MULTIARM STAR POLYISOBUTYLENES .2. THE EFFECT OF SYNTHESIS CONDITIONS ON THE STRUCTURE OF STAR PIBS

Multi-arm star polyisobutylenes (*-(PIB)(n)) have been prepared by the ''arm-first'' method. This synthesis was accomplished by adding various linking agents (''core builders'') such as p- and m-divinylbenzene (DVB) and p- and m-diisopropenylbenzene (DIB) to living PIB+ charges and thus obtaining a crosslinked aromatic core holding together a corona of well-defined arms. The products were characterized in terms of overall arm/core composition, molecular weight, and molecular weight distribution ((M(w)) over bar/(M(n)) over bar). The effect of reaction conditions (time, [linking agent]/[PIB], arm molecular weight) on the kinetics of the star formation and star structure were investigated. The multi-arm star nature of *-(PIB)(n)S was proven directly by determining the molecular weight (by light scattering) of the intact products, selectively destroying the aromatic polyDVB (or polyDIB) core (''core-destruction''), and finally determining the molecular weight of the surviving aliphatic PIB arms. The synthetic strategy, overall kinetics, and observations during the preparation of star-PIBs were discussed. Among the critical parameters that determine product structures are the rate of crossover PIB+ + DVB (or DIB) --> PIB-DVB+ (or PIB-DIB+), the concentration of the linking agent DVB (or DIB), and the molecular weight of the PIB arm. Evidence for the formation of higher order stars (''secondary'', etc.) by star-star- coupling has been presented.