Effect of stereochemistry on nanoscale assembly of ABA triblock copolymers with crystallizable blocks

Xuechen Yin; David R.O. Hewitt; Bingqian Zheng; Suan P. Quah; Christopher B. Stanley; Robert B. Grubbs; Surita R. Bhatia

doi:10.1016/j.polymer.2021.123683

Effect of stereochemistry on nanoscale assembly of ABA triblock copolymers with crystallizable blocks

Xuechen Yin, David R.O. Hewitt, Bingqian Zheng, Suan P. Quah, Christopher B. Stanley, Robert B. Grubbs, Surita R. Bhatia

Scalable Biomedical Modeling

Stony Brook University

Research output: Contribution to journal › Article › peer-review

4 Scopus citations

Abstract

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 of L-lactide and D-lactide with L/D ratios of 100/0, 95/5, 90/10, 85/15, 75/25, and 50/50. Small-angle neutron scattering (SANS) shows a nearly constant d-spacing as concentration varies in triblock systems with L/D ratios 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 with L/D ratios 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.

Original language	English
Article number	123683
Journal	Polymer
Volume	223
DOIs	https://doi.org/10.1016/j.polymer.2021.123683
State	Published - May 3 2021

Bibliographical note

Publisher Copyright:
© 2021 Elsevier Ltd

Funding

The authors gratefully acknowledge financial support from NSF awards CBET-1335787 and DMR-1905547; ACS PRF grant 55729-ND9; a Turner Dissertation Fellowship for D.R.O.H; and a Department of Education GAANN Fellowship (Award P200A160163) for S.P.Q. and B.Z. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. This research work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union's Horizon 2020 research and innovation programme under the SINE2020 project, grant agreement No 654000.

Funders	Funder number
National Science Foundation	1905547, CBET-1335787, DMR-1905547
American Cancer Society	55729-ND9
U.S. Department of Education	P200A160163
Office of Science
Oak Ridge National Laboratory	DMR-0520547
Horizon 2020	654000

Keywords

Block copolymer
Hydrogel
Poly(lactic acid)

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10.1016/j.polymer.2021.123683

Cite this

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title = "Effect of stereochemistry on nanoscale assembly of ABA triblock copolymers with crystallizable blocks",

abstract = "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 of L-lactide and D-lactide with L/D ratios of 100/0, 95/5, 90/10, 85/15, 75/25, and 50/50. Small-angle neutron scattering (SANS) shows a nearly constant d-spacing as concentration varies in triblock systems with L/D ratios 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 with L/D ratios 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.",

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AU - Stanley, Christopher B.

AU - Grubbs, Robert B.

AU - Bhatia, Surita R.

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AB - 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 of L-lactide and D-lactide with L/D ratios of 100/0, 95/5, 90/10, 85/15, 75/25, and 50/50. Small-angle neutron scattering (SANS) shows a nearly constant d-spacing as concentration varies in triblock systems with L/D ratios 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 with L/D ratios 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.

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Effect of stereochemistry on nanoscale assembly of ABA triblock copolymers with crystallizable blocks

Abstract

Bibliographical note

Funding

Keywords

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