Shear-Induced Crystallization of Star and Linear Poly(L-lactide)s
The influence of macromolecular architecture on shear-induced crystallization of poly(L-lactide) (PLLA) was studied. To this aim, three star PLLAs, 6-arm with M<sub>w</sub> of 120 and 245 kg/mol, 4-arm with M<sub>w</sub> of 123 kg/mol, and three linear PLLAs with M<sub>...
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| Autores principales: | , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/4d68ffd1e02446fe92a3ba985545339d |
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| Sumario: | The influence of macromolecular architecture on shear-induced crystallization of poly(L-lactide) (PLLA) was studied. To this aim, three star PLLAs, 6-arm with M<sub>w</sub> of 120 and 245 kg/mol, 4-arm with M<sub>w</sub> of 123 kg/mol, and three linear PLLAs with M<sub>w</sub> of 121, 240 and 339 kg/mol, were synthesized and examined. The PLLAs were sheared at 170 and 150 °C, at 5/s, 10/s and 20/s for 20 s, 10 s and 5 s, respectively, and then cooled at 10 or 30 °C/min. Shear-induced crystallization during cooling was followed by a light depolarization method, whereas the crystallized specimens were examined by DSC, 2D-WAXS, 2D-SAXS and SEM. The effect of shear depended on the shearing conditions, cooling rate and polymer molar mass but it was also affected by the macromolecular architecture. The shear-induced crystallization of linear PLLA with M<sub>w</sub> of 240 kg/mol was more intense than that of the 6-arm polymer with similar M<sub>w</sub>, most possibly due to its higher M<sub>z</sub>. However, the influence of shear on the crystallization of the star polymers with M<sub>w</sub> close to 120 kg/mol was stronger than on that of their linear analog. This was reflected in higher crystallization temperature, as well as crystallinity achieved during cooling. |
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