THE INFLUENCE OF STEREOREGULARITY ON THE MISCIBILITY OF POLY(PROPYLENE)S

The melt miscibility of atactic poly(propylene) (a-PP) with isotactic (i-PP) and syndiotactic poly(propylene) (s-PP), respectively, is inves tigated by diffusion experiments ofi-PP/a-PP/i-PP or s-PP/a-PP/s-PP sa ndwich specimens using polarized light microscopy. It is shown that th e system a PP/i-PP is miscible in the melt, whereas for the system a-P P/s-PP no evidence for melt mixing is found. Pressure-volume-temperatu re (PVT) measurements of the three poly(propylene)s are carried out in order to determine the characteristic parameters of the Flory-Orwoll- Vrij equation-of-state theory. Theoretical predictions using the solub ility parameter concept are in agreement with the observed miscibility behavior of the blends. Differences in the cohesive energy densities of a-PP and i-PP on the one side, and s-PP on the other side, are foun d to be responsible for the phase behavior of the mixtures of poly(pro pylene)s with different stereoregularity. (C) 1997 John Wiley & Sons, Inc.