Chitosan-Transition Metal Coordination Biopolymer: A Promising Heterogeneous Catalyst for Radical Ion Polymerization of Vinyl Acetate at Ambient Temperature.

Abstract

The\npresent study utilized chitosan obtained from crab shell and transition metal\nsalts as precursors to synthesize chitosan-metal coordination biopolymers of\nMn(II), Fe(III), Co(II) and Ni(II) [i.e Chit-Mn(II), Chit-Fe(III), Chit-Co(II)\nand Chit-NI(II) respectively]. The synthesized coordination biopolymers have\nbeen characterized using different instrumental techniques such as\nspectroscopic (UV-visible, FT-IR, XRD, EDS, and ICP-OES), thermal analysis (TGA\nand DTA), surface analysis (SEM), and hydrogen-temperature programmed reduction\n(H2-TPR) analysis. Spectroscopic studies confirmed the successful\nincorporation of the metals into the biopolymer matrix. Thermal analysis and H2-TPR\nrevealed the reducibility of the Chit-Fe(III) at 120 ℃. While Chit-Fe(III) and\nChit-Ni(II) were inactive, Chit-Co(II) and Chit-Mn(II) were found to be active\ntowards vinyl acetate polymerization in the presence of aqueous Na2SO3.\nFurthermore, the polyvinyl acetate (PVAc) produced from Chit-Co(II) compared\nperfectly with a commercial PVAc and was in higher yield than PVAc produced\nfrom Chit-Mn(II). The polymerization has been shown to proceed via\nsurface-initiated atom transfer radical polymerization (SI-ATRP), and the viscosity\naverage molecular weight of PVAc produced has been measured as 25, 078. The density\nfunctional theory approach has been used to ascertain the coordination\norientation of the Chit-Co(II) and explain its high efficiency towards vinyl\nacetate polymerization. The catalyst reusability test revealed an insignificant\nloss of activity for the Chit-Co(II) after seven cycles of polymerization.\nKinetic studies show that the vinyl acetate polymerization suits the\nsecond-order kinetic model at ambient temperature. Thermodynamic studies also\nrevealed that chain initiation is an endothermic process while chain\npropagation is an exothermic process. The result of this work also suggests an\ninvestigation of chitosan-metal coordination biopolymer via low-ppm ATRP\napproach for possible biomedical application.