The first synthesis of a multi-arm radial-star polyisobutylene (*-PIB) is described. The synthesis occurred by the addition of excess divinylbenzene (DVB) linking reagent to a living polyisobutylene (PIB+) charge i.e., by the "arm first" method under specific conditions. The radial structure of the *-PIB was proven by determining the molecular weight of a sample by light scattering, then selectively destroying the aromatic polydivinylbenzene (PDVB) core, and finally determining the molecular weight of the surviving aliphatic PIB arms. The synthesis kinetic observations during synthesis, and procedures leading to a representative *-PIB are described. This product whose M(w)BAR=1,134,400 g/mole with M(w)BAR/M(n)=2.83, contained approximately 90.3 mole% (approximately 78 wt.%) PIB arms and approximately 9.7 mole% (approximately 22 wt.%) aromatic core; thus the number of PIB arms emanating from the core was N(n,arm)BAR (number average number of arms)=56 or N(w,arm)BAR (weight average number of arms)=110.