Condensation reactions, using spinning

As with interfacial polycondensation an acid-acceptor is necessary to neutralize the hydrochloric acid formed in the reaction. These low-temperature poly condensation reactions are irreversible, and the acid-acceptor is necessary only to keep the reacting diamine free for reaction with the acid chloride. iV,iV-Dimethylacetamide and related solvents are often employed. Ar,A-Dimethylformamide cannot be used as it reacts with the acid chloride, and only low-molecular-weight polymer results. These amide solvents form loose complexes with the hydrochloric acid produced during the polymerization, and no additional acid-acceptor is needed. However, the final solutions are usually neutralized to minimize corrosion of metallic equipment during later steps such as spinning, and to provide small amounts of water often found necessary for the long-term stability of the polymer solutions [111]. 

In order to improve the heat transfer in a reactor, use can be made of gravitational forces. This concept is used in the spinning disc reactor (SDR) as developed at Newcastle University. The reaction mixture flows in a thin layer in axial direction over a rotating disc. A typical heat transfer coefficient is 10 kW/m2K. This reactor however is dedicated for liquid-liquid reactions. Especially condensation reactions can be enhanced by removing the gaseous by-products thus shifting the chemical equilibrium to the right. 

A 10-mL round-bottom flask containing a spin bar and fitted with an air cooled condenser is used in place of the conical reaction vial ( ). 

ABSTRACT. The conventional approach to produce polymeric ceramic precursors of non-oxidic materials involves condensation reactions of reactive intermediates. In many cases these reactions lead to intractable products. An alternative approach was examined which could afford better control over the properties of the product. This involved the derivatization of preformed polymers of appropriate molecular weight and functionality. Polyethyleneimine, (CH2-CH2-NH)n was derivatized to introduce the -BH2, -BH2CN, and -BH2-CH2-NBH functionalities. These materials produced boron nitride upon pyrolysis and could be used to spin-coat a variety of substrates. 

The simplest method of spin labelling is to utilise a functional group on the polymer to attach the label, usually via a condensation reaction (Scheme 1). Labels can also be introduced by less rect methods. For example, the Keana synthesis [6] (Scheme 2) has been used to label polyethylene that had been copolymerised with a small amount of carbon monoxide [7]. Polystyrene has been labelled by reacting the lightly lithiated polymer with either 2-methyl-2-nitrosopropane or nitrosobenzene (Scheme 3) [8]. 

In contrast, the preparation of hydrogels from prepolymers via cross-linking condensation reaction offers a simple method for the preparation of films/mem-branes and coated surfaces. Here, in addition to the aforementioned laboratory equipment, a spin coater is necessary as well as a cabinet for drying and curing. The use of inert gas techniques is not required, since the underlying reaction is not affected by oxygen. 

The first stage involves the preparation of a sol having an appropriate rheological behavior adapted to the porous substrate using molecular precursors, either metal salts or metal organics. The sol is coated by dip-coating or spin-coating on porous supports. Condensation reactions... 

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