Properties of crystallized trans 1,4-polyisoprene

Stirrer crystallization of a trans-1,4-polyisoprene fraction(M?_n = 3 × 10⁵) was carried out from n-butyl acetate and from n-heptane solutions (2% w/v). Fibrous crystals in the ß form were obtained at temperatures of 46-48°C in the two solvents, respectively. At 36-46°C from n-butyl acetate and 25-35°C from n-heptane lamellar crystallization took place leading predominantly to the α form. Melting endotherms and densities for various samples were obtained. The maximum TENDO for α was 74°C and for ß 79°C and the maximum weight fraction crystallinity for ß was 0.78. The stability of performed α nuclei in n-butyl acetate and n-heptane using a fraction with M?_n = 2.5 × 10⁵ was monitored as a function of temperature. The dissolution temperature of fibrous ß-TPI with the maximum TENDO was measured in 13 liquids and the results analyzed in terms of the Flory-Huggins parameter. The heats of fusion for the α and ß forms, obtained by extrapolation of heat of fusion versus change in specific volume, were found to be 8.0 and 10 kJ mol^?1, respectively. The pressure coefficients of the melting temperature were calculated to be 38 and 43 K kbar^?1 and the fold-surface free energies recalculated to be 42 ± 1 and 53 ± 1 erg cm^?2 for the α and ß forms, respectively. The number of monomer units per average noncrystalline chain traverse for the most crystalline fibrous ß-TPI was estimated at 36.