A process for manufacturing a polymer having a molecular weight in excess of 5,000, and preferably in excess of 40,000, comprises, producing a polymerized reaction mass in which the polymer is dispersed, the reaction mass including solvent(s), unreacted monomer and other unwanted contaminants; feeding the reaction mass to a means for disentangling the polymer's molecules to produce a modified polymer in the reaction mass; feeding the modified polymer in the reaction mass to a polymer-recovering means; removing the unwanted volatiles and other byproducts; and, recovering a high molecular weight substantially pure modified polymer having substantially the same molecular weight as the polymer fed to the disentangling means and a viscosity at least 10% lower than that of the polymer fed to the disentangling means.