Association and Aggregation Behavior of Poly(ethylene oxide)-b-Poly (N-isopropylacrylamide) in Aqueous Solution

• Published in: Macromolecules Vol. 41; no. 13; pp. 4908 - 4913
• Main Authors: Yan, Jingjing, Ji, Wenxi, Chen, Erqiang, Li, Zichen, Liang, Dehai
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 08.07.2008
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties; Hydrodynamic radius; Temperature effect; Radius of gyration; Acrylamide derivative copolymer; Ethylene oxide copolymer; Experimental study; Monodispersed polymer; Concentration effect; Dilute solution; Diblock copolymer; Molecular aggregation; Aqueous solution; Micellization
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma7026726

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.