Polymerization with Siliceous Earth

A laboratory procedure for the polymerization of THF with siliceous earth can be outlined as follows  

After 3 hours, the degree of conversion will be 50 to 60 percent. At this point, the content of the reactor is removed, and the TONSIL is separated from the polymer solution by centrifugation. After being dried and stored in the absence of oxygen, it can be reused. 

With the separation of the TONSIL, the polymerization is terminated. The remaining monomer and the acetic anhydride are distilled off in a rotary evaporator, at the end under vacuum. The remaining viscous liquid is pure PTHF in the form of its diacetate. 

In general, the PTHF is needed in the diol form (with OH end groups). This form is called PTMEG which stands for polytetramethylene ether glycol. It is also known as POLYMEG (a trade name of QUAKER OATS). Conversion of the diacetate form to the diol form can be carried out as follows  

The polymer is dissolved in 100 ml of methanol and mixed with a solution of 15 g of NaOH in 100 ml of methanol. In a round bottom flask equipped with a feed pipe and a reflux condenser, the mixture is boiled under nitrogen for a period of 2 hours. Then the methanol is distilled off as far as foam formation will permit. After addition of 200 ml of toluene, the mixture is distilled under a weak vacuum until the distillation temperature becomes constant. After cooling and addition of another 200 ml of toluene, the mixture is extracted with 100 ml quantities of water in a separating fiinnel until the aqueous phase is neutral. The toluene phase is dried with anhydrous sodium sulfate and clarified before the toluene is removed in a rotary evaporator. The remaining viscous liquid is an almost colorless PTMEG having a mean molecular weight between 800 and 1000. 

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The original patent on the polymerization of THF with siliceous earth, granted to C. Dorfelt in 1967 [94], with FARBWERKE HOECHST AG as assignee, has long expired. 

Unlike the rather ill-defined acid sites of siliceous earth, with fluosulfonic acid the intensity of polymerization catalysis (i.e. the number of chain initiations) is clearly dictated by the quantity of fluosulfonic acid added to the THF. The more fluosulfonic acid is added, the more chains are initiated, which means that the more fluosulfonic acid is added, the lower will be the molecular weight of the polymer product. 

Metalloporphyrinosilicas as a new class of hybrid organic-inorganic materials were prepared by polymerization of 3- er -butyl-5-vinylsalicylaldehyde with styrene and divinylbenzene and used as selective biomimetic oxidation catalyst.27 Synthesis and structural characterization of rare-earth bisfdimethyl-silyl)amides and their surface organometallic chemistry on mesoporous silicate MCM-41 have been reported.28... 

For all plants and animals, and for virtually all microbes, with the exception of some Lactobacilli and a Borrelia species, life without iron is impossible. A multitude of essential enzymes bind iron in their active centers. Therefore, up to 10 Fe-ions are typically required in key metabohc processes of a single bacterial cell. Why iron has gained such an eminent role in the course of biological evolution remains open to speculation. Though iron is the fourth most abundant element in the Earth s crust, it is present imder aerobic conditions at nearly neutral pH in the form of extremely insoluble minerals like hematite, goethite, and pyrite, or as polymeric oxidehydrates, carbonates, and silicates, which severely restricts the bioavaUability of this... 

All of these catalysts were active for ethylene polymerization. The average activity values are shown in Table 44. The activity was mostly unaffected by the presence of alkaline earth metal hydroxide, with the exception of barium hydroxide, which lowered the polymer yield by about 50%. Magnesium hydroxide caused a major change in the physical structure of the catalyst, which is an indication that a new material, perhaps magnesium silicate, was formed, with smaller primary particles. It is not clear whether the Cr(VI) becomes attached to the new material or whether it remains with the silica phase, perhaps now etched or otherwise changed. 

Apart from nitrate ions, the direct reduction of carbonate, phosphate, and silicate anions have all been reported. Some controversy surrounds the electroreduction of sulfate ions water may be implicated in this process. Inman and Wrench could only induce cathodic electroactivity of sulfate ions dissolved in a chloride melt by release of SO3, the conjugate acid, with a stronger Lux-Flood acid, metaphosphate, P03. While the alkali metal and alkaline earth sulfates, carbonates, and nitrates are clearly ionic, borate, phosphate, and silicate melts are highly polymerized. In such systems, the mobile cations move freely about the anion lattice network, which comprises a temperature- and compositional-dependent equilibrium between ion fragments of variable chain length. Inman and Franks observed kinetically limited electroreduction processes in a phosphate melt, as might be expected if only the smallest fragments of the dynamic polymer equilibrium are electroactive. 

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