Inspired by nature, scientists in Australia have united light and chlorophyll to generate a range of polymers that have biomedical applications.
During photosynthesis, chlorophyll is activated by visible light, and an electron is promoted from its ground state to an excited state. In plants, this excited electron goes on to react with carbon dioxide and water, via photoinduced electron transfer (PET). However, in the system devised by Cyrille Boyer and colleagues at the University of New South Wales, the excited electron is donated to a monomer, generating a radical, which then goes on to further react and generate polymers through a process known as living radical polymerisation.
One of the challenges in polymer synthesis is achieving control over the length and structure of the polymers generated. Boyer’s team has addressed this using a form of living polymerisation called reversible addition fragmentation chain transfer, or RAFT, polymerisation, which incorporates an agent, normally a thiocarbonlythio compound, as a mediating species. The RAFT agent is capable of accepting and donating radicals, thus ‘sharing’ the radicals around evenly between the species present, ensuring each polymer chain has the opportunity to grow at an equal rate. This leads to a narrow range of polymer lengths and molecular weights (a low polydispersity index), and a high degree of control over the reaction. Various architectures, including star-shaped, comb-shaped and ring-shaped polymers can be synthesised in this way.
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