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Abstract
Using a combination of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), we document the composition-dependent morphologies of 39 new poly(lactide-block-1,4-butadiene-block-lactide) (LBL) block polymers, comprising a broad dispersity B segment (Mn = 4.5-17.7 kg/mol; D= Mw/Mn = 1.72-1.88) and narrow dispersity L end blocks (Mn = 0.6-15.3 kg/mol; D= 1.10-1.21) with volume fractions 0.26 ≤ fB ≤ 0.95. A subset of these samples undergo melt self-assembly into cylindrical, lamellar, and apparently bicontinuous morphologies. By assessing the states of order and disorder in these triblock polymer melts using temperature-dependent SAXS, we find that broad B segment dispersity increases the minimum segregation strength xN ≳ 27 required for LBL triblock self-assembly relative to the self-consistent mean-field theory prediction xN ≥ 17.9 for narrow dispersity analogues. While B segment dispersity has previously been shown to thermodynamically stabilize the self-assembled morphologies of low x/high N ABA triblocks, the present study indicates that broad B block dispersity in related high x/low N systems destabilizes the microphase-separated melt. These observations are rationalized in terms of recent theories that suggest that broad segmental dispersity substantially enhances fluctuation effects at low N, thus disfavoring melt segregation.
Original language | English (US) |
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Pages (from-to) | 6779-6787 |
Number of pages | 9 |
Journal | Macromolecules |
Volume | 50 |
Issue number | 17 |
DOIs | |
State | Published - Sep 12 2017 |
Bibliographical note
Funding Information:We gratefully acknowledge financial support from the National Science Foundation (DMR-1307606 and DMR-1631598). This work also relied on critical core instrumentation facilities funded in part by NSF grants (CHE-9974839) and the University of Wisconsin NSEC (DMR-0832760) and CEMRI (DMR-1121288), which are part of the NSF-funded Materials Research Facilities Network. Synchrotron SAXS analyses were conducted at the DuPont−Northwestern−Dow Collaborative Access Team (DND-CAT) beamline located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co., and The Dow Chemical Company. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357.
Publisher Copyright:
© 2017 American Chemical Society.
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