The fractionation of polypropylene

Abstract

Polypropylene has been fractionated by two methods of column fractionation. One, a gradient elution fractionation a t 150 "C., fractionates according to molecular weight only: the other, elution with one solvent a t increasing temperatures separates also according to crystallinity. The two methods are compared and it is shown that polypropylene is best characterized by applying the two methods successively. It is demonstrated that fractions obtained in this way between 60 and 95°C. in an increasing temperature fractionation consist of material possessing a wide range in molecular weight and in crystallinity. ZUSAMMENFASSUNG:Polypropylen wurde nach zwei verschiedenen Verfahren in einer Kolonne fraktioniert.Das eine, ein bei 150 "C. durchgefuhrtes Elutionsverfahren mit sich kontinuierlich andernder Losungsmittelzusammensetzung, bewirkt eine Trennung nur nach Molekulargewicht ; das andere, eine Elution mit cinem einzigen Losungsmittel bei steigender Temperatur, trennt auch nach Kristallinitat. Die beiden Methoden werden verglichen, und es wird gezeigt, dal3 der Aufbau des Polypropylens sich am besten bestimmen laBt, wenn man sie nacheinander anwendet. Es wird ferner gezeigt, dal3 in dieser Weise nach der Methode mit steigender Temperatur zwischen 60 und 95 O C erhaltene Fraktionen aus Material mit weiten Molekulargewichts-und Kristallinitatsbereichen bestehen.

Investigation of the stereodefect distribution and conformational behavior of isotactic polypropylene polymerized with different Ziegler–Natta catalysts

“…In the characterization of stereodefect distribution of iPP, solvent fractionation3–8 (usually an extremely time consuming and tedious work), high‐resolution high‐temperature 13 C NMR (HRHT 13 C NMR), temperature rising elution fractionation,7 crystallization analysis fractionation,3, 10–13 crystallization elution fractionation,14, 15 and thermal fractionation methods are often used. Among which, the thermal fractionation methods, such as stepwise isothermal crystallization16–19 and successive self‐nucleation and annealing (SSA),16, 20–23 are increasingly used in analyzing the microstructure of polyolefin, due to their enhanced resolution, effective molecular segregation, relatively short measurement times, free of solvent, and additional molecular structural information.…”

Chromatographic fractionation of polyolefins

“…The results for fractionation of a high-density polyethylene and a polypropylene sample are compared in (16) in his fractionation of polypropylene by a similar extraction method. Wesslau's data on the fractionation of linear polyethylene did not show this upward curvature in the experimental points, but he did conclude that there must be some upward curvature in the highest portions of the curve, because the weightaverage viscosities calculated from the straight-line curves were considerably higher than the measured values.…”

Fractionation and Characterization for a Propylene–Ethylene Random Copolymer

“…In order to investigate thoroughly the relationship between performance and macromolecular chain structure, it is necessary to make samples uniform. Temperature rising elution fractionation (TREF) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] has been shown to be a powerful technique to make crystal polyolefins uniform on the basis of their crystallizability and molecular weight. Through TREF experiments, a set of fraction polymers with uniform molecular weight and content of ethylene comonomer can be obtained; hereafter crystallization analysis fractionation (Crystaf) will be used to check the effect of fractionation by analyzing such parameters as σ and R, 16 which can define the broadness of the crystallization temperature distribution of the fraction polymers.…”

“…[16][17][18][19][20][21][22] Up to now most samples of propylene copolymers on investigation are the impact propylene-ethylene copolymers, a very complex blend. Even though after they have been fractionated by TREF, [3][4][5][6][7][8][9][10][11] each fraction polymer also consists of PE, PP, propylene-ethylene copolymer and so on, so it is difficult to make sure the relationship among performance, macromolecular chain structure and elution temperature. However the corresponding random copolymers of propylene are not blends, but has received much less attention, and our knowledge of the topic is very limited.…”