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.

The commercialization of poly(butylene succinate-co-adipate) (PBSA), a biodegradable and potentially fully biobased random copolyester, is still ongoing. Due to its high relevance as mono material or as blend component in flexible film applications, a sound understanding of compounding, further processing and film properties is necessary. In this work, PBSA, poly (lactic acid) (PLA) and blends at three different compositions thereof were processed into flat films and blown films, respectively. Investigating the films with X-ray diffraction (XRD), multivariate confocal Raman microscopy (CRM) and scanning electron microscopy (SEM) revealed the semicrystalline order as well as the blend morphology. While PBSA is semicrystalline, PLA remains amorphous after the processing step. As imaged by CRM, flat films exhibit lamellar-like domains formed during uniaxial stretching and rapid cooling, whereas blown films show no pronounced preferential orientation. Tensile tests in both the machine and transverse directions demonstrate the versatility of PBSA and its blends in spanning a wide range of mechanical strength and flexibility, covering and partly exceeding the stiffness and strength ranges typically reported for commodity polyolefins while exhibiting reduced ductility. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) provide further insights into the thermal properties of the pure and blend materials.