Introducing functionality into a polymer is often synthetically challenging. The ability to rapidly generate a diverse array of polymers in a controlled fashion from a common intermediate is highly desirable, because polymers featuring different functional groups engender different physical properties. On this premise, Albéniz and co-worker utilized olefin metathesis to produce a polymer with a reactive group that can undergo post-synthetic modification to introduce different side chains. This approach allows for rapid access to a library of functionalized polymers.
Employing ruthenium-catalyzed ring opening metathesis copolymerization of norbornene and w-bromoalkylnorbornenes leads to the corresponding polymer 1-Br with an unsaturated backbone. Hydrogenation of 1-Br produced saturated polynorbornenes (1-Br*) containing an alkyl bromide group for further synthetic manipulation (Scheme 1).
To introduce different side chains, reactions of 1-Br* with various nucleophiles produced modified polymers containing cyano, carbamate, thiol, azido, and stannyl groups in high yields (Scheme 2). Moreover, these groups can undergo further chemistry to make different functionalities. In a representative example of this methodology, the azido-containing polymer (1-N3) was subjected to copper-catalyzed 1,3-dipolar cycloaddition (click chemistry) with various alkynes to produce the corresponding triazole products. Specifically, reaction of 1-N3 with phenylacetylene in the presence of catalytic amount of copper at room temperature produced the triazole-containing polymer (1-TAZ) in 99% isolated yield (Scheme 3). The rapid diversification of a common intermediate via established high-yielding reactions to functionalized materials offers many possibilities for creative solutions.
Use of olefin metathesis to generate a polymer containing a reactive functional group that is amenable to further synthetic elaboration is highly attractive and has tremendous potential. One can envision using the vast toolbox of chemical reactions to tether transition metal catalysts, organocatalysts, chemical sensors, and proteins onto these supports for advanced functionalized materials.