Methacrylate Ester Model Systems

Disproportionation increases in the series where the ester is methyl ethyl butyl suggesting that this process is favored by increasing the bulk of the ester alkyl group. This trend is also seen for polymeric radicals (Section 

Bizilj et at reported that disproportionation is more important for oligomeric radicals. While combination products were unequivocally identified, analytical difficulties prevented a precise determination of the disproportionation products. Accordingly, they were only able to state a maximum value of kt j/kK. Their data show that kl(i/ktc 1.85 for the self reaction of 11 and 1.50 for reaction between 8 and 11. 

Serelis and Solomon108 found that primary radical termination of oligo(MAN) radicals (16) with 15 also gives predominantly combination. The ratio kllt/klc was found to have little, if any, dependence on the oligomer chain length (n 4). As with PMMA, disproportionation involves preferential abstraction of a methyl 

8) have been extensively studied. In contrast with the analogous esters 8-10 (Section 5.2.2.1.2), combination is by far the dominant process (Table 5.4). 

Cyanoisopropyl radicals (15) undergo unsymmetrical C-N coupling in preference to C-C coupling. The preferential formation of the ketenimine is a reflection of the importance of polar and steric influences. However, the ketenimine is itself thermally unstable and a source of 15, thus the predominant isolated product is often from C-C coupling. 

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Table 5.3 Values for Methacrylate Ester Model Systems...

The termination mode of poly(alkyl methacrylate) radicals has also been the subject of much research.[9] Model compound studies of the bimolecular reactions of l-methoxycarbonyH-methylethyl radicals and the higher esters ethyl and butyl have resulted in for MMA, 0.72 for EMA, and 1.17 for nBMA.[9,10]. A k /k =4.37 was obtained by means of Matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF MS) to the end-group analysis of low MW PMMA.[11] The use of fluorinated derivatives of BPO in combination with F NMR analysis of PMMA also indicated that the termination occurred mainly due to the disproportionation in this system.[12]... 

The monomers which have been investigated include methyl methacrylate, ethyl acrylate ester, hydroxy acrylates and methacrylates, acrylonitrile, vinyl acetate, vinyl chloride, acrylamide, vinylidene chloride, acrylic acid, vinyl pyrollidone and styrenec Many copolymer latexes of these monomers have also been preparedc Undoubtedly the most amenable system for model studies is methyl methacrylate in aliphatic hydrocarbono... 

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