The Semicrystalline Morphology of Polybutylene Succinate Supports a General Scheme Based on Intracrystalline Dynamics

Based on a limited set of model samples it has been recently shown that semicrystalline polymers exhibit different morphological characteristics depending on the existence and timescale of intracrystalline chain diffusion (ICD) relative to the kinetics of crystal growth. Here, the generality of these reports for the case of so-called crystal-fixed polymers without or very slow ICD is tested by providing a detailed nuclear magnetic resonance (NMR) and small-angle X-ray scattering analysis of polybutylene succinate (PBS), a biodegradable polyester. By using a combination of NMR techniques covering different timescales it is shown that there is no intracrystalline dynamics on a time scale faster than 1 s, that is, PBS is crystal-fixed. An expected crystallinity below 50% and the typical morphology consisting of lamellar crystals with a well-defined crystal thickness and a broad thickness distribution of the amorphous interlayers are confirmed. By combining these results with differential scanning calorimetry measurements, a more precise value could be provided for the enthalpy of melting than previously available. The mechanical properties at room temperature are furthermore influenced by additional insertion crystallization taking place during cooling, which leads to an increase of the mechanical modulus by a factor of ≈2.5 as compared to the state at the end of isothermal crystallization.