nearvitrimer

Nearvitrimers are covalently crosslinked polymer networks that approach the behavior of vitrimer materials but do not fully meet all of their defining criteria. In covalent adaptable networks, vitrimers enable topology rearrangement through associative exchange reactions at elevated temperature, allowing reprocessing and recycling while preserving crosslink density. Nearvitrimers exhibit similar thermo-activated bond exchange, but the extent, rate, or completeness of network rearrangement is limited. This can result in properties that lie between a conventional thermoset and a vitrimer, with reprocessing sometimes possible only under more demanding conditions or only partially.

Chemistry and mechanisms in nearvitrimers rely on dynamic covalent bonds that can undergo exchange, such as transesterification, imine or oxime exchange, disulfide metathesis, or boron–oxygen ester exchange. The exchange reactions tend to be associative in principle, but practical factors—kinetic barriers, side reactions, phase separation, or network heterogeneity—can reduce the efficiency of network rearrangement and thus limit reprocessability.

Properties and potential applications: nearvitrimers offer partial recyclability, repair, and reshaping of crosslinked materials, and have been explored in networks based on epoxies, polyurethanes, and polyesters. They can provide improved recovery after damage or extended lifetime relative to conventional thermosets, though with mechanical or thermal performance that is typically more conservative than true vitrimers.

Distinction from vitrimers: the key difference is that nearvitrimers do not always achieve full topology reconfiguration with constant crosslink density under dynamic covalent exchange. Their exchange kinetics and extent are often insufficient for complete, rapid reprocessing, placing them in an intermediate class.