Synthesis of water-soluble poly[oligo(ethylene glycol) methacrylate]s by living anionic polymerization of oligo(ethylene glycol) vinyl ether methacrylates

Anionic polymerizations of 2-(2-vinyloxyethoxy)ethyl methacrylate (V2), 2-[2-(2-vinyloxyethoxy)ethoxy]ethyl methacrylate (V3), and 2-[2-(2-(2-vinyloxyethoxy)ethoxy)ethoxy]ethyl methacrylate (V4) were carried out with either 1,1-diphenyl-3-methylpentyllithium/lithium chloride or diphenylmethylpotassium/diethylzinc in THF at −78 °C for 2–20 h. All the anionic polymerizations of V2–V4 chemoselectively proceeded on the methacryloyl groups, while the vinyloxyl groups in the side chains were intact during the polymerization. The resulting polymers possessed the predicted molecular weights based on the molar ratios between monomers and initiators and narrow molecular weight distributions (M_w/M_n < 1.1). The vinyloxyl groups in the side chain terminals of anionically obtained poly(V2–V4) were quantitatively hydrolyzed with aqueous HCl in THF to afford a series of well-defined poly[oligo(ethylene glycol) methacrylate]s, poly(OH2–OH4), possessing OH groups in the side chains. The hydrolyzed poly(OH2–OH4) showed water solubility, while the poly(V2–V4) having vinyloxyl protecting groups in the side chains were insoluble in water. On the other hand, cationic polymerization of V2 exclusively occurred on a vinyloxyl group with 1-isobutoxyethyl acetate in toluene at 25 °C in the presence of ethylaluminium dichloride and THF to give a polymer of controlled M_n and relatively narrow molecular weight distribution (M_w/M_n < 1.2).