Structural transformations of anisotactic polypropylene submitted to low-frequency plasma treatment
Polimery 2001, No 3, 173
Anisotactic PP was prepared over the rac-Et (Ind)2ZrCl2 - MAO catalyst system and PP films were treated with a low-frequency (50 Hz) glow discharge plasma. The treatment resulted in whole-volume structural modifications whose extent was related to the initial α-/γ-phase ratio in original PP. At γ-phase contents ≤ 60%, nearly all the γ- became the α-phase, the m. p. of the PP treated rose (from 130 °C to 164 °C, Table 2), isotactic pentad fraction rose (13C NMR spectra, Table 5), stereoregularity increased (IR spectra, Table 4), and MW and MWD rose (Table 6). The PP treated thus acquired the properties of a PP prepared over heterogeneous Ziegler-Natta catalysts. As the γ-phase content was raised to 72%, only 10% of the γ- turned into the α-phase. At γ-phase contents ≥ 80%, the PP remained unaffected. The VUV component of the low frequency discharge plasma is believed to be responsible for the modifications observed. The VUV is believed to be too weak to modify PP containing high γ-phase proportions.
Keywords: polypropylene, low-frequency glow discharge plasma, structural modifications, α- and γ-phases