Protection and Polymerization of Functional Monomers. 29. Syntheses of Well-Defined Poly[(4-vinylphenyl)acetic acid], Poly[3-(4-vinylphenyl)propionic acid], and Poly(3-vinylbenzoic acid) by Means of Anionic Living Polymerizations of Protected Monomers Bearing Bicyclic Ortho Ester Moieties

Abstract

Anionic polymerizations of four styrenes protected with bicyclic ortho ester moieties, 1-(4-vinylphenyl)methyl-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane (1), 1-[2-(4-vinylphenyl)ethyl]-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane (2), 1-(3-vinylphenyl)-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane (3), and 1-(4-vinylphenyl)-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane (4), were carried out in THF at −78 °C for 0.5 h with oligo(α-methylstyryl)lithium and -dipotassium and potassium naphthalenide. Poly(1)−(3) were quantitatively obtained, and the resulting polymers possessed the predicted molecular weights based on the molar ratios of monomers to initiators and narrow molecular weight distributions (MWDs, Mw/Mn < 1.1). By contrast, polymerization of 4 did not go to completion and gave insoluble polymeric product in low yield due to the side reactions under the similar conditions. The substituent position in the monomer was very important for the success of the polymerization, although the bicyclic ortho ester was found to be stable under the polymerization conditions of 1−3. Well-defined block copolymers of 1 and 2 with styrene were synthesized by the sequential block copolymerizations regardless of the order of addition of the monomers. Hydrolyses of bicyclic ortho ester moieties of the resulting polymers were performed at room temperature by treating with 6 N HCl in THF/MeOH for 1 h and subsequently with 10% NaOH(aq) in THF/MeOH for 12 h. Deprotections of poly(1), poly(2), and poly(3) quantitatively proceeded to afford poly[(4-vinylphenyl)acetic acid], poly[3-(4-vinylphenyl)propionic acid], and poly(3-vinylbenzoic acid) having tailored chain structures, respectively.