Details of the chemistry of linking living polyisobutylene (PIB⊕) pre-arms with divinylbenzene (DVB) to multi-arm PIB stars have been studied by triple-detector size-exclusion chromatography (SEC). Computer-aided deconvolution of multimodal differential refractive index (RI), laser light scattering (LLS), and ultraviolet (UV) traces obtained by SEC indicates the formation of complex product mixtures. The observations were interpreted in terms of inter-and intramolecular reactions of initially-formed active stars. Thus intermolecular or star-star couplings are proposed to lead to higher order (secondary, tertiary, etc.) stars, whereas intramolecular reactions result in core-contraction. The mechanism of these reactions has been outlined. The effect of PIB⊕ pre-arm length on star-star coupling was analyzed.