New Enantiomeric Polylactide-block-Poly(butylene succinate)-block-Polylactides: Syntheses, Characterization and in situ Self-Assembly
✍ Scribed by Lin Jia; Lingzhi Yin; Yang Li; Qiaobo Li; Jing Yang; Jianyong Yu; Zhen Shi; Qiang Fang; Amin Cao
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 286 KB
- Volume
- 5
- Category
- Article
- ISSN
- 1616-5187
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✦ Synopsis
Abstract
Summary: In situ self‐assemblies of new biodegradable triblock PLLA‐b‐PBS‐b‐PLLA and PDLA‐b‐PBS‐b‐PDLA have been investigated in acetonitrile solution. At first, two series of PLLA‐b‐PBS‐b‐PLLA and PDLA‐b‐PBS‐b‐PDLA, respectively denoted as the P and Q triblock copolyester series, were prepared with fixed PBS block ($\overline M _{{\rm n},{\rm NMR}}$ = 6.9 kDa) and diverse enantiomeric PLLA/PDLA blocks. Further, their chemical structures and thermal properties were characterized by means of titration, nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), polarimeter, wide‐angle X‐ray diffraction (WAXD) and thermal analytical instruments. When mixing the synthesized enantiomeric copolyester pairs denoted as P~1~/Q~1~ – P~8~/Q~8~ in acetonitrile solution at 60 °C, in situ self‐assemblies were found to happen for the P~4~/Q~4~ to P~8~/Q~8~ pairs, bearing longer enantiomeric PLA block lengths. DSC and WAXD analysis of the self‐assembled microparticles demonstrated that PLLA/PDLA racemic crystals were formed for the P~5~/Q~5~ – P~8~/Q~8~ systems, as evidenced by their melting points over 200 °C, and a new X‐ray diffraction peak detected at 2__θ__ = 11.8°. Moreover, morphological studies by scanning electron microscopy (SEM) indicated the formation of disk‐ or platelet‐like microparticles. It was noted that the diameters of the microparticles self‐assembled in situ decreased from 1.28–1.50 μm down to 480–660 nm, through tailoring the enantiomeric PLA block length. Other factors, such as a central PBS block, the enantiomeric block length and the preparation conditions were suggested to play important roles in the in situ self‐assembly of these enantiomeric triblock copolyesters. These results provide a facile way to self‐assemble hydrophobic, biodegradable microparticles, through tuning the important van der Waals stereocomplexation interactions between two enantiomeric blocks in solution.
In situ self‐organisation of new PLLA‐b‐PBS‐b‐PLLA and PDLA‐b‐PBS‐b‐PDLA triblock copolyester pairs in dilute solution.
magnified imageIn situ self‐organisation of new PLLA‐b‐PBS‐b‐PLLA and PDLA‐b‐PBS‐b‐PDLA triblock copolyester pairs in dilute solution.