Precision Synthesis of Tunable Polyallenamers from ?Masked? Precursors

Incorporating reactive functional groups within polymer matrices is a promising avenue toward achieving intrinsically tunable materials. Motifs that respond to external stimuli and/or participate in a diverse array of chemical transformations are particularly enabling in the context of designing multipurpose materials. For example, polyallenamers are an emerging class of materials that exhibit stimulus-responsive behavior and are readily tailored through post-synthetic manipulations. Unfortunately, current synthetic methods for accessing these scaffolds suffer from poor control (either with respect to molecular weight or the preparation of more complex microstructures). Here, we report a new synthetic strategy that addresses these limitations by polymerizing "masked" allene precursors. Ring-opening metathesis polymerization (ROMP) of a gem-dibromobicyclo[6.1.0]non-4-ene monomer, and a subsequent Skattebol rearrangement, afforded the target polymers in good yields (85-88%, Mn = 7900-55,000 Da). Saturated congeners of these materials, which exhibit structural homology to polyolefins, could also be prepared using a simple hydrogenation protocol. Solid films of this reduced material were susceptible to photochemical tuning of bulk mechanical properties (via network formation). Moreover, our saturated polymers were readily transformed into 1,8-octandioic acid (a valuable feedstock for polyesters) using a simple ozonolysis protocol. Finally, we could leverage our synthetic strategy to prepare discrete block-like copolymer architectures with controlled allene content.