The Study Of Cationic Ring-Opening Polymerization And Photochromism Of Tungstophosphoric-Acid/Epoxy System

In this dissertation, the cationic ring-opening polymerization (CROP) and photochromic behaviors of tungstophosphoric-acid(PW₁₂)/epoxy system were studied by means of various spectroscopies. In CROP, FT-NIR spectroscopy was chosen to in situ monitor the copolymerization of PW₁₂/Epoxy/THF and homopolymerization of PW₁₂/Epoxy. With ARES, DSC and TGA, the polymerizing behavior and mechanism were studied. In photochromism, FT-MIR and UV-Vis spectroscopies were used to reveal the photochromic mechanism of PW₁₂/PEG. Based on the mechanism, different types of epoxy resins were introduced into PW₁₂/PEG to study the effect of epoxy structure and temperature on bleaching behavior.The analysis of NIR spectra of PW₁₂/Epoxy/THF indicated that epoxy group reacted at a constant rate nearly till the end of reaction where the rate began to fall. For more information, peak deconvolution and 2D correlation techniques were developed. With ARES, DSC and TGA, we came to following conclusions: PW₁₂, as a highly reactive initiator, gave the system a feature of living polymerization. The propagating chain was led by ring opening of THF to react with stagnant epoxy. Thus, the reaction of epoxy group was a reactivity-controlled thermodynamic process while the reaction of THF was a diffusion-controlled kinetic process.The homopolymerizaion of PW₁₂/Epoxy showed similar behavior: epoxy with a flexible structure adopted a constant reaction rate, while the rate of epoxy with a rigid structure fell gradually as reaction proceeded. Further analysis indicated that the mechanism proposed in copolymerization system was a general lesson to the CROP of cyclic ethers. The differences lied in mobility and nucleophilicity of reactive group of monomers. The more nucleophilic and more mobile, the more reactive it was.As to photochromism, the photochromic mechanism of PW₁₂/PEG was studied first. The absorption band at～490 nm came from the d-d transition of the single d-orbit electron of W⁵⁺ in the reduced state "heteroblue". Meanwhile, this d-orbit electron was highly delocalized and its transfer between different WO₆ octehedron gave rise to the inter-valence charge transfer (IVCT) absorption of W⁵⁺-O-W⁶⁺ at～740 nm. The bleaching behavior of PW₁₂/PEG/Epoxy thermosetting system indicated higher chain flexibility and higher temperature would lead to higher bleaching speed.