Effects of aging on some anionic initiators



The effects of aging on sodium naphthalene and sodium α-methylstyrene initiators, prepared in 1957, were investigated. The green sodium naphthalene had turned brown and faded; the aged sample failed to initiate the polymerization of α-methylstyrene at low temperature. Naphthalene had been completely converted into dihydronaphthalene; the retention of the brown color reflected a relative stability of anions of the latter. The freshly prepared brown sodium-dihydronaphthalene complex was also ineffective for polymerization of α-methylstyrene. No evidence for the cleavage of the ether solvent (tetrahydrofuran) on aging was obtained. The aged sodium α-methylstyrene initiator retained its vivid red color and effectiveness in the polymerization of α-methylstyrene. The inherent better stability of dianions than of radical anions was thus confirmed. Since the sodium α-methylstyrene initiator was actually a low molecular weight “living” polymer, the 7-yr. aging test demonstrated, in effect, the “longevity” of living polymers. The structure of the “living tetramer” of α-methylstyrene was discussed in the light of previous studies and present results. Apparent discrepancies were pointed out, and the necessity of more comprehensive studies was indicated.