The effect of low-frequency plasma on the crystallization of unisotactic poly(propylene)

Effect of a low-frequency glow discharge on the structure of unisotactic PP films synthesized using a rac-EtInd(2)ZrCl(2)-methylalumoxane catalyst was studied. Exposure to the glow discharge plasma leads to changes in the hul k polymer structure, which depend on the relative content of gamma and alph a phases in the initial sample. An especially pronounced effect is observed in the samples containing less than or equal to 60% gamma-PP, where a near ly complete gamma --> alpha transition takes place. The transition is accom panied by increasing melting temperature (from 130 to 164 degrees C), growi ng molecular mass, and broadening molecular mass distribution; as a result, the properties of the initial unisotactic PP approaches those characterist ic of the polymer obtained with conventional Ziegler-Natta catalysts. In ad dition, the structural transformations lead to an increase in the polymer c rystallization rate and the Avrami parameter. When the gamma-PP content in the initial sample increases to 72%, only 10% of this phase transform into the alpha-PP. In samples with the gamma-PP content exceeding 80%, no struct ural transformations at all are observed upon exposure to the glow discharg e plasma.