FRACTIONATION OF POLYPROPYLENE ACCORDING TO MOLECULAR-WEIGHT AND TACTICITY

Different extraction techniques were applied to the fractionation of i sotactic polypropylene. In solvent gradient extraction experiments two different solvent/non-solvent systems were studied. Investigation of the fractions obtained by GPC, DSC and FTIR indicated that the fractio nation proceeded according to molecular weight when ethylene glycol mo nobutyl ether/diethylene glycol monobutyl ether was used as a solvent/ non-solvent system at 159 - 161-degrees-C. The fractions covered a bro ad molecular weight range, had narrow molecular weight distribution an d showed only small variations in their isotacticity. Xylene/ethylene glycol monoethyl ether combination at 121 - 128-degrees-C separated po lypropylene in fractions mainly according to stereoregularity the sepa ration being less dependent on molecular weight. A large number of fra ctions with varying stereoregularity could be produced. Successive ext raction with solvents of increasing boiling temperature gave fractions differing both in molecular weight and isotacticity, and was the only method to separate the stereoblock copolymer. Comparison of heptane e xtractables and xylene solubles methods showed differences in the stru cture and molecular weight of heptane and xylene soluble fractions and heptane and xylene insoluble fractions, respectively.