Thiol-ene click chemistry incorporates carboxylic acid-terminated alkane pendants on polycyclooctene to tune properties

Abstract

Dehydrogenation and subsequent chemical modification of polyolefins emerges as a promising polymer-to-polymer upcycling pathway. We report the functionalization of polycyclooctene (PCOE), a model for dehydrogenated polyethylene, by thiol-ene click chemistry to install carboxylic acid (COOH) terminated alkane pendant groups. This functionalization approach attached three pendants of different alkane spacer length: thioglycolic acid, mercaptopropionic acid, and mercaptooctanoic acid. Functionalization attached pendants to 3–22 mol% of the ethylene monomeric units, was well controlled by varying reaction stoichiometry and time, and did not require acid groups protections. Greater than 95% of the COOH groups participated in secondary bonding, forming aggregates detectable in X-ray scattering at high COOH mass fractions. Crystallinity and melting temperature decreased with increasing COOH mass fraction. Dynamic mechanical analysis (DMA) reveals both COOH mass fraction and pendant architecture tunes the rubbery plateau moduli, which is well described by the molar mass per backbone bond. This functionalized polymer exhibits commensurate surface and mechanical properties to commercial poly(ethylene-co-acrylic acid).

Keywords

• Polymer upcycling
• Thiol-ene click chemistry
• Polycyclooctene
• Associating polymer
• Functionalization
• Dynamic mechanical analysis