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. © The Royal Society of Chemistry 2012.