Enriching an Exchangeable Network with One of Its Components: The Key to High-T_g Epoxy Vitrimers with Accelerated Relaxation

Abstract

The curing of epoxy-anhydride vitrimers involves anionic copolymerization of epoxide and anhydride along with anionic homopolymerization of excess epoxide, giving rise to a poly(ester-co-ether) network. By monitoring curing using infrared spectroscopy in different conditions and mapping the presence of OH groups, we demonstrate that generation of hydroxide groups, necessary for transesterification, exclusively relies on side reactions induced by protic impurities and water. To increase the yield in esters and hydroxides, without depressing the thermal properties, we enrich the network with one of its components, DHEBA (bisphenol A bis(2,3-dihydroxypropyl) ether), potentially available from hydroxylation of the starting epoxy monomer as well as from chemical recycling of the final vitrimer network. In the DHEBA-enriched network, the modulus drop associated with the alpha transition occurs at higher temperatures and more steeply than in the pristine network, demonstrating better homogeneity together with improved heat resistance and 3-fold shortened relaxation time throughout the 140−180 °C range.

Meldrum's acid mediated ketene chemistry in the formation of ester bonds for the synthesis of vitrimers with high glass transition temperatures

“…Similar results are reported in a recent publication. 59,60 The side reactions in the recycling processes generate additional covalent linkages in the network so as to contribute to the increased crosslinking densities of the vitrimer during recycles.…”

N-Sulfonyl Urethanes to Design Polyurethane Networks with Temperature-Controlled Dynamicity

“…One popular approach to impart plastic flow and processability into various types of infusible thermosets has been to introduce reversible bonds that respond to a specific trigger (e.g., temperature). The resulting materials, known as covalent adaptable networks (CANs) or dynamic covalent polymer networks, should ideally be able to withstand deformation during use while still flowing significantly after activation (e.g., at high temperatures). − As a result, a wide array of dynamic chemistries have been introduced to common thermoset matrices including furan–maleimides, − imines, , transesterification, − disulfides, , and boron-based chemistries. − Moreover, all of the aforementioned chemistries have been introduced into a PU matrix …”

Epoxy Vitrimer Materials by Lipase-Catalyzed Network Formation and Exchange Reactions

“…A general difficulty is to obtain activation at low temperatures. In high- T g vitrimers ( T g = glass transition), the reprocessing window located between the T g and the degradation temperature ensures that transesterification takes place at a temperature high enough for the catalysis to be active. , However, there are applications were the lowest possible T g is sought. Soft robotics is an example where the self-healing ability of vitrimer-like elastomers would be an asset to extend the lifetime of body parts; a low healing temperature range is then required to avoid damage to circuitry.…”

“…The reaction was observed but at 200 °C. 27 Yet, it could still play a part over a long time. Surface analysis of torsion bars revealed an increase in IR absorption at 1150 cm −1 after 7 days at 100 °C, compatible with this interpretation.…”

“…Dehydration of the networks, leading to ether cross-links, is another hypothesis. The reaction was observed but at 200 °C . Yet, it could still play a part over a long time.…”