Metallic Iron And Zinc Catalyzed Ring-opening Polymerization Of ε-caprolactone

As one of the earliest synthetic polymers, poly(ε-caprolactone)(PCL) has special physical and chemical properties, good biodegradability, miscibility and biocompatibility. Therefore PCL has been widely used in various fields such as biomaterials, tissue engineering, drug delivery, microelectronics, adhesive and packaging. It is therefore critical to find biocompatible, environmentally benign, cheap and readily available catalysts for the polymerization of ε-caprolactone(CL).In this thesis, we study the polymerization of CL using iron and zinc powder respectively. Iron powder itself fails to initiate the polymerization of CL, while the introduction of a bifunctional compound 2-hydroxyethyl 2-bromoisobutyrate(HEBiB) can efficiently catalyze the ring-opening polymerization of CL under facile conditions, forming PCL with appreciably high molecular weight(Mn), narrow molecular weight distribution and high yield. Contrast experiments indicate that both iron and bromide are indispensable, and hydroxyl initiators lead to controlled polymerization. In sharp contrast, zinc powder can initiate the polymerization of CL alone. The introduction of bromides broaden the molecular weight distribution, while the presence of hydroxyl compounds lead to controlled polymerization and higher product yields. For the above two catalyst systems, the contribution of reaction temperatures, solvents, reaction times, hydroxyl initiators and amounts of metals are investigated, and their mechanisms are also discussed. The kinetic studies of both systems indicate living/controlled polymerization. The molecular weight and polydispersity index are measured by gel permeation chromatography. The chain ends of the obtained polymers are analyzed by 1H NMR, and the results suggest that the hydroxyl compounds are initiators in these reactions.