Improvements in and relating to polyacrylonitrile solutions

In an example, p-anisidine diazonium fluoborate was prepared by diazotization of p-anisidine in the presence of hydrofluoric and boric acids, the product being reprecipitated from methanol. Specification 732,135 also is referred to.ALSO:In a modification of the process described in the parent Specification acrylonitrile polymers are made by polymerizing acrylonitrile alone or in admixture with up to 20% of one or more other ethylenically unsaturated monomers in a concentrated aqueous or aqueous-alcoholic solution of an inorganic thiocyanate and in the presence of an aromatic diazonium fluoborate as catalyst. The other monomer may be styrene, methyl acrylate, vinyl acetate or dyeable additives, e.g. vinyl pyridine. The catalyst may be p-chlorobenzene or p-anisidine diazonium fluoborates and a small quantity of a reducing agent, e.g. sodium hydrosulphite may be present in the polymerization mixture. In an example the polymerization is carried out at a specified pH. The polymerization process may be further carried out as described in the parent Specification. Specification 732,135 also is referred to.