Chain transfer agents: Characterization and their use in polymerization reactions

Abstract

The primary aim of this dissertation was to prepare catalysts of Co(II) and their use in polymerization reactions. For this purpose, dioxime complexes of Co(II) have been synthesized and characterized by elemental and spectroscopic techniques. This new class of metal-chelates was found to act as Chain Transfer Agent (CTA) for controlled polymerization of Methyl methacrylate (MMA), Butyl methacrylate (BMA) and Styrene. By using [Co(afdo-2H.BF2) 2] and [Co(dmg-2H.BF2)2], (afdo = α-furil glyoxime and dmg = dimethyl glyoxime) complexes as Chain Transfer Agents low molecular weight of the PMMA, PBMA and PSTY were obtained. It has been noted that [Co(afdo-2H.BF2)2] catalyst acts as less efficient CTA as compared to [Co(dmg-2H.BF2)2] catalyst for the polymerization of Methyl methacrylate. However, this is more efficient for polymerization of BMA. We have also investigated the effect of [Co(afdo-2H.BF 2)2] catalyst at 60, 70 and 80°C for polymerization of styrene and it was noted that efficiency of the catalyst decreased at higher temperature. The efficiency of a chain transfer agent is reflected by chain transfer constant (CS) value, which was calculated from the slope of Mayo plot. The CS value for Pulsed Laser Polymerization (PLP) of MMA using [Co(afdo-2H.BF 2)2] as CTA was found to be around 2500, while for PLP of MMA, with [Co(dmg-2H.BF2)2] catalyst was about 13,400. We believe that for PLP of MMA electronic factors are dominant and for the PLP of BMA probably steric effects are dominant. It has been noted that polydispersity index (PDI) value for PLP of MMA with [Co(afdo-2H.BF2)2] catalyst is less than 1.5, which probably indicates living free-radical polymerization. We have also successfully determined various kinetic parameters such as activation energy for degree of polymerization (Exn), activation energy for propagation reactions (Ep) and transfer rate constant (ktr's ) for polymerization of Styrene and MMA at higher temperatures. We have also investigated the effect of [Rh(afdo-2H.BF2) 2]Cl and Wilkinson's catalyst [RhP(Ph)3Cl] on the polymerization MMA. Both these catalysts were found to promote the polymerization process. For all the polymerization studies either Benzoyl Peroxide or 2,2′ -Azobis-(2-methylpropionitrile) [AIBN] were used as initiators. Excimer Laser (308 nm input at 10 Hz) was used as a laser source for Pulsed Laser Polymerization.