ABA block copolymers without tapering by isokinetic living anionic polymerization in a series of stirred tank reactors.
Equations for the mol.-wt. distribution and the av. mol. wts. of a living anionic polymn. with very rapid or slow initiation are presented for a series of stirred tank reactors. Polydispersity of the polymer in the last vessel of a cascade is at a min. for nearly complete conversion of monomer, when the reaction is performed isokinetically with respect to monomer conversion--when monomer conversion in each vessel of a cascade of n tanks is 1/n. Polydispersity of the polymer in the mth vessel of the cascade (1 ? m ? n) is Dm = 1 + 1/m. Values of all system variables needed for isokinetic control of the polymn. may be precalcd. from kinetic models. For vessels of equal size and with equal residence times, reaction temp. is suggested as a control variable, increasing stepwise from vessel to vessel. The proposed procedure is checked for the systems styrene (I)/n-BuLi/PhMe, I/sec-BuLi/C6H6, and isoprene/sec-BuLi/n-heptane. There is good agreement between calcd. and measured values of monomer conversion, no.-av. mol. wt., and polydispersity. Use of the described procedure for the prepn. of ABA block copolymers with negligible tapering between the blocks by living anionic polymn. in a series of stirred tank reactors is proposed.
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