Production of tert-butyl esters of ethylenically unsaturated carboxylic acids

A process for continuously producing the tert-butyl ester of an ethylenically unsaturated carboxylic acid where a) an ethylenically unsaturated carboxylic acid is reacted with isobutene in the presence of an acidic catalyst to give an esterification mixture; b) the acidic catalyst is removed; c) low-boiling-point constituents are removed; and d) a liquid containing tert-butyl ester is introduced into a distillation device and the product is purified by distillation in the distillation device, where d1) the liquid containing tert-butyl ester is separated in the distillation device to give a gaseous overhead product containing tert-butyl ester and a liquid bottom product containing carboxylic acid; d2) the gaseous overhead product containing tert-butyl ester is at least to some extent condensed and some of the condensate is returned to the distillation device; d3) the liquid bottom product containing carboxylic acid is at least to some extent returned to step a); d4) liquid bottom product containing carboxylic acid is drawn off and conducted to a heater, a superheated liquid return stream is taken from the heater and the superheated return stream is depressurized into the distillation device; and d5) at least in the overhead region of the distillation device those walls of the distillation device that are in contact with the vapours are thermally insulated and/or heated at least in some regions. The separation of the tert-butyl ester from unreacted carboxylic acid in the process proceeds with a particularly small extent of polymerization both of the tert-butyl ester and of the carboxylic acid.