Single Crystals of the Poly(l-lactide) Block and the Poly(ethylene glycol) Block in Poly(l-lactide)−poly(ethylene glycol) Diblock Copolymer

Abstract

Single crystals of the poly(l-lactide) (PLLA) block and the poly(ethylene glycol) (PEG) block in poly(l-lactide)−poly(ethylene glycol) diblock copolymer were obtained by melt crystallization. The morphology, structure, and evolution process of the single crystals were investigated using transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and real-time atomic force microscopy (AFM). Two types of crystal morphology were obtained. One was the regular morphology of a single crystal: lozenge-spiral dislocation, lozenge multilayer, and hexagonal (or truncated-lozenge) multilayer, which was layer-by-layer structure. The foregoing crystallization of the PLLA block determined the regular morphology of single crystal. The other type of crystal morphology was that the layer-dendritic crystal, which was affirmed to be the PEG crystal by real-time AFM, formed at the edge of the regular single crystal and grew along some certain directions on the crystal surface of the PLLA block. The forming of layer-dendritic crystal was through the reorganization of metastable phase crystal of the PEG block. The SAED results indicated that the (001) plane of the PLLA crystal was parallel to the (10−4) plane of the PEG crystal and the substrate. The foregoing crystallization of the PLLA block had an effect on the crystal orientation of the PEG block.

Crystalline and Spherulitic Morphology of Polymers Crystallized in Confined Systems

“…This makes the crystallizable block copolymers representative systems having confined crystallization behavior, especially in the strong segregation regime [52]. Confined crystallization has been widely observed in the diblock copolymers having double crystalline blocks, such as PEO-b-PCL [112][113][114][115][116], PLLA-b-PEO [117][118][119][120][121][122], PLLA-b-PCL [123][124][125], poly(p-dioxanone) (PPDX)-b-PCL [126][127][128], polyolefin-based block copolymers [129][130][131][132][133][134][135], and so on. The confined crystallization kinetics and crystalline morphology of such block copolymers have been extensively studied.…”

Solution Crystallization Behavior of Crystalline−Crystalline Diblock Copolymers of Poly(ethylene oxide)-block-poly(ε-caprolactone)

“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] One prominent system is a diblock copolymer composed of poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL) because of their biocompatibility, biodegradability, and reasonable strength. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] These properties are derived from both their chemical structure as well as their physical structures. Because both PEO and PCL are semicrystalline polymers, their crystallinity greatly affects their mechanical and biorelated properties; therefore, it is important to understand how their crystals grow in this unique architecture.…”

“…Similar results have also been shown for thin film growth of PEO-b-poly(L-lactide) (PLLA) copolymers with identical molecular weights between the two blocks. [18][19][20][21] Here, the PLLA crystallizes first due to a higher crystallization temperature.…”

Crystallization Behaviors and Structure Transitions of Biocompatible and Biodegradable Diblock Copolymers

“…We speculated that the T c -dependent morphological behavior of the asymmetric copolymers is the result of soft confinement crystallization. It has been confirmed that the PEO-b-PLA copolymers are disordered in the melt [6,10,55]; the two components, PLA and PEO blocks, are weakly segregated. Microphase separation of the copolymers is driven by the crystallization of PLA block, which will influence the diffusion PLA component, growth and orientation of PLA lamellae.…”

“…The crystalline morphology is formed by stacking flat-on growing lamellae in the thin film. Lozenge-shaped single crystal with screw dislocation of PLA has been reported in thin film of PLA or its copolymers that the thickness is less than 100 nm [6,7,12,[55][56][57]. However, the special crystalline morphology of hexagonal dendrite stacked with PLA single crystals has never been reported.…”