Synthesis and Isomeric Characterization of Well-Defined 8‑Shaped Polystyrene Using Anionic Polymerization, Silicon Chloride Linking Chemistry, and Metathesis Ring Closure

A methodology to efficiently synthesize well-defined, 8-shaped polystyrene using anionic polymerization, silicon chloride linking chemistry, and metathesis ring closure has been developed, and the 8-shaped architecture was ascertained using the fragmentation pattern of the corresponding Ag+ adduct, acquired with tandem mass spectrometry. The 4-arm star precursor, 4-star-α-4-pentenyl­polystyrene, was formed by linking α-4-pentenyl­poly­(styryl)­lithium (PSLi) with 1,2-bis­(methyl­dichlorosilyl)­ethane and reacting the excess PSLi with 1,2-epoxybutane to facilitate purification. Ring closure of 4-star-α-4-pentenyl­polystyrene was carried out in dichloromethane under mild conditions using a Grubbs metathesis catalyst, bis­(tricyclohexyl­phosphine)­benzylidine ruthenium­(IV) chloride. Both the 4-arm star precursor and resulting 8-shaped polystyrene were characterized using SEC, NMR, and MALDI-ToF mass spectrometry (MS). Tandem mass spectrometry (MS2) was used for the first time to study the fragmentation pattern of 8-shaped polystyrene. The results confirmed the formation of the intra-silicon-linked, 8-shaped polystyrene isomer, but the observed spectra left open the possibility that the inter-silicon-linked, 8-shaped polystyrene isomer was also produced.