Synthesis inorganic polymers

The synthesis of a new class of inorganic polymers (21) with a backbone consisting of alternating sulfur(VI) and nitrogen atoms, and with variable alkyl or aryl substituents as well as a fixed oxygen substituent on sulfur, has recentiy been accompHshed (83—85). These polymers are stmcturaHy analogous to poly(alk5l/arylphosphazenes). 

Solid phase synthesis is a polymer-supported or solid-supported synthesis, i.e., stepwise construction of product molecules attached to an insoluble organic or inorganic polymer. 

Allcock HR. Controlled synthesis of organic-inorganic polymers that possess a backbone of phosphorus and nitrogen atoms. Makromol Chem, 1981, (Suppl 4), 3-19. 

Another example of interesting new inorganic polymers is found in the work of Lasocki (p. 166), who reports the synthesis of polysilazoxanes, -[(R.SiO) (I SiNR) ] and finds surprisingly better thermal stability compared wltfi their polysiloxane analogs. 

Many of the structural features of sol-gel-derived inorganic polymers are rationalized on the basis of the stability of the M-O-M condensation products in their synthesis environments. Structures which emerge in solution reflect a successive series of hydrolysis, condensation and, depending on the acid or base concentration, restructuring reactions. M-O-M bonds which are unstable with respect to hydrolysis or alcoholysis are generally absent. During... 

The structures of sol-gel-derived inorganic polymers evolve continually as products of successive hydrolysis, condensation and restructuring (reverse of Equations 1-3) reactions. Therefore, to understand structural evolution in detail, we must understand the physical and chemical mechanisms which control the sequence and pattern of these reactions during gelation, drying, and consolidation. Although it is known that gel structure is affected by many factors including catalytic conditions, solvent composition and water to alkoxide ratio (13-141, we will show that many of the observed trends can be explained on the basis of the stability of the M-O-M condensation product in its synthesis environment. 

The synthesis of 5 lan thick Ti02 Si02 layers on a porous support can be performed using the procedure given below. First a mixed Ti[(OMe)3]4 alkoxide is synthesized by reacting partially hydrolyzed Si(OMe)4 with Ti-isopropoxide. This inorganic polymer is hydrolyzed at pH 11.0 and treated with 2-methyl-2-4-pentanediol and a binder. This solution is then slip-cast onto a porous support, dried and calcined at 700°C. The membrane can be useful in reverse osmosis applications. 

Finally the synthesis of inorganic-polymer composite membranes should be mentioned. Several attempts have been made to combine the high permeability of inorganic membranes with the good selectivity of polymer membranes. Furneaux and Davidson (1987) coated a anodized alumina with polymer films. The permeability increased by a factor of 100, as compared to that in the polymer fiber, but the selectivities were low (H2/O2 = 4). Ansorge (1985) made a supported polymer film and coated this film with a thin silica layer. Surprisingly, the silica layer was found to be selective for the separation mixture He-CH4 with a separation factor of 5 towards CH4. The function of the polymer film is only to increase the permeability. No further data are given. 

The structural and chemical diversity of compounds containing the Si-N-P linkage is a result of both the variety of coordination numbers which phosphorus may assume and the reactivity of the Si-N bond. The combination of these features gives Si-N-P compounds very promising synthetic utility, particularly in the area of inorganic polymer synthesis. 

The majority of inorganic reactions can be placed into one of two broad classes (1) oxidation-reduction (redox) reactions including atom and electron transfer reactions and (2) substitution reactions. Terms such as inner sphere, outer sphere, and photo-related reactions are employed to describe redox reactions. Such reactions are important in the synthesis of polymers and monomers and in the use of metal-containing polymers as catalysts and in applications involving transfer of heat, electricity, and light. They will not be dealt with to any appreciable extent in this chapter. 

As noted in Sec. 2-15, there has been considerable interest in the synthesis of inorganic and partially inorganic polymers. Some of the polymers have been synthesized by ROP. 

This chapter initially provides an overview of the considerations associated with the synthesis of inorganic polymers and the reasons why inorganic rings are so important as polymer precursors. The methods commonly used to characterise polymers are then discussed. As in Chapter 3, which describes the techniques used for the characterisation of inorganic rings, this section focuses on utility rather than on theoretical and practical details of the different methods. The reader is referred to a variety of texts for further details about these polymer structural characterisation techniques. ... 

Worthy of attention are the attempts to produce LC polymers on the basis of inorganic polymers those are polyphosphazenes with mesogenic side groups (cholesterol) although the first results to have been published were not promising40. A broad class of heterocyclic compounds could have probably contributed to the synthesis of new systems. The synthetic possibilities of this approach are quite evidently far from being exhausted. 

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