Intracrystalline chain diffusion, semicrystallinity and mechanical modulus of aliphatic polyesters

Recently, based upon encompassing studies on three model polymers [1,2], we concluded that semicrystalline polymers exhibit qualitatively different morphological features, depending on the timescale of intracrystalline chain motion (ICD) relative to the kinetics of crystal growth. In extending the materials basis and testing the generality of this concept, we have now investigated a series of selected aliphatic polyesters [3].

We have characterized the crystallinity, ICD, crystallization kinetics and the semicrystalline morphology by various nuclear magnetic resonance (NMR) techniques, polarization microscopy and small-angle X-ray scattering (SAXS), respectively. The latter could be used to quantify rather slow ICD, undetectable by NMR, through crystal-thickening slopes during long-time crystallization. We can thus confirm that the observed relation between morphology and ICD is valid for all investigated polyesters. We consequently propose a further refinement and expansion of the classification of “crystal-fixed” polymers, a terminology often found in the literature. Our absolute-level crystallinity determinations by NMR and SAXS also allow us to delineate the effect of the formation of ester group layers in the crystals on the DSC-based enthalpy of melting. Finally, we also demonstrate a simple exponential correlation of the shear modulus of the selected polyesters with their crystallinity.

References

[1] M. Schulz et al., Macromolecules 51, 8377 (2018), DOI: 10.1021/acs.macromol.8b01102

[2] M. Schulz et al., Nat. Commun. 13, 119 (2022), DOI: 10.1038/s41467-021-27752-0

[3] Y. Qiang et al., Polymer (2025), in press, DOI: 10.1016/j.polymer.2025.129131