Association and Aggregation Behavior of Poly(ethylene oxide)-b-Poly (N-isopropylacrylamide) in Aqueous Solution
The well-defined block copolymer of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO-b-PNIPAm) was synthesized by the reversible addition fragmentation transfer (RAFT) polymerization, and its thermo-induced aggregation process in dilute aqueous solution was studied by laser light scattering....
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Published in | Macromolecules Vol. 41; no. 13; pp. 4908 - 4913 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Washington, DC
American Chemical Society
08.07.2008
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Subjects | |
Online Access | Get full text |
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Summary: | The well-defined block copolymer of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO-b-PNIPAm) was synthesized by the reversible addition fragmentation transfer (RAFT) polymerization, and its thermo-induced aggregation process in dilute aqueous solution was studied by laser light scattering. At temperatures below the cloud point of PNIPAm, the PEO-b-PNIPAm chains were associated together to form large and loose structures, which were in a fast equilibrium with the single chains. The association was weakened with increasing concentration, which was against the common ideas about aggregation. Because of such “abnormal” behavior, PEO-b-PNIPAm underwent three stages of transformation during the heating process at 0.1 mg/mL: the disassociation of loose associates at temperatures below 28 °C, the micellization above 42 °C, and the aggregation in between. At each stage, the size and M w,app exhibited distinct features. On the basis of these observations, possible mechanisms of the association and aggregation were also proposed. |
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ISSN: | 0024-9297 1520-5835 |
DOI: | 10.1021/ma7026726 |