Tension Trapping of Carbonyl Ylides Facilitated by a Change in Polymer Backbone

Abstract

Epoxidized polybutadiene and epoxidized polynorbornene were subjected to pulsed ultrasound in the presence of small molecules capable of being trapped by carbonyl ylides. When epoxidized polybutadiene was sonicated, there was no observable small molecule addition to the polymer. Concurrently, no appreciable isomerization (cis to trans epoxide) was observed, indicating that the epoxide rings along the backbone are not mechanically active under the experimental conditions employed. In contrast, when epoxidized polynorbornene was subjected to the same conditions, both addition of ylide trapping reagents and net isomerization of cis to trans epoxide were observed. The results demonstrate the mechanical activity of epoxides, show that mechanophore activity is determined not only by the functional group but also the polymer backbone in which it is embedded, and facilitate a characterization of the reactivity of the ring-opened dialkyl epoxide.

Molecular engineering of mechanophore activity for stress-responsive polymeric materials

“…Motivated by an observation that the mechanical activity of epoxide mechanophores in sonication experiments is enhanced when the epoxides are embedded along the main chain of a poly(norbornene) (PNB), as opposed to a poly(butadiene) (PB), scaffold, 45 the backbone-related mechanical advantage was quantified in the g DHC polymers using SMFS. 30 As noted above, the rate-dependent force required for the ring opening of g DCC and g DBC activation is 1210 and 1330 pN, respectively, in PB (time scale ∼ 0.1 s).…”

Polymer Mechanochemistry: From Destructive to Productive

“…For strong bonds with BDEs exceeding 72 kcal mol −1 (e.g., C−O, C−C, and C−N bonds), a bond weakening strategy is generally employed to achieve mechanochemical selectivity. When strong bonds are incorporated into cyclic moieties, such as three58,70 and four24,71,72 membered rings and fused, 73,27 bridged, 74,75 and spiro22,23 bicyclic rings, ring strain (and in some cases electronic factors as in spiropyran) significantly reduces otherwise high BDEs and differentiates the bond from the rest of chemical connections…”

Mechanical gating of a mechanochemical reaction cascade

“…Covalent polymer mechanochemistry12345 has been extensively explored in recent years for a variety of purposes, including biasing reaction pathways6789, trapping transition states and intermediates1011, catalysis12131415, release of small molecules and protons161718, stress reporting19202122, stress strengthening222324 and soft devices2526. These efforts are largely facilitated by the fact that, unlike other energy sources, mechanical force is directional and regulated by local molecular structure.…”