For understanding the correlation chain from the polymer structure to the final application properties of propylene-ethylene random copolymers, four commercial grades with different ethylene content (0 -8 mol %) but identical molecular weight distributions were investigated. Structural investigations concerning the comonomer distribution, using two different techniques (temperature rising elution fractionation and stepwise isothermal segregation), showed an increase of inhomogeneity with the total comonomer content, which was reflected for temperature rising elution fractionation in a widening of the elution temperature range. Crystallinity and crystallization speed studies confirmed the reduced overall crystallinity and increase of ␥-modification content as reported previously, but they also showed the reason for these effects in the distinctive decrease of the spherulitic growth speed. Good correlations of all these parameters to the mechanical performance of the four materials were obtained.

ABSTRACT:The influence of the molecular weight of the dispersed phase of ethylene-propylene rubber modified isotactic polypropylene (iPP/EPR) reactor blends was studied in a systematic way by varying their intrinsic viscosity (IV) from 1.7 to 6 dg/L while keeping the matrix melt flow rate (MFR) constant. Standard Charpy measurements were completed by a continuous analysis of the impact properties over a wide range of temperatures at fixed test speed. As expected, the higher the IV, the tougher the iPP/EPR blends. However, ductile-brittle transitions as key mechanical descriptors did not correlate linearly with M w , suggesting the macroscopic behavior of the blend to be controlled primarily by the morphology of the EPR particles. Moreover, strong correlations were found between impact mechanical properties, amount of stress-whitening, and strength of the molecular relaxations estimated from dynamical mechanical analysis.

The evolution of crystallinity and mechanical properties of two different series of PPhomopolymers (RE grades coming directly from the polymerization reactor and CR grades priorly subjected to a defined degradation process) as influenced by the molar mass and heterogeneous nucleation was investigated, including one highly isotactic material to check the tacticity influence. In principle, the effects seem explainable by differences in the number of nuclei and the spherulithic growth speed, which were determined separately. The nucleation effects are similar for all materials, but strongly dependent of the molar mass of the materials. Apart from the bulk material properties, also the development of shearinduced structures is strongly influenced by molar mass and nucleation, contributing additionally to mechanics. 0 1996 John Wiley & Sons, Inc.

The evolution of crystallinity and mechanical properties of two different series of PPhomopolymers (RE grades coming directly from the polymerization reactor and CR grades priorly subjected to a defined degradation process) as influenced by the molar mass and heterogeneous nucleation was investigated, including one highly isotactic material to check the tacticity influence. In principle, the effects seem explainable by differences in the number of nuclei and the spherulithic growth speed, which were determined separately. The nucleation effects are similar for all materials, but strongly dependent of the molar mass of the materials. Apart from the bulk material properties, also the development of shearinduced structures is strongly influenced by molar mass and nucleation, contributing additionally to mechanics. 0

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