Self-healable functional polymers based on Diels–Alder ‘click chemistry’ involving substituted furan and triazolinedione derivatives: a simple and very fast approach

Nowadays, the design of functional polymer materials that can mimic natural phenomena, e.g., the self-healing of skin cuts, has received tremendous interest in materials science and engineering. Recently, 1,2,4-triazoline-3,5-dione (TAD) derivatives have been widely utilized in the functionalization of different functional polymer systems via several ‘click’ approaches within a relatively shorter period at room temperature (r.t.) compared to the widely used conventional furfuryl–maleimide Diels–Alder ‘click chemistry’, which requires elevated temperatures and longer times. In the present investigation, the dynamic DA-click reaction based on 2,5-disubstituted furan (diene) and TAD (dienophile) functionalisation was executed for developing self-healable functional tailor-made polymethacrylates. For this purpose, polymethacrylates bearing 5-methyl-2-furoate pendants (which can act as the ‘click’ partner of the TAD derivative) were prepared via the reversible addition–fragmentation chain transfer (RAFT) polymerization of 2-hydroxyethyl methacrylate (HEMA), followed by the esterification of the hydroxyl groups of poly(2-hydroxyethyl methacrylate) (PHEMA) using 5-methyl-2-furoic acid (MFA). Then, the TAD derivative was added for the DA post-polymerization modification of the polymers containing 2,5-disubstituted furan moieties, which was accomplished within 2 h under ambient conditions. For a better understanding, a model DA reaction using smaller organic molecules (which were analogous to the polymer system) was studied through density functional theory (DFT) based calculations and related spectroscopic analysis. As evidenced by the differential scanning calorimetry (DSC) analysis, the furan–TAD DA σ-bonds were reversible at 130 °C. The thermoreversible nature of the TAD ‘clicked’ bonds induced the self-healing feature within the DA polymethacrylates, which was monitored using different microscopy analyses.