Table 1. Comparisons between Catalysts for PLLA Chemical Recycling to l-LA, Using Sn(Oct)2, Zn(Oct)2, and Ca(Oct)2a.
| entry | catalyst | loadingb | temp (°C) | kobs (h –1)c | TOF (h –1)d | mass loss rate (g g –1 h–1)e | % l-LAf |
|---|---|---|---|---|---|---|---|
| 1 | Sn(Oct)2 | 1:1000 | 160 | 38.2 (±2.7) | 380 (±28) | 67 (±5) | >99 |
| 2 | Zn(Oct)2 | 1:1000 | 160 | 3.2 (±0.2) | 15 (±1) | 3 (±1) | - |
| 3 | Ca(Oct)2 | 1:1000 | 160 | 1.4 (±0.1) | 17 (±1) | 4 (±1) | - |
| 4 | Sn(Oct)2 | 1:1000 | 170 | 80.9 (±5.1) | 788 (±58) | 139 (±11) | >99 |
| 5 | Sn(Oct)2 | 1:1000 | 180 | 152.2 (±23.7) | 1440 (±240) | 269 (±42) | >99 |
| 6 | Sn(Oct)2 | 0.5:1000 | 160 | 18.2 (±2.6) | 370 (±50) | 72 (±1) | >99 |
| 7 | Sn(Oct)2 | 0.33:1000 | 160 | 12.3 (±1.9) | 380 (±50) | 73 (±6) | >99 |
| 8 | Sn(Oct)2 | 0.25:1000 | 160 | 9.8 (±1.0) | 400 (±40) | 72 (±7) | >99 |
| 9 | Sn(Oct)2 | 0.2:1000 | 160 | 7.8 (±1.7) | 374 (±50) | 66 (±10) | >99 |
| 10 | Sn(OnBu)2 | 0.1:1000 | 160 | 38.6 (±2.4) | 381 (±28) | 104 (±8) | >99 |
Depolymerization experiments conducted using thin films, analyzed using TGA over 5 h or until >95% mass loss (see SI for details of experimental setup).
Catalyst loadings calculated per Mr of PLLA repeat unit (Mr = 72.06 g mol–1).
Rate constant is the gradient of the linear fits to plots of %PLLA mass loss vs time. Average errors are determined from repeat runs see SI for details.
Activity as TOF defined as moles of lactic acid repeat unit consumed from 0 to 80% mass loss/mol of catalyst/time taken for 0–80% mass loss. In a few cases, 80% mass loss was not reached, and in these cases, TOF is reported for the appropriate conversion at 5 h. Average errors were taken from repeat runs.
Mass loss rate = TOF × Mr of lactic acid repeat unit (72.06)/Mr of catalyst.
Selectivity for monomer, % L-LA, was determined by 1H NMR spectroscopy and GC-MS of monomer isolated from sublimation depolymerization experiments (see SI for details). 5% meso-LA formed from 5% d-lactic acid repeat units in the PLLA sample.