Effect of stereochemistry on nanoscale assembly of ABA triblock copolymers with crystallizable blocks
Effect of stereochemistry on nanoscale assembly of ABA triblock copolymers with crystallizable blocks
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DOI：
10.1016/j.polymer.2021.123683
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发表时间：
2021-04-07
期刊：
影响因子：
4.6
通讯作者：
Bhatia，Surita R.
中科院分区：
文献类型：
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作者：
Yin，Xuechen;Hewitt，David R. O.;Bhatia，Surita R.
我们报道了聚乳酸-b-聚环氧乙烷-b-聚乳酸（PLA-PEO-PLA）三嵌段共聚物在水中的纳米级组装，着重于立体化学的影响，其中PLA嵌段是l/ratio为100/0、95/5、90/10、85/15、75/25和50/50的l-丙交酯和d-丙交酯的统计共聚物。小角中子散射（SANS）显示了一个几乎恒定的间距，随着浓度的变化，在三嵌段系统与l/dratios的90/10和95/5，我们归因于这些凝胶的结构的不均匀性，支持以前的USANS和共聚焦显微镜研究。SANS数据很好地拟合了具有硬球结构因子的核壳椭球形状因子模型。l/dratios从75/25到85/15的聚合物胶束显示出非常高的聚集数，与PLA链之间的强相互作用和在这些系统的流变学研究中观察到的增强的储能模量一致。虽然90/10和95/5样品显示出较低的聚集数，但它们的SANS曲线显示胶束之间的紧密间距，这可能促进高比例的胶束间桥接链，也与较高的储能模量一致。总体而言，这些结果提供了对具有可结晶嵌段的嵌段共聚物的胶束组装行为的深入了解，并且表明调整PLA基嵌段共聚物的立体化学是针对特定应用修改胶束性质的有效手段。
We report on the nanoscale assembly of poly(lactic acid)-b-poly(ethylene oxide)-b-poly(lactic acid) (PLA-PEO-PLA) triblock copolymers in water, focusing on the effect of stereochemistry, where the PLA blocks are statistical copolymers ofl-lactide andd-lactide withl/dratios of 100/0, 95/5, 90/10, 85/15, 75/25, and 50/50. Small-angle neutron scattering (SANS) shows a nearly constantd-spacing as concentration varies in triblock systems withl/dratios of 90/10 and 95/5, which we attribute to inhomogeneity in the structure of these gels, supported by previous USANS and confocal microscopy studies. The SANS data fit well to a core-shell ellipsoid form factor model with a hard-sphere structure factor. Polymeric micelles withl/dratios from 75/25 to 85/15 displayed very high aggregation numbers, consistent with a strong interaction between PLA chains and the enhanced storage modulus observed in rheological studies of these systems. While the 90/10 and 95/5 samples showed lower aggregation numbers, their SANS profiles shows close spacing between micelles, which may promote a high fraction of intermicellar bridging chains, also consistent with a higher storage modulus. Overall, these results provide insight into the micellar assembly behavior of block copolymers with a crystallizable block, and indicate that tuning stereochemistry of PLA-based block copolymers is an effective means of modifying micellar properties for specific applications.