Microstructural details and polymorphs in poly(propylene-co-1-nonene) copolymers synthesized at different polymerization temperatures

Several copolymers based on propylene with 1-nonene as comonomer have been synthesized within a wide range of compositions using a metallocene catalyst and different temperatures. The effect of the two main variables, comonomer content and polymerization temperature, on the final microstructure obtained (polymerization activity, stereochemistry and molar mass, among other details) as well as on the capability of crystallization, formation of distinct polymorphs and phase transitions, is examined. Different ordered entities are developed in these isotactic poly(propylene-co-1-nonene) copolymers depending on 1-nonene molar content: monoclinic, orthorhombic, and mesomorphic ones. A detailed analysis of the phase transitions involved is performed using real-time variable-temperature wide-angle diffraction experiments with synchrotron radiation on the sample with the highest comonomer amount. Different crystallization conditions were tested in order to attain information of the whole phase behavior. From these results, it was found that the mesophase of isotactic poly(propylene) is competing with the crystalline structures, although it recrystallizes on melting into the monoclinic phase at common differential scanning calorimetry rates.