Investigation on Chain Microstructure of Metallocene Polyethylene

Polyethylene synthesized by metallocene catalysts exhibits excellent tear resistance and optical transparency， and can be used for high-end consumer products. The global and domestic demand for such materials has been increasing annually. To address the complexity and heterogeneity of the chain microstructure of metallocene polyethylene （M-PE）， preparative temperature rising elution fractionation （P-TREF） technique was employed to separate M-PE into eight fractions according to crystallizability. The composition， chain length， and sequence distribution of each fraction were analyzed to provide a complete chain microstructure distribution of M-PE. As the elution temperature of P-TREF increased， the molar fraction of hexene in the fractions decreased， while the melting temperature and crystallization temperature increased， indicating a gradual enhancement in crystallizability. 42.35% of M-PE resin corresponds to the fraction eluted at 60 ℃， which has the weakest crystallizability （Tm=99.5 ℃） and a moderate relative molecular mass （Mw=10.43×104）. Additionally， 24.38% of M-PE resin corresponds to the fractions eluted at 86~100 ℃， characterized by very strong crystallizability （Tm=119.4~127.4 ℃） and mass-average relative molecular masses of 8.37×104~10.57×104. Furthermore， 11.17% of M-PE resin was eluted at 73 °C， which has the highest relative molecular mass （Mw=11.58×104） but relatively weaker crystallizability （Tm=109.6 ℃）. Analysis of the detailed chain microstructure distribution of the metallocene polyethylene resins is a critical foundation for the production and development of high-performance metallocene polyethylene materials.