Synthesis, Characterization And Catalytic Reactivity Of Zirconium-doped PHTS For THF Polymerization

PolyTHF (PTMEG) is a kind of polymers widely used as versatile intermediate in synthetic spandex, polyether ester elastomers and ether ester copolymer elastomer. PTMEG is prepared by cationic ring-opening polymerization from THE Catalyst performance played a key role to produce polyTHF. Mineral acid catalyst (fuming sulfuric acid, perchloric acids) had been applied to the PTMEG production due to their high activity and easy preparation. Nowadays, the solid acid catalyst for THF polymerization was developed owing to the little corrosion, easy separation, environmentally friendly and so on. All of above, the synthesis of the desired solid acid catalyst has become the research focus.Mesoporous PHTS material (Plugged hexagonal templated silica) has high specific surface area, uniform pore size distribution. Moreover, material with large mesopore size and volume will offer an improved diffusion rate for transport in catalytic processes, and a better reactor to process a large variety of macromolecules feedstocks. However, the purely siliceous PHTS has low acidity, so THF polymerization can not be perfectly completed. It is well known that mesoporous PHTS material should been modified to create active sites for THF polymerization. It was known that the incorporation of aluminum, zirconium into the amorphous silica walls to form Si-O-M bond were valuable paths to generate acidic sites. With our preliminary studies (Al-PHTS), we propose a study that synthesis, characterization and reactivity of Zr-doped PHTS catalyst for THF polymerization.A series of Zr-doped PHTS with different silicon/zirconium molar ratio were prepared via direct hydrothermal method or impregnation method. All catalysts were characterized by XRD, TEM, nitrogen adsorption-desorption, NH3-TPD, Py-IR spectroscopy, in addition the structure, acidity, and catalytic performance of Zr-doped PHTS prepared by different methods were debated, which help to optimize the synthesis method for THF polymerization catalyst.1. The Zr-PHTS materials with different silicon/zirconium molar ratio from10to100were prepared via direct hydrothermal synthesis method in organic solvent-sulfuric acid-water system, while using P123as template, zirconium oxychloride as zirconium precursor, TEOS as siliceous precursor. The structure, acidity, and catalytic performance for all Zr-PHTS were tested. The results showed that all Zr-PHTS samples possessed ordered two-dimensional hexagonal mesostructures and featured a unique two-step desorption isotherm, which implied all samples belonged to PHTS family. These results also indicated that Zr-PHTS materials had weak and medium acid sites. With the increase of Si/Zr molar ratios from10to100, Zr-PHTS materials showed an18.3%increase in the specific surface area, and a66.7%decrease in acid amounts; but all Zr-PHTS maintained similar pore diameter of9.5nm. Which was related to the expand function of introduced organic agent. The resultant data showed a64.8%decrease in the yield of THF polymerization, but these samples perfected the similar average molecular weight of2500, which indicated the presence of larger pore diameter helped to synthesize high molecular weight polymer.2. The Zr/PHTS materials with varied silicon/zirconium molar ratio from10to100were prepared via impregnation method. The structure, acidity, and catalytic performance for Zr/PHTS materials were tested. The results showed that zirconium species dispersed on the PHTS surface, and retained ordered two-dimensional hexagonal mesostructures and featured a unique two-step desorption isotherm. Compared with the PHTS, with the increase of the content of zirconium, Zr/PHTS materials showed a41.7%decrease in the specific surface area, a33.3%decrease in the pore volume, and a19.2%decrease in the pore diameter. We can infer that zirconium species may adsorbed physically in the plugs (silica nanoparticles) inside the mesoporous channels or micro-and mesoporosities. Compared to Zr-PHTS, acid amounts of Zr/PHTS were less. The resultant data showed low yield of14%in the THF polymerization reaction, and average molecular weight around2000. 3. Compared catalytic activity of Zr-doped PHTS with ZrO2-SiO2mixed oxide for THF polymerization, all samples had activity, but Zr-PHTS materials via direct hydrothermal method had obvious advantage. With the decrease of Si/Zr molar ratios from100to10, Zr-PHTS materials showed an increase in the yield, and reached the highest value (40.66%) when silicon/zirconium molar ratio was10:1, average molecular weight was2428. Zr/PHTS materials showed the lowest in the yield; and the highest yield of THF polymerization using Zr/PHTS-30catalyst was12.42%. Compared to Zr-PHTS-10, the yield of Zr/PHTS-10with the same zirconium contents as Zr-PHTS-10was27%, and average molecular weight of Zr/PHTS-10changed10%. The yield and average molecular weight of THF polymerization using ZrO2-SiO2mixed oxide as catalyst first increased and then decreased with silicon/zirconium molar ratio from9:1to1:1, and reached the highest value (28.22%and2199) when silicon/zirconium molar ratio was7:3. Combined with the structure and acidity characterization, the mesoporous solid acid via direct hydrothermal method possessed the medium acid site and more acid amounts, which was the desired catalyst for THF polymerization.On the basis of exploring the synthesis, characterization and reactivity of Zr-doped PHTS catalyst for THF polymerization, we proposed the practice that the synthesis conditions affect the structure, acidity and catalysis of solid acid. Further work would be valuable to develop their catalytic activity in various catalytic reactions, and study the simultaneous effect of functionality and pore structure on the reaction.