KINETICS OF ANIONIC POLYMERIZATION OF ALPHA-METHYLSTYRENE IN TETRAHYDROPYRAN

The kinetics of anionic polymerization of α-methylstyrene in tetrahydropyran have been studied dilatometrically over the temperature range -20 to 9°. The concentration of living ends was determined spectrophotometrically. The rate constant for ion-pair propagation decreases a hundredfold when the counter-ion is changed from Li+ to Na+, rises a factor of 5 from Na+ to Rb+ and decreases slightly from Rb+ to Cs+; the activation energy is about zero for Li+ and 5·7, 6·5, 7·0 and 7·3 kcal mole-1 (24, 27, 29 and 31 kJ mole-1) for Na+, K+, Rb+ and Cs+ respectively. The results are discussed in terms of the participation of two types of ion-pair in the propagation process for the smaller cations. The rate constant for the propagation by free anions at -11·5° is about 250 1. mole-1 sec-1, which is much higher than for propagation by any of the ion-pairs at this temperature, but much smaller than for propagation of the polymerization of styrene by free anions in tetrahydrofuran. © 1969.