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.
Bibliographical noteFunding Information:
We thank Steven Weigand for the SAXS data collections. SAXS experiments were performed at the DuPont–Northwestern–Dow Collaborative Access Team (DND-CAT) located at the Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by E.I. DuPont de Nemours & Co., the Dow Chemical Company, and Northwestern University. Use of the APS, an Office of Science User Facility operated for the U.S. DOE Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract DE-AC02-06CH11357. We thank Christopher A. DeRosa and Huiqun Wang for helpful discussions and critical evaluation. We thank Marianne S. Meyersohn and Stephanie Liffland for their critical evaluation. Financial support for this work was provided by the Minnesota Corn Growers’ Association. We also acknowledge the Center for Sustainable Polymers at the University of Minnesota, a National Science Foundation supported center for Chemical Innovation (CHE-1901635).
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