Molecular motions and solid-state polymerization. An n.m.r. study of acrylic and methacrylic acids and barium and lithium methacrylates

Abstract

Variations in the second moment of the n.m.r. absorption lines with temperature are reported for several crystalline vinyl monomers which are of interest in the field of solid-state polymerization. A comparison of the n.m.r. data and the known crystal structure of acrylic acid has allowed the predominant mode of molecular motion in the crystal lattice above –80°C to be identified as rotational oscillation. The crystal structures of the other monomers are unknown and suggestions for possible modes of molecular motion are made. The n.m.r. data for methacrylic acid are compared with contradictory results obtained by previous workers. Narrow lines which appear in the centre of the absorption spectra under certain conditions are attributed to enhanced molecular motions in lattice defects. In all cases the n.m.r. data are compared with available information on reactions in the crystalline monomers and the importance of molecular mobility in controlling these reactions is discussed.