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

Abstract

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.

From free radical to atom transfer radical polymerization of poly(ethylene oxide) macromonomers in nanostructured media

“…Ito et al observed unusually high polymerization rates, they explained by the organization of the polymerizable groups in hydrophobic domains, the micelle and they called it micellar organization polymerization. Kinetic studies by ESR [17] confirmed the very rapid polymerization due to high local concentration of radicals and (macro)monomers corresponding to enhanced rate of propagation and reduced termination. Micelle formation was confirmed unambiguously by surface tension and light scattering experiments.…”

“…Special attention was given to the influence of the presence of the hydrophobic co-monomer on the final properties of the resulting hydrogels. The relevance of this approach has been demonstrated recently by the group of Ito [17] who performed micellar co-polymerization of monofunctional PEO macromonomers with styrene to design a new type of nanoparticular system. Results of the free radical copolymerization of bifunctional PEO macromonomers with styrene are presented in Tables 2 and 3. As expected, cross-linking occurs.…”

Core–Shell Type Polystyrene Latex Possessing Reactive Poly(ethylene glycol) Brushes on the Surface for High Performance Immunodiagnostics

“…[10][11][12][13][14][15][16] PEG macromonomers possessing a hydrophobic spacer in between the PEG chain and the polymerizable double bond was prepared as a monomer with an appreciable surfactant ability for dispersion polymerization. Because most of the PEG macromonomers prepared so far possess no functional group at the distal chain end, the prepared latex lacks functionality on the surface.…”

Micelle Formation of “Nonamphiphilic” Poly(vinylphenol-co-styrene) Random Copolymers by Hydrogen Bond Cross-linking by α,ω-Diamine

“…23,24 An increase in the number of publications on them has been accelerated since well-defined block and graft copolymers came to be prepared more easily by living radical polymerization techniques than by living ionic polymerization. [25][26][27] Micelles for amphiphilic random copolymers have also been well-studied on the basis of the advantage of convenient procedure for preparing the random copolymers over block and graft copolymers. …”

“…23,24 An increase in the number of publications on them has been accelerated since well-defined block and graft copolymers came to be prepared more easily by living radical polymerization techniques than by living ionic polymerization. [25][26][27] Micelles for amphiphilic random copolymers have also been well-studied on the basis of the advantage of convenient procedure for preparing the random copolymers over block and graft copolymers. [28][29][30][31][32] While many amphiphilic copolymers are utilized for preparing micelles, ''nonamphiphilic'' copolymers attract considerable attention in recent years because of the advantages in the molecular design.…”