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ABSTRACT:On the basis of so-called linear free enthalpy correlations, a method is developed to predict vinyl contents of polybutadienes from anionic polymerizations with butyllithium in nonpolar solvents in the presence of bases. According to Reichardt with an extension by Langhals, a transition energy scale for the solvatochromic dye N,Ndimethyl indoaniline in dependence of concentrations of some bases is established. The bases were taken from polymerizations of butadiene of Antkowiak et al. and of Jin et al. It could be shown that vinyl contents determined by these authors correlate well with measured transition energies over the whole concentration range of the bases. Also, temperature dependences of vinyl contents can be predicted satisfactorily. Furthermore, it was found that vinyl contents in polybutadienes depend for weak bases primarily on the polarity of the solution mixture determined by the base concentration and not on the molar ratio of base to initiator. The results are extensively discussed in comparison with earlier attempts in the literature to predict the microstructure in polybutadienes in dependence of polar modifiers.

Equations for the molecular weight distribution and the average molecular weights of a living anionic polymerization with very rapid or slow initiation are presented for a series of stirred tank reactors. It is shown that polydispersity of the polymer in the last vessel of a cascade takes for nearly complete conversion of monomer then a minimum, when the reaction is performed isokinetically with concern to monomer conversion, i. e. when monomer conversion in each vessel of a cascade of n tanks is l/n. Now, polydispersity of the polymer in the mth vessel of the cascade (1 5 m 5 n) is D, = 1 + l/m. Values of all system variables needed for isokinetic control of the polymerization may be precalculated from kinetic models. For vessels of equal size and with equal residence times reaction temperature is suggested as control variable increasing stepwise from vessel to vessel. The proposed procedure was checked for the systems styreneh-butyllithium/toluene, styreneh-butyllithium/benzene, and isoprene/s-butyllithium/n-heptane. A satisfying agreement between calculated and measured values of the objectives monomers conversion, number average molecular weight, and polydispersity was found. It is proposed to use the described procedure for the preparation of ABA block copolymers with negligible tapering between the blocks by living anionic polymerization in a series of stirred tank reactors. ZUSAMMENFASSUNGFur den Fall einer lebenden anionischen Polymerisation in einer Ruhrkesselkaskade werden fur sehr schnelle bzw. fur langsame Initiierung Gleichungen fur die Molekulargewichtsverteilung und die mittleren Molekulargewichte vorgestellt. Es wird gezeigt, dal3 die Polydispersitat des Polymeren im letzten Kessel der Kaskade bei vollstandigem Monomerumsatz dann ein Minimum annimmt, wenn die Reaktion im Hinblick auf den Monomerumsatz isokinetisch gefahren wird, d. h. wenn der Monomerumsatz in jedem Kessel einer n-Kesselkaskade 1 /n betragt. Die Polydispersitat des Polymeren im m-ten Kessel der Kaskade (1 5 m I n) ist dann D, = 1 + l/m. Fur eine Kaskade aus gleich grol3en Kesseln und unter der Annahme gleicher Verweilzeiten in allen Kesseln wird als Kontrollvariable die Reaktionstemperatur vorgeschlagen, die stufenweise von Kessel zu Kessel anzuheben ist. Die fur eine isokinetische Fahrweise einer Kaskade notwendigen Werte aller Systemvariablen konnen uber kinetische Modelle vorausberechnet werden. Der entwickelte Formalismus wurde fur die Systeme Styrolh-Butyllithium/Toluol, Styrolls-Butyllithium/Benzol und Isoprenh-Butyllithiumh-Heptan uberpruft und eine befriedigende ubereinstimmung zwischen vorausberechneten und gemessenen Werten der ZielgriSDen Monomerumsatz, Zahlenmittel des Molekulargewichts und Polydispersitgt festgestellt. Es wird vorgeschlagen, die beschriebene Fahrweise zur Darstellung eines ABA-Blockcopolymeren mit minimaler Uberlappung der einzelnen BliScke durch lebende anionische Polymerisation in einer Ruhrkesselkaskade anzuwenden.