A Haake (R) viscometer with the NV cup- and-bob sensor is used to measure the viscosity, eta, of poly-methyl methacrylate (PMMA) solutions in methyl methacrylate (MMA) at several polymer concentrations, weight-average molecular weights, and temperatures, and under nonreacting conditions. Six polymer samples having different average molecular weights are prepared by polymerizing MMA in a 1-L batch reactor using 2,2'-azoisobutyronitrile (AIBN) as the initiator. Our earlier experimental data (at moderate concentrations of the polymer) on the viscosity of PMMA solutions in MMA under reacting conditions is also used. Two general correlations are developed between eta/eta(soL) and CpolyMw0.76 with the parameters obtained using genetic algorithm. The tuned correlations for viscosity can be used over an extended range of monomer conversions for model-based state estimation and on-line optimal control of the bulk polymerization of MMA. (c) 2008 Wiley Periodicals, Inc.