SynopsisA method to produce homopolymers of preestablished molecular weight distribution (MWD), through "living" anionic polymerizations carried out in homogeneous semibatch reactors is proposed and theoretically justified. In the direct form of the technique, very fast reactions are assumed, and the monomer and "killing" agent feed flows are obtained from the knowledge of the desired MWD, the system spreading function, the total reaction time, the initial reaction volume, and the reagent concentrations. Alternatively, by controlling a reactor outlet flow instead of the "killing" agent feed, an external deactivation of the "living" ends can be implemented. The method can be extended to slow reactions, to more elaborated mechanisms, and to take into account the unwanted deactivation of "living" ends by impurities in the monomer solution feed.

SynopsisThis work constitutes an indirect verification of a theoretical method that allows the production of polymers with p r e s p d e d molecular weight distributions (MWDs), through semibatch living-anionic homopolymerizations. The chemical system consisted of styrene with sec-butyllithium, in a solvent mixture of cyclohexane and tetrahydrofurme (THF). The necessary flow profiles were applied by a pair of computer-controlled pumps, and the produced MWDs were measured by size exclusion chromatography, with correction for nonuniform instrumental spreading. The main difficulty was the estimation of the initial moles of initiator and of the concentration of impurities in the monomer solution. For such estimation, a precalibration experiment was implemented.