The synthesis and properties of poly(ester-alt-ether)-b-PLLA block copolymers as toughening agents for commercial polylactide Alexander Craze, Ryan W F Kerr, Charlotte K Williams University of Oxford, UK A more sustainable future for plastics relies on materials that can be bio-sourced, recycled, reused or composted/ biodegraded and not suffer losses in performance. One popular candidate is Poly(lactide) (PLA), the largest scale commercial bio-derived plastic, produced on ~ 1.8 Mt/annum globally. 1,2 This study aimed to address two major pitfalls that hinder the widespread application of PLA as a sustainable alternative plastic; its (1) brittleness and (2) poor processibility. Recently, our group reported a Zr(IV) catalyst (4) that selectively formed poly(ester- alt -ethers) with ABB / ABC sequences (where A = anhydride, B = epoxide and C = THF/oxirane). 3 A series of new poly(ester- alt -ethers) exhibiting ABB or ABC sequences were prepared from different monomer combinations allowing for preparation of polymers with a range of thermal properties. All the new polymers were fully amorphous, with T g values ranging from 17 to -44 °C. The polymers were then targeted, as part of copolymers, as toughening agents for commercial bioplastic PLLA. Diblock copolymers of the form ABB - b -PLLA could be synthesised by either sequential addition or switch catalysis (presenting the first ‘ ABB -switch’), and were found to be effective polymeric toughening agents for high weight commercial PLLA. The influence of block polymer additive wt%, molecular weight and block size were explored via tensile mechanical testing, DTMA, melt rheology, SEM and thermal analysis. The best performing toughening agent (at 15 wt% block polymer additive) was found to retain a high modulus (E = 3.1 ± 0.1 GPa) and tensile strength (48.7 MPa) and increase the elongation at break by 7 times and tensile toughness by 8 times, and importantly, without changing the thermal properties such as the T g , crystallinity or T m . Together with a reduced melt viscosity and earlier onset of shear thinning, these toughening agents produce a material that is more readily processible than PLLA and may be open to a wider range of applications. Moreover, chemical degradation experiments showed that the block polymer can be selectively isolated from high weight PLLA in order to reuse the material. References 1. Yuntawattana, N.; Gregory, G. L.; Carrodeguas, L. P.; Williams, C. K. ACS Macro Lett. 2021, 774–779.
2. Shen, L.; Worrell, E.; Patel, M. Biofuels Bioprod. Biorefining 2010, 4 (1), 25–40. 3. Kerr, R. W. F.; Williams, C. K. J. Am. Chem. Soc. 2022, 144 (15), 6882–6893.
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