Tuning the Mechanical and Dynamic Healing Properties of Bio-Degradable Supramolecular Polylactone Copolymers by Controlling the Arm-Chain Crystallinity

Recently, supramolecular polymeric networks have attracted great scientific interests due to their healing ability of damaged fractures, which can significantly enhance the reliability and sustainability of materials. In particular, the multiple healing capability of supramolecular polymers can be imposed by the dynamic dissociation/re-association of various supramolecular interactions such as hydrogen bonding, ionic bonds, metal-ligand coordination, and π-π interaction etc. In general, most supramolecular polymer networks are consist of low <i>T</i>_g amorphous polymeric chains with more dynamic supramolecular bonds for faster healing performances. Although the more dynamic supramolecular polymeric networks, which is composed of flexible chain and rather weaker supramolecular bonds, exhibit an improved healing ability, the mechanically robust supramolecular network structure may not be facilitated. Thus, to resolve these challenges, most research has been focused on developing the alternative supramolecular polymeric network structures with mechanically robustness and excellent healing performances, simultaneously.<br/>In this study, a quadruple hydrogen-bonded supramolecular polylactone copolymer (QSCP) was successfully synthesized using an alkyl-branched ε-decalactone (ε-DL), which is renewable and bio-degradable ring-shaped lactone derivative, and ε-caprolactone (ε-CL), via ring-opening copolymerization. The effects of P(ε-DL) on structural, mechanical, and dynamic healing properties of QSCP were comprehensively characterized. The degree of polymerization (DP) and segment compositions of QSCP arm-chain are precisely adjusted by controlling the feed monomers-to-core ratio and monomeric fractions. As the composition of ε-DL increased for QSCPs, the maximum melting temperature (<i>T</i>_m) and enthalpy (<i>DH</i>_m) values gradually decreased. These indicates that the alkyl-branched P(ε-DL) disrupted the formation of hard P(ε-CL) crystalline phases. Especially, the prepared QSCP s with ~ 10 mol% of P(ε-DL) (i.e., QSCP90) displayed a significantly improved elongation at break (~ 700%) with a highly enhanced tensile strength (~ 6 MPa). In addition, the optically- and mechanically-measured self-healing of QSCP90 were found that the mechanically-damaged QSCP90 was sufficiently recovered after ambient self-healing conditions (50 °C). These results clearly suggested that an optimum composition of arm-chain enabled QSCPs to form the complementary hard/soft multi-phase system, i.e., a hard phase bearing crystalline PCL and a soft phase containing P(ε-DL) with quadruple hydrogen bonding moieties, eventually resulting in highly improved tensile properties with a facile healing behavior.