Free radical polymerization kinetics of hindered monomers

Erwin Schrödinger Fellowship J 1965 Free radical polymerization kinetics of "hindered" monomers Philipp VANA 09.10.2000 The primary aim of this project is to investigate the mechanisms of propagation, termination and transfer in vinyl monomers with 1,1-disubstitution where the substituents are bulky and exercise a significant entropic barrier to free radical reactions. Since the development of Pulsed-Laser Polymerization a number of monomer systems have been investigated, particularly with regard to the propagation rate coefficient kp, but recently this method was expanded to the termination rate coefficient kt, too. However, monomers that have a signiflcant steric barrier to propagation, termination and transfer have not received much attention. Thus, the significance of the proposed program lies in the determination of kinetic parameters for hindered monomers, for the first time, which should provide considerable insight into the mechanisms of free radical polymerization. Polymerization kinetics of the hindered monomers will be investigated by means of Pulsed-Laser Polymerization (PLP) and subsequent accurate analysis of the chain-length distribution by Size-Exclusion Chromatography. Besides the well known method of kp, determination by PLP newly invented methods for the measurement of kt will be used. These methods are capable of determining the chain-length dependence of the termination rate coefficient kt which will allow predictions about the bimolecular termination process. Both homopolymerization and copolymerization experiments of the monomers diniethyl itaconate, 2- (hydroxymethyl) ethyl acrylate and 2-(benzoyloxmethyl) ethyl acrylate, also with not hindered monomers like styrene and methyl methacrylate, will be realized. Especially the kinetics of copolymerization which differ extremely from traditional models like the terminal model has to be explained. This project will try to illuminate reaction mechanisms of the free radical polymerization, which has many advantages for chemical industries as it is robust, versatile and relatively insensitive to impurities.