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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.

Initially developed to overcome the limited low-temperature impact resistance of polypropylene (PP) and allow its application in subzero temperatures, the PP/elastomer blends became a very important and industrially relevant material class. Within the last 40 years, a whole range of PP impact copolymers from multireactor processes have been developed that are capable of covering wide application areas. This review summarizes their developmental history and presents options for the in-reactor design of these polymers and their modification by compounding with elastomers and fillers or reinforcements after the polymerization. An overview of the application range is also presented together with a glimpse into the future of this material class.

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.