Iterative synthesis for precision manufacture of high value polymers

Abstract

The precise chemical synthesis of monodisperse and sequence-defined polymers has been studied intensively by synthetic chemists. Monodisperse sequence-defined synthetic polymers have a wide range of applications in healthcare and nanotechnology, due to their unique structural complexity. In addition, controlling monomer sequence can also affect polymer functionality and properties. Currently, the industrial fabrication of synthetic macromolecules is generally poorly controlled and difficult to scale up. In this thesis, a universal strategy for iterative synthesis with organic solvent nanofiltration (ItSyN) is proposed for fabricating monodisperse and sequence-defined PEG polymers with different side chains. This technology combines iterative monomer couplings and selective membrane separations in a fully liquid environment. It offers advantages for optimising reaction kinetics, online monitoring and the potential to scale up. Polymers were assembled on a soluble three-armed support to triple the production and maximise efficiency during membrane purification.

For ItSyN, polybenzimidazole (PBI) organic solvent nanofiltration (OSN) membranes with surface modifications were fabricated and characterised. The surface modified membranes showed good tolerance towards different organic solvents and extreme pH conditions in chemical synthesis processes.

A series of chemical kinetic studies of building block coupling were undertaken. Optimisation of the reaction conditions guaranteed up to 99.6% three-arm completion and impurities were minimised. The excellent coupling efficiency aided membrane purification and the preparation of precise monodisperse PEG oligomers. Using the same strategy, two sequence-defined PEG polymers with different orders of the side-arms were synthesized with a purity of 99%. They were characterised with respect to the diversity of their polymer structures and physical properties using ultraviolet–visible spectroscopy (UV-VIS) and differential scanning calorimetry (DSC).

ItSyN offers a versatile platform to synthesize a wide diversity of sequence-defined polymers with good purities and yields. It also unlocks the potential of sequence-defined polymers for real-life applications in nanotechnology, healthcare and information storage.