Toward Sustainable Elastomers from the Grafting-Through Polymerization of Lactone-Containing Polyester Macromonomers

As the need for renewable and degradable alternative plastics grows, efforts have been made to develop biobased polymer architectures with tunable properties. We developed the synthesis of a new, biobased, and degradable graft copolymer using a grafting-through approach. A one-pot strategy was developed for the synthesis of telechelic poly(l-lactide) (PLLA) with a polymerizable lactone group at one chain-end. Using mild conditions, we obtained the lactone-functionalized polymer after three steps. Conditions were optimized, and complete conversion was reached in each step. The polyesters were characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopies, size exclusion chromatography (SEC), and matrix-assisted laser desorption ionization–time-of-flight (MALDI-TOF) mass spectrometry. The macromonomers were then copolymerized with γ-methyl-ε-caprolactone (γMCL) to prepare fully aliphatic polyester graft copolymers. Using optimized conditions, we analyzed a series of graft copolymers with graft length, backbone length, and graft density variations by NMR spectroscopy, SEC, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Mechanical properties were also evaluated, and the corresponding structure–property relationships were studied. Materials with highly tunable mechanical properties were obtained. One of the graft polymers with 30 wt % PLLA showed impressive elastomeric behavior with about 17 MPa stress at break and 1400% strain at break and a residual strain at 25% after the second cycle and 40% after the 10th cycle. This study opens the door to the use of ring-opening transesterification polymerization (ROTEP) for the synthesis of new fully biobased graft copolymers.