STATES OF ORDER IN MACROMOLECULAR MULTICOMPONENT SYSTEMS OF LINEAR POLYETHYLENES OF DIFFERENT DENSITIES AND POLYISOBUTENE .2. MULTISTEP CRYSTALLIZATION

The phenomenon of multistep crystallization was observed In binary sys tems of four different polyethylenes (PE) and polyisobutene (PIB) with a surplus of PIB by means of thermoanalytical examinations and X-ray diffraction experiments with synchrotron radiation. If PE in the blend s is homogeneously dispersed, three crystallization steps were found, depending on the thermal treatment of the melt. Two steps (those with higher crystallization temperatures) of crystallization in the PE-aggr egations are initiated by heterogeneous nucleation. Those nuclei initi ating crystallization at the highest temperature change with longer an nealing periods and/or higher temperature in the melt irreversibly int o much less efficient nuclei or lose their capability of initiating th e crystallization process completely. In the latter case at the lower temperature PE may crystallize at a different type of nuclei occasiona lly present in the aggregations. In a third step with the lowest cryst allization temperature nucleation may be initiated by Interactions at the interfaces between the two components. This is at least an indicat ion for a compatibility of the components in the melt of systems with a surplus of PIB.