Preparation of a Tough Elastomer by the Introduction of Multiple Flexible Hydrogen Bonds via Simple Modification

The introduction of multiple hydrogen bonds (H-bonds) into polymers as dynamic cross-links can increase toughness and enable dynamic functions. In this work, we report a simple and versatile method to introduce a novel flexible H-bond group, namely, vicinal amino alcohol (VAA), into commercially available diene-based polymers. We found that structurally simple and flexible H-bonding groups can act as effective dynamic cross-links, conferring mechanical robustness without sacrificing dynamic properties. These VAA-modified polybutadiene (PB) were synthesized by the epoxidation of PB followed by a ring-opening reaction with various amines. PB modified with vicinal (ethylamino)alcohol presented approximately a 90-fold increase in stress at break and approximately a 75-fold increase in toughness. The VAA modification endowed PB with mechanical strength comparable to that of covalently cross-linked elastomers while maintaining dynamic properties such as self-recoverability. Quantum chemical calculations revealed that VAA adopted a wide variety of stable H-bonded dimer structures, which stabilized the dimer both enthalpically and entropically. Moreover, this method is applicable to other diene polymers, such as polystyrene-block-polybutadiene-block-polystyrene. This study paves the way to transform various diene-based polymers into robust yet dynamic high-performance materials by utilizing the unique features of flexible H-bonds.