Methacrylic acid, from decomposition

The second generation includes latices made with functional monomers like methacrylic acid, 2-hydroxyethyl acrylate [818-61 -17, acrylamide/75 -(9ti-/7, 2-dimethylaminoethylmethacrylate [2867-47-2] and sodiumT -vinyl-benzenesulfonate [98-70-4] that create in polymeric emulsifier. The initiator decomposition products, like the sulfate groups arising from persulfate decomposition, can also act as chemically bound surfactants. These surfactants are difficult to remove from the latex particle. 

Since formation of citraconic anhydride from pyruvic acid is one of "acid to acid type" transformations, such as reactions from isobutyric acid to methacrylic acid and from lactic acid to pyruvic acid, the required catalysts must be acidic [11). If the catalysts are basic, it may be impossible to obtained acidic products, because basic catalysts activate selectively acidic molecules and, as a result, they show a very high activity for the decomposition of acidic products [11]. 

It was proposed that the increase in activity during the equilibration period was due to the generation of new active sites,consisting of the Mo species located in the cationic position in the secondary framework of the POM. A similar hypothesis was formulated by other authors for the methacrolein oxidation to methacrylic acid." " More generally, it is currently believed that for exothermic reactions, and specifically for oxidations, the true working state of the POM, does not correspond to its crystalline form." The presence of steam and the large amount of heat released provoke an incipient surface decomposition, which leads to the expulsion of the Mo species from the anion as a metastable defective... 

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It was fonnd that the pyrolysis of the ATH-filled PMMA yielded only 58% MMA monomer instead of 97% fonnd with a pure PMMA feed. Hydrolysis products from MMA such as methacrylic acid, methanol and isobutyric acid were found to be the other main by-prodncts from the thermal decomposition of this composite material. Pyrolysis-GC-MS experiments showed that the yield of the monomer MMA can be increased to 65 wt% by lowering the process temperature to 400°C. Water released during pyrolysis of ATH and the chemical starter/stabilizer in the composite material were found to be responsible for the low monomer yield. The high amount of the alnmininm components in this material has almost no catalytic influence on the hydrolysis reaction because the same result was found if steam was used as fluidizing medinm instead of nitrogen. 

As seen from Table 6.7.18, the thermal decomposition of poly(methacrylic acid) generates at lower temperature the anhydride, and at higher temperatures undergoes decarboxylation. It can be assumed that the process leads to the formation of unsaturated chains that further decompose to form small hydrocarbon molecules and some aromatic compounds. Residual carboxyl groups may be retained on some of these molecules. 

Pyrolysis process for poly(2-hydroxyethyl methacrylate) occurs similarly to that for other methacrylic acid esters. The formation of 2-methyl-2-propenoic acid 2-hydroxyethyl ester, the monomer, shows that unzipping is a significant part of the process. Some other compounds in the pyrolysate also are generated from the polymer cleavage, such compounds including 2-methyl-2-propenoic acid ethenyl ester, propanoic acid, 2-methyl-2-propenoic acid, ethanol, etc. On the other hand, some compounds are not expected in the pyrolysate and they can be impurities or additives. Examples of such compounds are the hydrocarbons (undecene, dodecane, 1-dodecene, etc.), the esters of ethylene diol and the free 1,2-ethandiol, etc. The initiator AIBN and its decomposition products 2-methyl-2-propenenitrile and 2-methylpropanenitrile identified in the pyrolysate show that the polymer was obtained using AIBN as initiator. 

The alkyl radical may dimerize, hydrogen abstract, disproportionate, or initiate polymerization. One such example is the polymerization of methacrylic acid on CdS, CdS/HgS, or CdS/TiOj particles [Eq. (11)] [113-116]. Through a similar mechanism, benzyl radicals can be obtained from the decomposition of benzyltrimethylsilanes on illuminated TiOj. Dimerization of benzyl radicals gives diarylethanes in a high yield [Eq. (12)] [117]. 

The degradation of poly-oc-esters was studied on poly(isopropylidine carboxylate) [518] over a range of temperatures, from 200 to 800°C. Among the decomposition products were found tetramethyl glacolide, acetone carbon monoxide, and to a lesser extent methacrylic acid. The primary decomposition product appears to be tetramethylene glacolide that becomes an intermediate upon further pyrolysis ... 

The polymerization of acrylic acid when initiated by y-radiation leads to observations that vary significantly from those made on the polymerization of methacrylic acid [78-80]. The hypotheses of Chapiro are such that even polymerizations initiated by the thermal decomposition of free-radical generators should be reexamined in their light. 

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