Chemical modification of organosolv lignin using boronic acid-containing reagents

Organosolv lignin was chemically modified with boron-containing reagents using a novel “graft-to” approach. The newly synthesized graft copolymers were prepared by covalently linking boron end-functionalized polycaprolactone (PCL) macromolecular reagents with organosolv lignin via reversible covalent bonds. Using a combination of 1H, 13C, 19F, and 11B NMR, it has been shown that arylboronate ester bonds are involved in the key linkages between the polyester grafts and the lignin core. Using a straightforward synthetic procedure and altering both the PCL graft density and the PCL molecular weight, a selection of compositions were studied. The newly prepared lignin-g-PCL copolymers were analyzed by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The Lignin-PCL5200 series shows an increase in PCL crystallinity with an increase PCL graft density. However, the crystallinity of the PCL in the lignin-g-PCL9100 set of materials remained constant throughout the series. TGA analysis for all lignin-g-PCL copolymers prepared herein show thermal decomposition near 300 °C.