Facile modification of hydroxyl group containing macromolecules provides autonomously self-healing polymers through the formation of dynamic Schiff base linkages

Abstract

Self-healing polymers are the next-generation materials for high-performance structures and play a major role in the field of study and research in materials. Biopolymers with biodegradability and biocompatibility, for understandable reasons, are increasingly becoming the focus of attention. Since numerous natural and synthetic polymers are known to contain free hydroxyl groups in their repeating units, the appropriate modification of these macromolecules through their OH groups can be applied for many different polymers. Here, we used poly(vinyl alcohol) (PVA) as model macromolecule with OH groups and reported the synthetic process and modification possibility of this biocompatible polymer. A series of modified PVA samples were synthesized by functionalization with 4-formylbenzoic acid (4-FBA) and 3,4-diaminobenzoic acid (3,4-DABA) via Steglich esterification reaction, thus, the obtained polymer contains both aldehyde and amino groups which are able to form autonomously self-healing polymer via Schiff base reaction. ATR-FTIR measurements confirmed the successful modification of the initial PVA, while optical microscopy, scanning electron microscopy, and X-ray micro-computed tomography (micro-CT) measurements verified the self-healing ability of the polymer without the need for any external stimulus or healing agent. According to the mechanical and thermoanalytical testing, the synthesized polymer shows not only the characteristics of pristine PVA (thermoplastic, biocompatible, biodegradable) but also has advantageous mechanical properties (elasticity, relatively high extensibility) that can be tuned by varying the degree of functionalization. The aforementioned synthetic procedure offers a simple solution for the functionalization of OH group containing polymers, even with low (1-–3 mol%) hydroxyl group content. In this work, the first candidate of a new class of functional polymers is demonstrated that may have promising potential applications in the field of biomedicine or could be used as structural components such as coatings and medical implants.