In this paper the performance of a thin ®lm reactor using the spinning disc technology has been described. The objective of the study was to develop a compact reactor with good heat and mass transfer characteristics for continuous processing of free radical polymerisation. Solution polymerisation of styrene was therefore chosen as an example of free-radical polymerisation system and it may be concluded that a spinning disc reactor (SDR) can signi®cantly enhance the reaction rates when the viscosity of the polymer mass is in excess of 3±4 N/m2 s. It also improves the product quality by producing polystyrene with tight molecular weight distribution (MWD). The inherent safety of the process is also improved. 7 2000 Elsevier Science Ltd. All rights reserved.