Molecular Catalysis: Development for Better Catalysts
Catalysis has been the forefront of chemical industry for century. The development of better, faster, controllable and robust catalysts is an endless task leading to safer, greener, cheaper, and more reliable processes. The catalyst development is crucial for materials design allowing a preparation of materials with novel properties. Our research focuses on the development of homogeneous catalysts for industrially important polymers and chemicals using molecular design of the catalysts that allows a precise control of polymer architecture and reaction mechanism.
Due to the biodegradable and renewable properties, biodegradable polymers such as polylactide, poly(ε-caprolactone), poly(hydroxy- alkanoate) are of great interests in pharmaceutical industries. The idea of homogeneous single-site catalysis is being exploited in our research group that allows precise control of the polymerization. With the right ligand design, we can synthesize materials with controlled and predictable microstructures and perhaps properties and functions.
Oligomer Building Blocks
Starting from the monomers such as lactide and ε-caprolactone, very simple but valuable molecules such as alkyl lactate and alkyl lactyllactate can be synthesized. These compounds are often used as high-boiling green solvents, biocompatible plasticizers, and flavorings. The previous synthesis requires high temperature and days of work-up. We have discovered a catalyst system that allows the quantitative synthesis in just 5 min at room temperature using group I and II metal amides. Their applications as biodegradable plasticizers are of great importance.
Biodegradable Polymeric Materials
The physical properties of the materials can be adjusted by changing the topologies of the polymers such as star, graft, cross-linked, and hyperbranched structures. Cyclic biodegradable polymers, on the other hand, are not well studied due to synthetic limitation. However, we have now developed novel tin(II) catalyst systems that can effectively polymerize lactide and lactone giving cyclic polymers in high yield. More effective catalyst systems are being developed to expand the library of cyclic polymers having unique properties. In addition, systematic modifications of the catalyst structures are possible leading to insight information of the catalytic cycles.
Applications as Anti-cancer Drug Delivery System
Cyclic polyesters used in drug delivery system were shown to have longer blood circulation times than their linear analog, which may lead to a controlled release of medicines and better treatment of symptoms. With this in mind, anti-cancer drug-polymer conjugate are being designed. Armed with the catalyst design capability, functionalized cyclic polymers can be synthesized. With different drug loading, various drug formula is now possible. The cyclic structure of the polymer backbone is believed to facilitate prolonged circulation in the blood system. Effective chemotherapeutic drug delivery depends on a balance between elimination of the polymeric drug from blood steam by the kidneys, liver, and other organs and extravasation of the drug into the cancer cells. The key to control these factors lies in the understanding of polymer architecture including the effect of size, flexibility, and in vivo molecular conformation.
Fluorescene micrograph of HepG2 cells incubated for 12 h with DOX-conjugated polymer.
PCL-g-PEG/DOX brush polymer