| Abstract: | The crystallographic unit cells of melt-crystallized 3,3-bischloromethyloxetane and 3,3-bisbromomethyloxetane were determined by the Weissenberg method. The two isomorphous lattices are triclinic with two molecules in the unit cell. 3,3-Bisfluoromethyloxetane forms plastic crystals in the temperature range between ?36°C and +22°C, as shown by differential calorimetry and NMR broad-line spectroscopy. The Debye-Scherrer diagram and the general physical properties indicate the formation of a face-centered cubic lattice. No correlation between the lattice parameters of the monomer and polymer can be found On the basis of these results, the question is raised as to whether a topochemical polymerization of bishalomethloxetanes, i.e., a solid-state polymerization without destruction of the crystal lattice, can take place at all. The halomethyl side groups of the oxetanes can be shown to possess different conformations in monomer and polymer crystals, so that a conformational change of the groups and rearrangement of the molecules must take place during polymerization. Therefore, a topochemical mechanism for the solid-state polymerization of bishalomethyloxetanes seems to be impossible. |
