Abstract: Production method of polyvinyl chloride in an agitated reactor under pressure, including polymerization of vinyl monomers in aqueous suspension, of the type in which at least one vinyl monomer in aqueous solution is introduced into a reactor under agitation, having the following steps: a)—adding a stabilizing-suspending agent in hydroalcoholic suspension of an inorganic mineral powder containing at least magnesium and hydroxyl groups to said reactor, b)—adding to said reactor b1) a base; b2) a peroxide compound; b3) a chloroformate; and b4) an organic acid anhydride whereupon the separate addition of b1), b2), b3), b4), to form the reaction catalyst in situ is only and exclusively in said reactor in order to create said catalyst progressively and under the control of the addition of said stabilizing-suspending agent a).