Abstract: The present invention relates to novel hydroxyl-terminated polyisobutylenes and methods of making and using them. The hydroxyl-terminated polyisobutylenes contain a sulfur unit, —S—, within each terminal end group. The well-defined, sulfur containing, primary hydroxyl-terminated polyisobutylenes of the present invention can be simply, rapidly, and essentially quantitatively obtained by subjecting the unsaturated telechelic PIBs and mercapto alcohols to UV light-activated thiol-ene reactions. The resultant sulfur containing, primary hydroxyl-terminated polyisobutylenes can then be used in the production of polyurethanes and like materials.