New enantiomeric polylactide-block-poly(butylene succinate)-block-polylactides: syntheses, characterization and in situ self-assembly.
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(n,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 degrees 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 degrees C, and a new X-ray diffraction peak detected at 2theta = 11.8 degrees . 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 mum 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.
Jia
Lin
L
Department of Chemistry, Northwest University, 229 North Taibai Road, Xi'an, Shanxi 710069, China.
Yin
Lingzhi
L
Li
Yang
Y
Li
Qiaobo
Q
Yang
Jing
J
Yu
Jianyong
J
Shi
Zhen
Z
Fang
Qiang
Q
Cao
Amin
A
D000097:Acetonitriles; D001673:Biodegradation, Environmental; D018360:Crystallography, X-Ray; D006358:Hot Temperature; D009682:Magnetic Resonance Spectroscopy; D008855:Microscopy, Electron, Scanning; D011090:Polyenes; D011091:Polyesters; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry; D012997:Solvents; D013386:Succinates
D000097:Acetonitriles; D011090:Polyenes; D011091:Polyesters; D011108:Polymers; D012997:Solvents; D013386:Succinates; C033616:poly(lactide); C008952:polybutene; C032159:acetonitrile