The kinetics of anionic polymerization of styrene and α‐methylstyrene. Effects of counter‐ion and solvent

Abstract

I n non-terminat ed anionic polymerization the propagating species may be a free anion or an ion-pair and the latter may dimerize to a relatively unreactive species1*2). VCi e wish t o report here some results of an attempt to study systematically the effects of the alkali metal cation and of the solvent on the ARRHENIW parameters in the propagation of ion-pairs involving (a) polystyryl anions and (b) poly-a-methylstyryl anions.X'hese resalts are given here in summary forni i n view of the current interest in these systems. A fuller account, with a more detailed discussion of the data, will be published shortly.The kinetics of polymerization were followed dilatometrically. a-Methylstyrene is a particularly convenient monomer since the polymerization can be reversed by an increase of temperature and a number of runs performed at different temperatures without recharging the dilatometer. Alkali salts of naphthalene, biphenyl or a-methylstyrene tetramer were used as initiators. Good &st-order decay curves were obtained with half-lives ranging from 20 seconds to 24 hours. Living-end concentrations, [LEI, were estimated either from optical density measurements or from the molecular weight of the polymer, using the SZWARC relation3).In tetrahydrofuran (THF) or tetrahydropyran (THP) it was necessary either to suppress ion-pair dissociation by the addition of excess alkali cations (in the form of alkali tetraphenylboron) or to extrapolate the apparent second-order rate constants to = 0. In the less polar solvents the proportionality between rate and [LEI, or the absence of a decrease of viscosity on killing the living ends, provides a check on the absence of ion-pair dimerization *--6).Our results t o date are summarized in Tables 1 and 2. The uncertainties in the values of log A, are commensurate with those in E,. Rather surprisingly it was possible t o obtain rate constants using cyclohexane as solvent; ion-pair dimerization is apparently not important for the larger counter-ions provided the living-end concentration is not too high. 257

Absolute propagation constants in vinyl polymerization

“…There are, however, lower values of A reported in dioxane, 69 THP, 78 and THF. 46 In some cases with sodium and potassium as the counterions, this is artificial and caused by the small temperature range studied, 78 only down to 2°.…”

“…Because no problems of this type exist for ␣-methylstyrene, Potter and Metz 68 concluded that the process with styrene cannot be as simple as the free-cation chain mechanism suggests and must include other species propagating, including free anions. Because ␣-methylstyrene does not polymerize free radically (except at very high pressures) and only very slowly anionically, 69 this seems a reasonable explanation of the difference between the two monomers. The more recent higher values for the free polystyryl anion in ether solvents average 48 39,42 is, of course, much lower than that reported for bulk monomer.…”

Living Anionic Polymerization of 4‐(1‐Adamantyl)‐α‐Methylstyrene

“…The anionic polymerization system of α‐methylstyrenes usually shows equilibrium behaviors known as the thermodynamically reversible polymerization due to the steric strain caused by the α‐methyl group . The polymerization of AdαMS was first carried out with K‐Naph in THF at −78 °C for 8 h in order to achieve the complete consumption of monomer similar to the previous experiment (run 5).…”

“…In this study, we newly designed and anionically polymerized an adamantyl‐substituted α‐methylstyrene derivative, 4‐(1‐adamantyl)‐α‐methylstyrene ( AdαMS ), in order to check the polymerizability of the monomer and the thermal properties of the resulting polymer. It is well known that α‐methylstyrene derivatives usually undergo the equilibrium polymerization under the anionic conditions due to the low ceiling temperatures . The polymerization and depolymerization of α‐methylstyrene derivatives reversibly occur under the equilibrium conditions.…”

Anionic polymerization of styrene in oxepane (hexamethylene oxide)•counter-ion, sodium

“…The anionic polymerization of styrene has been studied in a series of ethereal solvents of varying dielectric constant, dimethoxyethane (l,2), tetrahydrofuran (3)(4)(5), tetrahydropyran (7)(8)(9), and dioxane (9,10). Evidence has been presented for the presence of three types of active species, the free anion, a solvent-separated ion-pair, and a contact ion-pair, in order of decreasing reactivity.…”