Dynamic models for styrene/butadiene (SBR) cold emulsion copolymerization reactors refrigerated by vertical thermosyphons were implemented and studied. A detailed first-principle model was used to evaluate the influence of the thermosyphon upon the operation of the reaction system. It was shown that the dynamics of the thermosyphon is fundamental for the proper understanding of the process dynamics. Particularly, the thermosyphon works as a robust and versatile cooling system, removing process perturbations efficiently. A second hybrid model was then developed to allow the on-line implementation of a model of a reactor train comprised of 15 reactors in series. Both models were shown to agree with each other and with industrial plant data.