A Highly Active and Selective Zirconium-Based Catalyst System for the Industrial Production of Poly(lactic acid)

TY - JOUR

T1 - A Highly Active and Selective Zirconium-Based Catalyst System for the Industrial Production of Poly(lactic acid)

AU - Buchard, Antoine

AU - Chuck, Christopher J

AU - Davidson, Matthew G

AU - Gobius du Sart, Gerrit

AU - Jones, Matthew D

AU - McCormick, Strachan N

AU - Russell, Andrew D

N1 - Engineering and Physical Sciences Research Council - EP/L016354/1; University of Bath Royal Society - UF/160021 Funding Information: We wish to thank the University of Bath for a studentship to SNM and the EPSRC (EP/L016354/1) and TotalEnergies Corbion for financially supporting this work. AB acknowledges the Royal Society (UF/160021 fellowship). Analytical facilities and expertise were provided through the Material and Chemical Characterization Facility (MC) at the University of Bath ( https://www.bath.ac.uk/research-facilities/material-and-chemical-characterisation-facility-mc2/ ). We also wish to thank Wilko de Lang and Taco van Doorn of TotalEnergies Corbion for providing their technical assistance during kg-scale polymerization studies. 2

PY - 2023/2/17

Y1 - 2023/2/17

N2 - The biodegradable, aliphatic polyester poly(lactic acid), PLA, is a leading bio-based alternative to petrochemical-derived plastic materials across a range of applications. Widely reported in the available literature as a benchmark for PLA production via the bulk ring-opening polymerization of lactides is the use of divalent tin catalysts, and particularly tin(II) bis(2-ethylhexanoate). We present an alternative zirconium-based system that combines an inexpensive Group IV metal with the robustness, high activity, control, and designed compatibility with existing facilities and processes, that are required for industrial use. We have carried out a comprehensive kinetic study and applied a combined experimental and theoretical approach to understanding the mechanism by which the polymerization of lactide proceeds in the presence of this system. In the laboratory-scale (20 g) polymerization of recrystallized racemic d,l-lactide (rac-lactide), we have measured catalyst turnover frequencies up to at least 56,000 h -1, and confirmed the reported protocols’ resistance toward undesirable epimerization, transesterification, and chain scission processes, deleterious to the properties of the polymer product. Further optimization and scale-up under industrial conditions have confirmed the relevance of the catalytic protocol to the commercial production of melt-polymerized PLA. We were able to undertake the efficient preparation of high-molecular-weight PLA on the 500-2000 g scale, via the selective and well-controlled polymerization of commercial polymer-grade l-lactide under challenging, industrially relevant conditions, and at metal concentrations as low as 8-12 ppm Zr by weight ([Zr] = 1.3 × 10 -3 to 1.9 × 10 -3 mol %). Under those conditions, a catalyst turnover number of at least 60,000 was attained, and the activity of the catalyst was comparable to that of tin(II) bis(2-ethylhexanoate).

AB - The biodegradable, aliphatic polyester poly(lactic acid), PLA, is a leading bio-based alternative to petrochemical-derived plastic materials across a range of applications. Widely reported in the available literature as a benchmark for PLA production via the bulk ring-opening polymerization of lactides is the use of divalent tin catalysts, and particularly tin(II) bis(2-ethylhexanoate). We present an alternative zirconium-based system that combines an inexpensive Group IV metal with the robustness, high activity, control, and designed compatibility with existing facilities and processes, that are required for industrial use. We have carried out a comprehensive kinetic study and applied a combined experimental and theoretical approach to understanding the mechanism by which the polymerization of lactide proceeds in the presence of this system. In the laboratory-scale (20 g) polymerization of recrystallized racemic d,l-lactide (rac-lactide), we have measured catalyst turnover frequencies up to at least 56,000 h -1, and confirmed the reported protocols’ resistance toward undesirable epimerization, transesterification, and chain scission processes, deleterious to the properties of the polymer product. Further optimization and scale-up under industrial conditions have confirmed the relevance of the catalytic protocol to the commercial production of melt-polymerized PLA. We were able to undertake the efficient preparation of high-molecular-weight PLA on the 500-2000 g scale, via the selective and well-controlled polymerization of commercial polymer-grade l-lactide under challenging, industrially relevant conditions, and at metal concentrations as low as 8-12 ppm Zr by weight ([Zr] = 1.3 × 10 -3 to 1.9 × 10 -3 mol %). Under those conditions, a catalyst turnover number of at least 60,000 was attained, and the activity of the catalyst was comparable to that of tin(II) bis(2-ethylhexanoate).

KW - amine tris(phenolate)

KW - industrially relevant

KW - lactide

KW - liquid catalyst formulation

KW - melt polymerization

KW - poly(lactic acid)

KW - ring-opening polymerization

KW - zirconium

U2 - 10.1021/acscatal.2c05690

DO - 10.1021/acscatal.2c05690

M3 - Article

SN - 2155-5435

VL - 13

SP - 2681

EP - 2695

JO - ACS Catalysis

JF - ACS Catalysis

IS - 4

ER -