Controlled polymerization of alkyl vinyl ethers via 'covalent' propagating species
The study of the polymerization of alkyl vinyl ethers initiated by HI/I₂ catalyst is directed into two areas: the kinetics of the polymerization and the strategy of amine functionalized prepolymer synthesis.
The polymerization reactions show living behavior in nonpolar solvents at low temperatures. The observed rate of polymerization under reaction conditions is linearly dependent on the initial concentration of hydrogen iodide and iodine, respectively. However, the monomer concentration does not influence the rate of polymerization(apparent zero-order). Two possible reaction schemes are proposed from the observed rate equation and attempts are made to distinguish them by using UV/visible spectroscopy and carbon-13 NMR spectroscopy. In both schemes a reversible interaction between a monomer and an iodine molecule is postulated as a necessary elemental reaction to fit the observed expression for the rate of polymerization. From spectroscopic analysis results, the interaction between the iodide compound(chain end) and the iodine molecule seems to be very weak compared to the interaction between the monomer and the iodine molecule.
A synthetic strategy for amine functionalized prepolymer synthesis has been developed via a series of model reactions. Incorporation of a styrenic monomer at the propagating chain end of living poly(alkyl vinyl ethers) provides a convenient intermediate synthesis of a relatively stable amine functionalized prepolymer. Proper selection of substituents at the styrenic monomer optimizes the cross addition reaction and amination reactions. Linear alkylamines with lower carbon numbers are used in the amination reaction in order to promote the nucleophilic substitution reaction and to minimize possible elimination reactions. A series of amine functionalized oligomers are synthesized by employing the synthetic strategy in combination with the previous kinetic result of the homopolymerization. For oligomers, incorporation of a few units of ethyl vinyl ethers at the chain end facilitates the cross addition reaction. Synthesized amines are characterized by various spectroscopic methods. Then, titrated molecular weights show good agreement with their theoretical molecular weights in several cases.