Theoretical Investigation of Nano-Scale Organization in Blends of Semicrystalline/Semicrystalline Polymers by Small Angle X-ray Scattering

A theoretical model has been derived for the calculation of small-angle X-ray scattering (SAXS) data from stacks of crystalline lamellae in which two or more kinds of lamellae are mixed within the same stack according to different statisticalmodels, ranging from the fully randommode, to alternated one, up to block configurations. The model has been used to study the complex lamellar morphology which develops from melt in some blends obtained bymixing two semicrystalline samples of isotactic polypropylene (iPP) characterized by different degree of stereoreoregularity, similar molecular masses, and melting temperatures of ≈162 C for the more stereoregular component iPP1 and ≈74 C for the less stereoregular one iPP2. It is shown that for samples crystallized in conditions far from thermodynamic equilibrium, the observed SAXS intensity profiles may easily show absence of correlation peaks, associated with high amount of diffuse scattering, not easy to unravel. Using our theoretical approach we show that featureless SAXS intensity distribution may correspond to formation of disordered lamellar stacks with lamellae of the two components randomly mixed within the same stacks. The tendency of iPP1 and iPP2 to form mixed lamellar stackswith a random configuration provides clear evidence that the two components are miscible in the melt.