writer：Jie Qiu, Donghua Xu, Junchai Zhao, Yanhua Niu, Zhigang Wang*.
keywords：crystallization,polyolefins,thermal properties
source：期刊
specific source：Journal of Polymer Science: Part B: Polymer Physics 2008, 46, 2100-2115.
Issue time：2008年

A semicrystalline ethylene-hexene copolymer (PEH) was subjected to a

simple thermal treatment procedure as follows: the sample was isothermally crystallized

at a certain isothermal crystallization temperature from melt, and then was

quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating

scan of the sample by using differential scanning calorimeter (DSC). Particularly, an

intriguing endothermic peak (termed as Peak 0) was found to locate at about 45
C.

The multiple melting behaviors for this semicrystalline ethylene-hexene copolymer

were investigated in details by using DSC. Wide-angle X-ray diffraction (WAXD) technique

was applied to examine the crystal forms to provide complementary information

for interpreting the multiple melting behaviors. Convincing results indicated that

Peak 0 was due to the melting of crystals formed at room temperature from the much

highly branched ethylene sequences. Direct heating scans from isothermal crystallization

temperature (Tc, 104–118
C) were examined for comparison, which indicated

that the multiple melting behaviors depended on isothermal crystallization temperature

and time. A triple melting behavior could be observed after a relatively short isothermal

crystallization time at a low Tc (104–112
C), which could be attributed to a

combination of melting of two coexistent lamellar stack populations with different lamellar

thicknesses and the melting-recrystallization-remelting (mrr) event. A dual

melting behavior could be observed for isothermal crystallization with both a long

enough time at a low Tc and a short or long time at an intermediate Tc (114
C), which

was ascribed to two different crystal populations. At a high Tc (116–118
C), crystallizable

ethylene sequences were so few that only one single broad melting peak could be

observed.