J. Varga et Gw. Ehrenstein, CRYSTALLIZATION AND MELTING OF POLYMERS . 26. HIGH-TEMPERATURE HEDRITIC CRYSTALLIZATION OF THE BETA-MODIFICATION OF ISOTACTIC POLYPROPYLENE, Magyar kemiai folyoirat, 103(8), 1997, pp. 352-358
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.