Influence of syndiotacticity and annealing temperature on the double melting peak behaviour of syndiotactic polypropylene

Abstract

Fractionated syndiotactic polypropylene (sPP) samples with homogeneous tacticity were annealed at different temperatures. The influence of syndiotacticity and annealing temperature on the double melting peak phenomena were investigated. It is found that all fractions show double melting peaks at 75°C annealing temperature, while the low peak disappears when the fractions with higher syndiotacticity are annealed at 85°C and above. The fraction with the lowest syndiotacticity remains the same at any annealing temperature. In combination with wide‐angle X‐ray diffraction experiments, the double peaks are believed to correspond to the melting of cell II and III. The results indicate that higher temperature and syndiotacticity are the external conditions and internal structural factor that permit cell II to transform into cell III. © 1999 Society of Chemical Industry