Effects of mercaptides on anionic polymerization. II. Polymerization of acrylonitrile initiated by mercaptides

The polymerization of acrylonitrile by the several alkali metal mercaptides was investigated. The initiation reaction was found spectroscopically and by the sodium fusion method to proceed in a Michael-like form similar to a cyanoethylation reaction. From the results of the copolymerization of acrylonitrile and methyl methacrylate by the mercaptides, it was found that the mercaptides behaved as the anionic initiators. The effects of the counterions on the rate of polymerization were found to increase with increasing the electropositivites in the order of Li < Na < K. A negative overall activation energy was obtained, ?2.2 kcal/mole, in the temperature region of ?30°C to +20°C. The catalytic reactivities of the mercaptides were smaller than those of the corresponding oxygen analogs, except in the case of the phenyl substituent. Only in the case of the phenyl substituent, thiophenoxide was found to be much more effective than phenoxide, phenyl-SNa ? phenyl-ONa. The catalytic reactivities of the various sodium mercaptides were also determined to follow not only the basicities of the nucleophiles, but also the polarizabilities as follows: tert-butyl-SNa ≈ n-dodecyl-SNa > phenyl-SNa > n-octyl-SNa > isopropyl-SNa > n-propyl-SNa > ethyl-SNa. The enhanced reactivity of thiphenoxide in spite of the low pK_a value was attributed to the higher polarizability based on the low α effect.