Unusual Crystallization Behavior of Polyethylene Having Precisely Spaced Branches

Systematic Studies of Morphological Changes of Precision Polyethylene

“…The isothermal crystallization at 14.5 °C of a polymer with random ethyl branch placement ( Et‐random ) reveals rapidly formed (within 6 s), disordered, or small‐sized, orthorhombic structures according to the WAXS profile . The small structure could be similar to the block‐like crystal suggested by Strobl .…”

“…In metallocene PE, which contains random branching, Mirabella found that the longer ethylene sequences crystallize before the shorter sequences, forming thick orthorhombic crystals composed of the longer ethylene sequences, with the shorter run lengths remaining in the amorphous phase. Conversely, in precisely branched PE, all run lengths are the same without long sequences to crystallize rapidly at higher temperatures, thereby allowing a transient hexagonal mesophase to form and persist long enough for the formation of energetically stable crystals …”

“…The transient hexagonal phase is absent in Et‐random , in which crystallization is relatively rapid . The differences in crystallization behavior between Et‐21 and Et‐random have been attributed to the ethylene sequence length distribution (precise in Et‐21, random in Et‐random ) …”

“…Below the nominal melting temperature ( T m ) determined by differential scanning calorimetry (DSC), Hex‐21 crystallizes through a transient hexagonal phase without branch inclusion . The thickening that occurs in Et‐21 does not occur in Hex‐21 . Above its T m , Hex‐21 does not exhibit crystallization.…”

Morphology control in precision polyolefins

“…Such interactions in the amorphous region were first observed at Sumitomo Chemical Company [31]. When ADMET polyethylene with either an ethyl branch or an n-hexyl was isothermally crystallized at the crystallization temperature, the formation of a transient-ordered mesophase and subsequent crystallization through packing optimization was observed.…”