The influence of stereoregularity on the miscibility of poly(propylene)s

Abstract

The melt miscibility of atactic poly(propylene) (a‐PP) with isotactic (i‐PP) and syndiotactic poly(propylene) (s‐PP), respectively, is investigated by diffusion experiments of i‐PP/a‐PP/i‐PP or s‐PP/a‐PP/s‐PP sandwich specimens using polarized light microscopy. It is shown that the system a‐PP/i‐PP is miscible in the melt, whereas for the system a‐PP/s‐PP no evidence for melt mixing is found. Pressure‐volume‐temperature (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 solubility 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 found to be responsible for the phase behavior of the mixtures of poly(propylene)s with different stereoregularity. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1135–1144, 1997

Macromorphology of polypropylene homopolymer tacticity mixtures

“…The results suggest that the iPP/aPP blend pair exhibits greater miscibility than the 9 and Thomann et al [13][14][15] This conclusion is also consistent with studies showing a rheological similarity of aPP with iPP 23,24 but not with sPP. 24 The conclusion that the iPP/aPP blend is of the UCST type is also in general agreement with the predictions of Maier et al, 9 although this study suggests absolute values of the UCST for equimolecular mixtures that are higher than predicted and accessible to technologically relevant molecular weights. This study suggests that the critical molecular weight for phase separation in the melt (200°C) lies between M w values of 200,000 and 400,000 for aPP based on the aPP1-type tacticity microstructure.…”

“…The apparent sensitivity of the phase behavior to changes in chain microstructure (and molecular weight) may also explain conflicting viewpoints regarding the miscibility of iPP with aPP. 9,10 Similar to the case of aPP chain microstructure, changes in molecular weight in the iPP/ aPP1 blends are consistent with the optical phase texture being related to thermodynamic-driven phase separation concurrent with crystallization if the influence of molecular weight on mobility is considered. The optical phase texture is lost when the molecular weight of the blend components is reduced (M w ϳ 100,000) and the aPP chain microstructure is kept constant (Fig.…”

“…8 -10 The aPP component is reported to be miscible with iPP in the molten state from the evaluation of an equation of state theory using low molecular weight [weight-average molecular weight (M w ) ϳ 50,000 g mol Ϫ1 ] aPP. 9 Similar conclusions have been drawn from small-angle neutron scattering measurements. 8 However, aPP has also been reported to be immiscible with iPP in the solid state, as observed by transmission electron microscopy (TEM) when the aPP sample has a high M w (Ͼ280,000 g mol Ϫ1 ) and a narrow molecular weight distribution [M w /number-average molecular weight (M n ) ϳ 2.3-2.5).…”

Orientation of Phenyl Rings and Methylene Bisectors at the Free Surface of Atactic Polystyrene

“…This level of coarsegraining has been successfully applied to simulations of polypropylene melts. 12 It successfully reproduces the known dependence of the miscibility of these melts on the stereochemical composition of the chains, [13][14][15][16] and also provides the mechanism responsible for the demixing of syndiotactic polypropylene from either isotactic or atactic polypropylenes in the melt. 12 Therefore our treatment of coarse-grained chains can successfully mimic subtle interactions in multichain systems.…”

Morphology development during isothermal crystallization. I. Isotactic and atactic polypropylene blends

“…5 The miscibility between iPP and aPP has also received attention. [5][6][7][8] The aPP component has been reported to be miscible with iPP in the molten state on the basis of an evaluation of an equation of state. 6 The aPP sample in this study had a low molecular weight [weight-average molecular weight (M w ) ϭ 50,000 g mol Ϫ1 ].…”