Thermal degradation of methacrylic and acrylic polymers

The thermal degradation of polymers of acrylic and methacrylic alkyl esters is a process of depolymerization to monomers at temperatures up to 250°C, provided that the alkyl group is small, less than butyl [468]. Poly(f-butyl methacrylate) yields quantitatively isobutene instead. It was shown that thermal depolymerization to monomers is probably common to all poly(methacrylate ester)s. As the size of the alkyl group increases, however, particularly within secondary or tertiary structures, there is increased tendency for the alkyl group to also decompose. This decomposition interferes with the depolymerization process 

Thermal stability of poly(methyl methacrylate) appears to vary with the molecular weight. For instance, a sample of the polymer of molecular weight of 150,000 when heated in vacuum for 30 min at 318°C yields 74.3% volatiles. By comparison, a sample of this polymer of molecular weight of 5,100,000 when heated for 30 min at 319°C yielded only 35.2% volatiles [456]. 

The thermal stability of copolymers of long-chained diol dimethacrylates was investigated [583]. These copolymers included 1,4-butane-, 1,5-pentane-, 1,6-hexane-, 1,8-octane-, 1,10-decane-, or 1,12-dodecanediol dimethacrylates, respectively, as well as 2,2-bis[4-(2-hydroxy-3-methacryloyl-oxypropoxy)-phenyl]propane and triethylene glycol dimethacrylate. The polymers were found to be thermally stable up to 250°C, as shown by the initial decomposition temperature and then-degradation profiles. 

A quantitative investigation of the thermal degradation of poly(ethyl acrylate), poly(/i-propyl acrylate), poly(isopropyl acrylate), poly(/i-butyl acrylate), and poly(2-ethylhexyl acrylate) demonstrated that the principle volatile products are carbon dioxide, olefin, and alcohol corresponding to the alkyl group [469,470]. The following mechanism of degradation was proposed [469,470]  

More recently, another study was carried out on the thermal decomposition of homopolymers of ethyl methacrylate, n-butyl methacrylate, and 2-hydroxyethyl methacrylate as weU as then-copolymers [471]. The copolymers of hydroxyethyl methacrylate with ethyl methacrylate and butyl methacrylate were found to degrade by unzipping to yield the monomers similarly to poly(methyl methacrylate). In addition, there is competition between imzipping and cross-linking in binary copolymers of hydroxyethyl methacrylate with ethyl methacrylate and in n-butyl methacrylate. 

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See also in sourсe #XX -- [ ]

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