Crystal Structures of Missing Links in the Early History of Solid-State Reactions: The Group IA Acrylates and Methacrylates

Abstract

The crystal structures of potassium acrylate and related compounds studied by the group of Herbert Morawetz (1915-2017) have remained unknown for 60 years. 60Co γ-irradiation of potassium acrylate, the most reactive of all materials studied, affords high yields of polyacrylate, with molecular weights in the range of 120,000-400,000. At the present time, the only alkali metal salts of acrylic and methacrylic acid whose structures appear in the Cambridge Structural Database are those of lithium. We report five new crystal structures: potassium acrylate (1), potassium methacrylate (2), potassium hydrogen dimethacrylate (3), rubidium hydrogen dimethacrylate (4), and sodium dihydrogen trimethacrylate (5). The discussion focuses on metal coordination, proposed reaction pathways for radical polymerization in the solid state, and possible reasons for differences in acrylate versus methacrylate reactivity.