Methyl acrylate polymerization thermodynamics

Because of the general lack of quantitative thermodynamic (ceiling temperature Tc) and kinetic (kp, kp/k[J 5) data for the polymerization of the captodative olefins, it is impossible to draw firm conclusions about the importance of electronic factors on their polymerizability. If we compare them with other 1,1-disubstituted olefins by replacing the heteroatom O, S, or N by a CH2 and check the polymerizability of the resulting olefins, we find that the latter are in fact also difficult to polymerize as shown in Table 8 [77], Only methyl acrylates and methacrylates give high polymers easily. The polymerizability decreases rapidly with the steric hindrance of the substituent. 

Organocobalt porphyrin complexes have also yielded useful mechanistic information. The reactions of (tetrakis(p-methoxyphenyl)porphyrinato)cobalt(II) ((TAP)Co(II)) with radicals derived from dialkylazo thermal initiators with acrylic monomers provide evidence for the intermediacy of Co(III)-H species in CCTP. Reaction of (TAP)Co (II) with tertiary alkyl radicals, for example, as derived from AIBN in the presence of monomers that form stable Co-alkyl complexes, such as methyl acrylate, results in quantitative formation of Co(III)-alkyl. Whereas with monomers leading to tertiary C-Co bonds, such as MMA, the Co (II) is very much a spectator as normal polymerization ensues. Thermodynamic and activation parameters have been measured for the dissociation of (TAP)Co(III)-C(CH3)2CN to Co(II) and organic radical in solution as a probe into CCTP mechanism by low-spin Co(II). ... 

There have been many studies on the polymerizability of cx-substituted acrylic monomers.It is established that the ceiling temperature for a-alkoxyacrylates decreases with the size of the alkoxy group. However, it is of interest that polymerizations of a-(alkoxymethyl)acrylates (67) and a-(acyloxymethyl)acrylates (68) and captodative substituted monomers (69, 70) appear to have much higher ceiling temperatures than the corresponding a-alkylacrylates (e.. methyl ethacrylate, MEA). For example, methyl a-ethoxymethacrylate readily polymerizes at 110 °C whereas MEA" has a very low ceiling temperature (Table 4.10). However, values of the thermodynamic parameters for these polymerizations have not yet been reported. 

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