Effect of adding lithium chloride on the radical copolymerization of lithium p-styrenesulfonate and acrylamide

Lithium p-styrenesulfonate (LiSS) is a water-soluble monomer that exhibits good solubility compared with sodium p-styrenesulfonate (NaSS). Radical copolymerization of LiSS was investigated using acrylamide (AAm) as the comonomer in water at 60 & DEG;C in the presence of various salts as additives. The copolymerization of LiSS and AAm as highly reactive and less reactive monomers, respectively, provided a random copolymer consisting of a large amount of LiSS repeating unit at an earlier stage in the reaction. Then, the homopolymerizations of AAm spontaneously proceeded after LiSS was consumed at a high conversion (over 99%). A large amount of lithium chloride was added to the copolymerization system, promoting the polymerization reactivity of LiSS. The addition of lithium bromide and sodium bromide suppressed the copolymerization of LiSS and AAm and completely prevented the spontaneous homopolymerization of AAm after copolymerization. The effects of other additives on the copolymerization systems were investigated, and the combination of sodium nitrite and ascorbic acid was revealed to inhibit the copolymerization of LiSS and AAm. The interactions between lithium cations and functional groups in the monomers and polymers that benefit the copolymerization reactivity is discussed.