Syntheses of Poly(ethylene oxide-b-styrene oxide) Macromonomers and Their Application to Emulsion and Dispersion Copolymerizations with Styrene

Abstract

ABSTRACT:Poly(ethylene oxide-b-styrene oxide) macromonomers carrying p-vinylbenzyl ether end group were prepared by sequential anionic polymerization of ethylene oxide and styrene oxide with potassium 2-methoxyethoxide, followed by reaction with p-vinylbenzyl bromide to the end-group functionality up to 85%. The macromonomers have been successfully applied to emulsion and dispersion copolymerizations with styrene to afford monodisperse polymeric microsheres in water and in methanol-water (9/1 v/v) mixture, respectively. Incorporation of the macromonomer into the particle is more effective, so resulting in smaller particle size, in the emulsion than in the dispersion system. The particle size in the latter system decreased with the macromonomer concentration in accord with a previously proposed power-law theory and with the chain length of the styrene oxide block.KEY WORDS Macromonomers / Ethylene Oxide / Styrene Oxide / Block / p-Vinylbenzyl EndGroup / Emulsion / Dispersion / Amphiphilic macromonomers find increasing concern in view of their potential use for preparation of polymeric microspheres of submicron to micron size by emulsion and dispersion copolymerizations with a hydrophobic monomer in water and alcoholic media, respectively, without conventional surfactants ('soapfree'). They are usually composed of hydrophilic polymer chains (tails) and the hydrophobic polymerizable end groups (heads), which copolymerize in situ with a substrate hydrophobic monomer to afford graft copolymers. So they serve as effective stabilizers firmly (covalently) attached on the particle surfaces in such a manner that the hydrophobic heads act as anchors while the hydrophilic tails work as steric stabilizers against flocculation. So far a lot of macromonomers have been reported for design of various kinds of polymer microspheres. [1][2][3][4][5] In design of such macromonomers, considerable attention has been paid for control of hydrophiliclyophilic balance (HLB). To our experience, properly hydrophobically enhanced heads as well as properly long hydrophilic tails appear to be important in fine size control and stability of the microspheres to be obtained. In case of poly(ethylene oxide) (PEO) macromonomers with styryl or methacrylate end groups, introduction of some alkylene spacers 6-9 has been successful in this regard. Also interesting is the amphiphilic macromonomer of block copolymer type, 10-14 in which hydrophilic segments are connected through hydrophobic segments to polymerizable end groups. Examples include block macromonomers from poly(2-oxazoline)s, 10, 11 PEO-b-polystyrene (PSt), 12 PEO-bpoly(butylene oxide), In extension of our PEO macromonomer studies, in this paper we discuss preparation of PEO-bpoly(styrene oxide) (PSO) macromonomers with pvinylbenzyl (VB) end groups for use in emulsion and dispersion copolymerization with styrene. Here we expected that PSO segments with VB would provide good balance with the hydrophilic PEO chains for particle size control. The surface properties of PEO-b-PSO block copolymer...