In the resin industry, a resin having a cyclic carbonate functional group may be used in the synthesis of non-isocyanate polyurethane resin (NIPU), and the isocyanate compounds having higher toxicity are abrogated from being applied in the synthesizing process. In the industry, the isocyanate monomer is produced using phosgene, in which both the raw materials and the end products are highly toxic chemicals. Accordingly, greener materials, for replacing the isocyanate polyurethane resin material, gradually become the focus of attention. Since the non-isocyanate material do not have moisture sensitive isocyanate functional groups, the storage and processing conditions are preferred over those of a conventional polyurethane resin.
The critical material for the non-isocyanate polyurethane resin is a cyclic carbonate compound, which is prepared by using carbon dioxide and an epoxy compound. The method of synthesis includes utilizing a Lewis base, an ionic liquid, a metal complex, a heterogeneous metal salt, a silica supported catalyst, an oxidized metal salt porous material or an ion exchange resin as a catalytic system to catalyze the reaction of carbon dioxide and the epoxy compound. Among the above catalysts, the salt type or the ionic liquid catalyst is the most commonly used. However, these catalysts are usually less soluble in an epoxy compound. Consequently, the amount of catalyst used is increased and the reaction conditions are adjusted to high temperature and high pressure in order to achieve the desired conversion rate. Further, by-products are generated. Alternatively, ligands synthesized through special designs or expensive metal ions may be utilized to prepare the catalyst. However, not only commercial production becomes difficult, the product cost increases and the recycling of catalyst is inevitable. Due to above reasons, the bar of the fabrication technology of cyclic carbonate is raised, and the yield of non-isocyanate polyurethane resin cannot be effectively improved.
Accordingly, the development of a new generation of catalyst system having high reaction activity, being producible under moderate reaction conditions, being able to preclude the requisite of being recycled from the product and being cost-effective has become the focus of attention in the fabrication technology of cyclic carbonate.