Effect of Tertiary Amine Methacrylate Structure on the pH-Responsive Release Behavior of Polyurethane/Acrylic Hybrid Films

Abstract

Stimuli-responsive polyurethane-based materials are promising candidates for controlled-release applications. In this study, polyurethane/acrylic hybrid films containing 2-(diethylamino)ethyl methacrylate (DEA) or 2-(diisopropylamino) ethyl methacrylate (DPA) at different acrylic contents were synthesized and systematically compared to elucidate the influence of variations in the tertiary amine structure on the pH-responsive release behavior. Rhodamine 6G (R6G) was used as the model cationic compound. The pH-responsive behavior of the hybrids was investigated through swelling studies, morphological and spectroscopic characterization, loading experiments, and release kinetics analyses. Both hybrid series exhibited reversible pH-dependent morphological changes and limited release at pH 8.0, whereas acidification to pH 4.0 triggered a significant increase in release. The release percentage increased with acrylic content, reaching 98.7% and 94.8% for the DEA- and DPA-based hybrids, respectively, with the highest acrylic content. Increasing the acrylic fraction also reduced the half-release time from 5.0 to 0.9 h for the DEA-based hybrids and from 15.0 to 1.5 h for the DPA-based systems. The DEA-containing hybrids exhibited faster release kinetics than their DPA counterparts. Korsmeyer–Peppas analysis revealed a transition from Fickian diffusion to anomalous and Super Case II transport as the acrylic content increased. These findings establish structure–property–release relationships that provide design guidelines for the development of tunable pH-responsive polyurethane/acrylic delivery materials.