Abstract:

Two types of cast polypropylene special materials， CPP1 and CPP2， were separated using a rising elution fractionation technology， and their chain structure and melting and crystallization behavior were characterized using infrared spectroscopy and differential scanning calorimeter. High?temperature gel permeation chromatography was performed to determine the comonomer content， sequence distribution， and the molecular weight and its distribution of the separated products. The results indicated that for the low?temperature elution components （<100 ℃）， the CPP1 and CPP2 exhibited low?temperature fractions of 9.29 wt%and 26.29 wt%， respectively. As for the high?temperature elution components （≥120 ℃）， the CPP1 presented a high?temperature fraction of 3.16 wt%， whereas the Sample CPP2 only showed a very small high?temperature fraction 0.18 wt%. In the CPP1， the fractions at 120 and 140 ℃ contain high ethylene content comprising of ethylene?propylene block copolymers. In the high?temperature fractions， the materials usually have higher isotacticity and crystallinity， which facilitates the enhancement in the rigidity of the resin. The CPP2 almost have higher molecular weights than the CPP1 in various fractions， and it showed a wider molecular weight distribution. The CPP1 contains two melting points at 127.2 and 148.4 ℃. The melting point at 127.2 ℃ was derived from the shorter PP sequence and the PE block in the ethylene?propylene block copolymer， whereas the melting point at 148.4 ℃ results from the higher isotactic PP sequence. The CPP2 exhibited a main melting peak at 150.7 ℃ along with a shoulder peak at 139.1 ℃ in its melting curve. The two higher melting temperatures were both caused by the melting of PP sequences with different lengths.

Key words: polypropylene, casting film, preparative temperature rising elution fractionation, molecular weigh, melting, crystallization behavior