Fractionation and Chain Microstructure of Polypropylene Homopolymer for Spinning

Polypropylene （PP） fibers have extensive applications in multiple fields such as clothing， baby diapers， non-woven fabrics， and geotextiles. The PP resins used for spinning need to have specific chain microstructure distribution to meet the special requirements of spinning process. In this paper， the effective fractionation of PP homopolymer （HPP） is achieved through preparative temperature rising elution fractionation （P-TREF） technique. A variety of characterization methods such as 13C nuclear magnetic resonance spectroscopy （13C NMR）， high-temperature gel permeation chromatography （HT-GPC）， and differential scanning calorimetry （DSC） were used to determine the pentad distribution， isotacticity， relative molecular mass and its distribution， melting temperature of the fractions at each elution temperature， aiming to reveal the chain microstructure distribution of PP homopolymers used for spinning. HPP is mainly composed of high-temperature fractions （110~125 ℃） with a total mass percentage as high as 91.21%. In contrast， the contents of low-temperature fractions （35~105 ℃） and extremely high-temperature fractions （130~140 ℃） are relatively low， with a mass percentage of 8.05% and 0.73% respectively. The mass-average relative molecular mass of the 110~125 ℃ fraction is 8.00×104~28.43×104， the isotacticity is 88.0%~93.4%， and the melting point is 159.0~165.3 ℃. These results indicate that HPP is mainly composed of fractions with strong crystallizability. The longer crystalline sequences in these fractions contribute to the orientation of the chains during fiber spinning.