A novel synthesis of linear acrylic acid containing polymers, poly(styrene-co-acrylic acid) and poly(acrylic acid), was accomplished through hydrolysis of the respective parent polymers, i.e, poly(styrene-co-methyl acrylate) and poly(methyl acrylate), with trimethylsilyl iodide under mild conditions. Combination of H-1 NMR,C-13 NMR, FTIR, DSC and chemical titration confirms that the conversion from methoxycarbonyl to carboxyl is almost complete. This method is further successfully applied to synthesize poly(ethyl methacrylate-co-acrylic acid) through selective hydrolysis of the methyl acrylate units in poly(ethyl methacrylate-co-methyl acrylate).