Mixtures of cationic and anionic surfactants form insoluble salts and are not useful. Other forms of chain growth polymerization include cationic addition polymerization and anionic addition polymerization. Some salts of cationic and anionic metal carbonyls are soluble in water or lower alcohols. Unlike molecular compounds, salts dissociate in solution into anionic and cationic components. Skin irritancy generally increases in the series non-ionic, amphoteric, anionic, cationic surfactants. Laundry detergents contain mostly anionic and non-ionic surfactants. Mixtures of surfactants are often used, including mixtures of anionic with nonionic surfactants. The reactive center can be radical, anionic or cationic. Ring-opening polymerization can proceed via radical, anionic, or cationic polymerization as described below. Free-radical polymerization is a type of chain-growth polymerization, along with anionic, cationic and coordination polymerization. The active chain-end is not ionic as in anionic or cationic polymeriation but is covalent. There are two main types of emulsions with different affinity for aggregates, cationic and anionic. Some examples of anionic surfactants are carboxylates, phosphates, sulfates, and sulfonates. Polyelectrolytes that bear both cationic and anionic repeat groups are called polyampholytes. The synthetic techniques used range from ROMP to generic anionic or cationic living polymerizations.