Increasing viscosity of polycaprolactam by removing extractables with solvents and further solid phase polymerizing the polymer

Claim 1

A PROCESS FOR INCREASING THE INHERENT VISCOSITY AND MOLECULAR WEIGHT OF A POLYMER FROM EPSILON CAPROLACTAM HAVING A NUMBER AVERAGE MOLECULAR WEIGHT OF LESS THAN 29,000 AND AN INHERENT VISCOSITY OF LESS THAN 1.5, SAID POLYMER CONTAINING AT LEAST 2% BY WEIGHT OF A MATERIAL THAT IS EXTRACTABLE IN A SOLVENT SELECTED FROM THE CLASS CONSISTING OF WATER, METHYL ALCOHOL, ETHYL ALCOHOL AND TRICHLOROETHYLENE, WHICH COMPRISES THE STEPS OF EXTRACTING SAID MATERIAL FROM SAID POLYMER WITH A SOLVENT SELECTED FROM SAID CLASS, UNTI, THE AMOUNST OF SAID MATERIAL IN SAID POLYMER IS REDUCED TO NO MORE THAN 1.5% BY WEIGHT, AND THEN INCREASING THE INHERENT VISCOSITY AND NUMBER AVERAGE MOLECULAR WEIGHT OF THE POLLYMER BY SOLID PHASE POLYMERIZATION IN AN ATMOSPHERE OF AN INERT GAS AT A TEMPERATURE BETWEEN 190*C, AND THE MELTING POINT OF THE POLYMER UNTIL THE INHERENT VISCOSITY IS INCREASED TO AT LEAST 1.75 AND THE NUMBER AVERAGE MOLECULAR WEIGHT IS INCREASED TO AT LEAST 33,000 THE INHERENT VISCOSITY