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RESEARCH PRODUCT

Kinetics and mechanism of group transfer polymerization of N-butyl acrylate catalyzed by Hgl2 /(CH3 )3 Sil in toluene

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description

The group transfer polymerization (GTP) of n-butyl acrylate (nBuA) using 1-methoxy-1-(trimethylsiloxy)-2-methyl-1-propene (MTS) as an initiator, mercuric iodide (HgI2) as a catalyst in toluene at room temperature gives a very good control of molecular weight and narrow molecular weight distribution. (Mw/Mn < 1.2). Kinetic studies in this system reveal that this reaction is rather slow, half-lives being in the range of hours. The kinetic order of the apparent rate constant of propagation with respect to initiator and catalyst concentrations were found to be near to unity. However, the first-order time-conversion plots exhibit considerable induction periods. Upon addition of trimethylsilyl iodide (TMSI) the induction periods vanish and the rates are increased by two orders of magnitude. The reaction is first-order with respect to TMSI indicating that it takes part in the reaction by activating the catalyst. The complex from HgI2 and TMSI acts as a nucleophilic catalyst, similar to oxyanions in the GTP of MMA in THF. It is proposed that the induction periods are due to the formation of TMSI from MTS and HgI2.