The Underestimated Effect of Intracrystalline Chain Dynamics on the Morphology and Stability of Semicrystalline Polymers

Abstract

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.

Intracrystalline Dynamics in Oligomer‐Diluted Poly(Ethylene Oxide)

“…In this context, it should be noted that our previous studies indicate that the final crystalline thickness in PEO results from reorganizations in the lamellae, caused by the helical jump motions which are fast in comparison to the lateral growth. Thus, the observed almost unchanged crystalline thickness of the long‐chain PEO at the given reduced growth velocity suggests that the crystalline thickness is not the one that is initially kinetically selected.…”

“…See refs. for details, which also provide information on the distribution of these quantities in terms of standard deviation σ (σ = 1.2 nm) of an assumed Gaussian distribution.…”

“…[5] Semicrystalline polymers can be subdivided into two major classes, namely crystal-fixed and crystal-mobile polymers. Diffusive chain mobility within and through the crystalline lamellae enables high crystallinity, [6,7] and is the molecular basis of the deformability of polymer crystals, explaining important performed by ref. [24], and were explained by a reduction of the entanglement density and likewise the topological constraints in the melt prior to crystallization.…”

“…Semicrystalline polymers can be subdivided into two major classes, namely crystal‐fixed and crystal‐mobile polymers. Diffusive chain mobility within and through the crystalline lamellae enables high crystallinity, and is the molecular basis of the deformability of polymer crystals, explaining important mechanical properties such as creep and ultradrawability . Also the process of reversible surface melting and crystallization, and the correlated changes in the crystalline‐amorphous interphase, which is reported for crystal‐mobile polymers such as poly(ethylene oxide) (PEO), is only feasible due to the intracrystalline dynamics in this polymer class.…”

Immobilized 13 C-labeled polyether chain ends confined to the crystallite surface detected by advanced NMR

“…1B ( 1 , 6 , 8 ). Whether other polymers with different chain mobility ( 11 ), chain conformation ( 1 ), interchain interactions ( 15 ), or crystallization kinetics ( 12 , 16 ) exhibit different chain-end distributions is not known.…”