Simultaneous crystalline-amorphous phase evolution during crystallization of polymer systems

– Despite the fact that polymer crystallization has been the object of intense research, this process is far from being fully understood. Traditional polymer crystallization studies using X-ray scattering techniques mainly provide information about the ordered regions. To obtain a more complete information about the time evolution of both the crystalline and the amorphous phase during polymer crystallization, we have developed a technique which allows one to obtain information about both the crystalline and the amorphous phase simultaneously. We report here simultaneous information about three key aspects of the isothermal polymer crystallization process: i) polymer chain ordering, through Wide-Angle X-ray Scattering; ii) lamellar crystals arrangement, through Small-Angle X-ray Scattering; iii) amorphous phase evolution through dielectric spectroscopy. Our results probe that during primary crystallization the average mobility of the amorphous phase is not notably affected. Upon passing through the crossover time, marking the transition from primary to secondary crystallization, the restriction to the mobility of the amorphous phase mainly occurs in the regions between the lamellar stacks regions and not in the amorphous regions within the lamellar stacks. We hypothesize that molecular mobility in the amorphous regions located between consecutive crystals become strongly arrested as soon as the lamellar stack is formed. Polymer systems may develop a characteristic folded chain crystalline lamellar morphology at the nanometer level upon thermal treatment within the temperature range between the glass transition temperature, Tg, and the equilibrium melting temperature, T 0 m [1,2]. The lamellar morphology consists of stacks of laminar crystals and amorphous regions intercalated between them. Although extended chain crystals are thermodynamically more stable, a kinetic factor induces that polymer chains fold many times building up thin (10–20 nm) crystal lamellae. For semicrystalline polymers, this characteristic crystalline nanostructure acts as an internal backbone in the polymer controlling the final mechanical properties of the material. (∗) Permanent address: Riga Technical University, Institute of Polymer Materials Riga, Latvia. (∗∗) Present address: J. J. Thomson Physics Laboratory, University of Reading Witheknights, Reading RG6 6AF, UK. (∗∗∗) Permanent address: Universidade do Minho, Campus de Azurém Guimarães 4800-058, Portugal.