Fe(iii)-catalyzed grafting copolymerization of lignin with styrene and methyl methacrylate through AGET ATRP using triphenyl phosphine as a ligand

Abstract

A novel activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) is presented to carry out the grafting copolymerization of lignin with styrene (St) and methyl methacrylate (MMA) using FeCl₃·6H₂O as a catalyst, PPh₃ as a ligand and ascorbic acid (Vc) as a reducing agent for the first time. The synthesized lignin-based copolymers, L-g-PS and L-g-PMMA, were characterized by ¹H NMR, FTIR, DSC, TGA and FE-SEM. ¹H NMR showed the detailed structural conformation of the lignin and its copolymers, L-g-PS and L-g-PMMA. FTIR analysis confirmed that the PS and PMMA chains have been successfully grafted onto the lignin backbone. The DSC indicated that the graft copolymer had two T_g values and both of them are higher than those of the original lignin. TGA showed that the thermal stability of the graft copolymers, L-g-PS and L-g-PMMA, are very different from the original lignin. The surface properties and apparent structure of the lignin were completely changed after grafting with PS and PMMA chains. The GPC results showed narrow molecular weight distributions of the copolymers, which indicated that Fe(III)-catalyzed AGET ATRP for grafting copolymerization of lignin with St and MMA is well-controlled. The results obtained from these analytical methods confirm that grafting copolymerization has successfully occurred from the surface of the lignin, and Fe(III)-catalyzed AGET ATRP provide a novel, effective, and environment friendly method to synthesize lignin-based copolymers.