Ionic liquid-based unconventional photoinitiators for aqueous polymerization. (5th January 2022) - Banerjee, Palash
Graphical abstract: Highlights: Ionic liquid-based unconventional photoinitiators are designed for polymerization of vinyl monomers. Photopolymerization proceeds through radical mechanism in water. Graft copolymers are prepared by using PIL-based photoinitiators in water. Graft copolymers show thermoresponsive behaviors. Abstract: A series of as-synthesized phosphonium and imidazolium ionic liquids (ILs) with high water-solubility are utilized as efficient photoinitiators (PIs) for the polymerization of vinyl monomers such as N-isopropylacrylamide (NIPAM) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) efficiently upon UV irradiation (λmax = 310 nm) in aqueous medium at ambient temperature and pressure. The photopolymerization proceeds through free radical pathway as established by EPR, 1 H NMR, SEC and MALDI-TOF-MS along with some control experiments. The kinetic study demonstrates that this photopolymerization is fast enough to produce high-molecular-weight polymers with ∼ 70% yield even after 30 mins of UV irradiation. Control experiments show that these IL-based PIs have high water solubility and capable of producing high-molecular-weight polymers compared to those of polymers obtained by other commercially available aqueous PIs. Additionally, poly(NIPAM) and poly(DMAEMA) are grafted from the photoactive pendent IL moiety of the poly(ionic liquid), poly(triphenyl-4-vinylbenzylphosphonium chloride) (P[VBTP][Cl]) backbone by the grafting-from copolymerization. The presence of either poly(NIPAM) or poly(DMAEMA) graft segment induces thermoresponsiveness to their P[VBTP][Cl]-based copolymers.