Adhesive Properties of Aromatic Polyesters with Cationic Side Chains Synthesized via Radical Ring-Opening Copolymerization

Abstract

Degradable adhesives that are both strong and cleanly debondable are highly desirable for progressing sustainable materials but are challenging to develop owing to the limited availability of polymer systems that are endowed with both sufficient cohesion and interfacial interactions. Herein, we report a series of novel P(METATFSI-co-BMDO) polymers as a new class of cationic-side-chain-bearing aromatic polyester synthesized via radical ring-opening copolymerization of [2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)imide (METATFSI), an ionic-liquid monomer, and 5,6-benzo-2-bromomethyl-1,3-dioxepane (BMDO), an aromatic cyclic ketene acetal. Incorporating BMDO endows the polymer backbone with ester linkages that facilitate main-chain degradability, while the combination of its aromatic units and dense cationic side chains provides pronounced cation−π interactions. The use of the ionic-liquid monomer significantly enhances the BMDO-polymerization efficiency to afford copolymers in high yields and with tunable compositions. Strong cation−π interactions are evidenced by lower solubilities and higher glass transition temperatures compared to those predicted by ideal mixing, indicative of superior cohesive interactions within the polymer matrix. Adhesion testing revealed that P(METATFSI-co-BMDO) is strongly adhesive toward aluminum as well as challenging low-surface-energy substrates, including polypropylene and polytetrafluoroethylene. Intermediate copolymer compositions led to optimal adhesion, which reflects a balance between cohesive strengthening via cation−π interactions and effective interfacial adhesion through ionic and dipolar interactions. Hence, radical ring-opening copolymerization is a powerful strategy for integrating cation−π interactions into degradable polyester adhesives, thereby offering a promising platform for high-performance, sustainable adhesive materials that are applicable to a wide range of substrates.