The synthesis of novel polymeric dyes by directly attaching toluidine blue O and MPPD via EDC and CDI coupling is described for polymers with enteric properties [poly(methacrylic acid-co-ethyl acrylate)]. The polymeric dyes are analyzed by SEC and UV/Vis measurements as well as investigated regarding their dissolution and permeation characteristics. Almost no changes between the modified and nonmodified polymer could be observed by conventional drug studies and a self-established method for dissolution rates. Also no influence on the film formation properties was observed by SEM measurements. In vitro toxicity studies showed no increase of toxicity compared to the non modified polymer. (C) 2016 Wiley Periodicals, Inc.