Amphiphilic diblock star polymer catalysts via atom transfer radical polymerization

Diblock brush-arm star copolymers via a core-first/graft-from approach using γ-cyclodextrin and ROMP: a modular platform for drug delivery

Water-soluble diblock brush-arm star copolymers using γ-CD-based core-first ring-opening metathesis polymerization, allowing for anticancer drug delivery via host–guest interaction.

Comb-shaped, temperature-tunable and water-soluble porphyrin-based thermoresponsive copolymer for enhanced photodynamic therapy

A novel comb-shaped porphyrin end-functionalized poly(N-isopropylacrylamide)-b-poly[oligo (ethylene glycol methyl ether methacrylate)] (Por-PNIPAM-b-POEGMA) was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Due to the incorporation of hydrophilic POEGMA contents, the copolymer shows the lower critical solution temperatures (LCST) of 37-41.8°C higher than PNIPAM. Moreover, this copolymer showed efficient singlet oxygen under light irradiation at 650nm, and the productivity of singlet oxygen was 0.59, which could be used for photodynamic therapy. In addition, the in vitro study indicated that this copolymer showed no significant dark cytotoxicity, while showed apparent photo-toxicity toward HeLa cancer cells under red light irradiation at 650nm. MTT results indicated that this copolymer with appropriate LCST could be accumulated on locally tumor tissues and killing of cancer cells (Hela), which may be a promising photosensitizer in photodynamic therapy for cancer treatment.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

PNIPAM-based heteroarm star-graft quarterpolymers: synthesis, characterization and pH-dependent thermoresponsiveness in aqueous media

We report the design of PS_n(P2VP-b-PAA-g-PNIPAM)_n heteroarm star-graft quarterpolymers, the thermoresponsiveness of which is strongly dependent on pH ionic strength, and their macromolecular features, e.g. arm number and grafting density.

Metallo-Folded Single-Chain Nanoparticles with Catalytic Selectivity

Mimicking the substrate specificity and catalytic activity of enzymes is of great interest for different fields (e.g., chemistry, biology, nanomedicine). Enhanced reaction rates using artificial, enzyme-mimic catalysts based on a variety of molecular structures and nanoentities (e.g., macrocyclic compounds, star and helical polymers, dendrimers) have been previously reported. However, examples of enzyme-sized soft entities displaying substrate specificity are certainly scarce. Herein, we report the synthesis and characterization of single-chain nanoparticles based on metallo-folded polymer chains containing complexed Cu(II) ions showing catalytic specificity during the oxidative coupling of mixtures of chemically related terminal acetylene substrates. This work paves the way for the easy and efficient construction of other Pd-, Ni-, Co-, Fe-, Mn-, or Mo-containing soft nanoentities approaching the substrate specificity of natural enzymes for a variety of organic reactions.

Fluorescent bowl-shaped nanoparticles from ‘clicked’ porphyrin–polymer conjugates

We report the synthesis and post-synthetic modification of a library of hydrophilic and hydrophobic ‘clicked’ triazole-linked porphyrin–polymer conjugates (PPCs), and their subsequent assembly into fluorescent bowl-shaped nanoparticles.

Star block-copolymers: enzyme-inspired catalysts for oxidation of alcohols in water

We describe a family of star block-copolymers rationally designed for enzyme-inspired catalysis of alcohol oxidation in water.

Development of star polymers as unimolecular containers for nanomaterials

Star polymers containing one central core surrounded by multiple radiating arms represent an intriguing type of globular platform to be used as unimolecular containers and reactors. The core domain can encapsulate guest "cargos", whereas protective shell and chain ends can be functionalized with reactive groups and ligands. This Feature Article highlights the recent development on using core-shell structured amphiphilic star polymers as unimolecular containers for applications in drug delivery, catalysis, and template of hybrid nanomaterials. As compared with dendrimers, star polymers enjoy advantages of facile synthesis, flexible compositions, and tunable sizes, which allow them being able to carry more and multiple "cargos" within one molecule.

RAFT Synthesis and Self-Assembly of Free-Base Porphyrin Cored Star Polymers

Reversible addition fragmentation chain transfer (RAFT) synthesis and self-assembly of free-base porphyrin cored star polymers are reported. The polymerization, in the presence of a free-base porphyrin cored chain transfer agent (CTA-FBP), produced porphyrin star polymers with controlled molecular weights and narrow polydispersities for a number of monomers includingN,N-dimethylacrylamide (DMA) and styrene (St). Well-defined amphiphilic star block copolymers, P-(PS-PDMA)4and P-(PDMA-PS)4(P: porphyrin), were also prepared and used for self-assembly studies. In methanol, a selective solvent for PDMA, spherical micelles were observed for both block copolymers as characterized by TEM. UV-vis studies suggested star-like micelles were formed from P-(PS-PDMA)4, while P-(PDMA-PS)4aggregated into flower-like micelles. Spectrophotometric titrations indicated that the optical response of these two micelles to external ions was a function of micellar structures. These structure-related properties will be used for micelle studies and functional material development in the future.

Dendritic phosphorescent probes for oxygen imaging in biological systems

Oxygen levels in biological systems can be measured by the phosphorescence quenching method using probes with controllable quenching parameters and defined biodistributions. We describe a general approach to the construction of phosphorescent nanosensors with tunable spectral characteristics, variable degrees of quenching, and a high selectivity for oxygen. The probes are based on bright phosphorescent Pt and Pd complexes of porphyrins and symmetrically pi-extended porphyrins (tetrabenzoporphyrins and tetranaphthoporphyrins). pi-Extension of the core macrocycle allows tuning of the spectral parameters of the probes in order to meet the requirements of a particular imaging application (e.g., oxygen tomography versus planar microscopic imaging). Metalloporphyrins are encapsulated into poly(arylglycine) dendrimers, which fold in aqueous environments and create diffusion barriers for oxygen, making it possible to regulate the sensitivity and the dynamic range of the method. The periphery of the dendrimers is modified with poly(ethylene glycol) residues, which enhance the probe's solubility, diminish toxicity, and help prevent interactions of the probes with the biological environment. The probe's parameters were measured under physiological conditions and shown to be unaffected by the presence of biomacromolecules. The performance of the probes was demonstrated in applications, including in vivo microscopy of vascular pO(2) in the rat brain.