Simultaneous study of anionic polymerization of ε-caprolactam and crystallization of polyamide 6 in an isothermal process by in situ WAXS

Abstract

We directly observed the polymerization and crystallization of polyamide 6 (PA6) via anionic polymerization with a combination of in situ wide-angle X-ray scattering (WAXS), temperature measurements, and real-time visualization. In situ WAXS discriminated polymerization and the crystallization of PA6. The peak temperatures produced by exothermic polymerization and crystallization were identified during the temperature measurements. Visual observations were consistent with the WAXS spectral changes. The WAXS results indicated that the molding process consisted of three stages: (1) polymerization induction, (2) polymerization, and (3) crystallization. We compared the polymerization rate, crystallization rate, and crystallinity at each molding temperature. Both polymerization and crystallization were slow at temperatures below 127 °C. Polymerization was fast at temperatures exceeding 166 °C, but PA6 was gelated, and the crystallization rate and crystallinity were low. In contrast, polymerization was fast at 139, 148, and 155 °C, and crystallization was faster at 148 and 155 °C than at 139 °C. Therefore, the total molding time of PA6 was shorter at 148 and 155 °C than at other temperatures. The crystallinity of PA6 decreased with increasing temperature due to increasing molecular weights. We concluded that molding temperatures between 148 and 155 °C were suitable for providing PA6 with high productivities and good properties.