Relationship between packing structure and monomer reactivity in the photoinduced solid-state polymerizations of muconic diesters with different sidegroups

To clarify the relation between packing structure and reactivity of monomer molecules in the photoinduced solid-state polymerization, we analyzed crys tal structures by X-ray diffraction for a series of dialkyl muconates with various types of side group. Single crystal of diethyl (Z,Z)-muconate (diet hyl (Z.Z)-2;4-hexadiendioate) changed into the stereoregular polymer crysta l by irradiating visible or ultraviolet light at room temperature. The dicy clohexyl (Z,Z)-muconate and the dibenzyl (Z,Z)-muconate showed the isomeriz ation reactions from (Z,Z) form to (E,E) form. The bisdecyl (Z,Z)-muconate and bis(2,2,2-trichloroethyl) (Z,Z)-muconate changed into amorphous polymer s. All the compounds used in this study have the columnar structures. The d istance of the butadiene carbon atoms of the neighboring molecules alone th e columnar axis was 3.5-6.4 Angstrom; almost no correlation could be found with the reactivity. The tilt angle of molecular axis from the columnar axi s was estimated to be 38-78 degrees, which could dot be assumed as a good i ndex to represent the reactivity of monomer molecules. Rather, a set of the distance and the tilting angle seems to be better index, but it could not necessarily explain the difference in the reactivity for all the substances . The free volume or the cavity between molecules is also not a proper meas ure. The degree of overlap of pi -electron orbitals between the butadiene c arbon atoms of the neighboring molecules was found to work as a relatively good measure of their reactivity. The systematic study of the molecular pac king geometry for a series of muconate derivatives brought up a very import ant warning about the conventionally made discussion on the factors governi ng the solid-state polymerization reaction based on only the interatomic di stance, the tilting angle of the molecules, etc.