Crystallization of trans ‐1,4‐polyisoprene

• Published in: Journal of polymer science. Polymer physics edition 1982-09, Vol.20 (9), p.1669-1676
• Main Authors: Anandakumaran, K., Kuo, C. C., Mukherji, S., Woodward, A. E.
• Format: Article
• Language: English
• ISSN: 0098-1273; 1542-9385
• DOI: 10.1002/pol.1982.180200916

Crystals 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 T C 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 T C and α at higher T C . The value for the DSC endotherm, characteristic of α‐form melting, increased with increasing T C , 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 .