Solid-state polymerization and polymer single crystals

The photopolymerization of distyrylpyrazine (DSP)–if carried out at a suitable wavelength of irradiation–and the thermal or radiation–induced polymerization of diacetylenes are examples of single crystal to single crystal reaction–transformations. The chain growth is controlled by the packing of the monomer on lattice sites and proceeds one-dimensionally in the crystal. The kinetics of chain growth in these systems is investigated via analysis of the molecular weight distribution as depending, on the reaction parameters. Polymerization of DSP proceeds stepwise by addition of photoexcited monomer to reactive oligomer chain ends. The probability of addition of a monomer to an already existing oligomer is 4 times larger than dimer formation leading to an inhomogeneity of the product distribution in the crystal. Polymerization of the bis-(p-toluene sulfonate) of dodeca-5, 7-diyne-1, 12-diol (PTS-12) proceeds as a true chain reaction via carbenes as the active chain ends. The kinetic chain length and degree of polymerization is essentially limited by the encounter with other chain ends in the same stack of units. Combination of chain ends is not observed.