Self-assembly of random copolymers

Effects of Hydrophobic Modifications on the Solution Self-Assembly of P(DMAEMA-co-QDMAEMA)-b-POEGMA Random Diblock Copolymers

In this work, the synthesis and the aqueous solution self-assembly behavior of novel partially hydrophobically modified poly(2-(dimethylamino) ethyl methacrylate)-b-poly(oligo(ethylelene glycol) methyl ether methacrylatetabel) pH and temperature responsive random diblock copolymers (P(DMAEMA-co-Q_6/12DMAEMA)-b-POEGMA), are reported. The chemical modifications were accomplished via quaternization with 1-iodohexane (Q₆) and 1-iodododecane (Q₁₂) and confirmed by ¹H-NMR spectroscopy. The successful synthesis of PDMAEMA-b-POEGMA precursor block copolymers was conducted by RAFT polymerization. The partial chemical modification of the diblocks resulted in the permanent attachment of long alkyl chains on the amine groups of the PDMAEMA block and the presence of tertiary and quaternary amines randomly distributed within the PDMAEMA block. Light scattering techniques confirmed that the increased hydrophobic character results in the formation of nanoaggregates of high mass and tunable pH and temperature response. The characteristics of the aggregates are also affected by the aqueous solution preparation protocol, the nature of the quaternizing agent and the quaternization degree. The incorporation of long alkyl chains allowed the encapsulation of indomethacin within the amphiphilic diblock copolymer aggregates. Nanostructures of increased size were detected due to the encapsulation of indomethacin into the interior of the hydrophobic domains. Drug release studies demonstrated that almost 50% of the encapsulated drug can be released on demand by aid of ultrasonication.

Effect of Molecular Architecture and Composition on the Aggregation Pathways of POEGMA Random Copolymers in Water

Understanding of the temperature-induced phase transition of poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) random copolymers with varied composition remains largely incomplete. Upon heating they can form either macroscopically phase-separated aggregates or micelles. We examined the effect of polymer architecture by rationally designing and synthesizing various POEGMA copolymer structures via atom transfer radical polymerization using OEGMA monomers of different EO lengths. Micelle formation occurred for copolymers with a small fraction of long side chains counterbalanced by an appropriate number of short side chains, while macroscopic phase separation occurred for other copolymer compositions. In some copolymer compositions and architectures, micelle formation followed by macroscopic phase separation occurred, and the temperature of these phase transitions could be tailored accordingly. This new strategy allows the control over the microstructure and specific transition temperatures enabling, for instance, the preparation of nanocarriers for encapsulating hydrophobic compounds.

Multiple-stimuli-responsiveness and conformational inversion of smart supramolecular nanoparticles assembled from spin labeled amphiphilic random copolymers

HYPOTHESIS

Organic radical polymers with tailored pendant functionalities have emerged as exciting and promising materials for their application versatility. Moreover, eco-friendly polymer-based organic nanomaterials with redox-active pendant side groups can replace the harmful heavy metal-based inorganic materials. On the other hand, self-assembled nanomaterials are of great interest and attracted more attention recently for their promising application in different advanced fields, but it is yet challenging to predict suitable hydrophilic-lipophilic balance (HLB) for stimuli-responsive random copolymers assembly due to structural irregularity. Among several experimental techniques, electron paramagnetic resonance (EPR) spectroscopy plays a unique and promising role in revealing structural and dynamic information of nanostructured radical containing materials.

EXPERIMENTS

In this study, a series of spin labeled amphiphilic random copolymers poly(methyl methacrylate-co-acrylic acid) have been synthesized and characterized by FT-IR, UV-Vis spectroscopies, TGA, DSC and water contact angle (CA) techniques. Their electrochemical properties have been determined by cyclic voltammetry (CV) in different organic solvents. EPR spectroscopy has been applied with other analytical techniques to elucidate the smart supramolecular nanoparticles (SNPs) formation, stimuli-responsiveness and structural changes through the dynamics of different molecular interactions.

FINDINGS

The structural and dynamic information of self-assembled nanoparticles have been observed to be dependent on multiple-stimuli-responsiveness in different microenvironments by applying physiological and chemical parameters such as the different concentration of radicals, pH, temperature, nature of the solvent and reducing agent. The obtained results reveal the knowledge to understand insight into the mechanism for the formation of stimuli-responsive colloidal nanoparticles assembled from amphiphilic random copolymers with apt HLB value. The CV results reveal that the charge transfer process of the nanoparticles in solution was diffusion regulated and depended on the accessibility of radicals. The radical (spin labeled) polymers offer a broad way to develop stimuli-responsive materials in various colloidal nanostructures by changing the microenvironment, appreciating their potential advanced applications in electronic devices, catalysis, stimuli-triggered drug/gene delivery and reactive oxygen species (ROS) scavenger.

Self-Assembled chitosan/phospholipid nanoparticles: from fundamentals to preparation for advanced drug delivery

With the development of nanotechnology, self-assembled chitosan/phospholipid nanoparticles (SACPNs) show great promise in a broad range of applications, including therapy, diagnosis, in suit imaging and on-demand drug delivery. Here, a brief review of the SACPNs is presented, and its critical underlying formation mechanisms are interpreted with an emphasis on the intrinsic physicochemical properties. The state-of-art preparation methods of SACPNs are summarized, with particular descriptions about the classic solvent injection method. Then SACPNs microstructures are characterized, revealing the unique spherical core-shell structure and the drug release mechanisms. Afterwards, a comprehensive and in-depth depiction of their emerging applications, with special attention to drug delivery areas, are categorized and reviewed. Finally, conclusions and outlooks on further advancing the SACPNs toward a more powerful and versatile platform for investigations covering from fundamental understanding to developing multi-functional drug delivery systems are discussed.

Novel Temperature/Reduction Dual-Stimulus Responsive Triblock Copolymer [P(MEO2MA-co- OEGMA)-b-PLLA-SS-PLLA-b-P(MEO2MA-co-OEGMA)] via a Combination of ROP and ATRP: Synthesis, Characterization and Application of Self-Assembled Micelles

Novel temperature/reduction dual stimulus-responsive triblock copolymers, poly [2-(2-methoxyethoxy) ethyl methacrylate-co-oligo (ethylene glycol) methacrylate]-b-(L-polylactic acid)-SS-b-(L-polylactic acid)-b-poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol)methacrylate] [P(MEO₂MA-co-OEGMA)-b-PLLA-SS-PLLA-b-P(MEO₂MA-co-OEGMA)] (SPMO), were synthesized by ring opening polymerization (ROP) of L-lactide and 2,2’-dithio diethanol (SS-DOH), and random copolymerization of MEO₂MA and OEGMA monomers via atom transfer radical polymerization (ATRP) technology. The chemical structures and compositions of the novel copolymers were demonstrated by proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared spectroscopy (FTIR). The molecular weights of the novel copolymers were measured by size exclusive chromatography (SEC) and proved to have a relatively narrow molecular weight distribution coefficient (ÐM ≤ 1.50). The water solubility and transmittance of the novel copolymers were tested via visual observation and UV–Vis spectroscopy, which proved the SPMO had a good hydrophilicity and suitable low critical solution temperature (LCST). The critical micelle concentration (CMC) of the novel polymeric micelles were determined using surface tension method and fluorescent probe technology. The particle size and morphology of the novel polymeric micelles were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The sol–gel transition behavior of the novel copolymers was studied via vial flip experiments. Finally, the hydrophobic anticancer drug doxorubicin (DOX) was used to study the in vitro release behavior of the novel drug-loaded micelles. The results show that the novel polymeric micelles are expected to become a favorable drug carrier. In addition, they exhibit reductive responsiveness to the small molecule reducing agent dithiothreitol (DTT) and temperature responsiveness with temperature changes.

Degradable Polyphosphoramidate via Ring-Opening Metathesis Polymerization

We report the synthesis of a degradable polyphosphoramidate via ring-opening metathesis polymerization (ROMP) with the Grubbs initiator (IMesH2)(C5H5N)2(Cl)2Ru═CHPh. Controlled ROMP of a low ring strain diazaphosphepine-based cyclic olefin was achieved at low temperatures to afford well-defined polymers that readily undergo degradation in acidic conditions via the cleavage of the acid-labile phosphoramidate linkages. The diazaphosphepine monomer was compatible in random and block copolymerizations with phenyl and oligo(ethylene glycol) bearing norbornenes. This approach introduced partial or complete degradability into the polymer backbones. With this chemistry, we accessed amphiphilic poly(diazaphosphepine-norbornene) copolymers that could be used to prepare micellar nanoparticles.

Flower Necklaces of Controllable Length Formed From N-(2-Hydroxypropyl) Methacrylamide-Based Amphiphilic Statistical Copolymers

N-(2-Hydroxypropyl)methacrylamide (HPMA)-based statistical copolymers bearing anticancer drugs have attracted attention for their efficacy in cancer treatments. However, controlling the size and morphology of aggregates of this type of polymer has been challenging and is far from being understood. In this study, small-angle X-ray scattering and asymmetric-flow field-flow fractionation with multiangle light scattering were used to investigate the structure of aggregates formed in aqueous solutions of HPMA-based statistical copolymers of different molecular weights with the model drug pyrene borne in different amounts. The analysis revealed that spherical objects (flower micelles) were formed by the assembly of pyrene moieties in low-molecular-weight copolymers, and the flower micelles connected linearly to form string-of-pearls assemblies (flower necklaces) in high-molecular-weight copolymers. The number of pyrene moieties per polymer chain likely dominates the size and morphology of the copolymer micelles. This study shows how to alter the aggregate structure by changing the molecular weight and composition of copolymers.

Homopolymer self-assembly of poly(propylene sulfone) hydrogels via dynamic noncovalent sulfone-sulfone bonding

Natural biomolecules such as peptides and DNA can dynamically self-organize into diverse hierarchical structures. Mimicry of this homopolymer self-assembly using synthetic systems has remained limited but would be advantageous for the design of adaptive bio/nanomaterials. Here, we report both experiments and simulations on the dynamic network self-assembly and subsequent collapse of the synthetic homopolymer poly(propylene sulfone). The assembly is directed by dynamic noncovalent sulfone–sulfone bonds that are susceptible to solvent polarity. The hydration history, specified by the stepwise increase in water ratio within lower polarity water-miscible solvents like dimethylsulfoxide, controls the homopolymer assembly into crystalline frameworks or uniform nanostructured hydrogels of spherical, vesicular, or cylindrical morphologies. These electrostatic hydrogels have a high affinity for a wide range of organic solutes, achieving >95% encapsulation efficiency for hydrophilic small molecules and biologics. This system validates sulfone–sulfone bonding for dynamic self-assembly, presenting a robust platform for controllable gelation, nanofabrication, and molecular encapsulation.

Natural biomolecules such as peptides and DNA can dynamically self-organize into diverse hierarchical structures. Here the authors report experiments and simulations on the dynamic network self-assembly and subsequent collapse of the synthetic homopolymer poly(propylene sulfone).

Synthesis of Amphiphilic Statistical Copolymers Bearing Methoxyethyl and Phosphorylcholine Groups and Their Self-Association Behavior in Water

Biocompatible amphiphilic statistical copolymers P(MEA/MPCm) composed of 2-methoxyethyl acrylate (MEA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) were prepared with three different mol% of the hydrophilic unit MPC (m = 6, 12 and 46 mol%). The monomer reactivity ratios of MEA (rMEA) and MPC (rMPC) were 0.53 and 2.21, respectively. The rMEA × rMPC value of 1.17 demonstrated that statistical copolymerization was successful. P(MEA/MPC12) and P(MEA/MPC46) copolymers did not undergo aggregation in water, whereas the P(MEA/MPC6) copolymer formed micelles in water with a hydrodynamic radius (Rh) of 96.9 nm and a critical aggregation concentration, which was determined using pyrene fluorescence, at 0.0082 g/L. The restricted motion of the protons in the hydrophobic MEA units in the micelles' cores provided additional evidence of self-association in P(MEA/MPC6).

The effect of macromolecular structure on the rheology and surface properties of amphiphilic random polystyrene-r-poly(meth)acrylate copolymers prepared by RDRP

In this work rheological and surface properties of various random copolymers of styrene and sodium (meth)acrylate, prepared using reversible deactivation radical polymerization (RDRP), were studied. It is shown that the properties of these polymers in water solution, relevant for several applications, are affected by their chemical structure and molecular weight. Cryo-TEM images of their concentrated water solutions do not show the presence of nano-objects as micelles, however the existence of some aggregates seems to be confirmed by fluorescence measurements using pyrene as a hydrophobic probe and by surface tension measurements. Moreover, interesting results are displayed about the viscosity as well as the surface tension of these water polymer solutions, due probably to different interactions at the molecular level as suggested by fluorescence measurements.

Folded amphiphilic homopolymer micelles in water: uniform self-assembly beyond amphiphilic random copolymers

Herein, we developed precision self-assembly systems of amphiphilic homopolymers into folded micelles in water.

Cellular Uptake Evaluation of Amphiphilic Polymer Assemblies: Importance of Interplay between Pharmacological and Genetic Approaches

Understanding the cellular uptake mechanism of materials is of fundamental importance that would be beneficial for materials design with enhanced biological functions. Herein, we report the interplay of pharmacological and genetic approaches to minimize the possible misinterpretation on cellular uptake mechanism. A library of amphiphilic polymers was used as a model system to evaluate the reliability of such methodological interplay. To probe the cellular uptake of amphiphilic polymers, we utilized an orthogonal end-group labeling strategy to conjugate one fluorescent molecule on each polymer chain. The results from the methodological interplay with these labeled polymers revealed the off-target effects of dynasore, a well-known dynamin inhibitor. Instead of dynamin, actin was found to be an essential cellular component during the cellular uptake of these amphiphilic polymers. Our study demonstrates the importance of interplaying pharmacological and genetic approaches when evaluating the endocytic mechanism of functional materials, providing insights on understanding the cellular uptake of future therapeutic materials.

Synergy, competition, and the "hanging" polymer layer: Interactions between a neutral amphiphilic 'tardigrade' comb co-polymer with an anionic surfactant at the air-water interface

Understanding the structure of polymer/surfactant mixtures at the air-water interface is of fundamental importance and also of relevance to a variety of practical applications. Here, the complexation between a neutral 'tardigrade' comb co-polymer (consisting of a hydrophilic polyethylene glycol backbone with hydrophobic polyvinyl acetate grafts, PEG-g-PVAc) with an anionic surfactant (sodium dodecyl sulfate, SDS) at the air-water interface has been studied. Contrast-matched neutron reflectivity (NR) complemented by surface tension measurements allowed elucidation of the interfacial composition and structure of these mixed systems, as well as providing physical insights into the polymer/surfactant interactions at the air-water interface. For both polymer concentrations studied, below and above its critical aggregation concentration, cac, (0.2 cac and 2 cac, corresponding to 0.0002 wt% or 0.013 mM and 0.002 wt% or 0.13 mM respectively), we observed a synergistic cooperative behaviour at low surfactant concentrations with a 1-2 nm mixed interfacial layer; a competitive adsorption behaviour at higher surfactant concentrations was observed where the polymer was depleted from the air-water interface, with an overall interfacial layer thickness ~1.6 nm independent of the polymer concentration. The weakly associated polymer layer "hanging" proximally to the interface, however, played a role in enhancing foam stability, thus was relevant to the detergency efficacy in such polymer/surfactant mixtures in industrial formulations.

Mechanistic Insights into Statistical Co-Assembly of Metal Complexes

Statistical copolymerization plays a key role in many biological and technological processes; however, mechanistic understanding of the formation of analogous supramolecular counterparts remains limited. Herein, we report detailed insights into the supramolecular co-assembly of two π-conjugated PdII and PtII complexes, which in isolation self-assemble into flexible fibers and nanodisks, respectively. An efficient single-step co-assembly into only one type of nanostructure (fibers or nanodisks) takes place if any of the components is in excess. In contrast, equimolar mixtures lead to PdII -rich fiber-like co-assemblies by a statistical co-nucleation event along with a residual amount of self-sorted nanodisks in a stepwise manner.

Orthogonal Folding of Amphiphilic/Fluorous Random Block Copolymers for Double and Multicompartment Micelles in Water

Here, we report orthogonal folding and self-assembly systems of amphiphilic/fluorous random block copolymers for double core and multicompartment micelles in water. For this, we developed the precision folding techniques of polymer chains via the selective self-assembly of the pendant groups. Typically, A/C-B/C random block copolymers were designed: Hydrophobic dodecyl groups (A) and fluorous fluorinated octyl groups (B) were introduced into the respective blocks, while hydrophilic poly(ethylene glycol) chains (C) were randomly incorporated into all the segments. By controlling the chain length and composition of the respective blocks, the copolymers induce orthogonal single-chain folding in water to form double-compartment micelles comprising hydrophobic and fluorous cores. The copolymers were site-selectively folded in a fluoroalcohol to result in tadpole unimer micelles comprising a hydrophobic A/C unimer micelle and an unfolded fluorous B/C chain. Additionally, asymmetric A/C-B/C random block copolymers with short and highly hydrophobic or fluorous segments were effective for multicompartment micelles in water.

Surface Segregation of Amphiphilic PDMS-Based Films Containing Terpolymers with Siloxane, Fluorinated and Ethoxylated Side Chains

(Meth)acrylic terpolymers carrying siloxane (Si), fluoroalkyl (F) and ethoxylated (EG) side chains were synthesized with comparable molar compositions and different lengths of the Si and EG side chains, while the length of the fluorinated side chain was kept constant. Such terpolymers were used as surface-active modifiers of polydimethylsiloxane (PDMS)-based films with a loading of 4 wt%. The surface chemical compositions of both the films and the pristine terpolymers were determined by angle-resolved X-ray photoelectron spectroscopy (AR-XPS) at different photoemission angles. The terpolymer was effectively segregated to the polymer−air interface of the films independent of the length of the constituent side chains. However, the specific details of the film surface modification depended upon the chemical structure of the terpolymer itself. The exceptionally high enrichment in F chains at the surface caused the accumulation of EG chains at the surface as well. The response of the films to the water environment was also proven to strictly depend on the type of terpolymer contained. While terpolymers with shorter EG chains appeared not to be affected by immersion in water for seven days, those containing longer EG chains underwent a massive surface reconstruction.

Polymeric nanoparticles-based multi-functional coatings on NiTi alloy with nickel ion release control, cytocompatibility, and antibacterial performance

Photo-cross-linked quaternized copolymer coatings on NiTi alloy show prominent inhibition of nickel ion release and antibacterial properties.

Self-assembly of amphiphilic block pendant polymers as microphase separation materials and folded flower micelles

Herein, we created amphiphilic polymers bearing hydrophilic/hydrophobic block pendants as a new class of self-assembled materials for microphase separation in the solid state and folded flower micelles in water.