Step polymerization inorganic polymer

Jang J, Lim B. Facile fabrication of inorganic-polymer core-shell nanostructures by a one-step vapor deposition polymerization. Angew Chem Int Ed 2003 42 5600-3. 

ABSTRACT. Polysilanes, (-SiRR -)n, represent a class of inorganic polymers that have unusual chemical properties and a number of potential applications. Currently the most practical synthesis is the Wurtz-type coupling of a dihalosilane with an alkali metal, which suffers from a number of limitations that discourage commercial development. A coordination polymerization route to polysilanes based on a transition metal catalyst offers a number of potential advantages. Both late and early metal dehydrogenative coupling catalysts have been reported, but the best to date appear to be based on titanocene and zirconocene derivatives. Our studies with transition metal silicon complexes have uncovered a number of observations that are relevant to this reaction chemistry, and hopefully important with respect to development of better catalysts. We have determined that many early transition metal silyl complexes are active catalysts for polysilane synthesis from monosilanes. A number of structure-reactivity correlations have been established, and reactivity studies have implicated a new metal-mediated polymerization mechanism. This mechanism, based on step growth of the polymer, has been tested in a number of ways. All proposed intermediates have now been observed in model reactions. 

For the production of inorganic/polymer composite nanoparticles via miniemul-sion polymerization, the emulsification step prior to the polymerization of the particle loaded monomer droplets is of great importance. By adjusting the surfactant concentration (see Sect. 3), coalescence as well as secondary nucleation during polymerization resulting in additional unfilled polymer particles can be prevented, and the composite particle size distribution is determined directly in the emulsification step [13, 61]. 

If a product of template polymerization is composed of a daughter polymer and a template involved in polymer complex, the first step of analysis is separation of these two parts. Separation of two polymers forming a complex is sometimes difficult and depends on interactions between the components. Very often polymeric complexes are insoluble in water and also in organic solvents. In order to dissolve such compounds, aqueous or non-aqueous solutions of inorganic salts such as LiBr, LiCl, NH4CNS are used. Dimethylformamide or dimethylacetamide are commonly used as non-aqueous solvents. If one of the components is a polyacid, alkali solutions are used as solvent. Ferguson and Shah reported that the complex obtained by polymerization of acrylic acid in... 

Several examples will help to illustrate this point. For the manufacture of a polymeric excipient, full GMPs are applied at the polymerization step because there is usually no significant purification after the polymer is formed. For a small molecule excipient such as a solvent or alcohol, full GMP principles must be applied no later than the start of purification, which is usually a distillation step. Finally for a salt or inorganic powder, full GMPs are applied at the formation of the salt or its purification step such as crystallization. 

The similar, older slurry process uses a less active catalyst. The monomer is dissolved in isooctane, the titanium catalyst and aluminium cocatalyst are added and this mixture is fed to the reactor which is maintained at 70°C. The inorganic corrosive (Cl) residues are removed in a washing step with alcohols. The atactic material is removed by extraction. A third process employs propene as the liquid in combination with a high activity catalyst. The Himont Spheripol process, which uses spherical catalyst particles, gives spherical polymer beads of millimetre size that need no extrusion for certain purposes. A more recent development is the gas-phase polymerization using an agitated bed. All processes are continuous processes, where the product is continuously removed from the reactor. Over the years we have seen a reduction of the number of process steps. The process costs are very low nowadays, propene feed costs amounting to more than 60% of the total cost. 

Glycidyl azide polymer is produced in a two-step process. First, epi-chlorhydrine in the presence of bortriflouride, is polymerized into poly-epichlorhydrine. Using dimethylformamide as a solvent, the polymer is then processed with sodium azide at high temperature. Nearly all the inorganic components as well as the solvent are removed, leaving the raw final product free of low molecular weight compounds. 

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