Dr Kei Saito

Green Chemistry

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

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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

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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

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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.

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4. Bioinspired Nano Micelles for Biotechnology Application

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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.

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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.