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 the presence of and elucidate rotator phases in DVOCB($n$), with comparison to well-studied n-alkanes. In DVOCB($n$), the crystal-to-rotator phase transition 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. Furthermore, rotational relaxation times decrease gradually upon heating, including through the transition to a rotator phase. This contrasts with n-alkanes, for which relaxation times are relatively constant and longer in the crystal phase before dropping sharply during the crystal-to-rotator phase transition. Such behavior is attributed to the unique enchained-ring architecture of DVOCB($n$), 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 conventional materials. The analyses and insights herein will inform future studies and applications of DVOCB($n$), as well as other materials with rotator phases.