Evaluation of Multiple Melting Peaks of Propylene-Ethylene Copolymers

Abstract

ABSTRACT:Multiple melting peaks phenomena have been investigated in terms of compositional heterogeneity, crystallization temperature, cooling rate, heating rate, annealing and crystal structure for low ethylene content block and random propylene-ethylene copolymers. The experimental results suggested that the compositional heterogeneity and crystal morphology play an important role in the cause of multiple melting behavior.

Effect of crystallization temperature and propylene sequence length on the crystalline structure of propylene-ethylene random copolymers

“…The shoulder peak is located at about 155℃. The double melting behavior of α-iPP was also observed by Feng et al in their study on the propylene-ethylene copolymers [22] . They associated these peaks with the melting of α-iPP and argued that with high supercooling, small and imperfect crystals were created.…”

“…This has been revived by the recent development of the new metallocene catalyst systems, which allow incorporation of large amount of comonomers, for producing well-defined iPP copolymers with high stereoregularity. As a result, the interest in the structural characterizations of γ-iPP increased in the past several years [12][13][14][15][16][17][18][19][20][21][22][23][24] .…”

Study of crystallization and melting behavior of polypropylene‐block‐polyethylenes copolymers fractionated from polypropylene and polyethylene mixtures

“…The complex microstructure has made it impossible to correlate the structure and properties of HIPP. As a result, this type of material was usually fractionated and the crystallization and morphology of the obtained fractions with different structures were investigated separately 6–12. These studies can help us understand the morphological formation and origin of improved mechanical properties of HIPP.…”

Origin of Chemical Composition of Ethylene/Propylene Copolymer Produced with Ziegler–Natta Catalyst

“…Moreover, their versatility and cost efficiency in existing plants keep the competitiveness of Ziegler–Natta catalysts even for ethylene‐based copolymer of certain grades. The multi‐site nature of Ziegler–Natta catalysts is essential for broad molecular weight distribution, while it simultaneously results in relatively broad chemical composition distribution . Copolymer produced with Ziegler–Natta catalysts is known to have a block‐wise chemical structure, in contrast to the random nature of metallocene‐based copolymer .…”

“…Moreover, states of active sites vary in the course of polymerization due to interaction/reactions with alkylaluminum activator and donors . Most of previous researches have assumed that states of active sites mainly affect the chemical composition and its distribution of produced copolymer . Kakugo et al studied the influence of the amount of an external donor on the chemical composition distribution of ethylene/propylene copolymer .…”