Simultaneous Physical Cross-Linking and Mechanical Strengthening of Elastomers by Enantiomeric Interactions through Reactive Processing

Abstract

Exploiting robust elastomers without sacrificing thermoplasticity has been extremely desired for decades, yet it is challenging. Noncovalent interactions are a versatile platform for the development of networks with reversible cross-linking joints. Herein, an alternative strategy is proposed to straightforwardly construct a mechanical strengthening elastomer with a dynamic cross-linking network via multiple H-bonding between enantiomeric polymer pairs. First, poly-L-lactic acid (PLLA)/poly-D-lactic acid (PDLA) were pregrafted onto polyolefin elastomer (POE) to obtain POE-g-PLLA and POE-g-PDLA, respectively. Due to the specific intermolecular interactions, stereocomplex crystals (SC) were formed and preserved during the subsequent melt-compounding. SC enabled the immobilization of the cross-linking point within the POE matrix, facilitating the construction of the SC noncovalent network (SC-N). As such, SC-N endowed the elastomer with synergistically enhanced modulus, strength, and heat resistance, as compared with traditional chemical cross-linked counterparts. More importantly, SC-N displayed desirable reprocessability upon the temporary dissociation of physical cross-linking linkages above T m,SC . These findings may open a feasible avenue of designing advanced elastomers with dynamic behaviors and provide deeper insights into the underlying mechanism of covalent adaptable cross-linking.