The thermodynamic properties of s-type trans-l,4-polyisoprene crystals grown from solution were investigated by differential scanning calorimetry and X-ray diffraction. The equilibrium melting temperature estimated from the plot of melting temperature against crystallization temperature was found to be 101.5°C. The surface free energy calculated from the slope of the plot of melting temperature against reciprocal lamellar thickness was found to be 9.6 kJ mol- 1, in good agreement with Keller and Martuscelli's work. The lamellar thickness of ~t-TPI crystals grown at high crystallization temperatures (10-35°C) increased with the increase of crystallization temperature. At low crystallization temperatures, e.g. - 10 and -20°C, the lamellar thickness was greater than the expected value. This may be caused by the occurrence of isothermal thickening. At such low temperatures, the lamellar thickness was independent of crystallization temperature. The chain-folded lamellae of ~-TPI crystals grown from hexane were estimated to have looser and longer surface folds than those grown from amyl acetate at the same crystallization temperature. Based on the crystallinity data, the stem lengths of lamellae grown from hexane were found to be slightly shorter than those of lamellae grown from amyl acetate. These findings are in agreement with the results determined by ozonolysis-g.p.c, measurements.
Посилання на статтю:
Structure of solution-grown trans-l,4- polyisoprene crystals: 3. Thermodynamic properties of -TPI crystals / Ploenpit Boochathum*, Yasuyuki Tanaka and Kenji Okuyama // Polymer. – 1993. – Vol 34. – P. 3699-3703.