Process for the manufacture of copolymers of vinyl chloride

Claim 1

IN A PROCESS WHEREIN 60-90% BY WEIGHT OF VINYL CHLORIDE IS COPOLYMERIZED IN THE PRESENCE OF A FREE RADICALLIBERATING CATALYST WITH (A) 5-35% BY WEIGHT OF A WEAK CROSS-LINKING MONOMER SELECTED FROM THE GROUP CONSISTING OF A VINYL ESTER OF A MONOBASIC ALIPHATIC ACID, VINYLIDENE CHLORIDE, AND MALEIC ACID ESTERS, THE ALCOHOL COMPONENT OF WHICH IS A SATURATED ALCOHOL CONTAINING 1-25 CARBON ATOMS, AND (B) 0.5-5% BY WEIGHT OF A MONOMER OF GREATER CROSS-LINKING TENDENCY WHICH IS SELECTED FROM THE GROUP CONSISTING OF ESTERS OF ALLYL ALCOHOL AND METHALLYL ALCOHOL WITH ALIPHATIC AND AROMATIC MONOBASIC AND DIBASIC ACIDS, MIXED ALLYL-ALLYL ESTERS OF PHTHALIC ACID, PHOSPHORIC ACID ALLYL ESTERS, CYANURIC ACID ALLYL ESTERS, MIXED ESTERS OF DIBASIC ACIDS WITH SATURATED AND UNSATURATED ALCOHOLS, AN ESTER OF AN UNSATURATED ACID WITH A GLYCOL, A DIVINYL COMPOUND, AND A VINYL PHOSPHONIC ACID DIALLYL ESTER, THE TOTAL WEIGHT OF MONOMERS EQUALING 100%, THE IMPROVEMENT COMPRISING CONDUCTING THE POLYMERIZATION IN TWO STEPS, IN THE FIRST STEP OF WHICH VINYL CHLORIDE IS POLYMERIZED WITH AT LEAST ONE MONOMER (A) AND A PORTION OF AT LEAST ONE OF THE MONOMERS (B) IN AQUEOUS SUSPENSION AND IN THE PRESENCE OF A SUSPENDING AGENT, UNTIL AT LEAST ABOUT 50% OF THE TOTAL REACTION MIXTURE HAS UNDERGONE CONVERSION, AND THEREAFTER IN A SECOND STEP ADDING A FURTHER AMOUNT OF SAID MONOMER (B) AND COMPLETING THE POLYMERIZATION AT AN ELEVATED TEMPERATURE OF 70*100*C., THE PROPORTION OF MONOMER (B)ADDED IN THE FIRST STEP OF POLYMERIZATION BEING FROM 10-85% BY WEIGHT, WITH THE REMAINING 90-15% BEING ADDED IN THE SECOND