Multi‐arm 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 (M̄w/Mn). 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)ns 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.