Sequence length and crystallinity in alpha‐olefin terpolymers

Abstract

AbstractThe minimum sequence length for crystallisation in a polymer was determined by a novel kinetic approach using sequence analysis of a series of blocky terpolymers.Copolymers and terpolymers of ethylene, propylene, and but‐l‐ene were prepared with a Ziegler–Natta catalyst system. Compositions of feeds and polymers were analysed, and kinetic reactivity parameters were calculated using both the Fineman–Ross and Alfrey–Goldfinger approaches. The parameters were then applied to determine the sequence length distribution of each component in the terpolymers. Also, deliberate control of sequence lengths enabled synthesis of heptane‐soluble, rubbery polymers even using a catalyst system which normally produced blocky materials.Crystalline contents of the terpolymers were determined experimentally by nitric acid digestion. A critical comparison of the measured crystallinities with the calculated sequence length distributions was thereby made possible. From this comparison a minimum sequence length of monomer below which crystallisation did not occur was estimated; this length was approximately 20 backbone carbon atoms.