THE MODIFICATION OF POLYPROPYLENE STRUCTURE BY LOW-FREQUENCY GLOW-DISCHARGE

The modification of polypropylene (PP) was carried by low-frequency gl ow discharge in air (or nitrogen). The PP samples had been obtained wi th the heterogeneous catalytic system delta-TiCl3-AlEt2Cl in the prese nce of hydrogen and with the homogeneous system racE-t(Ind)(2)ZrCl2-me thylalumoxane (MAO). It was shown that plasma treament results in cons iderable changes in the whole structure of PP. These changes manifest themselves in a great increase in molecular masses (MM) and melting te mperatures (T-m) of the all investigated samples. However, structural modfication is especially great for PP synthesized with the metallocen e system. In this case the molecular mass has increased approximately 10-fold and the melting temperature has risen from 130 to 164 degrees C. Simultaneously, the fraction of isotactic pentads and the steroregu larity parameters have increased, In the same case a drastic fall in t he solubility of the polymer took place. So the fraction of the polyme r insoluble in boiling heptane has increased from 7 to 96%, that is, P P has become highly isotactic. Before the treatment the crystalline st ructure of the above PP consisted of alpha- and gamma-modifications. W e have shown that plasma induces the transformation of the gamma-form into the alpha-form. We believe that these changes in PP structure wer e caused by the UV component of the plasma radiation. (C) 1998 Elsevie r Science Ltd. All rights reserved.