Dr Kei Saito
Green chemistry is an academic field in chemistry that is concerned with the design of safe processes and products. Our projects will focus on developing new synthesis and production methods for novel sustainable/environment benign materials based on the principles of green chemistry by understanding naturally occurring mechanisms that can be extrapolated to synthetic systems using polymer, supramolecular, catalyst, and nano chemistry.
1. Green Polymerization in Water
Controlled Polymerization to Form Engineering Plastics in Water. One of the critical factors in realizing a green chemical reaction process involves the choice of water, one of the greenest solvent, as the reaction solvent. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), an important engineering plastic for electric household and automotive parts, has been produced by the oxidative polymerization of 2,6-dimethylphenol. This polymerization proceeds at room temperature, and it is an ideal atom economical reaction that does not require any leaving groups for producing the polymer. However, the polymerization is carried out using an organic solvent like toluene and benzene under oxygen. Therefore, both a solvent recovery process and an anti-explosive reactor are needed for industrial production. The use of water as the solvent for the oxidative polymerization to form PPO is the desired approach from a green chemical process.1 On the other hand, nature provides a molecular weight controlled and regioselected polymer under air at room temperature in water using an enzymatic polymerization. We believe using water is the key not only for the green chemical process but also to controlling the molecular weight and the regioselectivity of the polymer.
From a green chemistry approach, this project will investigate a novel molecular weight and regioselectivity controlled polymerization to form PPO in water with a biomimic catalyst. This project will involve aspect of organic synthesis (biomimic catalysts synthesis from a series of tyrosinase model dinuclear copper catalyst), polymer synthesis (finding the condition that could form the PPO in water), and polymer characterization techniques.
2. Lignin Degradation and its Biomass Application
Depolymerization and Repolymerization of Lignin using Redistribution Mechanism Lignin, which composes 30 % of wood tissue, is produced by the oxidative polymerization of phenol derivatives (coniferyl alcohol) catalyzed by laccase, an enzyme in nature. Lignin is known as a stable and insoluble polymer and the disposal and recycle of lignin has been a big resolved issue for the paper industry.
Poly(2,6-dimethyl-1,4-phenylene oxide) has been depolymerized using quinone ketal redistribution mechanism.2 It can depolymerize by mixing the polymer with 2,6-dimethylphenol monomer. The formed oligomer could repolymerize using oxidative polymerization. Lignin has a same poly(phenyleneoxide) backbone in there network and we would like to extent this method to Lignin. The formed lignin oligomer will polymerize to form a biomass plastic. The aim of this project is to depolymerize lignin in water using redistribution mechanism to investigate a new recycle system for lignin. Depolymerization of lignin to a repolymerization has an apparent great advantage as a sustainable technology in the development of green chemistry.
3. Developing a Novel Polymer Recycling System
Solid-Crystalline Photoreversible Polymerization Thymine, one of the nucleic bases in DNA, features both the ability to form relatively strong hydrogen bonds as well as the ability to photocrosslink. Photocrosslinking of thymine occurs when irradiated > 270 nm UV. Crosslinking is reversed either by irradiation at < 249 nm UV or enzymatically. By using these mechanisms, thymine functionalized monomer can be photopolymerized and photodepolymerized. We will study the formation of crystals from alkyl bis-thymine derivatives and their solid state photopolymerization (topochemical polymerization3) and photodepolymerization.
This project will provide novel polymerization methods and also a novel polymer recycling method using the principles of green chemistry. Honours project in this area will involve the synthesis of bis-thymine derivatives synthesis and its characterization in crystalline state.
4. Bioinspired Nano Micelles for Biotechnology Application
Stability Controlled Nano Polymer Micelles and Its Capsulated Chemical Control Release Bioinspired mechanisms are being used to create alternatives materials using the principles of green chemistry. Thymine, one of the nucleic bases in DNA, features both the ability to form relatively strong hydrogen bonds as well as the ability to photocrosslink. Deriving inspiration from this biological mechanism, novel nano materials, core-bound micelles from poly(vinylbenzyl-thymine)-b-poly(styrene sulfonic acid sodium salt) based on the hydrogen bonding and photocrosslinking of polymeric thymines have been created.4
In this project, the research will extend to the study of reversible core-photocrosslinked micelle and its capsulated chemical control release for medical drug delivery system. Photocrosslinking of thymine inside the micelles is known that it can be reversed either by exposure to lower wavelength UV irradiation or enzymatically. Micelles from thymine functionalized block copolymers have the potential to encapsulate guest materials by hydrogen bonding with the attached thymine in the core. This project will involve aspect of polymer synthesis and nano material characterization techniques.
1. K. Saito, T. Tago, T. Masuyama, H. Nishide, Angew. Chem. Int. Ed, 2004, 43, 730-733.
2. K. Saito, T. Masuyama, K. Oyaizu, H. Nishide, Chem.Eur. J. 2003, 9, 4240-4246.
3. E. Mochizuki, N. Yashi, Y. Kai, Y. Inaki, W. Yuhua, T. Saito, N. Tohnai, M. Miyata, Bull. Chem. Soc. Jpn. 2001, 74, 193-200.
4. K. Saito, L. R. Ingalls, J. Lee, J. C. Warner, Chem. Comm., 2007, 24, 2503-2505.