ANIONIC POLYMERIZATION OF Α-Methylstyrene: PART II. KINETICS

Abstract

Dilatometric measurements have been made of the reaction rates in the reversible equilibrium anionic poly~nerization of a-methylstyrene initiated by sodium naphthalene in tetrahydrofuran solution, a t temperatllres of -loo, -40°, and -77". The kinetic results and measurements made of the viscosity of the polymer conform with the mechanisln of the reaction proposed by Szwarc el al., modified by the large degree of reversibility found with this monomer a t these temperatures.The mechanism of the polymerization of certain vinyl hydrocarbons initiated by the complexes of sodium with polynuclear aromatic hydrocarbons in solutioll in some aliphatic ethers has recently been proposed by Szwarc et al. (I). They visualize an initial donation of an electron to the monomer followed by rapid dimerization of the radical ion formed to give a dicarbanion capable of growth by repeated monomer addition a t both ends. In suitable solvents these carbanions are stable and no termination occurs and the chain ends remain active after the monomer has been consumed.This latter property was made use of in demonstrating the reversible nature of the propagation step of polymerization (2). All polymers produced under these conditions should have a certain concentration of monomer in equilibrium with the active chain end (3), but in the case of a-methylstyrene this reaches appreciable amounts, even below room temperature, and profoundly changes the behavior of the system. I t has been proposed that the chains are initiated rapidly and grow comparatively slowly a t the expense of the monomer until the latter is reduced to its equilibrium concentration when the rate of the bimolecular forward reaction equals that of the unimolecular depolymerization. From such a scheme it is easily shown that the approach of the monomer concentration to the equilibrium concentration will, a s a close approximation, follow a kinetic law first order in the initiator concentration and a t a rate proportional to the excess concentration of the monomer over the equilibrium value. The polymerization of this monomer has a half-life time of the order of minutes, as opposed to seconds for other monomers, so it has been found convenient to make some kinetic measurements on this system to see if they are in accord with the scheme outlined above. EXPERIMENTALThe purification of the solvent (tetrahydrofuran) and the monomer have been described before (3). The method adopted for measuring the rates was dilatometric using an annulus-shaped dilatometer to minimize, as far as possible, the temperature effects inherent in reactions of this speed. The dilatometer and adjacent mixing vessel were evacuated, and the monomer and solvent condensed into the mixing vessel. The catalyst solution was formed from naphthalene solution on a sodium film under vacuum in a n attached vessel. This solution was introduced into the mixing vessel by breaking a finely drawn tip by rotation of a ground joint after temperature equilibrium had been established. The reaction solution was then f...

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.…”

“…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. [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] 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). Then, the polymerization temperature of the system was raised to room temperature and the system was stood for 20 h. The characteristic red color of the polymerization system was maintained at room temperature until the termination with methanol.…”

“…It is well known that α-methylstyrene derivatives usually undergo the equilibrium polymerization under the anionic conditions due to the low ceiling temperatures. [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] The polymerization and depolymerization of α-methylstyrene derivatives reversibly occur under the equilibrium conditions. In addition, the poly(α-methylstyrene)s generally show higher T g values than those of the corresponding polystyrene derivatives and the ease of the chain degradation on heating.…”

Sequential Bulk Anionic Polymerization of α‐Methylstyrene and Isoprene to Form Diblock and Triblock Copolymers

“…There is a well-established ceiling temperature [3] for the polymerization of α-methylstyrene (AMS) that inhibits high conversion to polymer. [4,5] The ceiling temperature precludes the polymerization at moderate to high temperatures such that the most successful polymerizations of AMS are anionic [6][7][8][9][10][11][12][13][14][15] and cationic [16] polymerizations at low temperature.…”