High Pressure Solid State Polymerization

Conventional polymer synthesis involves gas or liquid phase polymerization using a catalyst. For example, polyacetylene is synthesized by using a Ziegler-Natta catalyst. In this method, acetylene gas is sprayed on the catalyst and polymer is produced on the catalyst surface. The produced polymer is a thin film with many gaps. The bulk density of this polymer is 1/2 or 1/3 times the density of the monomer crystal. The solid-state polymerization reaction can generate high-density polymer or single-crystal polymer. Solid-state polymerization is studied for diacetylene in detail. It is reported that polymerization is initiated by irradiating light or radiation onto the crystal and by heating the crystal for diacetylene compounds. This led us to study solid-state polymerization under high pressure. Even a simple molecule like acetylene becomes a crystal under high pressure. Moreover, the intermolecular distance in a crystal can be changed by controlling the pressure. The intermolecular distance in molecular crystals shrinks by about 10 % at a pressure of 10 GPa. Such an approach between molecules will cause reconstruction of chemical bonds or rearrangement of molecules. This suggests that polymerization can be caused by pressure. Generation of high-density polymer was expected by high pressure solid-state polymerization.