Harnessing Activated Alkyne-Hydroxyl “Click” Chemistry for Degradable and Self-Healing Poly(urea vinyl ether ester)s

Abstract

The growing impact of polymers in modern-day applications necessitates the development of novel polymeric materials with versatile properties derived from readily available chemicals by employing experimentally simple and efficient polymerization techniques. The "click" reaction between activated alkynes and heteronucleophiles has emerged as a transition-metal catalyst-free, mild, and facile approach to synthesize a wide range of valuable polymeric materials. Interestingly, despite the abundance of hydroxyl groups in organic molecules, their weak nucleophilicity has resulted in their underutilization in "click" reactions. Herein, we harness the potential of hydroxyl nucleophiles for the "click" reaction with activated alkynes, leading to the development of a distinct class of polyureas (PUs) referred to as poly(urea vinyl ether ester)s (PUVEE)s. Utilizing systematically optimized mild polymerization conditions, we successfully obtained thermally stable PUVEEs, soluble in common polar organic solvents, exhibiting weight-average molecular weights of up to 14,000 g mol −1 . The current activated alkyne-hydroxyl "click" polymerization approach represents a sustainable, isocyanate (functional group with high toxicity)-free method for PU synthesis, wherein the commodity chemical urea serves as the direct source of urea functionality. Moreover, tuning the spacer chain length and the density of urea hydrogen bonds in the polymer backbone imparts diverse features to the developed PUVEEs, ranging from high stiffness to stretchability, with intriguing capacity for room-temperature self-healability. Additionally, the incorporated vinyl ether and ester functionalities contribute to the degradability of our PUVEEs into small molecules or oligomers under acidic conditions. Consequently, this class of PUs demonstrates high relevance in promoting sustainability through material reprocessability, via their self-healing property, and reduced environmental impact thanks to their degradability.

High-Molecular-Weight Poly[2]catenanes Prepared by Hydroxyl-Alkyne Click Chemistry

“…Thus, it was obvious that hydroxyl–yne click polymerization possessed the merits of obtaining polymers with high DP values. Besides, it also possessed the features of short reaction time, mild condition, high yield, and avoiding the use of expensive transition-metal catalysts. , Owing to these advantages, the hydroxyl–yne click polymerization has the potential to be employed for preparing polycatenanes with high DP values.…”

“…This inevitable issue has stimulated the development of a series of alkyne-based click polymerizations, such as thiol–yne, hydroxyl–yne, and amino–yne click polymerizations . Hydroxyl–yne click chemistry, − developed in recent years, has been applied to synthesize various linear polymers with high DP values. In 2017, Tang, Ling, Qin, and their co-workers used the hydroxyl–yne click reaction to prepare poly­(vinylene ether ketone)­s, for which the molecular weight was up to 35,200 with a high yield of 99%.…”