Kinetics of Inverse Melting/Crystallization of Poly(dialkoxyphosphazenes)

Abstract

We have carried out a study of an unusual phase behavior of poly(dialkoxyphosphazenes) with pentoxy, butoxy, and propoxy substituents forming columnar mesophases which undergo a reversible transition into amorphous rubberlike state on cooling and reverse conversion into the original mesophases upon subsequent heating. On heating to around 200 °C they also yield isotropic melts. The DLI technique and polarized light microscopy were used for monitoring the overall rate of inverse 2D crystallization and linear growth rate of mesomorphic lamellae. The obtained kinetic data were treated in the framework of the Avrami approach and classical nucleation-controlled crystallization theory. Summarizing the results of our optical studies, we have concluded that the formation of 2D columnar mesophases in PDAP-C(3÷5) both in the usual way from the isotropic melt on cooling and via inverse freezing (crystallization) on heating the low-temperature reentrant amorphous phases is induced by heterogeneous athermal nuclei growing in two dimensions and yielding eventually a lamellar mesophase morphology.