Synthesis and Self-Assembly of Thermoresponsive Biohybrid Graft Copolymers Based on a Combination of Passerini Multicomponent Reaction and Molecular Recognition

Amphiphilic graft copolymers exhibit fascinating self-assembly behaviors. Their molecular architectures significantly affect the morphology and functionality of the self-assemblies. Considering the potential application of amphiphilic graft copolymers in the fabrication of nanocarriers, it is essential to synthesize well-defined graft copolymers with desired functional groups. Herein, the Passerini reaction and molecular recognition are introduced to the synthesis of functional thermoresponsive graft copolymers. A bifunctional monomer 2-((adamantan-1-yl)amino)-1-(4-((2-bromo-2-methylpropanoyl)oxy)phenyl)-2-oxoethyl methacrylate (ABMA) with a bromo group for atom transfer radical polymerization (ATRP) and an adamantyl group for molecular recognition is synthesized through the Passerini reaction. The graft copolymers are prepared by reversible addition-fragmentation transfer (RAFT) copolymerization of ABMA and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) followed by RAFT end group removal and ATRP of di(ethylene glycol)methyl ether methacrylate (DEGMA) initiated by the ABMA units. The graft copolymer P(OEGMA-co-ABMA)-g-PDEGMA can be functionalized with β-cyclodextrin modified peptides, affording a thermoresponsive biohybrid graft copolymer. At a temperature above its lower critical solution temperature, the biohybrid graft copolymer self-assembles into peptide-modified polymersomes.

Amphiphilic hyperbranched polymers: synthesis, characterization and self-assembly performance

Abstract

A series of amphiphilic hyperbranched polymers (AHP-s, the “s” refers to the algebra of AHP) were synthesized by the reaction between hydroxyl-terminated hyperbranched polymers (HBP-s, the “s” refers to the algebra of HBP) and palmitoyl chloride. FTIR, NMR and GPC were used to determine the structure of AHP-s, the results showed that AHP-s exhibits core-shell structure. The thermal properties of polymers were investigated by DSC and TGA. It was found that AHP-2, AHP-3 and AHP-4 display higher thermal stability than AHP-1 (AHP-1, AHP-2, AHP-3 and AHP-4 represent the first, second, third and fourth generation AHP, respectively). Furthermore, the self-assembly performance of AHP-s in THF solvent was investigated by TEM and SEM. Finally, the encapsulation capacity of the AHP-s for methyl orange (MO) was explored at different concentrations of AHP-s and pH conditions. It was found that AHP-s is capable of accommodating hydrophilic guest MO. Moreover, the higher generation of AHP-s, the stronger encapsulation capacity obtained. And the encapsulation capacity closely associated with the pH of encapsulation system.

Graphical abstract

Predicting the role of seed morphology in the evolution of anisotropic nanocatalysts

Controlling the structure of nanocrystals is an effective way to tune their properties and improve performance in a wide variety of applications. However, the atomic pathways for achieving this goal are difficult to identify and exercise, due to competing kinetic and thermodynamic influences during formation. In particular, an understanding of how symmetry, and symmetry breaking, determine nanocrystal morphology would significantly advance our ability to produce nanomaterials with prescribed functions. In this study we present results of a detailed computational study into the atomic structure of platinum nanoparticles at early growth stages of formation, as a function of temperature and atomic deposition rates. We investigate the impact of different types of crystalline seeds and characterize the emergent structures via simulated High Resolution Transmission Electron Microscopy (HRTEM) images. We find that the choice of initial seed is an important driver for symmetry breaking, due to a combination of atomic deposition and etching on different seed facets. A mix of low index facets causes the formation of important surface defects, in addition to the absorption/adsorption of single atoms, which can be correlated with different catalytic reactions as the process perpetuates. These findings provide new insights into nanocrystal shape-control mechanisms and suggest new opportunities for future design of this important class of nanomaterials.

Star-shaped and star-block polymers with a porphyrin core: from LCST–UCST thermoresponsive transition to tunable self-assembly behaviour and fluorescence performance

The micelles self-assembled from star-shaped and star-block copolymers present a transition of LCST–UCST thermoresponsive properties through a facile quaternization reaction.

Morphological Control of Anisotropic Self-Assemblies from Alternating Poly(p-dioxanone)-poly(ethylene glycol) Multiblock Copolymer Depending on the Combination Effect of Crystallization and Micellization

A novel and facile method was developed for morphological controlling of self-assemblies prepared by crystallization induced self-assembly of crystalline-coil copolymer depending on the combination effect of crystallization and micellization. The morphological evolution of the self-assemblies of alternating poly(p-dioxanone)-block-poly(ethylene glycol) (PPDO-PEG) multiblock copolymer prepared by different solvent mixing methods in aqueous solution were investigated. "Chrysanthemum"-like and "star anise"-like self-assemblies were obtained at different rates of solvent mixing. The results suggested gradually change in solvent quality (slowly dropping water into DMF solution) leaded to a hierarchical micellization-crystallization process of core-forming PPDO blocks, and flake-like particles were formed at the initial stage of crystallization. Meanwhile, crystallization induced micellization process occurred when solvent quality changed drastically. Shuttle-like particles, which have much smaller size than those of flake-like particles, were formed at the initial stage of crystallization when quickly injecting water into DMF solution of the copolymer. Therefore, owing to the different changing rate of solvent quality, which may result in different combination effect of crystallization and micellization during self-assembly of the copolymer, PPDO-PEG self-assemblies with different hierarchical morphology in nano scale could be obtained.

Direct Aqueous Self-Assembly of an Amphiphilic Diblock Copolymer toward Multistimuli-Responsive Fluorescent Anisotropic Micelles

It is extremely important for emerging applications and still enormously challenging to develop multifunctional stimuli-responsive anisotropic polymeric micelles with integration of potentially targeted therapeutic and diagnostic function. Herein, we report a first example of fluorescent anisotropic micelles (FAMs) with Fe(3+), DTT, H2O2, and thermal responsive fluorescence and morphology. FAMs from direct aqueous self-assembly of amphiphilic diblock copolymer showed reversible "switch off/on" of aqua fluorescent emission and controllable structural change by sequential addition of Fe(3+) and DTT. In addition, the FAMs had reversible dual-thermal responsiveness of fluorescence and morphology. This micelle could serve as a promising candidate for all-in-one application of quantitative detecting, imaging, drug delivery, and targeted release.

Facile synthesis and characterization of novel biodegradable amphiphilic block copolymers bearing pendant hydroxyl groups

Novel amphiphilic block copolymers bearing pendant hydroxyl groups polylactide-b-poly(3,3-bis(Hydroxymethyl-triazolylmethyl) oxetane)-b-polylactide (PLA-b-PHMTYO-b-PLA) were synthesized via a facile and efficient method. First, the block copolymer intermediates polylactide-b-poly(3,3-Diazidomethyloxetane)-b-polylactide (PLA-b-PBAMO-b-PLA) were synthesized through ring-opening polymerization of lactide using PBAMO as a macroinitiator. Following "Click" reaction of PLA-b-PBAMO-b-PLA with propargyl alcohol provided the targeted amphiphilic block copolymers PLA-b-PHMTYO-b-PLA with pendant hydroxyl groups. The composition and structure of prepared copolymers were characterized by (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy, Fourier transform infrared (FT-IR) and gel permeation chromatography (GPC). The self-assembly behavior of the copolymers in water was investigated by transmission electron microscope (TEM), dynamic light scattering (DLS) and static light scattering (SLS). The results showed that the novel copolymers PLA-b-PHMTYO-b-PLA self-assembled into spherical micelles with diameters ranging from 100 nm to 200 nm in aqueous solution. These copolymers also exhibited low critical micellar concentrations (CMC: 6.9 × 10(-4)mg/mL and 3.9 × 10(-5)mg/mL, respectively). In addition, the in vitro cytotoxicity of these copolymers was determined in the presence of L929 cells. The results showed that the block copolymers PLA-b-PHMTYO-b-PLA exhibited better biocompatibility. Therefore, these well-defined copolymers are expected to find some applications in drug delivery or tissue engineering.

Nanofibers with very fine core-shell morphology from anisotropic micelle of amphiphilic crystalline-coil block copolymer

A novel and facile strategy, combining anisotropic micellization of amphiphilic crystalline-coil copolymer in water and reassembly during single spinneret electrospinning, was developed for preparing nanofibers with very fine core-shell structure. Polyvinyl alcohol (PVA) and polyethylene glycol-block-poly(p-dioxanone) (PEG-b-PPDO) were used as the shell and the crystallizable core layer, respectively. The core-shell structure could be controllably produced by altering concentration of PEG-b-PPDO, and the chain length of the PPDO block. The morphology of the nanofibers was investigated by Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). X-ray rocking curve measurements were performed to investigate the degree of ordered alignment of the PPDO crystalline lamellae in the nanofiber. The results suggested that the morphology of nanoparticles in spinning solution plays very important role in determining the phase separation of nanofibers. The amphiphilic PEG-b-PPDO copolymer self-assembled into star anise nanoaggregates in water solution induced by the crystallization of PPDO blocks. When incorporated with PVA, the interaction between PVA and PEG-b-PPDO caused a morphological transition of the nanoaggregates from star anise to small flake. For flake-like particles, their flat surface is in favor of compact stacking of PPDO crystalline lamellae and interfusion of amorphous PPDO in the core of nanofibers, leading to a relatively ordered alignment of PPDO crystalline lamellae and well-defined core-shell phase separation. However, for star anise-like nanoaggregates, their multibranched morphology may inevitably prohibit the compact interfusion of PPDO phase, resulting in a random microphase separation.