Rotator Phases\nin Chemically Recyclable Oligocyclobutanes

Rotator phases are rotationally disordered yet crystalline\nstable\nstates found in many materials. The presence of a rotator phase leads\nto unique properties that influence processing methods and offer potential\napplications in areas such as thermal energy storage, lubrication,\nand sensing. Recently, a novel family of chemically recyclable oligomers,\n(1,<i>n</i>′-divinyl)oligocyclobutane (DVOCB(<i>n</i>)), has shown evidence of rotator phases. This study combines\nexperimental characterization and molecular dynamics simulations to\nconfirm and elucidate the rotator phases in DVOCB(<i>n</i>). Compared with well-studied <i>n</i>-alkanes, DVOCB(<i>n</i>) exhibits distinct structural, thermodynamic, and dynamical\ncharacteristics. The crystal-to-rotator phase transition of DVOCB(<i>n</i>) involves a shift from stretched to isotropic hexagonal\nlamellar packing, captured by a rotational order parameter tracking\nlocal chain orientations orthogonal to the chain axis. Unlike <i>n</i>-alkanes, where rotational relaxation times are constant\nand long in the crystal phase before dropping dramatically during\nthe crystal-to-rotator phase transition, relaxation times decrease\nmore gradually upon heating in DVOCB(<i>n</i>), including\ncontinuously throughout the transition. This behavior is attributed\nto its unique enchained-ring architecture, which allows for semi-independent\nrotation of chain segments that promotes overall rotational disorder.\nThis work provides a fundamental understanding of rotator phases in\nDVOCB(<i>n</i>) and highlights differences from those of\nconventional materials. The analyses and insights herein will inform\nfuture studies and applications of DVOCB(<i>n</i>) as well\nas other materials with rotator phases.