Rotator Phases in Chemically Recyclable Oligocyclobutanes

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.