Rotator Phases in Chemically Recyclable Oligocyclobutanes

26 August 2024, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

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 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.

Keywords

Phase behavior
alkanes
olefins
rotational disorder
crystallinity
phase transitions

Supplementary materials

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Supporting Information Text
Description
Wide-angle and small-angle X-ray scattering; differential scanning calorimetry; sample variability for WAXS; DVOCB(n) parameterization; comparison of experimental and simulated X-ray scattering peaks; order parameters for n-alkane systems; simulated melting temperature dependencies; additional orientation autocorrelation analysis; additional orientation correlation analysis.
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