Lignocellulosic biomass fractionation has been conducted using a synthetic polymeric solid acid catalyst consisting of dual polymer chains. The acidic polymeric chain, poly(styrene sulfonic acid) (PSSA) catalyzes biomass hydrolysis. A neighboring poly(vinyl imidazolium chloride) (PIL) chain helps solubilize lignocellulosic biomass and enhance the catalytic activity. Hydrolysis was conducted for crystalline cellulose and acid, base or steam pretreated corn stover samples in ionic liquids (IL) and mixtures of IL with H2O or gamma-valerolactone (GVL) or other organic solvents. Near quantitative total reducing sugar (TRS) yields for cellulose hydrolysis as well as pretreated corn stover biomass were achieved at mild conditions and in less than 12 h. Our designed polymeric solid acid catalysts are superior to cellulases as they can be operated at a higher temperature and at a much higher hydrolysis rate. These catalysts are stable and maintain high catalytic activity after repeated runs. Moreover, they can be easily regenerated and are environmental friendly.