Hyperbranched polyglycerols (HPGs)-Based Platform for the Development of New Materials

Abstract

Sustainable polymer materials with high performance properties, such as adhesives that can debond on-demand, or reprocessable thermosets with high-tensile strength, are of rapidly growing interest. The demands of their material properties are challenging based on their applications. For instance, the qualities responsible for debondability in an adhesive often counteracts adhesion strength, and the toughness required for sustainable engineering plastics can be incompatible with reprocessability. Herein, we demonstrate hyperbranched polyglycerols (HPGs) as precursors for water-debondable adhesives and sustainable thermosets. The advantages of HPG include its potential as a sustainable polymer, the high valency, low viscosity, and reversible hydrogen bonding. Chapter 1 contains a brief overview of bio-derived plastics with a focus on the characteristics of HPGs. In chapter 2, mixtures of HPG and pyromellitic dianhydride (PMDA) were spread on aluminum substrates and thermally cured, exhibiting an adhesion strength of 9.9 MPa—over twice that of a commercially available epoxy adhesive. This adhesion strength was maintained for 3 days under ambient conditions, and after only 15 minutes of immersing in hot water at 90oC the adhered samples were debonded. In chapter 3, the copolymerization of hydrophobic phthalic anhydride (PA) as a crosslinker was used to extend the service life of these adhesives under ambient conditions. The HPG-PA copolymer showed higher adhesion strength (14.6 MPa) and maintained water-debondability within 5 min in hot water. Additionally, the adhesives maintained high adhesion strength of over 10 MPa for 6 weeks under ambient conditions. Chapter 4 concerns HPG-based cross-linked materials as sustainable thermosets. The HPG-based thermosets cross-linked by PMDA exhibited an excellent tensile strength of 82 MPa and the original HPG was recovered through chemical recycling. In addition, the incorporation of the transesterification catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), together with switching the cross-linker from PMDA to terephthalic acid (TPA) endowed the HPG-based cross-linked materials with thermal reprocessability. These results establish HPG-based thermosets as a promising platform for high-strength, recyclable, and reprocessable materials for advanced manufacturing applications.