In Situ and Time-Resolved Small-Angle Neutron Scattering Observation of Star Polymer Formation via Arm-Linking Reaction in Ruthenium-Catalyzed Living Radical Polymerization(1).

In situand time-resolved small-angle neutron scattering (SANS) was employed for the elucidation of star polymer formation mechanism via linking reaction of living linear polymers in ruthenium-catalyzed living radical polymerization. Here, methyl methacrylate (MMA) was first polymerized with R−Cl/RuCl2(PPh3)3/tribuylamine (n-Bu3N) initiating system, followed by the addition of ethylene glycol dimethacrylate (EGDMA: 3) as a linking agent. After the in situaddition of a small amount of 3to living linear PMMA, the SANS analysis revealed the following three steps: (process II-1) formation of block copolymers (4) and competitive formation of the small star polymers via the linking reaction of 4and 4; (process II-2) star−star linking of the small star polymers into star polymers and putting 4into the core of the star polymers, leading to formation of the microgel-core star polymers; (process II-3) growth of the microgel-core star polymers (5) via placement of 4into the microgel-core star polymers. Furthermore, the SANS profiles, obtained as a function of polymerization time, were quantitatively analyzed with a core−shell spherical model in order to determine the microstructures of the star polymers: The final reaction product had an average radius of microgel-core (∼1 nm), and average arm numbers N∼ 17. [ABSTRACT FROM AUTHOR]