Polymerization of methyl methacrylate by anions–II. Influence of initiation procedures on the kinetics of the subsequent polymerization in tetrahydrofuran-toluene solution initiated by disodium salt of tetrameric α-methyl styrene

Abstract Conditions for optimum efficiency of initiation ( ƒ ) by the disodium salt of α-methyl styrene tetramer in toluene-tetrahydrofuran (THF) solution are established. Under these conditions, ƒ = 0·35–0·45 . The propagating species are stable k p which fitted the Arrhenius equation ( A p ⋍ 10 2 M −1 sec −1 , E p ⋍ 16 KJ mol −1 ) and depended linearly on [THF]. If, however, the whole aliquot of monomer was added to initiator in one step at ca. 200 K, the rate is > 10 3 times that observed after a two-step initiation in which a trace of monomer is added some few minutes before the bulk. At higher temperatures there is no such discrepancy. It is postulated that the reactive species is a rare, solvated ion-pair in equilibrium with a less reactive, less solvated, contact ion-pair. The high rates observed after single step initiations at low temperatures are attributed to the slow relaxation of propagating ion-pairs which initially contain a non-equilibrium excess of the reactive form. On the basis of this hypothesis, the propagation coefficient for contact ion pairs: k c = 1·2 × 10 −2 M −1 sec −1 at 283 K while that of the solvated (or solvent-separated) ion pairs: k s > 25 M −1 sec −1 at ca. 200 K. The polymer produced was essentially stereo-random. Molecular weight distributions were broad and bimodal, showing a high mol. wt. peak in the 10 5 range and a low mol. wt. in the 10 3 range. The polymers produced in rapid polymerization after single step initiation at low temperatures had narrower high mol. wt. peaks than those prepared under equilibrated conditions.