the PTFEMA core-forming block at 70 °C, which ensures high light transmittance when targeting 33 nm spherical nanoparticles. Such isorefractivity enables visible absorption spectra to be recorded with minimal light scattering even at 30% w/w solids. However, in situ monitoring of the trithiocarbonate RAFT end-groups during PISA requires selection of a weak n → π* band at 446 nm. Conversion of TFEMA into PTFEMA causes a contraction in the reaction solution volume, leading to an initial increase in absorbance that enables the kinetics of polymerization to be monitored via dilatometry. At ∼98% TFEMA conversion, this 446 nm band remains constant for 2 h at 70 °C, indicating surprisingly high RAFT chain-end fidelity (and hence pseudoliving character) under monomer-starved conditions. In situ 19F NMR spectroscopy studies provide evidence for (i) the onset of micellar nucleation, (ii) solvation of the nanoparticle cores by TFEMA monomer, and (iii) surface plasticization of the nanoparticle cores by n-tetradecane at 70 °C. Finally, the kinetics of RAFT chain-end removal can be conveniently monitored by in situ visible absorption spectroscopy: addition of excess initiator at 70 °C causes complete discoloration of the dispersion, with small-angle X-ray scattering studies confirming no change in nanoparticle morphology under these conditions.

Controlling Nanomaterial Size and Shape for Biomedical Applications via Polymerization-Induced Self-Assembly

Rapid developments in the polymerization-induced self-assembly (PISA) technique have paved the way for the environmentally friendly production of nanoparticles with tunable size and shape for a diverse range of applications. In this feature article, the biomedical applications of PISA nanoparticles and the substantial progress made in controlling their size and shape are highlighted. In addition to early investigations into drug delivery, applications such as medical imaging, tissue culture, and blood cryopreservation are also described. Various parameters for controlling the morphology of PISA nanoparticles are discussed, including the degree of polymerization of the macro-CTA and core-forming polymers, the concentration of macro-CTA and core-forming monomers, the solid content of the final products, the solution pH, the thermoresponsitivity of the macro-CTA, the macro-CTA end group, and the initiator concentration. Finally, several limitations and challenges for the PISA technique that have been recently addressed, along with those that will require further efforts into the future, will be highlighted.

Thermoreversible crystallization-driven aggregation of diblock copolymer nanoparticles in mineral oil

A poly(behenyl methacrylate)37 (PBeMA37) macromolecular chain transfer agent is utilized for the reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) directly in mineral oil at 90 °C. Polymerization-induced self-assembly (PISA) occurs under these conditions, yielding a series of sterically-stabilized PBeMA37-PBzMA x diblock copolymer spheres of tunable diameter as confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies. Rheological studies indicate that a relatively transparent, free-flowing, concentrated dispersion of non-interacting 32 nm PBeMA37-PBzMA100 spheres at 50 °C forms a turbid, paste-like dispersion on cooling to 20 °C. Turbidimetry and differential scanning calorimetry (DSC) studies conducted on solutions of PBeMA37 homopolymer in mineral oil suggest that this switchable colloidal stability is linked to crystallization-induced phase separation exhibited by this stabilizer block. Indeed, variable-temperature small-angle X-ray scattering (SAXS) indicates that a loose mass fractal network of strongly interacting spheres is formed on cooling to 20 °C, which accounts for this thermoreversible sol-gel transition. Moreover, SAXS, DSC and wide-angle X-ray scattering (WAXS) analyses indicate that the behenyl (C22H45) side-chains first form crystalline domains comprising adjacent stabilizer chains within individual spherical nanoparticles, with subsequent crystallization between neighboring nanoparticles leading to the formation of the mass fractal aggregates.

Zwitterionic Polyester-Based Nanoparticles with Tunable Size, Polymer Molecular Weight, and Degradation Time

Biodegradable polymer nanoparticles are an important class of materials used in several applications for their unique characteristics. In particular, the ones stabilized by zwitterionic materials are gaining increased interest in medicine as alternative to the more common ones based on poly(ethylene glycol) thanks to their superior stability and ability to avoid both the accelerated blood clearance and allergic reactions. In this work, a novel class of zwitterionic based NPs has been produced, and a method to independently control the nanoparticle size, degradation time, and polymer molecular weight has been developed and demonstrated. This has been possible by the synthesis and the fine-tuning of zwitterionic amphiphilic block copolymers obtained via the combination of ring-opening polymerization and reversible addition-fragmentation chain transfer polymerization. The final results showed that when two block copolymers contain the same number of caprolactone units, the one with longer oligoester lateral chains degrades faster. This phenomenon is in sharp contrast with the one seen so far for the common linear polyester systems where longer chains result in longer degradation times, and it can be used to better tailor the degradation behavior of the nanoparticles.

Polymerization-induced self-assembly of liquid crystalline ABC triblock copolymers with long solvophilic chains

Polymerization-induced self-assembly was exploited to investigate the self-assembly behavior of liquid crystalline triblock copolymers with long solvophilic chains.

Topological engineering of amphiphilic copolymers via RAFT dispersion copolymerization of benzyl methacrylate and 2-(perfluorooctyl)ethyl methacrylate for polymeric assemblies with tunable nanostructures

RAFT dispersion copolymerization of benzyl methacrylate and 2-(perfluorooctyl)ethyl methacrylate enables the regulation of the nanostructure of polymer assemblies.

Vesicles in Multiple Shapes: Fine-Tuning Polymersomes' Shape and Stability by Setting Membrane Hydrophobicity

Amphiphilic block-copolymers are known to self-assemble into micelles and vesicles. In this paper, we discuss the multiple options between and beyond these boundaries using amphiphilic AB diblock and ABC triblock copolymers. We adjust the final structure reached by the composition of the mixture, by the preparation temperature, and by varying the time-scale of formation. This leads to the formation of vesicles and micelles, but also internal micelles in larger sheets, lamellar vesicles, and closed tubes, thus broadening the amount of self-assembly structures available and deepening our understanding of them.

Folate-decorated PEGylated triblock copolymer as a pH/reduction dual-responsive nanovehicle for targeted intracellular co-delivery of doxorubicin and Bcl-2 siRNA

Co-delivery of chemotherapeutic drug and small interfering RNA (siRNA) within a single nanovehicle has emerged as a promising combination therapy approach to treating cancers because of their synergistic effect. Nanocarrier delivery systems with low cytotoxicity and high efficiency are needed for such a purpose. In this study, a novel folate-conjugated PEGylated cationic triblock copolymer, poly(acrylhydrazine)-block-poly(3-dimethylaminopropyl methacrylamide)-block-poly(acrylhydrazine) (PAH-b-PDMAPMA-b-PAH), was synthesized and evaluated as a stimuli-sensitive vehicle for the targeted co-delivery of doxorubicin (DOX) and Bcl-2 siRNA into breast cancer MCF-7 cells. The synthetic process of the PEGylated triblock copolymer involved sequential reversible addition-fragmentation chain transfer polymerization, PEGylation and removal of tert-butoxy carbamate protecting groups. Folate-conjugated and/or -unconjugated poly(ethylene glycol) segments were grafted onto PAH-b-PDMAPMA-b-PAH via a reduction-sensitive disulfide linkage. The synthetic polymers were characterized by ¹H NMR and gel permeation chromatography. The PEGylated triblock copolymer could chemically conjugate DOX onto PAH blocks via pH-responsive hydrazone bonds and simultaneously complex negatively charged Bcl-2 siRNA with cationic PDMAPMA blocks through electrostatic interactions at N/P ratios≥32:1 to form multifunctional nanomicelleplexes. The nanomicelleplexes exhibited spherical shape, possessed a positively charged surface with a zeta potential of +22.5mV and had a desirable and uniform particle size of 187nm. In vitro release studies revealed that the nanomicelleplexes could release DOX and Bcl-2 siRNA in a reduction and pH dual-sensitive manner and the payload release was significantly enhanced in a reductive acidic environment mimicking the endosomes/lysosomes of cancer cells compared to under physiology conditions. Furthermore, the release of both DOX and siRNA was found to follow Higuchi kinetic model. Confocal laser scanning microscopy, flow cytometry and MTT analyses confirmed that, compared with folate-undecorated nanomicelleplexes, folate-decorated nanomicelleplexes could more effectively co-deliver DOX and Bcl-2 siRNA into MCF-7 cells and showed a stronger cell-killing effect. The pristine PEGylated triblock copolymer exhibited good cytocompatibility. Moreover, co-delivery of DOX and Bcl-2 siRNA achieved a significant synergistic antitumor efficacy. These findings suggested that the folate-decorated PEGylated cationic triblock copolymer might be a promising vehicle for targeted intracellular co-delivery of DOX and siRNA in MCF-7 cells, representing a potential clinical combination therapy for breast cancer treatment.

Adsorption of Small Cationic Nanoparticles onto Large Anionic Particles from Aqueous Solution: A Model System for Understanding Pigment Dispersion and the Problem of Effective Particle Density

The present study focuses on the use of copolymer nanoparticles as a dispersant for a model pigment (silica). Reversible addition-fragmentation chain transfer (RAFT) alcoholic dispersion polymerization was used to synthesize sterically stabilized diblock copolymer nanoparticles. The steric stabilizer block was poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and the core-forming block was poly(benzyl methacrylate) (PBzMA). The mean degrees of polymerization for the PDMA and PBzMA blocks were 71 and 100, respectively. Transmission electron microscopy (TEM) studies confirmed a near-monodisperse spherical morphology, while dynamic light scattering (DLS) studies indicated an intensity-average diameter of 30 nm. Small-angle X-ray scattering (SAXS) reported a volume-average diameter of 29 ± 0.5 nm and a mean aggregation number of 154. Aqueous electrophoresis measurements confirmed that these PDMA71-PBzMA100 nanoparticles acquired cationic character when transferred from ethanol to water as a result of protonation of the weakly basic PDMA chains. Electrostatic adsorption of these nanoparticles from aqueous solution onto 470 nm silica particles led to either flocculation at submonolayer coverage or steric stabilization at or above monolayer coverage, as judged by DLS. This technique indicated that saturation coverage was achieved on addition of approximately 465 copolymer nanoparticles per silica particle, which corresponds to a fractional surface coverage of around 0.42. These adsorption data were corroborated using thermogravimetry, UV spectroscopy and X-ray photoelectron spectroscopy. TEM studies indicated that the cationic nanoparticles remained intact on the silica surface after electrostatic adsorption, while aqueous electrophoresis confirmed that surface charge reversal occurred below pH 7. The relatively thick layer of adsorbed nanoparticles led to a significant reduction in the effective particle density of the silica particles from 1.99 g cm-3 to approximately 1.74 g cm-3, as judged by disk centrifuge photosedimentometry (DCP). Combining the DCP and SAXS data suggests that essentially no deformation of the PBzMA cores occurs during nanoparticle adsorption onto the silica particles.

In situ synthesis of the Ag/poly(4-vinylpyridine)-block-polystyrene composite nanoparticles by dispersion RAFT polymerization

A new method for the synthesis of metal/block-copolymer nanocomposites of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS) and Ag nanoparticles by dispersion RAFT polymerization is proposed.

In situ synthesis of thermoresponsive 4-arm star block copolymer nano-assemblies by dispersion RAFT polymerization

Thermoresponsive 4-arm star block copolymer nano-assemblies were synthesized, and their interesting thermoresponse was investigated.