The aim of this study was to compare the mucoadhesive properties of thiolated chitosans with regard to their molecular mass and type of immobilized thiol ligand. Mediated by a carbodiimide, aromatic- and aliphatic-thiol-bearing compounds were covalently attached to low- and medium-molecular-mass chitosan. All synthesized conjugates displayed on average 320 +/- 50 mu mol of immobilized free thiol groups per gram of polymer. The rheological synergy was observed by the mixture of equal volumes of polymer with mucin solution. Because of the increase in viscosity of the conjugate/mucin mixture, the self-crosslinking properties and the interaction of thiomers with the mucus layer could be confirmed. Further mucoadhesion of the chitosan conjugates was evaluated in vitro with the rotating cylinder method and tensile studies on excised porcine intestinal mucosa. The results show a significantly enhanced residence time (p < 0.05) on the mucosa of all thiolated chitosans compared to the unmodified polymer. Among all of the conjugates tested, the following rank order of mucoadhesion could be determined: Chitosanthiobutylamidine > Chitosan4-mercaptobenzoic acid > Chitosanglutathione > Chitosan6-mercaptonicotinic acid > ChitosanN-acetyl cysteine > Chitosanthioglycolic acid > Unmodified chitosan. The charge, pKa, and reactivity of the attached compounds were found to be important factors influencing the mucoadhesive potential of the polymer. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011