CRYSTALLIZATION AND MELTING OF POLYMERS . 26. HIGH-TEMPERATURE HEDRITIC CRYSTALLIZATION OF THE BETA-MODIFICATION OF ISOTACTIC POLYPROPYLENE

The high-temperature crystallization of the beta-modification of polyp ropylene (beta-IPP) induced by an active beta-nucleating agent was stu died by polarizing light microscopy. It was established that, in the e arly stage of crystallization of beta-IPP, hedrites were formed as pre cursors of the spherulitic crystallization. Hedrites seen flat-on were characteristic hexagonal formations (hexagonites) with low birefringe nce. The central core of hexagonites had positive birefringence. Hedri tes seen edge-on were rod-like formations with strong negative birefri ngence which would transform into a radially symmetric spherulitic for m through sheaf-like then oval (ovalite) arrengements. Hedrites may re ach considerable sizes (several hundred micrometers). At temperatures of isothermal crystallization higher than the critical (T(beta alpha) = 140 C-), hedrites with mixed polymorphic structures of alpha- and be ta-modifications were formed.