Topochemical Reactions of Monomers with Conjugated Triple‐Bonds VII Mechanism of Transition from Monomer to Polymer Phase During Solid‐State Polymerisation

The lattice‐controlled solid‐state polymerisation of three different modifications of 2,4‐hexadiin‐1,6‐diol‐bis(phenylurethane) was investigated by X‐ray and optical methods. The polymerisation is a homogeneous reaction. The polymer grows in the form of single chains within the crystal of the monomer. The chains extend along a definite crystallographic direction. Monomer and polymer are isomorphous and monomer‐polymer single crystals of various compositions are obtained up to a quantitative conversion in the case of modification I or III. Phase separation into a mesomorphic polymer and oriented monomer phase was observed on annealing partially polymerised single‐crystals of modification II below the transition point to modification III.