Photoinduced electron transfer RAFT polymerization of N,N-dimethylacrylamide via plasmonic excitation of gold nanoparticles in water†

The plasmonic excitation of gold nanoparticles (AuNPs) as catalysts for photoinduced electron transfer reversible addition–fragmentation chain transfer (PET-RAFT) polymerization of N,N-dimethylacrylamide (DMA) in aqueous media at room temperature was explored. The impact of different irradiation wavelengths (460, 514, 611, and 630 nm) on polymerization kinetics and macromolecular control was examined in the presence and absence of AuNPs. While light-induced radical polymerization of DMA without an initiator and light-induced RAFT polymerization without AuNPs failed under green (514 nm), orange (611 nm), and red (630 nm) LED irradiation, significant conversion (98% in 72 h, Đ = 1.10) was observed under blue (460 nm) LED irradiation due to the direct activation of the RAFT agent. Under green light, AuNPs enabled PET-RAFT polymerization of DMA in water, with the conversion depending on the position of the plasmon resonance and the nanoparticle concentration. At a low concentration (0.365 pM), conversion remained limited (5%), while higher concentrations (3.65 pM and 36.5 pM) led to improved conversions of 57% and 64%, respectively. In terms of the plasmon position, higher conversion (up to 82%) is reached when the plasmon resonance is closer to the excitation wavelength due to better light absorption. Kinetic analysis revealed a controlled radical polymerization, with low dispersities (Đ ≤ 1.19) and well-controlled molecular weight evolution. These results highlight the potential of plasmonic AuNP-mediated PET-RAFT polymerization for initiating polymerization under visible light in water while maintaining excellent control over polymerization parameters.