One-shot synthesis

It is already well known that the PUs are obtained by reacting a diisocyanate (I) with a macrodiol (MD) of a polyesteric or polyetheric type, and with a glycol as a chain extender (CE). The simplest approach seems to be the simultaneous mixing of the three components on approaching the one shot synthesis route ... 

Thus, when employing the one shot synthesis in solution (PU 4, Table 3.11), it obtained a suspension containing 2 copolymers simultaneously one of which was soluble in DMF (71.2%), and the other was insoluble in DMF (28.85% — Table... 

Batch systems using a one-shot synthesis technique, again employing catalyst to reduce reaction times and eliminate post-curing. 

BEN 14] Ben Haj Salah K., Inguimbert N., Efficient microwave-assisted one shot synthesis of peptaibols using inexpensive coupling reagents . Organic Letters, vol. 16, pp. 1783-1785,2014. 

In order to obtain polyurethanes with highly regular chains, the polymerization should be carried out in solution. Dimethylformamide (DMF), dimethylacet-amide, dimethylsulfoxide, etc., may serve as solvents. Tien and Wei [26] studied the effect of benzidine-modified montmorillonite (MMT) on the hydrogen bonding in the hard segments of TPU. The latter was produced in random one-shot synthesis in DMF, It was established that the H-bonding in the hard... 

One-shot techniques, 216, 217, 236-237 Optical fiber waveguide, 271-272 Optically active poly(arylene), synthesis of, 518-519... 

Figure 10.2 shows four screen shots of the GUIs for the problem of equimolar mixtures of amino acids, i. e., 5% of each amino acid and 0% of stop codons. In Figures 10.2a-c the results of a standard one-pot, two-pot, and three-pot synthesis are given, respectively. Figure 10.2d shows the result of a one-pot synthesis optimized for E. coli codon usage. 

In any case, the prepolymer synthesis results in somewhat better defined domains, characterized by the relative translucency of the prepolymer route material relative to the one-shot route, and as illustrated in the transition behavior. Figure 3. Better defined domains mean a purer rubber phase, which in turn may yield greater toughness to this form of the material. Important questions as to the development of intermediate Tg s with extensive interfacial boundary material (48) or on complete thermodynamic miscibility (49) remain for the future. 

It will be realized from Chapter 1 that in urethane elastomer formation from liquid components there is the possibility of several reactions occurring simultaneously during a prepolymer or one-shot process, and that the relative proportion of one to the other will affect the overall properties of the final polymer. Thermoplastic and millable urethanes are not, during their processing and fabrication stages, subjected to the type of catalysis discussed in this chapter during their polymer synthesis operations, however, reaction rate-structure considerations will apply. 

Both processes may be carried out in one or two reaction steps, the so-called one-shot process and prepolymer method , respectively (Vermette et al., 2001). In two-step synthesis (Fig. 6.3), an isocyanate end-capped prepolymer is first synthesised through the reaction between a polyol and a diisocyanate then, adding a chain extender that reacts with the residual isocyanate functionality, the chain is extended producing a multi-block copolymer (Lamba et al., 1998 Vermette et al., 2001 ... 

The reaction was carried out as a one-shot, two-step procedure. At room temperature, dibutyltin-dilaurate (DBTL) was the urethane catalyst. Trifunctional polyols served to crosslink the polyurethane. The temperature was then raised to initiate the MMA polymerization. An example of the Allen et synthesis is as follows. 

The change in the monomer feed rates during reactions allowed simultaneous influence and verification of the evolution of these parameters during the synthesis. The adjustable feed rate confers great power for controlUng during the reaction. Thus, the hybrid reaction shown in Figure 12.10 [50] starts in semicontinuous mode, under starved conditions, achieved by slow monomer feed in the reactor, and becomes essentially a batch reaction upon the one-shot addition of MM A at 15% conversion. 

Prior to TPU synthesis, polyester polyol was dried at 80 C for 12 hours under a full vacuum prior to use. Both TPUs were prepared using the one-shot polymerization technique from equal raw material starting temperatures. Homogenized TPU reactant mixtures were then poured onto polytetrafluoroethylene coated steel pans and polymerized in a convection oven at a temperature above the hard segment Tg of either TPU. Complete conversion was assured by the absence of an asymmetric isocyanate stretching vibration in the infiared spectra of the final TPUs. 

Example 2. Two-Shot Cast Elastomer (Prepolymer Method). Synthesis of polyurethane elastomers via the prepolymer method is challenging and requires especial attention to details and techniques. This example is a relatively easy one, using a low-viscosity, 9.6% NCO MDI-based poly(tetramethylene ether) glycol prepolymer. It is adapted from the Bayer Product Information Bulletin for Baytec ME-090 prepolymer. 

The reasoning which led the author to make this first shot in the dark regarding the usefulness of combinations of solid compounds as ammonia catalysts was as follows If we assume that a labile iron nitride is an interminate in the catalytic ammonia synthesis, every addition to the iron which favors the formation of the iron nitride ought to be of advantage. In other words, the hypothesis was used that surface catalysis acts via the formation of intermediate compounds between the catalyst and one or more of the reactants. An experimental support for this theory was the fact that a stepwise synthesis via the formation and successive hydrogen reduction of nitrides had been carried out with calcium nitrides (Haber), and cerium nitrides (Lipski). Later, the author found molybdenum nitride as being the best intermediate for such a stepwise synthesis. 

An interpretation of LSD-progenitor Albert Hofmann s patented one-pot shot method of LSD synthesis, plus purification and storage techniques... 

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