Effect of Annealing and Pressure on Structure and Melting of a Polypropylene Random Copolymer

The effect of annealing and pressure were studied on the crystalline structure and melting of a random copolymer of propylene with low content of ethylene. The copolymer samples were compression molded at different pressures and while the sample remained under the press, slowly cooled to room temperature. The result was a crystalline structure of both a- and 7-form with no substantial increase in proportion of the 7-phase with the amount of pressure. Annealing of the samples at temperatures higher than 408 K, showed two melting endotherms which were attributed to the melting of species produced by molecular segregation during annealing and rapid cooling. Observation of the sharp melting endotherm at higher temperature after annealing could be related to the transformation of less ordered a1 - structure to a more ordered a2- form.