Addition of Corona Block Homopolymer Retards Chain Exchange in Solutions of Block Copolymer Micelles

Journal Article · Thu Feb 11 00:00:00 EST 2016 · Macromolecules

DOI:https://doi.org/10.1021/acs.macromol.5b02395· OSTI ID:1241057

Lu, J. ^[1]; Bates, F. S. ^[1]; Lodge, T. P. ^[1]

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1. Univ. of Minnesota, Minneapolis, MN (United States)

The exchange of copolymer chains between 1 vol % PS–PEP (poly(styrene-b-ethylene-alt-propylene)) diblock copolymer micelles in squalane (selective for PEP) is investigated in this work using time-resolved small-angle neutron scattering (TR-SANS) as a function of added PEP homopolymer. The solvent squalane, C₃₀H₆₂, is substituted in part or completely with PEP homopolymers that are the same molecular weight as the corona blocks. Polymer solutions/mixtures (1 vol % PS–PEP, plus 2, 7, or 15 vol % PEP in squalane, and 1 vol % PS–PEP in PEP) were separately prepared using normal (h-PS) or deuterated equivalent (d-PS) PS–PEP diblock copolymers. The solvent was contrast matched to a 50/50 mixed h-/d-PS micelle core, so that the scattering intensity decays with the mixing of h- and d-PS–PEP chains undergoing exchange between micelles. The chain exchange rate can therefore be assessed quantitatively. As the concentration of added homopolymer in solution increases above the overlap concentration of PEP chains, the chain exchange rate drops significantly. The results are compared to an earlier study of chain exchange between PS–PEP micelles in a 15% solution in squalane, which was also found to be significantly slower than when the solution is dilute. The primary factor in this slowing down of chain exchange is an increased screening of excluded volume interactions among the corona blocks. The role of increasing micelle aggregation number with PEP concentration is found not to be the dominant effect up to 15% added PEP but may play an increasingly important role in the PEP melt matrix, where no chain exchange could be detected in these experiments.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1241057
• Journal Information: Macromolecules, Vol. 49, Issue 4; ISSN 0024-9297
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
X-ray scattering
Micelles
Scattering
Solvents
Homopolymers