PP prepared (a) over a δ-TiCl3—AlEt2Cl heterogeneous catalytic system in the presence of hydrogen and (b) rac-Et(Ind)2ZrCl2—methylalumoxane homogeneous system, was modified by low-frequency glow discharges in air. Functional groups containing oxygen were found to appear in a thin surface layer. Under some conditions changes of the whole structure of PP were determined, evident in a great increase in the molecular mass (M) and melting temperature (Tm). The structural modification is especially considerable for the PP synthesized with the metallocene system b. M rose by a factor of ~10, the melting temperature rose from 130°C to 164°C, stereoregularity parameters enhanced and the fractional composition changed. The boiling ≪-heptane-soluble fraction increased from 7 to 96% (PP became highly isotactic). The crystalline structure of this PP was found to consist of the α- and the γ-modifications, the latter passing into the former when exposed to plasma. The UV-component of the plasma is believed to be responsible for the modifications observed.
Keywords: PP, modification by low-frequency glow discharge, stereoregularity, crystal structure