Copolymerization of carbon dioxide and propylene oxide using an aluminum porphyrin system and its components

Abstract

The catalytic activities of tetraphenylporphinatoaluminum chloride (TPPAlCl) and its propylene oxide adduct (TPPAl(PO)(2)Cl) were investigated in detail together with a quarternary salt Et4NBr for the copolymerization of carbon dioxide and propylene oxide. In addition, for the components and starting raw materials of the catalyst systems, catalytic activities were examined for the copolymerization. The TPPAlCl catalyst delivered oligomers containing ether linkages to a large extent, regardless of its PO adduction. And cyclic propylene carbonate, as byproduct, was formed in a very small portion. Using the TPPAlCl coupled with Et4NBr as a catalyst system, the formation of ether linkages was reduced significantly in the copolymerization; however, the obtained oligomer still contained ether linkages of 25.0 mol % in the backbone. On the other hand, the formation of cyclic carbonate was increased to 22.4 mol % relative to the oligomer product. The results indicate that the salt, which was coupled with the TPPAlCl catalyst, plays a key role in reducing the formation of ether linkage in the oligomer and, however, in enhancing the formation of cyclic carbonate. Similar results were obtained for the copolymerization catalyzed by the TPPAl(PO)(2)Cl/ Et4NBr system. That is, the formation of ether linkages was not restricted further by the PO adduction of the TPPAlCl component in the catalyst system. Only oligomers with a relatively high molecular weight were produced. This indicates that the PO adduction of the TPPAlCl component contributes highly to the initiation and propagation step in the oligomerization, consequently leading to a relatively high molecular weight oligomer. In contrast, the Et4NBr, as well as the Et2AlCl, produced only cyclic carbonate in a very low yield. Furthermore, tetraphenylporphine exhibited no catalytic activity, regardless of using together with Et4NBr. On the other hand, the Et2AlCl coupled with Et4NBr provided a low molecular weight oligomer having ether linkages of 92.3 mol % in addition to the cyclic carbonate. (C) 1999 John Wiley & Sons, Inc.