Trans-Rich Structures in Early Stage Crystallization of Polyethylene

The kinetic pathway by;which molten polymers transform into multi-length-scale, semicrystalline structures upon cooling is critical to their processing, properties, and ultimate performance. However, for the case of polyethylene (PE), critical questions remain concerning early stage kinetics of isothermal crystallization. Here we utilize Raman spectroscopy, in conjunction with turbidity and depolarization measurements, to probe crystallization kinetics in PE because of its unique ability to simultaneously measure intrachain consecutive trans conformations (locally straight) and interchain orthorhombic crystallinity. We analyze the spectra within the context of a three-state model to extract the mass fraction of conformations that are locally straight but not part of the orthorhombic crystal, which we term noncrystalline consecutive trans (NCCT). We first validate this methodology on the n-alkane C21H44 where the NCCT mass fraction is expected to be large and then apply it to the early stage crystallization kinetics of PE. We find that the NCCT conformations appear in conjunction with orthorhombic crystallinity, indicating that the growing early stage clusters are rich in NCCT conformations.