Polar dissolvent dimethylsulfoxide

The Japanese researchers report [ 175-179] on the syntheses of aromatic polysulfones via the method of polycondensation in the environment of polar dissolvent (dimethylformamide, dimethylacetamide, and dimethylsulfoxide) at 60-400 °C in the presence of alkali metal carbonates within 10 min to 100 h. The s mthesized thermoplastic polysulfones possess good melt fluidity [175]. 

Pyrazol-3-ones are known to be ambient compounds and depending on the solvent in which they are dissolved can exist in several tautomeric forms. Usually is less polar solvents such as chloroform pyrazol-3-one tautomers are dominant, whereas in more polar solvents such as dimethylsulfoxide 3-hydroxypyrazole tautomers are dominant. The most recent review article on this topic has been presented by Katritzky and co-workers (00AHC(76)157). 

TPUs are polar materials and are therefore resistant to nonpolar organic fluids such as oils, fuels, and greases, but they are readily attacked and even dissolved by polar organic fluids such as dimethylformamide and dimethylsulfoxide. TPUs behave like copolyester TPEs toward water and aqueous solutions, being resistant to these media except at very high or low pH. Polyether TPUs are more resistant to such hydrolytic degradation than are the polyester TPUs. 

Dimethylsulfoxide (DMSO) is a colorless organosulfur solvent, which dissolves both polar and non-polar compounds and is miscible in a wide range of organic solvents as well as in water. It penetrates the skin very readily. 

The first step is crucial to attain high molecular weight, and the second has a great influence in the final nature of the polyimide since a quantitative conversion in the cyclodehydration process is needed to have a pure, fully cyclized polyimide. Highly polar solvents are suitable media to dissolve monomers and poly(amic acid)s. A, A -dimethyl-acetamide (DMA), A,A-dimethylformamide (DMF), dimethylsulfoxide (DMSO), and A-methyl-2-pyrrolidinone (NMP) are the most adequate. Purity of solvents and reactants, and strict stoichiometric balance are requirements of polycondensation reactions that fully fit polyimides synthesis, where a careful control of the reaction variables is essential to achieve high molecular weight [17-19]. For instance, rigorous exclusion of water is a key condition, as well as a moderate polymerization temperature (about 0 °C or less) in poly(amic acid) formation in order to limit the competition of side reactions and a premature release of imidation water. 

Good solvents for PBl are polar aprotic solvents such as iV,A/-dimethylacetamide (DMAc), A -methyl-2-pynolidOTie (NMP) or dimethylsulfoxide (DMSO), and strmig protic acids like phosphoric acid, sulfuric acid (risking sulfonation reactions), or methylsulfonic acid. In order to dissolve PBl in organic solvents, great care must be taken to remove all phosphoric acid traces from the polymer, since it strongly hinders dissolution in DMAc. 

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