| Abstract: | The polymerization reactivity of isobutylene/SnCl4 mixtures in the absence of polar solvent, was investigated in a temperature interval from ?78 to 60 °C. The mixture is nonreactive below ?20 °C but slow polymerization proceeds from ?20 to 20 °C with the initial rate r0 of the order 10?5 mol · l?1 · s?1. The rate of the process increases with increasing temperature up to ～10?2 mol · l?1 · s?1 at 60 °C. Logarithmic plots of r0 and M?n versus 1/T exhibit a break in the range from 20 to 35 °C. Activation energy is positive with values E = 21.7 ± 4.2 kJ/mol in the temperature interval from ?20 to 35 °C and E = 159.5 ± 4.2 kJ/mol in the interval from 35 to 60 °C. The values of activation enthalpy difference of molecular weights in these temperature intervals are ΔHMn = ?12.7 ± 4.2 kJ/mol and ?38.3 ± 4.2 kJ/mol, respectively. The polymerization proceeds quantitatively, the molecular weights of products are relatively high, M?n = 1500–2500 at 35 °C and about 600 at 60 °C. It is assumed that initiation proceeds via isobutylene · SnCl4] charge transfer complex which is thermally excited and gives isobutylene radical‐cations. Oxygen inhibits the polymerization from ?20 to 20 °C. Possible role of traces of water at temperatures above 20 °C is discussed. It was verified by NMR analysis that only low molecular weight polyisobutylenes are formed with high contents of exo‐ terminal unsaturated structures. In addition to standard unsaturated groups, new structures were detected in the products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1568–1579, 2000 |
