Isothermal crystallization of metallocene‐based propylene/α‐olefin copolymers

Abstract

Isothermal crystallization and subsequent melting behavior of two propylene/hexene-1 copolymers and two propylene/octene-1 copolymers prepared with metallocene catalyst were investigated. It is found that ␥-modification is predominant in all copolymers. The Avrami exponent shows a weak dependency on comonomer content and comonomer type. At higher crystallization temperatures (T c ) the crystallization rate constant changes more rapidly with T c and the crystallization half-time substantially increases. Double melting peaks were also observed at high T c , which is attributed to the inhomogeneous distribution of comonomer units along the polymer chains and the existence of crystals with different lamellar thicknesses. The equilibrium melting temperatures (T°m) of the copolymers were obtained by Hoffman-Weeks extrapolation. It was found that the T°m decreases with increasing comonomer content, but are independent of comonomer type, implying that comonomer units are excluded from the crystal lattice. Dilation of the crystal lattice was also observed, which depends on crystallization, comonomer content, and comonomer type.

Overall crystallization kinetics of polymorphic propylene–ethylene random copolymers: A two-stage parallel model of Avrami kinetics

“…Avrami exponents were found to be non-integer, ranging from 3.0 to 1.6 with increasing comonomer content. Fractional Avrami exponents in the same range were also obtained in a recent comparative study of the crystallization kinetics of copolymers of propylene and 1-hexene and propylene 1-octene obtained with a metallocene catalyst [16]. In all these studies the crystallization kinetics were analyzed with simple onestage Avrami expressions.…”

Copolymerization of propylene with 1‐octene catalyzed by MgCl2/TiCl4/diether catalyst

“…Alloying with non‐crystalline polyolefin elastomers has been shown to be one of the most useful methods to modify the properties of PP materials. Although much attention has been focused on metallocene‐catalyzed propylene copolymerization and the resulting copolymer structures,1–18 there are very few reports on copolymerization using a Ziegler–Natta catalyst other than ethylene and propylene.…”

Study on the Phase Behavior of High Density Polyethylene – Ethylene Octene Copolymer Blends

“…Their blends with conventional polyolefins such as poly(propylene) and PEs produce new materials easily processable and having tailored properties for specific purposes. [4][5][6] It should be expected that the properties of blends of high density polyethylene (HDPE) and ethylene copolymers, with not very high content of the comonomer, will mostly depend on crystallinity, morphology and degree of dispersion, but on the contrary the properties seem to be considerably affected by the polymer miscibility in the molten state. [4,[7][8][9][10] Therefore the investigations on the kinetics of polymer crystallization are significant in both…”