2-(Pyridin-2-yl)ethanol as a protecting group for carboxylic acids: chemical and thermal cleavage, and conversion of poly[2-(pyridin-2-yl)ethyl methacrylate] to poly(methacrylic acid)

Abstract

In this communication, we show that 2-(pyridin-2-yl)ethanol is a good protecting group for methacrylic acid (MAA), which can be selectively removed, after polymerization, either chemically under alkaline conditions or thermally at or above 110 °C, while it is stable under acidic conditions and resists catalytic hydrogenolysis. To this end, the monomer 2-(pyridin-2-yl)ethyl methacrylate was synthesized, purified, and homo- and co-polymerized via two controlled polymerization methods, group transfer polymerization (GTP) and reversible addition–fragmentation chain transfer (RAFT) polymerization, to obtain homopolymers and diblock copolymers with methyl methacrylate (GTP) and styrene (RAFT), whose 2-(pyridin-2-yl)ethyl groups could be readily cleaved by chemical or thermal treatment, yielding diblock copolymers with polyMAA segments. The 2-(pyridin-2-yl)ethyl protecting group is one of the very few moieties that can be hydrolyzed under alkaline conditions, and, owing to the commercial availability and relatively low cost of 2-(pyridin-2-yl)ethanol, the present group is expected to find extensive use by the polymer community.