Crystallization, morphology and mechanical property enhancement of block copolymer-based metallosupramolecular polymers by incorporating metal coordinating ligand into poly(L-lactic acid) block

We propose a new strategy to prepare robust films with unusual mechanical properties for low molecular weight block copolymers-based materials by utilizing metal−ligand (M−L) coordination to create physical crosslinking into the hard block. Using an amine-terminated triazole as an initiator, a poly(L-lactic acid) (PLLA) containing a triazole group was prepared by ring opening polymerization. The hydroxy group of this polymer was subsequently reacted with isocyanate-poly(butadiene) (PB), resulting for the first time in PLLA/PB block copolymers bearing metal-coordinating ligands on PLLA chain. The subsequent addition of Co 2+ , Fe 3+ , or Cu 2+ metal ions resulted in formation of metallosupramolecular polymers (MSP) through M−L bonds, as could be shown by viscosimetry and UV–vis spectra. The influence of blend of different types of metal, L/M ratio, the chain length of PLLA blocks (1.6 or 3.0 kg/mol) of block copolymers on the properties has been investigated in detail. Compared to the mechanical properties of uncoordinated block copolymer, MSP showed significantly larger Young's modulus, higher elongation at break, and larger break strength. For uncoordinated oligomer with a toughness of 0.82 J/m 3 , the toughness increased by 101- and 348-fold with the incorporation of Co 2+ and Cu 2+ , respectively. Because of the particularly weak bond strength associated with the Fe 3+ −triazole bond, MSP containing Fe 3+ had lower Young's modulus, break strength than MSPs containing Co 2+ and Cu 2+ . Incorporation of 50% Cu 2+ and 50% Co 2+ into block copolymers was found to be beneficial to prepare MSPs with high extensibility and large Young's modulus simultaneously. For all MSPs, M−L complex and polymer matrix were found to microphase separate into nano-domains. Crystallization rate of PLLA in MSP featuring Co 2+ metal ion was lower than that of Cu 2+ and Fe 3+ , demonstrating that chain mobility relied on both the dynamic character and bond strength. Our work represents a novel strategy for robust films by low molecular weight block copolymers-based materials utilizing metal−ligand coordination. The modulus, tensile strength and toughness of metallosupramolecular polymers are simultaneously improved by addition of metal, and these properties can be tuned by varying structure parameters and type of metals. • PLLA/PB block copolymer-based metallosupramolecular polymers were prepared to study how nature of metal ion, composition of block copolymers influence morphology, crystallization and mechanical properties of metallosupramolecular polymers. • Comparison between mechanical properties of uncoordinated block copolymer, metallosupramolecular polymer showed significantly larger Young's modulus, higher elongation at break, and larger break strength. • For all metallosupramolecular polymers, metal−ligand complexes and polymer matrix was found to microphase-separated into nano-domains with a D around 4.5 nm due to the stacking of metal−ligand complexes. • Crystallization rate of PLLA in metallosupramolecular polymer featuring Co 2+ was lower than that of Cu 2+ and Fe 3+ , demonstrating that chain mobility relied on both dynamic character and bond strengths.