Synthesis of well-defined miktoarm star polymers of poly(dimethylsiloxane) by the combination of chlorosilane and benzyl chloride linking chemistry

A series of novel four-arm A₂B₂ and A₂BC and five-arm A₂B₂C miktoarm star polymers, where A is poly(dimethylsiloxane) (PDMS), B is polystyrene (PS), and C is polyisoprene (PI), were successfully synthesized by the combination of chlorosilane and benzyl chloride linking chemistry. This new and general methodology is based on the linking reaction of in-chain benzyl chloride functionalized poly(dimethylsiloxane) (icBnCl-PDMS) with the in-chain diphenylalkyl (icD) living centers of PS-DLi-PS, PS-DLi-PI, or (PS)₂-DLi-PI. icBnCl-PDMS was synthesized by the selective reaction of lithium PDMS enolate (PDMSOLi) with the chlorosilane groups of dichloro[2-(chloromethylphenyl)ethyl]methylsilane, leaving the benzyl chloride group intact. The icD living polymers, characterized by the low basicity of DLi to avoid side reactions with PDMS, were prepared by the reaction of the corresponding living chains with the appropriate chloro/bromo derivatives of diphenylethylene, followed by a reaction with BuLi or the living polymer. The combined molecular characterization results of size exclusion chromatography, ¹H NMR, and right-angle laser light scattering revealed a high degree of structural and compositional homogeneity in all miktoarm stars prepared. The power of this general approach was demonstrated by the synthesis of a morphologically interesting complex miktoarm star polymer composed of two triblock terpolymer (PS-b-PI-b-PDMS) and two diblock copolymer (PS-b-PI) arms.