Effect of high polymerization temperature on the microstructure of isotactic polypropylene prepared using heterogeneous ticl 4 /mgcl 2 catalysts

The effects of alkylaluminum and polymerization temperature on propylene polymerization without an external donor in the use of a TiCl 4 –MgCl 2 –diether(BMMF) catalyst were investigated. The results indicated that with increasing polymerization temperature the concentrations of [mmmm] of heptane‐insoluble poly(propylene) (PP) fraction increased. Crystallization analysis fractionation (CRYSTAF) results showed the fractions of different crystallization temperatures were changed according to various polymerization temperatures. The activity with Et 3 Al as cocatalyst at 100°C was much lower than that at 70°C. However, the activity with i ‐Bu 3 Al at 100°C was as high as that at 70°C. The fraction of high‐crystallization temperature of PPs obtained with i ‐Bu 3 Al increased with increasing polymerization temperature, which was opposite to that with Et 3 Al, thus implying that the copolymerization of propylene with the monomer arising from Et 3 Al led to the lower crystallization ability of PPs obtained with Et 3 Al. The terminal groups of PP suggested that the chain‐transfer reaction by β‐H abstraction was the main chain‐transfer reaction at 120°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3980–3986, 2003