Development of Green Catalysts for Ring-Opening Polymerization of Cyclic Esters

Sen, Tamal Kumar (2013) Development of Green Catalysts for Ring-Opening Polymerization of Cyclic Esters. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The aliphatic polyesters are an important class of biologically relevant macromolecules. These polyesters have many applications as temporary therapeutic systems such as sutures, osteosynthetic devices, sustained drug-delivery systems, and scaffolds in tissue engineering. Again in the present era of depleting petrochemical feedstocks and increasing environmental awareness, these polyesters have become an attractive alternative to conventional polyolefins. Thus there is always an interest in academia, as well as in industry for the synthesis and development of these polyesters. These polyesters can be synthesized in two process; polycondensation of hydroxy-carboxylic acids and catalytic ring opening polymerization (ROP) of cyclic esters. Catalytic ROP is favoured over the polycondensation technique because of its versatile applicability. During the last few decades, there have been enormous efforts to develop an efficient catalytic system for this demanding polymerization. Transition metal based catalysts are mostly used for the synthesis of these polyesters. Since these polyesters are highly applicable in biomedical and pharmaceutical fields thus the toxic transition metals impurities should be removed from these polymers. Thus there is always search for an alternative green catalytic process. In this context, there has been a growing trend to use metal free organocatalyst and nontoxic, low cost, green main group metals such as zinc, aluminum etc. based catalyst in the ROP reaction. Thus the major objectives of the present investigation have been; development of abnormal carbene (aNHC) based organocatalyst for ROP under mild condition and development of main group metal (zinc and aluminum) based organometallic catalytic systems using aNHC and phenalenyl as ligands for the ROP of cyclic esters. Chapter 1 gives a brief overview on the ring opening polymerization reaction using different metal catalysts with emphasis on the results obtained with main group metal and the early transition metal based systems. The aim and the scope of the present investigation are outlined at the end of this chapter. Chapter 2 presents the results obtained in the present investigation and a discussion of these results, especially kinetic study, DFT study are mentioned in detailed. Also the mechanistic aspects of the ring opening polymerization reaction carried out in detailed way. The highlights of the present investigation and possible future directions are summarized at the end of this chapter. Chapter 3 contains relevant details of the experimental procedures for the synthesis of these complexes used for the polymerization reaction. Detailed procedure including catalysis reaction as well as the kinetic study, DFT calculation and single crystal diffraction studies are also given in this chapter.

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