Manufacture of functional derivatives of polyvinylic copolymers

Claim 1

A PROCESS FOR THE PRODUCTION OF A POLYVINYL ACETAL FROM A COPOLYMER OF POLYVINYL CHLORIDE AND A POLYVINYL ESTER OF A LOWER ALIPHATIC ACID AT SUBSTANTIALLY ORDINARY TEMPERATURE IN AN AQUEOUS MEDIUM AND IN ABSENCE OF ADDED SOLVENT, SAID PROCESS COMPRISING (A) A TWO-STAGE HYDROLYSIS OF THE SAID COPOLYMER BY SUBJECTING THE SAME, IN A FIRST STAGE, TO THE ACTION OF AN AQUEOUS HYDROCHLORIC ACID SOLUTION OF 25 TO 36% CONCENTRATION IN SUCH AMOUNT THAT THE WEIGHT OF HYDROCHLORIC ACID, EXPRESSED AS ANHYDROUS HC1, IS INCREASES TO MORE THAN 50% OF THE WEIGHT OF COPOLYMER, UNTIL A HOMOGENEOUS REACTION MASS IS OBTAINED, AND THEN, IN A SECOND STAGE, DILUTING THE SAID REACTION MASS WITH WATER UNTIL THE TOTAL WEIGHT OF WATER IS EQUAL TO ABOUT 5 TIMES THE WEIGHT OF THE COPOLYMER, AND (B) THE ACETALIZATION OF THE RESULTANT HYDROLYSIS PRODUCT IN THE SAME MEDIUM BY THE ACTION THEREON FOR A PERIOD OF MORE THAN ONE HOUR OF AT LEAST ONE UNSUBSTITUTED ALIPHATIC ALDEHYDE.