Mechanisms and kinetics of the anionic polymerization of acrylates, 2. Polymerization of tert-butyl acrylate in a flow tube reactor and effect of lithium chloride and lithium tert-butoxide

The kinetics and the molecular weight distributions (MWD) in the anionic polymerization of tert-butyl acrylate (tBuA) in tetrahydrofuran at 23 ± 3°C were investigated. Tert-butyl α-lithioisobutyrate (tBiB-Li) was used as the initiator in the absence and presence of the additives lithium chloride and lithium tert-butoxide (tBuOLi). A flow tube reactor was used which allowed very rapid mixing of reagents, within milliseconds. The polymerization is extremely fast, half-lives being 0,01 s for the system without additive, 0,05 s for LiCl and 3 s for tBuOLi as an additive. The rate of termination was estimated from the strong UV absorption of the enolized β-oxoester end group formed. The number-average degree of polymerization is a linear function of conversion, the absolute values, however, demonstrate initiator efficiencies of only ca. 30%. The MWD's of the polymers formed are narrow (M _w/M _n = 1,35 without additive, M /M _n = 1,08 in the presence of LiCl and M _w/M _n = 1,77 in the presence of tBuOLi). After precipitation these values are reduced to 1,17; 1,06 and 1,32, respectively. Experiments in a stirred tank reactor and in ampoules lead to much broader MWD's. This shows that the rate of mixing has a strong effect on the MWD and is of substantial importance in these rapid polymerizations.