Self-curable Thermoplastic Polymer Realized by Bond Exchange
Exchange reactions, such as transesterification, have been widely utilized in the polymer industry, including condensation and glycolysis. Recently, functional cross-linked polymers, known as "vitrimers"1）, have been developed, where exchange reactions occur within cross-linked molecular networks. At elevated temperatures where bond exchange is activated, network segments are temporarily released from the constraints of cross-links to relax, resulting in sustainable properties such as recyclability and repairability2）.
As an extension of the bond exchange concept, we propose a design of self-curable polymers based on intermolecular bond exchange as the cross-linking reaction, transforming initially soft thermoplastic polymers into hard cross-linked polymers3）. The molecular design is straightforward, involving the synthesis of hydroxy-functionalized linear polyesters, which, upon heating above a certain temperature, undergo intermolecular ester exchange to form cross-links. Incorporation of ester exchange catalysts during polymer synthesis enables seamless conversion through simple heating. Importantly, hydroxy groups are not consumed during cross-link formation but are regenerated via exchange cross-linking reactions, thereby imparting the final cured material to the vitrimer nature operated by transesterification in the network, demonstrating sustainability.
Conventional wisdom dictates that physical properties cannot be altered after polymer synthesis. Therefore, this concept, that is, self-curable thermoplastic polymer, is expected to pioneer a new trend in polymer functionalization methods, breaking down the traditional distinction between thermoplastic and cross-linked (thermosetting) polymers.
1） L. Leibler et al., Science 2011, 334, 965.
2） M. Hayashi et al., J. Mater. Chem. A 2022, 34, 17406.
3） M. Hayashi et al., Macromol. Rapid Commun. 2024, 45, 2400125.
Mikihiro Hayashi, Nagoya Institute of Technology