The simultaneous solution of the optimal sequencing and optimal dynamic transitions of two multigrade polymerization continuous stirred-tank reactors (CSTRs) is presented. The simultaneous formulation leads to a mixed-integer dynamic optimization (MIDO) problem. The profiles of the state variables during dynamic transitions are discretized using orthogonal collocation on finite elements, transforming the MIDO problem into a mixed-integer nonlinear programming (MINLP) problem. The objective of this formulation is to maximize the profit of the manufacturing operation, considering polymer sales, inventory costs and transition costs. The transition cost term is determined by the duration of the transition stages and the manipulated variable profile during transitions. Two industrial reaction systems are used to analyze the optimal solution and compare it to other solutions obtained using different methods. Finally, a sensitivity analysis is carried out to describe the impact of changes in certain problem parameters. (C) 2007 American Institute of Chemical Engineers.