LIVING COUPLING REACTION IN LIVING CATIONIC POLYMERIZATION .1. COUPLING REACTION OF LIVING POLYISOBUTYLENE

The living coupling reaction of living polyisobutylene (PIE), prepared by the ,4,4-trimethyl-2-chloropentane/TiCl4/hexane:methyl chloride (6 0:40, v:v)/-80 degrees C system, has been studied using 1,3-bis(1-phen ylethenyl)benzene (MDDPE), 2,2-bis[4-(1-phenylethenyl)phenyl]propan (B DPEP), and 2,2-bis[4-(1-tolylethenyl)phenyl]propane (BDTEP) as couplin g agents. The reaction of Living PIE with MDDPE yielded the monoadduct , possibly due to delocalization of positive charge over the meta-subs tituted benzene ring upon monoaddition and thereby decreased reactivit y of the second double bond. Using BDPEP and BDTEP which have two diph enylethylene (DPE) moieties separated by an electron-donating spacer g roup, rapid and quantitative coupling was achieved independently of th e chain length of the original PIE. The coupled product exhibited doub led molecular weight and narrowed molecular weight distribution. Direc t evidence of the quantitative coupling reaction was also obtained by comparison of the H-1 NMR spectra of the samples before and after the coupling reaction. Kinetic studies by H-1 NMR spectroscopy indicated t he coupling reaction of living PIE by BDPEP is a consecutive reaction where the second addition is faster than the first one. By kinetic tre atment of the experimental results, it was found that the second addit ion is about 5 times faster than the first one. As a result, high coup ling efficiency was also observed when excess BDPEP was used.