The well-defined poly(styrene-b-isoprene-b-styrene) triblock copolymers (SIpS) with different microstructures were synthesized by living anionic polymerization and used as macromonomers in cationic polymerization.The branched butyl rubber (IIR) with bimodal distribution was successfully synthesized by cationic polymeriazation of isobutylene

isoprene and SIpS in 2-chloro-2

4

4-trimethylpentane (TMPCl) ethylaluminum sesquichloride (Al2Et3Cl3)/2

6-di-tert-butylpyridine (DtBP) initiating system in hexane/methyl chloride solvents 50/50(V/V) at -80 ℃.The double bonds in SIpS triblock copolymers were activated as starting points for cationic polymerization.Results showed that the SIpS tribolck copolymer with high 3

4-PI content is more reactive than that with high 1

4-PI content in cationic polymerization.The yields

Mw and intrinsic viscosity of branched IIR were remarkably dependent on PI content in SIpS.The yield and Mw of branched IIR increased with increasing PI content in SIpS.While

the intrinsic viscosity of obtained polymer solution decreased with increasing PI content in SIpS.The formation of branched structures by using SIpS tribolck copolymer as macromonomers was supported by Rg as a function of molecular weight obtained by size-exclusion chromatography (SEC) with triple detection:refractive index (RI)

multiangle laser light scattering (MALLS)

and viscometric (Vis) detectors.The Rg of the polymer formed by addition of SIpS tribolck copolymer was significantly lower than that of linear IIR

which indicated the formation of branched structures.Also

GPC-UV confirmed that the polymer in high-molecular region was not generated by physical mixing of the macromonomers.Compared with linear butyl rubber

branched butyl rubber has the faster stress relaxation velocity and better mechanical properties.