Crystallization of trans‐1,4‐polyisoprene

Abstract

AbstractCrystals of fractionated trans‐1,4‐polyisoprene (TPI) were grown from amyl acetate solution at two weight fractions, 5.7 × 10−4 and 0.011; for the lower concentration a precooling followed by heating and then crystallization at temperatures in the 10–32°C range was used, while for the higher concentration this method and direct crystallization at a temperature TC in the 0–32°C range were employed. The precooling method yielded samples crystallized in the α form, while direct crystallization led to formation of β‐TPI at low TC and α at higher TC. The value for the DSC endotherm, characteristic of α‐form melting, increased with increasing TC, with a shift to lower values with increasing concentration for precooled samples. A β to α transformation was found to occur for synthetic unfractionated TPI when swollen with amyl acetate at 35°C for 17h. Swelling in n‐butyl acetate for one day at 25°C or 17 h at 35°C also led to this transformation. From experimental results 74°C is chosen as the temperature at which the α and β forms coexist in the bulk, and this is used to calculate the enthalpy of fusion of β‐TPI, yielding a value of 8.6 kJ mol−1.