Heptane‐soluble material from atactic polypropylene. I. Fractionation and characterization of fractions

Abstract

A sample of commercial atactic polypropylene was extracted with ether and the residue extracted with boiling n-heptane. S i fractions of the heptane-soluble material, which is very similar to that obtained by heptane extraction of isotactic polypropylene, were obtained by stepwise addition of acetone to a solution in cyclohexane. Densities, melting points, and x-ray photographs of the fractions and the unfractionated material were obtained and infrared absorption spectra used to estimate tacticity. Molecular weights, determined by m a n s of a vapor pressure osmometer, ranged from about 3000 to about 25,000. That of the fraction of highest molecular weight was in good agreement with a separate determination by means of osmotic pressure measurements. Separation in fractionation occurred in order of decreasing molecular weight and increasing crystallinity as estimated from densities and x-ray photographs. Tacticity also seems to increase with decressing molecular weight. Melting points of the fractions were not entirely in the order expected from their molecular weights and estimated crystallinities, and it is possible that low D P isotactic material may be preferentially concentrated in the highest molecular weight fraction. It is emphasized that the unfractionated material may contain polymers possessing a range of order intermediate between those of purely atactic and purely isotactic polymer and that refractionation may be required in order to characterize the material completelv.

Thermoplastic Vulcanizates Based on Highly Compatible Blends of Isotactic Poly(propylene) and Copolymers of Atactic Poly(propylene) and 5‐Ethylidene‐2‐norbornene

“…[30] It has to be noted that the aPP that is reported to be miscible with iPP is often obtained as the heptane-soluble fraction of iPP, which also contains isotactic sequences. [33] Additionally, it is difficult to study the miscibility of iPP/aPP blends, since the blend components possess similar physical properties, such as electron density, scattering length density, refractive index, and T g . Figure 5 compares the influence of the type of rubber on the morphology of iPP/rubber blends containing 50 wt.-% of rubber, where the dark regions represent the rubber phase and the light regions the iPP phase.…”

Melting Point and Composition Distribution of Polyolefins by Fractionation

“…Hawkins and Smith (2) found a separation in polyethylene which occurred on the basis of short-chain branching frequency; Wija et al (3) found the column technique to be sensitive to crystallinity as well as molecular weight in the fractionation of polypropylene when the elution temperature was kept below the melting point of the polymer. Natta and several other workers (7)(8)(9)(10) reported the use of a series of two extraction steps to obtain three fractions for the characterization of polypropylene. The most refined experiments using different solvents of increasing boiling points to achieve fractionation of polypropylene on the basis of stereoregularity were recently reported by Nakajima and Fujiwara ( 1 1 ) and by Yamaguchi et al (12).…”

On the Evaluation of the Second Virial Coefficient and Activity in Dilute Solution by Vapor Pressure Osmometry

“…(1) in the form of product of molar fraction of solvent in solution drop m(=n(te)/no(te)+1}) by its activity. That is, (6) Considering dilute solution in which m01, m and 0 can be approximated by the following equations, respectively.…”