Abstract
Molecular weight (M) dependence of the equilibrium melting temperature (Tm0) of isotactic polypropylene (iPP) with high tacticity ([mmmm] = 99.6%) was studied. Four fractionated iPPs with Mn = 23 × 103, 64 × 103 94 × 103, and 263 × 103 were used. Tm0 was obtained by using an improved method based on the Gibbs-Thomson plot proposed in previous papers. The effect of "melting kinetics" on melting temperature (Tm) was eliminated by observing isothermal melting of spherulites. The effect of lamellar thickening on Tm during Tm measurement at high temperature was also eliminated by observing thick lamellae formed at high crystallization temperatures (Tc = 148-166°C). With increase of M, Tm0 increased significantly. The empirical equation, Tm0 = 199.5 + 23.6 × log M - 2.0 × (log M)2 (°C), was obtained. The molecular weight dependence of the α2-α2′ transition was observed. The transition temperature (Tα2-α2′) also increased with increase of M. The ΔT dependence of lamellar thickness was concluded to be controlled by that of lamellar thickening.
Original language | English |
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Pages (from-to) | 733-752 |
Number of pages | 20 |
Journal | Journal of Macromolecular Science - Physics |
Volume | 42 B |
Issue number | 3-4 SPEC. |
DOIs | |
Publication status | Published - 2003 |
Externally published | Yes |
Keywords
- Equilibrium melting temperature
- Gibbs - Thomson plot
- Isotactic polypropylene
- Lamellar thickening
- Melting kinetics
- Molecular weight dependence
ASJC Scopus subject areas
- Chemistry(all)
- Condensed Matter Physics
- Polymers and Plastics
- Materials Chemistry