Enzymatic syntheses of linear and hyperbranched poly-l-lactide using compressed R134a–ionic liquid media

• Compressed R134a/[C4MIM] [PF6] above the critical points of the mixture produces a useful homogenous solvent media.
• Compressed R134a and [C4MIM] [PF6] mixture media allows enzymatic activity for eROP of lactides.
• High poly-l-lactide molecular weights are achieved in eROP using R134a/[C4MIM] [PF6] solvent.
• Controlled eROP diminishes undesirable side cationic propagation mechanisms.
• R134a/IL is a new medium for enzymatic or chemical reactions in a relatively polar environment.

In this work, the use of homogenous media composed of the ionic liquid [C4MIM] [PF6] in combination with miscible compressed 1,1,1,2-tetrafluoroethane (R134a), above the critical points of the mixture, at 338.15 and 363.15 K and pressure of 30,000 kPa, lead to the successful enzyme-mediated syntheses of linear and hyperbranched poly-l-lactides. The attained polymer molecular weights were higher than those in previous reports using compressed fluids, even in the supercritical state, or individual ionic liquid media. The maximum attained Mn for linear PLLA in this work was 28,000 g/mol, and that for hyperbranched was 11,200 g/mol which were up to 3-fold higher than those obtained with the ionic liquid medium, and this is attributed to favored reaction media characteristics in this critical/miscible system. Additionally, non-enzymatic propagation side mechanisms were minimized or eliminated with the addition of the green compressed R134a.

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