A new N-sulfonic acid based on the polymer-support as a solid acid catalyst is prepared by the reaction of the modified poly(styrene-alt-maleic anhydride) with neat chlorosulfonic acid. 4H-Pyrimido[2,1-b]benzothiazole derivatives, tetrasubstituted imidazoles and benzoxanthenones as selected solvent-free multicomponent reactions were successfully synthesized using this catalyst. These eco-friendly protocols offer several advantages such as green and cost-effective procedures with excellent yield, shorter reaction time, simpler work-up, recovery, and reusability of metal-free solid acid heterogeneous catalyst along with tolerance of a wide range of functional groups. (C) 2014 Elsevier B.V. All rights reserved.