Boletín de Segovia: Número 44 - 1861 abril 10

Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 200

Trilayered Single Crystals with Epitaxial Growth in Poly(ethylene oxide)-<i>block</i>-poly(ε-caprolactone)-<i>block</i>-poly(l‑lactide) Thin Films

Manipulation of crystalline textures of biocompatible block copolymers is critical for the applications in the medical field. Here, we present the control of multiple-crystalline morphologies with flat-on chain orientation in biocompatible poly­(ethylene oxide)-<i>block</i>-poly­(ε-caprolactone)-<i>block</i>-poly­(l-lactide) (PEO–PCL–PLLA) triblock copolymer thin films using melt and solvent-induced crystallizations. Only single-crystalline morphologies of the first-crystallized blocks can be obtained in the melt-crystallized thin films due to the confinement effect. With solvent annealing by PCL-selective toluene, single-crystalline PLLA to double-crystalline PLLA/PCL and to triple-crystalline PLLA/PCL/PEO layered crystals in sequence are observed for the first time. With the control of solvent selectivity, different sequential crystallization involving first-crystallized PCL transferring to double-crystalline PCL/PLLA is obtained using PEO-selective <i>n</i>-hexanol for annealing. Surprisingly, the crystalline growth of the trilayered single crystal exhibits specific layer-by-layer epitaxial relationship. As a result, the multiple-crystalline textures of the PEO–PCL–PLLA thin films can be carried out by controlling solvent and polymer interaction

Nanoporous Crystalline Templates from Double-Crystalline Block Copolymers by Control of Interactive Confinement

Single, double, and coincident crystallizations under hard or soft confinement are all carried out using a single type of syndiotactic poly­(<i>p</i>-methyl­styrene)-<i>block</i>-poly­(l-lactide) (<i>s</i>PPMS–PLLA) block copolymers. The single crystallization of <i>s</i>PPMS matrix can lead to the disordered arrangement of hexagonally packed PLLA cylinders under soft confinement. In contrast, the lamellar nanostructure remained unchanged regardless of the PLLA crystallization under hard or soft confinement. Crystallization-induced morphological transitions from the confined monosized lamella to the metastable dual-sized lamella and finally to the breakout morphology are evident by transmission electron microscopy and small-angle X-ray scattering. The dual-sized lamella is attributed to the thermodynamically and kinetically controlled nanocrystallite growth templating along the ordered microphase separation. Despite crystalline sequences, the double-crystallized morphologies are determined by the first-crystallized event even though the subsequent crystallization temperature is performed under soft confinement. By the control of interactive confinement, ordered crystalline nanosheets and cylindrical monoliths are obtained, providing a novel means for the fabrication of nanoporous crystalline templates

Control of Nanostructural Dimension by Crystallization in a Double-Crystalline Syndiotactic Poly(4-methyl-1-pentene)-<i>block</i>-poly(l‑lactide) Block Copolymer

The control of nanostructural dimension by crystallization-induced chain stretching was investigated in a novel double-crystalline block copolymer, syndiotactic poly­(4-methyl-1-pentene)-<i>block</i>-poly­(l-lactide) (<i>s</i>PMP–PLLA), featuring a lamellar phase. Because of the similar glass transition temperatures of <i>s</i>PMP and PLLA, their blocks could crystallize under soft confinement (i.e., a crystallization temperature higher than the glass transition temperatures of the constituent blocks) in <i>s</i>PMP–PLLA. With the strong segregation of <i>s</i>PMP–PLLA, the first-crystallized <i>s</i>PMP block was templated by microphase separation to form confined crystalline <i>s</i>PMP lamellae within the microphase-separated lamellar texture. Most interestingly, the first-crystallized <i>s</i>PMP block may also induce significant stretching of the PLLA chains from the lamellar interface, resulting in the increase of microdomain thickness of the PLLA block. With the increase of crystallization temperature, this chain stretching may become more significant, resulting in a large increase (∼34%) of the lamellar long period. The double-crystalline lamellar morphologies having homeotropic orientation for both <i>s</i>PMP and PLLA crystals can be acquired in the shear-aligned <i>s</i>PMP–PLLA as evidenced by simultaneous 2D small-angle X-ray scattering and wide-angle X-ray diffraction, giving uniform birefringence under polarized light microscope with thermal reversibility. As a result, the switchable lamellar nanostructures having significant dimensional change can be carried out by simply controlling crystallization or melting of the crystallizable blocks