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

Abstract

A series of ethylene–propylene block copolymer fractions of differing compositions, while still retaining broad molecular weight distributions, were obtained by fractionation of polypropylene (PP) and polyethylene (PE) copolymers prepared by sequential polymerization of ethylene and propylene. The crystallization and melting behavior of the polypropylene‐block‐polyethylene fractions were studied. It was observed that the major component could suppress crystallization of the minor component, leading to a decrease in crystallinity and melting temperature. Non‐isothermal crystallization showed that crystallization of the ethylene block was less influenced by composition and cooling rate than the propylene block. At fast cooling rates, the ethylene block could crystallize prior to the propylene block. Isothermal crystallization kinetics experiments were also conducted. We found that the block copolymers with minor ethylene components had smaller Avrami exponents (n ≈ 1.0), hence indicating a reduced growth dimension of the PE crystals by the pre‐existing PP crystals. On the other hand, the ethylene block exhibited much larger Avrami exponents in those block copolymers with major ethylene contents. Copyright © 2004 Society of Chemical Industry

Morphology and nonisothermal crystallization of a polyacetal/poly(ε‐caprolactone) reactive blend prepared via a chain‐transfer reaction

“…In addition, the crystallization rate parameter of the PCL component ( Z c PCL ) for the reactive blend was always lower than that of the simple blend. The results are consistent with the fact that the reactive blend had a lower X c PCL value than the simple blend (Table II), indicating that the crystallization rate of the PCL part of the reactive blend was strongly retarded in the primary crystallization process 10, 11. It is reasonable to think that, in the case of the reactive blend, the POM segments crystallize first when the melt is cooling and give a frozen structure, and the crystallization of the PCL part with the covalent bonding to the POM chain is remarkably suppressed and perturbed in the confined microspace.…”

“…The reactive blend had an approximately 10% lower vale of X c PCL in comparison with the simple blend at each cooling rate. Similar conclusions about the reduction of the crystallinity of a minor block in block copolymers were reached by Xu et al10 and Gan et al11 The experimental results indicate that the major POM part in the reactive blend severely interferes with the crystallization of the minor PCL part, namely, the growth of the PCL crystallite, and eventually lowers X c PCL within the confined microspace.…”

“…However, the morphology and crystallization, which are the most important characteristics in determining the mechanical properties, have not yet been investigated for these modified POMs. In this case, these characteristics are expected to work in different and complicated manners because of the mutual influence of the POM and aliphatic polyester 1, 6–12. α,ω‐Dihydroxy poly(ε‐caprolactone) (PCL) is one of the useful chain‐transfer agents and is commercially available for practical use as a biodegradable plastic.…”

Structural and morphological development in polypropylene/poly(propylene‐1‐octene) in‐reactor alloy due to the competition between liquid–liquid phase separation and crystallization

“…The crystalline PP segments in the blocky copolymer fractions are chemically linked with other segments (such as propylene-octene random copolymer segments); leading to the lower melting temperature of PP segments. 32,33 Peaks also could due to different diffusion coefficient or kinetics. It should also be noted that the SSA technique only detects the defects distribution of propylene sequences long enough to crystallize, and the sequences too short to crystallize cannot be detected.…”

Fabrication of Nanostructures by Roll‐to‐Roll Extrusion Coating

“…Though PE is a semi‐crystalline polymer and can be supercooled, its crystallization rate is extremely high (compared to PP), which means that PE solidifies quickly below its static solidification temperature (110 °C). Hence, R does not become small enough to fill the nanoholes in the mold for PS and PE. From Figure , we see that the cooling rate of the PP melt near the mold is ≈10 7 K s −1 at V R = 60 m min −1 .…”