Epitaxy in Polybutene-1 Form II-on-Form I Cross-Nucleation Revealed by Nanofocused X-ray Diffraction on Ad Hoc Morphology

Abstract

The existence of epitaxy in polybutene-1 form IIon-form I cross-nucleation was investigated by nanofocused synchrotron X-ray diffraction. To this aim, form I hedrites, which show a lamellar stacking with a uniform crystal lattice orientation, were adopted as the substrate. The form II crystals develop a spherulitic transcrystalline layer on the lateral surface of the form I substrate, due to cross-nucleation. Through mapping both the intensity and azimuthal orientation of characteristic planes of the two polymorphs, a clearly defined nucleation area between form II (daughter) and form I (parent) could be identified. Comparing the two-dimensional diffraction patterns in that area, a preferred mutual orientation of the two structure is revealed. In particular, the (200) II plane of form II and the (110) I plane of form I are reciprocally oriented at a fixed angle of ∼8.5°. This orientation results in almost parallel (110) planes between the two structures. It is calculated that the mismatch between interchain distances within the common ( 110) planes is about 4%, while that along the chain axes is less than 10%, both well below the accepted mismatch criterion for epitaxial crystallization. These results provide solid evidence for the existence of an epitaxial relationship in the cross-nucleation between polybutene-1 form II and form I. We note that the (110) contact plane between the two structures in cross-nucleation is the same as the one involved in the well-studied solid-state phase transformation from form II to form I. Moreover, the X-ray nanofocus approach and the proposed data analysis could be effectively applied to other cross-nucleating systems to shed light on the role of epitaxy in this peculiar phenomenon of nucleation between polymorphs.

The II to I Phase Transition of Isotactic Poly(1-butene) Single Crystals at an Early Stage

“…As reported in refs and , the II–I phase transition results in anisotropic dimensional changes with a 15.5% increase along molecular chain direction (i.e., thickness direction of single crystals) but with a 17.7% overall reduction in chain cross section. The reduction i,s however, minimum in the common [110] directions of both form I (distance between adjacent chains of 1.01 nm) and form II (distance between adjacent chains of 1.05 nm), as schematically illustrated in Figure . Taking into account that stress plays an important role for the II–I transition, the preferred nucleation of form I crystals not occurring along the [110] II direction is then understandable.…”

“…Schematic illustration of the iPBu chain arrangements in form II and I crystals lattices. Reproduced with permission from ref .…”

“…The reduction i,s however, minimum in the common [110] directions of both form I (distance between adjacent chains of 1.01 nm) and form II (distance between adjacent chains of 1.05 nm), as schematically illustrated in Figure 5. 44 Taking into account that stress plays an important role for the II−I transition, the preferred nucleation of form I crystals not occurring along the [110] II direction is then understandable. Finally, the preferred nucleation of form I in dendritic single crystals along edges of each individual flat-on crystalline sheet, which are aligned in the [110] directions of the form II crystal as can be seen from Figure 1c, seems in contradiction with the regular single crystal.…”

Single Crystals Self‐Assembled to Sector‐Face Dendritic Aggregates by Synchrotron Microbeam X‐Ray Analysis on Poly(ethylene succinate)

“…Iwata, et al, [72] observed dendritic crystal assembly in solution-crystallized PESu, where individual lozenge-shaped single crystals fill the dendritic stalks with both left-and right-handed spirals on the basis of screw-dislocation mechanism. Wang et al, [73] observed the cross-nucleation of isotactic polybutene-1 from Form-II on Form-I with nano-focused X-ray diffraction. Zhang et al, [74,75] altered the physical properties of inorganic lattice by inserting polymers chains.…”

Retarded Crystallization and Promoted Phase Transition of Freeze-Dried Polybutene-1: Direct Evidence for the Critical Role of Chain Entanglement

“…This solid–solid phase transition results in a significant enhancement of the material’s stiffness, toughness, and thermal stability. Despite recent progress, , the phase transition mechanism of PB-1 has not been well explained at the molecular level. Previous studies reported that the II–I phase transition of PB-1 depended highly on molecular weight .…”