Vol. 70Mass Copolymerization.-The method for determining monomer-polymer composition curves for the five systems reported was essentially the same in each case. Solutions comprising 100 g. of total monomers were prepared by adding appropriate amounts of monomer, comonomer and benzoyl peroxide to 4-oz. French square bottles. The concentrations employed are given in Table I. Air above the monomers was swept out with nitrogen and a metal cap screwed tightly on the bottle mouth. Copolymerizations were carried out in an air oven regulated to ±1°w ithin the polymerization temperature given in Table I. Polymerization at that temperature was continued until a slight increase in viscosity was observed or, in the case of copolymer samples high in combined nitrile, until a small amount of insoluble copolymer had precipitated from the comonomer solution. The reaction was then poured into 3000 ml. of stirred denatured ethanol (2B) at room temperature and the bottle rinsed with ethanol.In the case of vinyl acetate copolymers, hexane was used in place of ethanol throughout. The mixture was boiled to complete the coagulation and filtered. Final purification was effected by similar treatment with two fresh 1500ml. portions of denatured ethanol. After drying in an evaporating dish for forty-eight hours in a circulating air oven at 60°, the copolymer was analyzed in duplicate for nitrogen by the micro-Dumas method. Analytical data and conversion values are summarized in Table I.