Micellar Copolymerization of Styrene with Poly(ethylene oxide) Macromonomer in Water:  Approach to Unimolecular Nanoparticles via Pseudo-Living Radical Polymerization

• Published in: Macromolecules Vol. 33; no. 5; pp. 1583 - 1592
• Main Authors: Maniruzzaman, Mohd, Kawaguchi, Seigou, Ito, Koichi
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07.03.2000
• Subjects: Applied sciences; Copolymerization; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Preparation, kinetics, thermodynamics, mechanism and catalysts; Hydrodynamic radius; Graft copolymer; Temperature effect; Solution copolymerization; Ethylene oxide copolymer; Experimental study; Reaction rate; Solution polymerization; Macromer; Ethylene oxide polymer; Free radical polymerization; Styrene; Molecular aggregation; Kinetics; Aqueous solution; Radical copolymerization; Micellar solution; Amphiphilic polymer; Styrene copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma991272t

Micellar copolymerizations of amphiphilic ω-methoxy-α-p-styrylalkyl poly(ethylene oxide) (PEO) macromonomers 1 (C1−PEO−C m −S-n, m = 1, 4, 7 and n = 18) with a limited amount of styrene solubilized therein have been investigated. The reactions were carried out with 4,4‘-azobis(4-cyanovaleric acid) (AVA) as a water-soluble initiator and 2,2‘-azobis(isobutyronitrile) (AIBN) as an oil-soluble initiator at 60 °C. Fractional time-evolution experiments revealed that the copolymerization rate of styrene is greatly enhanced by the presence of macromonomer micelles and that the rate increases with hydrophobicity (increase of m) of α-end group of 1. The characterization of the resulting graft copolymers revealed that the organized copolymerization proceeds in the manner of a pseudo-living radical copolymerization with highly limited terminations between compartmentalized (isolated) propagating radicals. That is, the molecular weight of the graft copolymers increased with the conversion of monomers. At an equimolar styrene with 1 (n = 18, m = 7) the copolymerization proceeded apparently transparently and azeotropically to afford a highly branched graft copolymer of poly(styrene-graft-PEO), which in water formed a “unimolecular particle” with 15 nm radius and 7.44 × 106 apparent molecular weight. A plausible mechanism for the present organized copolymerization behavior is presented and discussed.