After demonstrating the efficiency of a previously-developed method for the estimation of the rate of heat generation in a stirred tank polymerisation reactor, the use of a non-linear state observer that exploits this rate of heat generation for the evaluation of the copolymer composition, overall conversion, as well as of certain kinetic parameters associated with the reaction was tested. The results of the estimator were compared with both theoretical modelling studies and experimental results. It was also demonstrated that even in dilute solution polymerisation it is necessary to account for variation of the homopolymerisation rate constants with the concentration in the reaction medium. Standard kinetic models, when used with variable parameters, predict the heat of reaction much better than the same models with fixed parameters. This suggests that calorimetry could provide a valuable tool for the estimation of the kinetic parameters in a multiple monomer system.