Melt mixing synthesis

Solution method Melt mixing In itu polymerization Template synthesis... 

CdSe-CdS-ZnS core-multishell polymer nanocomposites were prepared by direct dispersion of CdSe-CdS-ZnS core-multishell QDs in an epoxy polymer matrix via a melt mixing technique. Nanocomposites filled with yellow-emitting QDs were more transparent than pure epoxy polymer. A shift in the luminescence of pure epoxy from the blue region to the yellow region was observed in the nanocomposite. Synthesized nanocomposites also showed enhanced tensile properties in comparison to pure epoxy polymer [236]. Several other studied reported the use of a melt blending process for the synthesis of semiconductor-polymer nanocomposites [237-241]. 

The emphasis in research and technological development of new products in the polymer industry has changed from synthesis of novel monomers to blending polymers in order to obtain desirable performance properties at a dial-in cost. Polymer blends offer improved performance/cost ratios and flexibility to tailor-make the product to suit customer needs. Polymer blends are intimate mixtures of two or more polymers. The individual components may be melt-mixed, solution blended, co-precipitated, controlled devolatilized, or coagulated before final processing. Finished articles are converted from blends by extrusion or molding processing operations. 

Properties. One of the characteristic properties of the polyphosphazene backbone is high chain dexibility which allows mobility of the chains even at quite low temperatures. Glass-transition temperatures down to —105° C are known with some alkoxy substituents. Symmetrically substituted alkoxy and aryloxy polymers often exhibit melting transitions if the substituents allow packing of the chains, but mixed-substituent polymers are amorphous. Thus the mixed substitution pattern is deUberately used for the synthesis of various phosphazene elastomers. On the other hand, as with many other flexible-chain polymers, glass-transition temperatures above 100°C can be obtained with bulky substituents on the phosphazene backbone. 

The first step for the synthesis of a melt spinnable polysilane is the alkoxylation and distillation of the residue (Figure 1). 1,2-dimethyltetramethoxydisilane and 1,1,2-trimethyltrimethoxydisilane are mixed in a special ratio and a poly silane will be obtained by a catalytic redistribution reaction. Catalysts for this reaction are alkali alkoxides like sodium methoxylate. Phenylmethoxydisilanes [22] or phenylchloride are used as additives. A mixture of methyltrimethoxysilane and dimethyldimethoxy-silane distils off as a byproduct of the redistribution reaction. Figure 2 shows the mechanism of the catalytic redistribution. 

Figure 4. shows the route from the high boiling residue of the direct synthesis to silicon carbo-nitride fibers. Methylchlorodisilanes and trichlorosilanes as additives are mixed in a specific ratio and react with methylamine and a small amount of ammonia to form an aminodisilane/oligosilazane. The subsequent polycondensation reaction of this mixture by heating to 250 °C yields a soluble and melt spinnable polysilazane. In comparision with the polysilane the properties of the polysilazane depend on the ratios of the disilanes/silanes and methylamine/ammonia and also on the reaction conditions. 

Experiment. E. Fischer s Indole Synthesis.—Mix 2 g. of phenylhydrazine with 2 c.c. of acetone in a test tube. Water is eliminated and a turbidity appears. Suspend the tube in the boiling water bath for forty-five minutes, then add 6 g. of dry zinc chloride and heat the mixture for a few minutes with stirring in an oil bath at 180°. Now wash the dark-coloured melt into a small round-bottomed flask with four volumes of dilute hydrochloric acid and separate the resultant a-methylindole by distillation with steam. The substance collects as an oil which soon solidifies. After drying crystallise it from a little petrol ether. Melting point 59°. 

Polv(ether) Synthesis. The poly(ethers) were made by a two-phase reaction with dibromoalkanes. In a typical reaction, 0.75 g (2.4 mmol) of (II, R=H)) was mixed with 70 ml of 2N NaOH in a 3-necked round-bottom flask equipped with a mechanical stirrer. To this was added an equimolar amount of 1,9-dibromononane in 20 mL nitrobenzene and approximately 10 mg of tetrabutylammonium iodide and the mixture was stirred overnight at 50°C. The resulting solid mass was washed with methanol and then with 2N NaOH. After washing with 0.1 N HC1, the product was Soxhlet-extracted with methanol and dried to yield 0.68g (64.7%) of a light green powder which melted to an anisotropic liquid at 290°C. The other poly(ethers) were prepared in the same manner, using spacer lengths of 7, 9,11, 7/9 mixture, and 9/11 mixture. The yields and IR spectra of the poly(ethers) is shown in Table I. 

Hijji and Benjamin also accomplished a microwave synthesis of thalidomide in acceptable yield in 2004 (Scheme 5) [36-39]. Ammonium chloride was found to be an effective source for nitrogen. Namely, phthalic anhydride (4), glutamic acid (8), and ammonium chloride were mixed in 1 1 1 ratio with a catalytic amount of DMAP and heated in a conventional microwave oven for 6.5 min. The mixture melted to a brown liquid. The heating continued for an additional 1 min to give thalidomide (1) in 52% yield in this two-step, one-pot reaction after solubilization, precipitation, and recrystal-lization. 

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