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.