Folding-Driven, Nucleation -Elongation Polymerization of Phenylene Ethynylene Imines
As a result of the helical structure of the polymeric product, the polymerization of oligo(m-phenylene ethynylene) imines in solution should inherently show nucleation-elongation in chain growth. The evidence for this behavior was obtained from polymerizations conducted under conditions of imbalanced stoichiometry. Since the polymerization proceeds via metathesis between a pair of bifunctional monomers of type A-A and B-B, the molar ratio of the polymerizing functional groups can be arbitrarily varied. Alternatively, stoichiometry can be controlled by the addition of a monofunctional oligomer. Similar results were obtained in both cases whereby high molecular weight polymers were observed to coexist with the monomer in excess. Thermodynamic equilibrium was established by showing that the same distribution was reached starting either from a monomer mixture or from high polymer to which one monomer was added. These results are in great contrast to the low molecular weight oligomers produced from a reaction that proceeds without the nucleation event. Equilibrium models that capture the features of nucleation-elongation under imbalanced stoichiometry have been developed and qualitatively support the experimental observation by showing the monomer-polymer coexisting state to be the thermodynamic equilibrium distribution.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign