Ethyl a-hydroxy methacrylates

This effect is attributed to the greater sterical hindrance in DMI. If MMA is compared to ethyl a-hydroxy methacrylates (EHMA) instead, the activation energy is reduced due to the electronic effect of the additional p-oxygen atom, while the pre-exponential factor remains unchanged. In a monomer that combines both effects in one molecule, like ethyl a-acetoxymethyl acrylate, a decrease in both Arrhenius parameters is observed (compare Scheme 1.9). 

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