Thermal Oligomerization of Barium Methacrylate in a Solid State

Abstract

Barium methacrylate undergoes facile oligomerization on heating in a solid state. The effect of heating temperature on the formation of dimers and trimers was investigated in the range 150240°C. At 150-460°C α-methylene-ε-methyladipate [2] was formed. At 170°C and above, however, α-methylene-γ, γ-dimethylglutarate [1] was formed together with [2], and yields of both dimers increased with a rise in temperature. At any temperature, yield of [2]was greater than that of [1]. The heating of barium methacrylate containing a small amount of water at 220°C in a liquid state resulted in remarkable decrease in the yield of C [1] and in large increase of [2].
Change of t he crystal lattice after the thermal oligomerization was observed by X-ray diffraction. A part of the crystal lattice of the monomer salt was transferred to another one with formation of oligomers without destruction of the crystal. When total oligomer formation reached to about 50% of the monomer, all of the crystal lattice changed to the new lattice, which was maintained during further formation of oligomer. From these results, it is concluded that [2] is formed in both the crystalline and amorphous states, and [1] only under lattice control.