On the origin of the multiple melting observed after izothermal crystallization
of homogeneous ethylene/1-octene copolymers (in English)
Polimery 2004, No 6, 414
The complex melting behavior of homogeneous ethylene/1-octene copolymer isothermally crystallized at 93oC was studied by means of DSC and time resolved SAXS and WAXS. Two melting peaks, observed in DSC during heating after the isothermal crystallization, point to the existence of two populations of crystals of different thermal stability. This hypothesis is confronted and supported with the results of SAXS and WAXS investigations. Two populations of crystals are created due to segregation of more branched (of higher 1-octene content) parts of copolymer chains into separate areas in the melt. More stable crystals, melting at higher temperatures, are formed at the beginning of crystallization. Less stable ones originate later in the areas enriched with 1-octene, segregated away from the growth front during primary crystallization. No evidences on the existence of isolated fringed micellar crystallites were found. The crystals of each group are of lamellar type. All lamellae show the same thickness. The difference in their thermal stability, as revealed by two melting peaks in DSC curves, most probably results from different state of their basal surfaces.
Keywords: homogeneous copolymers, ethylene/1-octene copolymers, morphology, isothermal crystallization, multiple melting, X-ray diffraction, differential scanning calorymetry
On the origin of the multiple melting observed after izothermal crystallization of homogeneous ethylene/1-octene copolymers (in English)