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Semicrystalline polymers have been classified into crystal-mobile and crystal-fixed polymers, depending on the existence or absence of intracrystalline chain dynamics. Although it was claimed that polymers with intracrystalline chain dynamics generally have a higher crystallinity, its effect on the semicrystalline morphology is not known in detail. Using a new approach for the quantitative analysis of small-angle X-ray scattering data, we compare the structural characteristics of fully crystallized samples for two model polymers with and without chain motion in the crystallites. Whereas for crystal-fixed polymers the semicrystalline morphology is characterized by lamellar crystals of well-defined thickness and marginal stability, the intracrystalline dynamics leads to additional stabilization of the crystals during growth and a minimization of the amorphous layers characterized by a well-defined thickness. Results of 1H solid-state NMR experiments enable us to determine the time scale of intracrystalline chain dynamics in the relevant temperature range and to relate it to the time scale of crystal growth. If both processes act on the same time scale, the crystallization process is an interplay between crystal growth and stabilization by reorganization enabled by intracrystalline mobility. Viewing this competition as fundamental for the formation of the semicrystalline morphology, seemingly contradictory models suggested in the past to describe polymer crystallization can at least be partially reconciled.

The knowledge acquired through this work might be very beneficial for future FDM applications in the field of immediate release tablets especially with respect to thermo-sensitive drugs.

This work focuses on the influence of amorphous-phase entanglements on the semicrystalline morphology of poly­(ϵ-caprolactone). This polyester is classified as crystal-fixed; i.e., it displays no translational chain dynamics in the crystals. We study a wide range of well-entangled samples with molecular weights up to several million using polarization microscopy to assess the lamellar growth rate, small-angle X-ray scattering and proton time-domain NMR to characterize the morphology, and proton multiple-quantum NMR, auxiliary carbon-13 NMR, rheology, and tensile deformation to assess the entangled chain dynamics in the melt and semicrystalline states. We demonstrate a significant increase in the density of entanglements in the amorphous phase relative to the melt. The dependencies of our observables on crystallization temperature and molecular weight suggest that entanglements control the thickness of the amorphous layers. This is rationalized by an only slowly relaxing exclusion zone with enhanced entanglement density acting as an entropically repulsive layer between adjacent lamellae.