Rotator Phases in Chemically Recyclable Oligocyclobutanes

Abstract

Rotator phases are rotationally disordered yet crystalline stable states found in many materials. The presence of a rotator phase leads to unique properties that influence processing methods and offer potential applications in areas such as thermal energy storage, lubrication, and sensing. Recently, a novel family of chemically recyclable oligomers, (1,n′-divinyl)oligocyclobutane (DVOCB(n)), has shown evidence of rotator phases. This study combines experimental characterization and molecular dynamics simulations to confirm and elucidate the rotator phases in DVOCB(n). Compared with well-studied n-alkanes, DVOCB(n) exhibits distinct structural, thermodynamic, and dynamical characteristics. The crystal-to-rotator phase transition of DVOCB(n) involves a shift from stretched to isotropic hexagonal lamellar packing, captured by a rotational order parameter tracking local chain orientations orthogonal to the chain axis. Unlike n-alkanes, where rotational relaxation times are constant and long in the crystal phase before dropping dramatically during the crystal-to-rotator phase transition, relaxation times decrease more gradually upon heating in DVOCB(n), including continuously throughout the transition. This behavior is attributed to its unique enchained-ring architecture, which allows for semi-independent rotation of chain segments that promotes overall rotational disorder. This work provides a fundamental understanding of rotator phases in DVOCB(n) and highlights differences from those of conventional materials. The analyses and insights herein will inform future studies and applications of DVOCB(n) as well as other materials with rotator phases.