Catalyst‐free reprocessable crosslinked biobased polybenzoxazine‐polyurethane based on dynamic carbamate chemistry

Abstract

The introduction of dynamic covalent chemistry into the field of polymer chemistry has resulted in a new class of network polymer materials named covalent adaptable networks (CANs). These new materials have effectively bridged two antagonistic materials, that is, conventional thermoplastic and thermoset polymers together, thanks to these dynamic exchangeable covalent bonds, making them recyclable. In this work, we report a catalyst-free reprocessable polybenzoxazine-polyurethane thermosetting system with activation of carbamate dynamic bond exchange. The curing characteristics and properties of this biobased polybenzoxazine-polyurethane network have been determined by Fourier transform infra-red (FTIR), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMA). Moreover, the tests of the recyclability of the material were successfully achieved under mild reprocess conditions (130 C, 10 min) thanks to the formation of abundant free phenolic hydroxyl groups. This work provides a promising potential for industrial applications as a new recyclable and reprocessable thermosetting polybenzoxazine material.

High‐Performance Vitrimeric Benzoxazines for Sustainable Advanced Materials: Design, Synthesis, and Applications

“…A recently reported polybenzoxazine‐polyurethane vitrimer featuring transcarbamoylation undergoes catalyst‐free associative bond exchange. [ 400 ] For a polybenzoxazine incorporating carbamate chemistry to be categorized as a vitrimer, the dynamic bond exchange must strictly follow the associative mechanism. The potential of transcarbamoylation for the design of new functional polymers has not been fully exploited.…”

“…A polybenzoxazine‐polyurethane vitrimer network endowed with carbamate bond can be derived from a solventless reaction between tyrosol, paraformaldehyde, and dodecylamine. [ 400 ] The resin features monomer melt temperature of 125 °C, which would pose a processing challenge. The polymer features low cure glass transition (55 °C), low activation energy of transcarbamoylation (92 kJ mol −1 ), accounting for full stress relaxation in 10 min at 130 °C with more than 90% recovery of tensile strength (11.7–10.2 MPa) and 80% strain recovery (from 51% to 41%).…”

Transcarbamoylation in Polyurethanes: Underestimated Exchange Reactions?

“…In this section, CANs based on TC exchange reactions that have been described so far are reported. Some examples of carbon–carbon backbone polymers playing with TC chemistry as exchange reactions have been reported recently, but a focus is given on PU or PHU derivatives. , Critical discussions about the mechanisms and rheological interpretations as well as comments on the remaining gray areas are provided herein.…”

Reprocessable Polybenzoxazine Thermosets with High Tgs and Mechanical Strength Retentions Using Boronic Ester Bonds as Crosslinkages

“…Benzoxazine resin, as a new class of thermosetting polymer, has gained considerable attention in recent years on account of its brilliant heat resistance, excellent flame retardance, and high hydrophobicity [ 13 , 14 , 15 ]. Recently, various dynamic covalent bonds have been introduced into polybenzoxazine networks to achieve self-healabilty or reprocessability [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. However, there have been few reports on introducing boronic ester bonds into benzoxazine resins until now.…”