Tough polymer with a gradual spatial change in the hydrogen bond density controlled by simple one-pot copolymerization

Abstract

We synthesized multiphase copolymers with a gradual change in hydrogen bond (H-bond) density at the phase boundary via simple one-pot copolymerization of two monomers. The copolymers had a gradient distribution of H-bonding groups along the chain due to the reaction rate difference between the two monomers. The gradient copolymers formed a microphase-separated structure consisting of hard phases surrounded by a soft phase, with a gradual change in monomer composition between the two phases. The mechanical properties of the copolymers depended on the total number of H-bonding units introduced in a chain; that is, more H-bonding groups led to higher rigidity and toughness, while fewer H-bonding groups contributed to better fatigue recoverability. The toughest polymer obtained in this study exhibited excellent stress at break (∼23 MPa) and toughness (∼38 MJ m−3) thanks to the efficient energy dissipation by H-bonds in the soft phase. We demonstrated that the simple one-pot copolymerization method could reproduce the gradual compositional change and multiphase structure, which provided a new design principle for tough polymers.