Yunqing Zhu

Sustainable polymers from renewable resources

Renewable resources are used increasingly in the production of polymers. In particular, monomers such as carbon dioxide, terpenes, vegetable oils and carbohydrates can be used as feedstocks for the manufacture of a variety of sustainable materials and products, including elastomers, plastics, hydrogels, flexible electronics, resins, engineering polymers and composites. Efficient catalysis is required to produce monomers, to facilitate selective polymerizations and to enable recycling or upcycling of waste materials. There are opportunities to use such sustainable polymers in both high-value areas and in basic applications such as packaging. Life-cycle assessment can be used to quantify the environmental benefits of sustainable polymers.

Di-magnesium and zinc catalysts for the copolymerization of phthalic anhydride and cyclohexene oxide

Two new homogeneous dinuclear catalysts for the ring-opening copolymerization of phthalic anhydride (PA)/cyclohexene oxide (CHO) and the terpolymerization of phthalic anhydride (PA)/cyclohexene oxide (CHO)/carbon dioxide (CO2) are reported. The catalysts are a di-magnesium (1) and a di-zinc complex (2), both are coordinated by the same macrocyclic ancillary ligand. Both catalysts show good polymerization control and activity (TOF = 97 (1) and 24 (2) h−1), with the di-magnesium complex (1) being approximately four times faster compared to the di-zinc (2) analogue. Their relative reactivity is closely related to that observed for well documented chromium salen/porphyrin catalysts. However, these results represent the first example of a well-defined magnesium catalyst which may be advantageous in terms of obviating use of co-catalysts, low cost, lack of colour and redox chemistry.

Chemoselective Polymerizations from Mixtures of Epoxide, Lactone, Anhydride, and Carbon Dioxide

Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymerization (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides, and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers-ε-caprolactone, cyclohexene oxide, phthalic anhydride, and carbon dioxide-are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity, resulting in block sequence control and predictable compositions (esters and carbonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically controlled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.

Selective Polymerization Catalysis: Controlling the Metal Chain End Group to Prepare Block Copolyesters

Selective catalysis is used to prepare block copolyesters by combining ring-opening polymerization of lactones and ring-opening copolymerization of epoxides/anhydrides. By using a dizinc complex with mixtures of up to three different monomers and controlling the chemistry of the Zn-O(polymer chain) it is possible to select for a particular polymerization route and thereby control the composition of block copolyesters.

Antibacterial vesicles by direct dissolution of a block copolymer in water

A novel thermo- and pH-responsive antimicrobial diblock copolymer has been synthesized and directly dissolved in water to form polymer vesicles upon simply raising the temperature. Compared to individual polymer chains, polymer vesicles exhibit much better antimicrobial efficacy against both Gram-negative and Gram-positive bacteria under physiological conditions with neither quaternary ammonium moieties nor the loading of any external antibiotics as a result of their increased local concentration of cationic charge.

How does a tiny terminal alkynyl end group drive fully hydrophilic homopolymers to self-assemble into multicompartment vesicles and flower-like complex particles?

It is a theoretical and technical challenge to construct well-defined nanostructures such as vesicles from fully hydrophilic homopolymers in pure water. In this paper, we incorporate one terminal alkynyl group into a fully hydrophilic linear or non-linear homopolymer to drive its unusual self-assembly in aqueous solution to form multicompartment vesicles, spherical compound micelles, flower-like complex particles, etc., which have been confirmed by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic/static light scattering (DLS/SLS) and drug encapsulation experiments. The formation of poly(N-isopropyl acrylamide) (NIPAM) and poly[oligo(ethylene glycol) methacrylate] (POEGMA475) self-assemblies is mainly determined by the terminal alkynyl group itself (typically 1–3 wt%) while it is independent of other factors such as traditional hydrophobic–hydrophilic balance. Moreover, upon increasing the chain length of PNIPAM homopolymers, multicompartment vesicles, spherical micelles, and large flower-like complex particles can be obtained during the self-assembly process. In contrast, smaller micelles were formed when the kind of terminal alkynyl group attached to the PNIPAM chain was changed from a propargyl isobutyrate group to a (di)propargyl 2-methylpropionamide group. Particularly, a long chain hyperbranched structure with lots of terminal alkynyl groups induces the formation of vesicles. Also, the encapsulation experiment of doxorubicin hydrochloride was employed to further distinguish vesicular and micellar nanostructures. Additionally, the terminal alkynyl group-driven self-assembly has been applied to hydrophilic POEGMA475 homopolymers to afford similar nanostructures to PNIPAM homopolymers such as multicompartment vesicles and spherical compound micelles. Our study has opened up a new way to prepare hydrophilic homopolymer self-assemblies with tunable morphology.

Template-free fabrication of nitrogen-doped hollow carbon spheres for high-performance supercapacitors based on a scalable homopolymer vesicle

Presented in this article is the template-free fabrication of nitrogen-doped hollow carbon spheres (N-HCSs) as electrode materials for high-performance supercapacitors based on scalable homopolymer vesicles, which are self-assembled from an amphiphilic homopolymer, poly(amic acid) (PAA). This homopolymer can be massively produced by simple stepwise polymerization at room temperature with a fast polymerization rate. For the first time, PAA homopolymer vesicles are carbonized to form N-HCSs with tunable porous structures and nitrogen contents (from 1.3% to 7.4%) by controlling the content of the cross-linker (melamine). This template-free method for fabricating N-HCSs is more environmentally friendly and does not involve tedious synthetic procedures compared to traditional template-based methods. More importantly, the N-HCSs exhibit excellent electrochemical performance with a very high specific capacitance (266.9 F g−1) after more than 1000 cycles when used as the active electrode material for the supercapacitor. The N-HCSs presented in this paper retain its specific capacitance as high as 84% at a very high current density (20 A g−1). Given the potential massive production and excellent electrochemical properties, the N-HCSs based on the carbonization of scalable PAA homopolymer vesicles are promising candidate electrode materials for energy storage devices.

Enzyme activated photodynamic therapy for methicillin-resistant Staphylococcus aureus infection both inv itro and in vivo.

In recent years, methicillin-resistant Staphylococcus aureus (MRSA) has become one of the most common multi-drug resistant bacteria in both hospital and community. The aim of this study is to investigate the selective inhibition of MRSA by a modified photosensitizer (LAEtNBS) in vitro and the efficacy of MRSA infection treatment by photodynamic therapy (PDT) with LAEtNBS in vivo. LAEtNBS was synthesized by adding a cationic photosensitizer molecule (EtNBS-COOH) and a quencher molecule to two side chains of cephalosporin, which was then shown to have similar absorption and emission wavelengths with EtNBS-COOH, but suppressed yields of fluorescence quantum and singlet oxygen. The selective inactivation and less phototoxicity of LAEtNBS, compared to that of EtNBS-COOH, were assessed and confirmed by conducting PDT to two Staphylococcus aureus strains and human skin cells at a fluence of 15 J/cm(2) with 640±10 nm LED light. Furthermore, using mouse skin wound model infected with 10(8) CFU of MRSA, we found that both LAEtNBS and EtNBS-COOH were able to treat MRSA infection and enhance wound repair. However, there was no significant difference in the two photosensitizers that might be due to the environment in vivo. Modification of the photosensitizer will be very beneficial for developing new strategies to treat drug resistant bacterial infection with less harm to host tissue.