Reactivities of Crotonic Acid and Isocrotonic Acid in Radical Copolymerizations

Studies on the Water-Soluble Polymers. XIX

Abstract

Two isomeric acrylic acid derivatives, crotonic acid and isocrotonic acid, failed to homopolymerize by the radical reaction. They, however, copolymerized with acrylamide and 2-methyl-N-vinylimidazole to some extent. They showed a slightly higher reactivity with 2-methyl-N-vinylimidazole than with acrylamide, and the reactivity of isocrotonic acid was higher than that of crotonic acid. The monomer reactivity ratios were determined, as follows :
for isocrotonic acid (1) - acrylamide (2), r₁ =0.11, r₂=4.72;
for crotonic acid (1) - acrylamide (2), r₁=0.12, r₂=5.32;
for isocrotonic acid (1) - 2-methyl-N-vinylimidazole (2), r₁=0.60, r₂=0.09;
for crotonic acid (1) - 2-methyl-N-vinylimidazole (2), r₁ =0.49, r₂=0.19.
It is confirmed that, in the radical copolymerization, the reactivity of the isomers can not be explained only by the thermodynamic stability. Other factors such as inductive, resonance, and steric effects of the substituents must also be taken into consideration. The comparative reactivities of the isomers of α, β-disubstituted olefins may be predicted based on the inductive substituent constants of theα-and β-substituents.