Thermally induced polymerization of isobutylene in the presence of SnCl4: Kinetic study of the polymerization and NMR structural investigation of lowmolecular weight products

The polymerization reactivity of isobutylene/SnCl4 mixtures in the absence of polar solvent, was investigated in a temperature interval from -78 to 60 degrees C. The mixture is nonreactive below -20 degrees C but slow polymer ization proceeds from -20 to 20 degrees C with the initial rate r(0) of the order 10(-5) mol.l(-1).s(-1). The rate of the process increases with incre asing temperature up to similar to 10(-2) mol.l(-1).s(-1) at 60 degrees C. Logarithmic plots of r(0) and (M) over bar(n) versus 1/T exhibit a break in the range from 20 to 35 degrees C. Activation energy is positive with valu es E = 21.7 +/- 4.2 kJ/mol in the temperature interval from -20 to 35 degre es C and E = 159.5 +/- 4.2 kJ/mol in the interval from 35 to 60 degrees C. The values of activation enthalpy difference of molecular weights in these temperature intervals are Delta H-Mn = -12.7 +/- 4.2 kJ/mol and -38.3 +/- 4 .2 kJ/mol, respectively. The polymerization proceeds quantitatively, the mo lecular weights of products are relatively high, (M) over bar(n) = 1500-250 0 at 35 degrees C and about 600 at 60 degrees C. It is assumed that initiat ion proceeds via [isobutylene . SnCl4] charge transfer complex which is the rmally excited and gives isobutylene radical-cations. Oxygen inhibits the p olymerization from -20 to 20 degrees C. Possible role of traces of water at temperatures above 20 degrees C is discussed. It was verified by NMR analy sis that only low molecular weight polyisobutylenes are formed with high co ntents of exo- terminal unsaturated structures. In addition to standard uns aturated groups, new structures were detected in the products. (C) 2000 Joh n Wiley & Sons, Inc.