Elucidating the Rotator Phase in a Chemically Recyclable Polyolefin

Between the fully ordered crystal phase and isotropic liquid phase, there is a remarkable intermediate phase called rotator phase for chain molecules like alkanes. In this phase, chains have a long-range positional order but also have rotational freedom. The rotator phase has significance in both science and engineering. It plays an important role in crystal nucleation, lubrication behavior, and bioprocess of phospholipids. Recently, a novel family of recyclable hydrocarbon material, (1,n'-divinyl)oligocyclobutane (DVOCB) has been synthesized and found to have evidences of rotator phase. Different from the alkane chains, the rotator phase in DVOCB has a large temperature range and is stable in polymers, which allows wide applications. To investigate the rotator phase in DVOCB, we performed a comparison study of DVOCB and alkane with molecular dynamic simulations. It is found that the relaxation time of rotation has a distinct change from crystal phase to rotator phase. The timescale change in alkane chains is more dramatic than in DVOCB, because ring structure in DVOCB disrupts its chain axial correlation. This finding could also explain the rotator phase in other polymers, such as hydrogenated polynorbornene (hPN). In the end, this work provides fundamental understanding of rotator phase in DVOCB and illustrates design rules of rotator phase polymers.