Sequential Preparations

Sequential preparations contain only estrogens in the first and a fixed estrogen/progestin combination in the second phase of the application period. 

This multi-step, one-pot process was taken further by integration of a third supported reagent for the sequential preparation of 3,5-diphenylpyrazole (Scheme 2.17). Following the previously established procedure, acetophenone was deprotonated and acylated to afford the 1,3-dicarbonyl species. This intermediate was easily separated from the spent polymers by filtration and passed without isolation into a suspension of the resin bound hydrazine salt (9), affording the desired pyrazole in 91% yield. In a subsequent publication, the authors reported that the depleted polymeric reagents from the first step of the conversion (i.e. (7) and (8)) were recovered and separated via a selective flotation procedure, enabhng them to... 

A second route is termed sequential anionic polymerization. More recently, also controlled radical techniques can be applied successfully for the sequential preparation of block copolymers but still with a less narrow molar mass distribution of the segments and the final product. In both cases, one starts with the polymerization of monomer A. After it is finished, monomer B is added and after this monomer is polymerized completely again monomer A is fed into the reaction mixture. This procedure is applied for the production of styrene/buta-diene/styrene and styrene/isoprene/styrene triblock copolymers on industrial scale. It can also be used for the preparation of multiblock copolymers. 

If the foamable composition Is to be used for printing, the composition Is designed to have a useful life of 8 to 10 hours after foaming for a very practical reason. For a multicolor printing operation, It would be Impractical to have a mechanical foamer for each color being applied to the fabric. Instead each foamed color composition Is sequentially prepared In the color shop. The foamed colors are then treated as conventional print pastes and applied to fabric by either screen or Intaglio printing techniques. 

Liquid-liquid two-phase extractions are sometimes suitable for parallel synthesis. Manual multichannel pipettes can handle a few tens of solutions and recover the desired liquid phase after the extraction. If numbers of individuals increase, partial or total automation is necessary and mono- or multichannel robotic pipettes deliver solutions and withdraw either the top or the bottom phase of a liquid-liquid system with extreme accuracy, transferring it to other reaction vessels. They allow the sequential preparation of medium-large libraries but are very time consuming when large libraries of > 1000 members are involved. 

Due to the number of experiments necessary in such studies which take typically times of several hours to several days, there is a strong incentive to work on acceleration of synthesis experiments in zeolite science. On the other hand, there are also major obstacles to overcome in such an endeavour. Zeolite syntheses are often carried out at elevated pressure, reaction media are typically corrosive, precursor solutions and the synthesis gel itself may be highly viscous and difficult to handle, the synthesis is very sensitive to preparation conditions, such as sequence of reagent addition, stirring (difficult for small volumes) may be necessary for some formulations, aging conditions may differ from batch to batch, if automated sequential preparation is chosen, the work-up involving many steps is complex, and the resulting materials are often not phase-pure and difficult to characterize. Nevertheless, in spite of these problems some of the earliest examples for the synthesis of catalytically relevant solids in parallelized and - some points -automated equipment were reported for zeolites [4]. 

Transparent impact polystyrene has been made with sequentially prepared triblocks containing 10-30% polybutadiene... 

Gong et al. [172] designed and prepared a series of well-defined dumbbellshaped tri-block copolymers (Fig. 4.13(c)) consisting of comb-like PLLA and linear PEG with narrow molecular weight distributions and varied PLLA arm lengths via the sequential preparation of terminal dendronized polyhydric PEG... 

Occasionally, treatment of an extract on two or more sequential preparative paper chromatograms is desirable if a large amount of contaminating nonsteroidal material is present. Similar techniques are applied in every case using the eluate of the desired region of the first paper chromatogram as the starting material of the second strip. 

PEMA epoxy Full and semi-IPNs (sequential) prepared 195... 

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