Initiation by alkylmetals

Bywater and Worsfold [145] have measured the initiation rate in the polymerization of styrene with w-BuLi and sec.-BuLi in benzene. The active centres 

The experimental verification of this relation indicates a rapid establishment of the deaggregation equilibrium, which is shifted far to the left (the concentration of free BuLi must be very small). The degradation intermediates are also inactive. Table 6 shows that similar dependences have also been observed with the polymerization of isoprene and the dimerization of 1,1-diphenylethylene in fluorene [150]. 

Parameters of the reaction of alkyllithium with styrene and isoprene in benzene at 303 K [ 151 ]a. 

In aliphatic solvents, centres are formed more slowly than in benzene (see Fig. 3). Evidently the deaggregation mechanism is different from that in the aromatics. The dependence of the initiation rate on the type of initiating alkyl is preserved. The apparent orders with respect to initiator are higher, around 1. In this case, initiation may be the result of direct contact between monomer and aggregate, yielding a mixed associate [152] 

The addition of lithium alkoxides to an alkyllithium initiator causes the induction period of active centre formation to disappear [152]. 

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