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-<i>star</i>-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-<i>star</i>-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

Rapid and Efficient Anionic Synthesis of Well-Defined Eight-Arm Star Polymers Using OctavinylPOSS and Poly(styryl)lithium

A new approach has been developed for the preparation of well-defined, eight-arm star polymers via the addition of poly­(styryl)lithium to octavinylPOSS in benzene. The reaction proceeds rapidly to completion (within 5 min for molecular weight of each arm up to 33 kg/mol), forming predominantly eight-arm star polymers. The products were purified by fractionation and fully characterized by ¹H NMR, ¹³C NMR, ²⁹Si NMR, FT-IR, MALDI-TOF mass spectrometry, and size exclusion chromatography. Compared to conventional coupling approaches, this process is found to be less sensitive to the stoichiometry of the reactants and the molecular weight of each arm. A mechanism based on cross-association and intra-aggregate addition is invoked to account for this unusual observation. As evidence, when a polar solvent, tetrahydrofuran, or a strongly coordinating and disassociating Lewis base, tetramethylethylenediamine, was used to dissociate the living polymer chains, star polymers with lower average arm numbers than those of the products synthesized in pure benzene were formed at the same stoichiometry of the reactants. The method has general implications in the understanding of the reactive nature of the living anionic polymerization and may find practical application in the synthesis of functional star polymers of diverse compositions and architectures

Synthesis of Shape Amphiphiles Based on POSS Tethered with Two Symmetric/Asymmetric Polymer Tails via Sequential “Grafting-from” and Thiol–Ene “Click” Chemistry

A series of shape amphiphiles based on functionalized polyhedral oligomeric silsesquioxane (POSS) head tethered with two polymeric tails of symmetric or asymmetric compositions was designed and synthesized using sequential “grafting-from” and “click” surface functionalization. The monofunctionalization of octavinylPOSS was performed using thiol–ene chemistry to afford a dihydroxyl-functionalized POSS that was further derived into precisely defined homo- and heterobifunctional macroinitiators. Polymer tails, such as polycaprolactone and polystyrene, could then be grown from these POSS-based macroinitiators with controlled molecular weight via ring-opening polymerization and atom transfer radical polymerization (ATRP). The vinyl groups on POSS were found to be compatible with ATRP conditions. These macromolecular precursors were further modified by thiol–ene chemistry to install surface functionalities onto the POSS cage. The polymer chain composition and POSS surface chemistry can thus be tuned separately in a modular and efficient way