Equilibrium melting temperature of isotactic polypropylene with high tacticity. 2. Determination by optical microscopy

Koji Yamada, Masamichi Hikosaka, Akihiko Toda, Shinichi Yamazaki, Katsuharu Tagashira

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Abstract

In part 1 of this series, we proposed a new method to determine the correct equilibrium melting temperature (Tm0), Effects of the "melting kinetics" and lamellar thickening were omitted from Tm. The correct Tm0 of isotactic polypropylene (iPP) ([mmmm] = 99.6%, Mn = 64 × 103, and Mw/Mn = 2.4) was observed to be 186.1 °C. In this paper, the rigorous Gibbs-Thomson plot was obtained by using the direct correspondence between maximum melting temperature (Tm,max) and maximum lamellar thickness (lmax).Tm, max and lmax were observed by means of optical microscope and transmission electron microscope (TEM), respectively. The validity of the Gibbs-Thomson plot obtained by means of a differential scanning calorimeter (DSC) (part 1 of this series) was confirmed by comparing it with the rigorous Gibbs-Thomson plot in this paper. The Hoffman-Weeks plot is widely used as one of the methods to obtain Tm0. It was shown that the Hoffman-Weeks plot is correct only when l ∝ 1/ΔT, where ΔT is the degree of supercooling, is satisfied. However, in the case of iPP, the condition is not satisfied, and so the result obtained by the Gibbs-Thomson plot is not equivalent to that obtained by the Hoffman-Weeks plot. The existence of α2′ phase was confirmed again by breakings in slopes of l and Tm against Tc at 159 °C. Furthermore, the broad bimodal distribution of l was caused by the difference between the lamellar thickening growth rate of isolated mother lamellae and the lamellae thickening rate of stacked daughter lamellae.

Original languageEnglish
Pages (from-to)4802-4812
Number of pages11
JournalMacromolecules
Volume36
Issue number13
DOIs
Publication statusPublished - Jul 1 2003
Externally publishedYes

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ASJC Scopus subject areas

  • Materials Chemistry

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