Multimechanophore Graft Polymers: Mechanochemical Reactions at Backbone–Arm Junctions

Abstract

Typical multimechanophore polymers (MMPs) are comprised of numerous mechanophores (force-responsive moieties) distributed throughout the backbone of linear polymers. We have developed a new MMP design based on graft polymers with mechanophores linking each arm to the backbone. By utilizing maleimide–anthracene cycloadducts, polymeric species containing anthracene were released from the parent polymer, enabling facile quantification of mechanophore activation. With pulsed ultrasound experiments, we observed that mechanophore activation was dependent on the arm length (a faster rate with longer arms), and we observed that 85% of the polystyrene (PS) arms underwent scission (64% specifically at the mechanophore site) for a graft polymer with 23 kDa arms. Solid-state activation was also investigated with hand-grinding experiments. Fast reactions were observed, with up to 96% of PS arms undergoing scission and 70–75% of mechanophores being activated, for all arm lengths studied. Multimechanophore graft polymers provide important insight into the distribution of forces in topologically complex polymers and may enable the development of new mechanoresponsive materials.

Mechanochemical Reactivity of Bottlebrush and Dendronized Polymers: Solid vs. Solution States

“…Bottlebrush polymers (P-PS and P-PLA)and dendronized polymers (P-eGX and P-FGX)w ere prepared with varying degrees of polymerization (DPs, Table 1). Linear poly(norbornene)-based polymers with benzyl side-chains (P-Bn from the monomer Bn)w ere also prepared to provide ab enchmark for comparisons.L astly,g raft MMPs were prepared from macromonomers (PS Xm and eG4 m )containing am aleimide-anthracene cycloadduct (a popular mechanophore) [38,45,65,66] located between the arm/dendron and norbornene units.F or brush polymers,t his MMP design pre-viously enabled efficient mechanophore activation. In total, 29 bottlebrush polymers,2 2d endronized polymers,a nd 4 linear polymers were synthesized.…”

“…[16,17] Va rious design principles influence mechanochemical reactivity including the location of mechanophores, [18] regio-and stereochemistry, [19][20][21][22][23] linkers, [24][25][26] polymer composition, [27,28] and polymer topology. [29] In regard to topology,i ntramolecularly cross-linked, [30][31][32][33][34] cyclic, [35] dendritic, [36,37] star, [38][39][40][41][42][43] bottlebrush, [44][45][46] and dendronized polymers, [47] have been utilized to tune mechanochemical reaction kinetics and/or mechanophore activation efficiency. Them ajority of these topology studies have been conducted using ultrasonication (US) or, to alesser extent, ball-mill grinding (BMG).…”

A Mechanochemical Reaction Cascade for Controlling Load‐Strengthening of a Mechanochromic Polymer

“…In our polymers, the mechanophores were confined to the side‐chains in the proximity of the branch points. We chose comb polymers to maximize the efficiency of transducing external mechanical load to the force acting on individual mechanophores [45, 46] . Doing so is expected to reduce the minimum concentration of mechanophores needed to elicit a detectable stress response, which is critical for practical applications of such polymers.…”

Ru-Catalyzed, cis-Selective Living Ring-Opening Metathesis Polymerization of Various Monomers, Including a Dendronized Macromonomer, and Implications to Enhanced Shear Stability

“…9 Degradation studies were conducted as previously described. 10,11 In short, an Arpurged solution of polymer in inhibitor-free, HPLC-grade THF (15 mg of polymer at 1 mg/mL concentration) was prepared in a sealed Suslick flask under Ar atmosphere. The Suslick flask was submerged in a cold bath (maintained at -10 ˚ C by a recirculating chiller) and the polymer solutions was sonicated at 16.9 W/cm 2 using a pulse sequence of 1 s "on", 4 s "off".…”