Functional pH-responsive polymers containing dynamic enaminone linkages for the release of active organic amines

Abstract

Dynamic covalent bonds have attracted considerable attention for the development of pH-responsive polymers, however, studies using acid-cleavable enaminone linkages as a means of controlled release are limited. Herein, we report pH-sensitive benzocaine-modified poly(ethylene glycol) monomethyl ether-block-poly[2-(acetoacetoxy)ethyl methacrylate] (mPEG_x-b-pAEMA_y)/BNZ nanoparticles (NPs) for the aqueous controlled release of benzocaine through enaminone bond cleavage. The system is based on the commercially available monomer 2-(acetoacetoxy)ethyl methacrylate (AEMA) which contains free pendant β-ketoester functionality. Well-defined poly[2-(acetoacetoxy)ethyl methacrylate] (pAEMA) homopolymers and poly[(ethylene glycol) monomethyl ether]-block-poly[2-(acetoacetoxy)ethyl methacrylate] (mPEG_x-b-pAEMA_y) amphiphilic block copolymers were prepared by photoinduced Cu(II)-mediated RDRP to investigate their modification with propylamine (a model amine) and benzocaine (a primary amine containing API) through an enaminone bond. Block copolymers were prepared via two poly(ethylene glycol) monomethyl ether-2-bromo-2-phenylacetate (mPEG_x-BPA, x = 43 or 113) macroinitiators synthesised by esterification which acted as the hydrophilic coronas of the ensuing NPs. The self-assembly of both mPEG_x-b-pAEMA_y and (mPEG_x-b-pAEMA_y)/BNZ was assessed in water by the direct dilution approach forming spherical NPs as characterised by dynamic light scattering (DLS) and dry-state transmission electron microscopy (TEM). Finally, the in vitro controlled release of benzocaine from mPEG_x-b-pAEMA_y/BNZ NPs was examined at different pH environments demonstrating faster release kinetics at lower pH with potential utility in applications with relevant chemical environments.