Anionic chain polymerization ketene

As the polymerization occurs, the reactive ketene silyl acetal group is transferred to the head of each new monomer as it is added to the growing chain (Equation 5.44). Similar to anionic polymerization, the molecular weight is controlled by the ratio of the concentration of... 

Twenty years have passed since DuPont announced a startling new process for polymerization of methacrylate monomers [1]. The method uses a trimethylsilyl ketene acetal initiator catalyzed by nucleophilic anions. It operates at 80 °C and gives unprecedented control over polymer chain architecture (Scheme 1). 

Early work on the GTP mechanism showed that the silyl groups on chain ends rapidly exchange in the presence of anionic catalysts [33, 34]. Without catalyst no exchange occurs [35]. No exchange occurred in the bifluoride catalyzed polymerization of MMA with dimethylphenylsilyl ketene acetal (Scheme 19a) in the presence of dimethyltolylsilyl fluoride [1]. However, in a similar experiment with trimethylsilyl acetate, TBA Ac, and dimethylphenylsilyl ketene acetal, complete exchange occurred within 5 min [36] (Scheme 19b). 

Alternatively, GTP may be an anionic polymerization in which a small concentration of enolate anions are in dynamic equilibrium with dormant silyl ketene acetal chain ends (Scheme 5). This dynamic equi-... 

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