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Herein, we aim to investigate the influence of the cooling rate from the melt on stereocomplex formation of equimolar blends of enantiomeric star-shaped poly(lactide)s with a dipyridamole core. As evidenced by differential scanning calorimetry, wide-angle X-ray scattering and Fourier-transform infrared spectroscopy, melt cooling of equimolar blends of star-shaped poly(L-lactide) (SSPLLA) and star-shaped poly(D-lactide) (SSPDLA) resulted in the non-crystalline state. A careful analysis of WAXS and FTIR data revealed that the slow-cooled sample (10 °C min−1) exhibited the amorphous phase and the fast-cooled sample (50 °C min−1) resulted in the mesophase. On subsequent heating, the slow-cooled sample remained in the amorphous phase, whereas the fast-cooled sample crystallized (cold crystallization) exclusively into the stereocomplex at ∼90 °C. Aging of the slow-cooled sample at room temperature and subsequent heating led to the formation of the stereocomplex. Photoluminescence studies revealed that the cooling rate from the melt has a strong influence on core molecule (dipyridamole) aggregation and determines the geometry of interactions between the branches of SSPLLA and SSPDLA. In the slow-cooled sample, because of the longer residence time above the glass transition temperature, dipyridamole molecules form aggregated structures, whereas in the fast-cooled sample, dipyridamole molecules are distributed within the polymer matrix without much aggregation. Based on these results, we propose antiparallel chain packing in fast-cooled SSPLLA/SSPDLA blends because of the non-aggregation of dipyridamole core molecules and this geometry favored the exclusive formation of stereocomplex. On the other hand, due to the possible aggregation of dipyridamole molecules, the slow-cooled sample led to topological and geometric constraints where the interactions between SSPLLA and SSPDLA chains prevented the crystallization. The present findings could open new avenues for the design of a variety of macromolecular architectures for a better understanding of the stereocomplex formation mechanism of chiral polymers.

Kinetically sluggish growth of poly(e-caprolactone) at high Tc = 50 °C leads to a peculiar banding morphology, where thick-stacked lamellae self-assemble into camellia-petal-like bands with their outer rims divided into a ca. 10 lobs of round-shaped petals. The sluggish growth at Tc = 50 °C thick films is inductive and the thickened lamellae self-assemble into aggregates of peculiar and novel camellia-petal-shaped ring bands. Using novel morphology analyses via 3D-dissection approaches, the lamellae underneath the ridge bands are shown to be all perpendicular to the substrate plane, i.e. normally-oriented with respect to the substrate surface; whereas, the interior lamellae underneath the valley band are all flat-on and horizontal to the substrate plane. Stereo-depiction clearly demonstrates that the interior lamellae are periodically grating architectures with a fixed crossbar pitch of 20–30 μm of the interior lamellar assembly, matching with the optical inter-ring spacing of optical bands. The mechanisms of growth and assembly are probed in detail.

Crystallized poly(nonamethylene terephthalate) (PNT) displays mirror-image and Fermat's-spiral ring-banded spherulites, respectively. The interior anatomy by SEM and AFM microscopic analyses shows that the lamellar arrangement of grating-board structures inside the 3D bulk banded PNT is correlated to top-surface topography of alternate ridge and valley bands. For the banded spherulites, tangential-oriented lamellae under the ridges and radial-oriented lamellae under the valleys are collectively arranged into mirror-image or spiral symmetry, where the tangential lamellae intersect at 90° angle with the branching radial lamellae. Moreover, the grating-layered structures of the tangential lamellae are viewed as the shish-crystals from which the kebab side-branches grow outwards in the radial direction. 3D models are proposed to illustrate the lamellar assemblies in both types of periodic bands. Morphological evolution and lamellar assembly with dual discontinuity are addressed to further establish 3-D models.

A small-molecule compound, phthalic acid (PA), crystallized in the presence of poly(ethylene oxide) (PEO) with various compositions was utilized as a model to investigate the morphology and crystal assembly of periodically ordered structures in banded spherulites. After etching off PEO from crystallized solids, detailed crystal assembly in PA was analyzed by utilizing atomic-force microscopy (AFM) and scanning electron microscopy (SEM) to reveal the mechanisms of the formation of fractal-shaped banded spherulites. A novel banded pattern with fractal-shaped lamellar structures is found when the composition of PEO is at or above 20%, and this pattern significantly differs from the ordinary extinction–bright banded morphology of neat PA. The diluent PEO is regarded as the main factor in transforming the crystalline morphology from a compact banded pattern to a fractal-shaped banded pattern. The banded spherulites are composed of numerous fractal structures periodically branching out. Each fractal unit contains two portions: a main stalk (ridge) whose discrete crystalline aggregates are arranged along the radial direction and a fern-like dendrite (valley) whose crystals are arranged along the tangential direction. In situ monitoring of the growth process of the fractal-shaped banded spherulites proves the fractal-branching growth mechanism for the formation of banded spherulites. The periodically perpendicular intersection of discrete crystals results in the contrasting birefringence bands of banded spherulites. A periodic grating structure with fractal branching leads to such a novel pattern of banded PA spherulites.