Hydroxy amic acid

The third method is a two-stage solution polymerization (Figure 5.26) that involves a low-temperature polycondensation of bis(o-aminophenol)s with aromatic tetracarhoxylic acid anhydrides to give high-molecular-weight soluble precursors poly(o-hydroxy amic acid)s (PHAAs), followed by a thermal conversion to form organic-insoluble PBOs [55,56],... 

IS-trans)A l-hydroxy-2-methyl-4-oxo-3-azetidinyl)carb-amic acid 1,1-dimcthylethyl ester (C.jHidN 80542-48-9) see A/.treonam 17P-hydroxy-l7-methyl-l-oxo-l,2-seco-A-nor-5a-an-drostan-2-oic acid... 

In an analogous manner, the generation of alkyl radicals in benzene solution by the O-acyl oxime method results in the formation of alkylbenzenes with moderate to good yields for simple acids (equation 55). Use of pyridine as solvent leads to the formation of alkylpyridines as mixtures of ortho, meta and para isomers in which the para isomer predominates. The 0-acyI benzophenone oxime chemistry can also be applied to aryl acids in benzene or pyridine, resulting in the formation of mixed biaryls. A closely related method involves photolysis of mixed anhydrides of arenecarboxylic acids with the hydrox-amic acid A -hydroxy-Z-pyridone in benzene solution (equation 56). 

The oxime 7, prepared from salicyl aldehyde, is converted with iV-chlorosuccinimide into the hydrox-amic acid chloride 8. From this, the nitrile oxide is obtained with KHCO3, which reacts regioselec-tively with styrene to give the 3,5-diaryl-4,5-dihydroisoxazole 9. Catalytic hydrogenation leads to the y -hydroxy ketone 10, which on acid-catalysed cyclodehydration gives the flavanone 11. 

Poly(isoimide)s received interest as intermediates for Pis, because the ring closure of the poly(amic acid) runs faster with carbodiimides, e.g., di-cyclohexylcarbodiimide, in comparison to acetic anhydride. " However, the use of a carbodiimide yields the isoimide moiety exclusively, whereas acetic anhydride yields the ordinary imide. However, by the treatment with suitable isomerizing agents, such as 1-hydroxyhenzotriazole, or 3-hydroxy-l,2,3-benzotriazin-4-one, the isoimide can he converted to the imide. This technique is suitable for the synthesis of Uquid thermosetting maleimide resins. 

In this context, some works investigated a series of blends obtained from hydroxy-propyl cellulose in lyotropic phase, and a new partial aHphatic polyimide (PI) or its poly(amic acid) precursor (PAA) [104]. The flow behavior of their mixed solutions in N,N-dimethylacetamide shows the effect of composition, temperature and shear rate on the orientation or mobiHty of the chain segments in the shear field. Specific interactions, such as the hydrogen bonds between PAA and the liquid crystalHne component, stabilized the resulted morphology. The band texture, typical for lyotropic HPC solutions, evidencing different intensities and dimensions is observed from atomic force microscopy images in PAA/HPC and PI/HPC blends (Figure 14.7) [104]. 

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