Precision Synthesis of Tunable Polyallenamers from “Masked” Precursors

Abstract

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 Skattebøl rearrangement, afforded the target polymers in good yields (85−88%, M n = 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.

Mechanochemical Backbone Editing for Controlled Degradation of Vinyl Polymers

“…23,24 Despite the de-cyclization editing of unsaturated linear polymers, it is also possible to alter the degradability of fully saturated hydrocarbon backbones. 25 Methods such as alkyl lithium promoted Skattebøl rearrangements of in-chain gemdihalocyclopropane units 26,27 and thermally induced retro-Diels-Alder reactions of in-chain norbornadiene-derived units 28,29 have subsequently been employed to introduce unsaturated carboncarbon bonds into fully saturated hydrocarbon chains. Unfortunately, backbone editing of commodity vinyl polymers, which can insert degradable groups into inert hydrocarbon chain, has not yet been successfully demonstrated.…”

Substituent Effects on Ring Opening Allene Metathesis: Polymerization Rate Enhancement and Regioregularity

“…Compared to traditional polymerization methodologies of allenes that yield alternating sp 2 - sp 3 -hybridized microstructures of limited utility, successful generation of polymeric material containing allenes has been accomplished through both cross-coupling polymerization strategies and postpolymerization modifications of polyalkenamers (Scheme ). , Although these methods impose limitations on either molecular weight or microstructural regularity, promising preliminary properties (helicity, fluorescence, degradability) of the resulting material have been demonstrated. Therefore, it is hypothesized that the generation of precision polyallenamers of appreciable size will lead to a new class of functionalizable materials with highly tailorable and adaptive properties.…”