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Fractionation of polypropylene according to molecular weight and tacticity

1994; Wiley; Volume: 195; Issue: 5 Linguagem: Inglês

10.1002/macp.1994.021950507

1521-3935

Arja Lehtinen, Ritva Paukkeri,

Membrane Separation and Gas Transport

Abstract Different extraction techniques were applied to the fractionation of isotactic 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 fractionation proceeded according to molecular weight when ethylene glycol monobutyl ether/diethylene glycol monobutyl ether was used as a solvent/non‐solvent system at 159–161°C. The fractions covered a broad molecular weight range, had narrow molecular weight distribution and showed only small variations in their isotacticity. Xylene/ethylene glycol monoethyl ether combination at 121–128°C separated polypropylene in fractions mainly according to stereoregularity, the separation being less dependent on molecular weight. A large number of fractions with varying stereoregularity could be produced. Successive extraction 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 extractables and xylene solubles methods showed differences in the structure and molecular weight of heptane and xylene soluble fractions and heptane and xylene insoluble fractions, respectively.