Acrylic acid free radical polymerization in aqueous solution was studied using a new experimental setup coupling Raman spectroscopy and flow rheology in a Couette-like geometry. In situ monitoring of polymer concentration and viscosity of reaction medium versus time was carried out, for different reactant concentrations (acrylic acid and initiator) and process conditions (temperature and shear rate). Experimental variations of polymer concentration and reaction medium viscosity before the occurrence of gel effect as a function of reactant concentration and process conditions were obtained. An overall model combining kinetic scheme and rheological equation was proposed. Kinetic and rheological parameters of the model were identified and found consistent with literature. Gel effect was detected as a sharp increase of polymer concentration much faster than the calculated trend. The occurrence of gel effect was mapped as a function of monomer feed concentration and shear rate. These lab-scale data provided experimental and theoretical bases for process scale up to pilot-scale plant. (C) 2013 Elsevier Ltd. All rights reserved.