Controlling polymer properties with stereochemistry Andrew Dove University of Birmingham, UK
Nature has evolved the ability to create large and complex molecules in which the precise control over both the sequence and spatial arrangement of the atoms is critical to their performance. The 3-dimensional control over the arrangement of bonds is as important to the function and behaviour of molecules as any other factor and is critical to the structure-function relationships that occur within biological systems. Specifically, the advantageous mechanical properties of most commodity plastics are intimately connected to their low glass transition temperature and crystallinity, the latter of which can be modulated by stereochemistry of the polymer. 1 For polypropylene (PP), stereochemical control of the pendant methyl group on the polymer backbone (isotactic, or alternating bond orientation) contributes to its useful properties. While this concept has similarly been leveraged to improve the thermomechanical properties (i.e. increase the melting temperature or tensile modulus) of bioplastic polyesters (e.g. polylactic acid (PLA)) these materials are incessantly plagued by brittleness, lacking the flexibility and toughness of petrol plastics. By controlling the stereochemistry of polymer backbones, much more significant changes to polymer mechanics can be achieved. The most well known example is stereochemical differences between natural rubber (poly(cis- isoprene)) and Gutta percha (poly(trans-isoprene)), which lead to a complete change in physical properties from an elastomeric to plastic material. Despite this being well known, the state of the are in synthesis has not made it possible to readily exploit this effect more widely. To this end, our work has focused on developing polymerization methods that can result in materials in which the stereochemistry can be used to leverage a wide range of materials properties with a high level of tuneability. References 1. Worch, J. C.; Prydderch, H.; Jimaja, S.; Bexis, P.; Becker, M. L.; Dove, A. P., Stereochemical enhancement of polymer properties. Nat. Rev. Chem. 2019, 3 (9), 514-535. 2. G. Natta et al., Crystalline high polymers of α-olefins. J. Am. Chem. Soc. 77, 1708-1710 (1955). 3. S. Farah, D. G. Anderson, R. Langer, Physical and mechanical properties of PLA, and their functions in widespread applications — A comprehensive review. Adv. Drug Deliv. Rev. 107, 367-392 (2016) 4. Kent, E. G.; Swinney, F. B., Properties and applications of trans-1, 4-polyisoprene. Ind. Eng. Chem. Prod. Res. Dev. 1966, 5 (2), 134-138. 5. Bell, C. A.; Yu, J.; Barker, I. A.; Truong, V. X.; Cao, Z.; Dobrinyin, A. V.; Becker, M. L.; Dove, A. P., Independent control of elastomer properties through stereocontrolled synthesis. Angew. Chem., Int. Ed. 2016, 55 (42), 13076-13080 6. Worch, J. C.; Weems, A. C.; Yu, J.; Arno, M. C.; Wilks, T. R.; Huckstepp, R. T. R.; O’Reilly, R. K.; Becker, M. L.; Dove, A. P., Elastomeric polyamide biomaterials with stereochemically tuneable mechanical properties and shape memory. Nat. Commun. 2020, 11 (1), 3250 7. Stubbs, C. J.; Worch, J. C.; Prydderch, H.; Becker, M. L.; Dove, A. P., Unsaturated Poly(ester-urethanes) with Stereochemically Dependent Thermomechanical Properties. Macromolecules 2020, 53 (1), 174-181
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