Sulfochlorinated, macroporous poly(styrene-co-divinylbenzene), 1, is a useful intermediate for synthesis of polymers with functional groups such as primary and secondary sulfonamides, sulfonylhydrazine, sulfinic acid, and thiol, all of which can be prepared by reaction of 1 with aqueous reagents. An improved method for preparing 1 consists of using dried, commercially available sulfonic acid cation exchange resins in the hydrogen ion or sodium ion form to react with PCl5 in a suspending medium of POCl3, separating the resin by filtration, and washing the resin with ice-water. The byproducts are POCl3, partially recoverable by atmospheric pressure distillation, small amounts of HCl or NaCl, and H3PO4. No organic solvents are required. Prompt conversion of 1 to the desired final product minimizes hydrolysis of 1.