Highly Efficient Synthesis of Low Polydispersity Core Cross-Linked Star Polymers by Ru-Catalyzed Living Radical Polymerization

The efficient formation of low polydispersity core cross‐linked star (CCS) polymers via controlled/living radical polymerization (LRP) and the arm‐first approach was found to be dependant on the mediating catalyst system. The Ru catalyst, Ru(Ind)Cl(PPh3)2 Cat. 1, and tertiary amine co‐catalyst were used to synthesize highly living poly(methyl methacrylate) (PMMA) macroinitiators, which were then linked together with ethylene glycol dimethacrylate (EGDMA) to form PMMAarmPEGDMAcore CCS polymers. The quantitative and near‐quantitative synthesis of CCS polymers were observed for low to moderate molecular weight macroinitiators ($\overline {M} _{{\rm n}} $ = 8 and 20 kDa), respectively. Lower conversions were observed for high‐molecular weight macroinitiators ($\overline {M} _{{\rm n}} $ ≥ 60 kDa). Overall, an improvement of between 10 and 20% was observed when comparing the Cat. 1 system to a conventional Cu‐catalyzed system. This significant improvement in macroinitiator‐to‐star conversion is explained in the context of catalyst system selection and CCS polymer formation. The efficient formation of low polydispersity core cross‐linked star (CCS) polymers via controlled/living radical polymerization (LRP) and the arm‐first approach is explored using the highly efficient Ru catalyst, Ru(Ind)Cl(PPh3)2. Increased conversion efficiencies (≤20%) are observed over a range of macroinitiator molecular weights ($\overline {M} _{{\rm n}} $) and quantitative synthesis is observed for low $\overline {M} _{{\rm n}} $ precursors. These findings are related to catalyst system efficiency and the star formation mechanism.