Controlled deprotection of poly(2-(tert-butoxycarbonyloxy)ethyl methacrylate) using p-toluenesulfonic esters as thermally latent acid catalysts

Poly(2-(tert-butoxycarbonyloxy)ethyl methacrylate) (PBHEMA) is converted to poly(2-hydroxyethyl methacrylate) with the release of isobutene and carbon dioxide gasses when it is heated at a high temperature over 200 degrees C. The deprotection of PBHEMA is accelerated by the addition of an acid, but it is simultaneously disadvantageous for the storage and handling of the polymer at an ambient temperature. In this study, we propose the use of thermal acid generators, i.e., thermally latent acids (TLAs) as the catalysts to control a reaction rate and a working temperature for the deprotection of PBHEMA. We investigated the thermal deprotection behavior of some sulfonates including isopropyl p-toluenesulfonate (IPTS) and cyclohexyl p-toluenesulfonate (CHTS). The kinetic parameters for the deprotection, which provides p-toluenesulfonic acid (TsOH) as the reaction product, were determined by thermogravimetric (TG) analysis under the isothermal condition. A remarkable autocatalytic effect actually resulted in a rapid deprotection to produce TsOH in a narrow temperature range under the non-isothermal conditions. The additive effect of the TLAs on the deprotection of the BOC groups contained in the side chain of PBHEMA was similarly investigated. It was revealed that the deprotection of PBHEMA rapidly proceeded by the addition of IPTS and CHTS under the heating conditions over 100 degrees C. PBHEMA was stable at a temperature below the onset temperature of the deprotection of the TLAs. The deprotection kinetics of PBHEMA and a detailed mechanism for the control of the reactions in the presence of the TLAs were clarified.