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 H-1, C-13, F-19, and B-11 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 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.