Catalytic emulsion polymerization of norbornene.

摘要

The use of late transition metal catalysts for the polymerization of olefins in aqueous media has created new opportunities to produce latex particles based on ethylene and its olefinic derivatives. This thesis reports on three different aspects of the catalytic emulsion polymerization of norbornene; (1) reaction parameters (e.g. reaction temperature, ionic strength), (2) addition of various classes of surfactants, and (3) polymerization of a variety of norbornene-derived monomers. These reactions have been carried out as ab initio batch emulsion polymerizations using allyl palladium catalysts and a lithium based activator, supported by a variety of surfactants.; The role of surfactants in traditional emulsion polymerization is to assist in particle nucleation and/or to stabilize latex particles. We studied the role of several classes of surfactants in the emulsion polymerization of norbornene with Pd catalysts, both with and without the activator LiFABA. In the catalytic emulsion polymerization of norbornene, some of these surfactants were found to act as weakly coordinating anions with the Pd based catalysts to promote polymerization. When the base latex recipe already contains an activator specifically designed to work effectively with Pd in organic media (e.g.LiFABA), certain classes of surfactants (e.g. sulfates) act to provide an alternative pathway for polymerization and latex particle formation. Other surfactants (e.g. cationics) can actually suppress all or part of the polymerization by destructively interfering with either the catalyst or the activator. Alkyl sulfates and sulfonates were both effective activators of allyl Pd catalysts and produced latex particles (ca. 40--50 nm) without significant amounts of coagulum. This activity is significantly dependent on the alkyl chain length, and alkyl sulfate anions are more active than the equivalent alkyl sulfonate anions. Cationic, fatty acid and non-ionic surfactants produced variable, but ineffective, results in our studies.; This work determined that the n-alkyl norbornenes can be polymerized in aqueous emulsion and that the mechanisms for latex particle formation are the same as that for norbornene monomer alone. As in the case of norbornene, large amounts of coagulum can be formed if the catalyst and activator are allowed to reach the emulsified monomer droplets and effect polymerization in that location. As the substituents on the norbornene become larger and non-polar, it is necessary to consider their effect on the water solubility of the monomers in order to analyze the experimental results in an effective manner. Our studies included butyl and decyl-norbornene, vinyl and butenyl-norbornene, and methanol-norbornene in ab initio emulsion polymerization and also the mini-emulsion polymerization of decyl-norbornene.