PRECIPITATION OF POLYPROPYLENE AND OF HIGH-DENSITY POLYETHYLENE FROM STIRRED, BINARY-SOLUTIONS

The precipitation of polypropylene (PP) and of high-density polyethyle ne (HDPE) from decalin solutions, under stirring, yields two polymer-r ich phases, one of which is globular and the other is fibrous. Infrare d spectra, X-ray diffractograms, optical microscopy and DSC curves sho wed that the fibrous PP precipitate is richer in stereoregular polymer and yields films more resistant to recrystallization than the globula r precipitate. The fibrous HDPE precipitate has a higher methylene/met hyl ratio and a higher crystallinity than the globular precipitate. Th ese results are consistent with the predictions of reduced flexibility and stored free-energy formalisms.