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.

The combination of moderately slow crystal growth at large undercoolings together with the practical absence of sporadic nucleation makes isotactic polypropylene (iPP) an ideal material for controlled nucleation. In this review the different types of nucleating agents -inorganic and organic, particulate and soluble -for the different crystal modifications of iPP (, b and c) are presented together with their working mechanism and criteria for activity. The interaction between polymer type, nucleating agent and processing conditions in determining mechanical and optical properties conclude the survey.

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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