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., self-healing of skin cuts, has got a tremendous interest in materials science and engineering. Recently, 1,2,4-triazoline-3,5-dione (TAD) derivatives are 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 widely used conventional furfuryl-maleimide Diels-Alder ‘click chemistry,’ which requires elevated temperature and longer time. In the present investigation, the dynamic DA-click reaction based on 2,5-disubstituted furan (diene) and TAD (dienophile) functionalities was executed in developing self-healable functional tailormade polymethacrylates. For this purpose, polymethacrylates bearing 5-methyl-2-furoate pendants (which can act as the ‘click’ partner of TAD derivative) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-hydroxyethyl methacrylate (HEMA) followed by esterification of 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 functionalities, which was accomplished within 2 h under ambient conditions. For a better understanding, a model DA reaction, using smaller organic molecules (analogous to 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 was monitored using different microscopy analyses.