Living Anionic Polymerization of 1-(Alkoxy)ethyl Methacrylates and the Preparation of Well-Defined Poly(methacrylic acid)

Abstract

Three novel methacrylate monomers, 1-(ethoxy)ethyl methacrylate (EEMA), 1-(butoxy)ethyl methacrylate (BEMA), and 1-(tert-butoxy)ethyl methacrylate (tBEMA), were prepared through the addition reaction of methacrylic acid (MAA) and ethyl, butyl, or tert-butyl vinyl ether, respectively. These monomers have been subjected to anionic polymerization in tetrahydrofuran (THF), using (1,1-diphenyl)hexyllithium (DPHL) as initiator. In contrast to the common alkyl methacrylates, their anionic polymerizations were very sensitive to temperature and to the amount of LiCl added. A [LiCl]/[DPHL]0 molar ratio of unity was most beneficial, but a high excess of LiCl had a negative effect. Suitable polymerization temperatures were found to be in the range −60 to −20 °C, with an optimum at about −40 °C, but even at +20 °C tBEMA could be polymerized quantitatively to a poly(tBEMA) with a relatively narrow molecular weight distribution (Mw/Mn = 1.18). However, the very low temperature of −80 °C, which is optimum for the common alkyl methacrylates, was not suitable for the new monomers. For [LiCl]/[DPHL]0 ≈ 1 and a temperature in the range −60 to −20 °C, the anionic polymerizations of EEMA, BEMA, and tBEMA could proceed in a living manner and generate polymers with controlled molecular weights and narrow molecular weight distributions (Mw/Mn = 1.06−1.09). Poly(EEMA), poly(BEMA), or poly(tBEMA) could be easily hydrolyzed, to generate well-defined poly(MAA).