Conformational Entropy as a Means to Control the Behavior of Poly(diketoenamine) Vitrimers In and Out of Equilibrium

Abstract

Control of equilibrium and non‐equilibrium thermomechanical behavior of poly(diketoenamine) vitrimers is shown by incorporating linear polymer segments varying in molecular weight (MW) and conformational degrees of freedom into the dynamic covalent network. While increasing MW of linear segments yields a lower storage modulus at the rubbery plateau after softening above the glass transition (Tg), both Tg and the characteristic time of stress relaxation are independently governed by the conformational entropy of the embodied linear segments. Activation energies for bond exchange in the solid state are lower for networks incorporating flexible chains; the network topology freezing temperature decreases with increasing MW of flexible linear segments but increases with increasing MW of stiff segments. Vitrimer reconfigurability is therefore influenced not only by the energetics of bond exchange for a given network density, but also the entropy of polymer chains within the network.

Circularity in mixed-plastic chemical recycling enabled by variable rates of polydiketoenamine hydrolysis

“…To address outstanding challenges in mixed-plastic recycling, we hypothesized that molecular engineering may provide access to PDK resins with tunable rates of diketoenamine hydrolysis, such that different monomers could be isolated at different stages of a chemical recycling process. PDK resins are synthesized from polytopic triketone and amine monomers via spontaneous “click” polycondensation reactions ( 24 , 25 ), which proceed under ambient conditions and do not require a promoter. Monomers used in PDK resins share structural similarities with those used to formulate a range of properties in polyurethanes and nylons.…”

“…The properties of PDK resins might be anticipated to be similar while bridging those of plastics and thermosets because of their dynamic covalent character ( 24 , 25 , 29 – 32 ). In prior work, we demonstrated that by varying the cross-linking density of PDK resins with flexible and rigid diamines used in polyamides and polyurethanes, we can control tensile strength (stress at break) over a range of 18 to 31 MPa ( 25 ). This range is similar to that reported for commercially available polyurethanes: 0.6 to 44.1 MPa ( 33 ).…”

“…Monomers used in PDK resins share structural similarities with those used to formulate a range of properties in polyurethanes and nylons. The properties of PDK resins might be anticipated to be similar while bridging those of plastics and thermosets because of their dynamic covalent character (24,25,(29)(30)(31)(32). In prior work, we demonstrated that by varying the cross-linking density of PDK resins with flexible and rigid diamines used in polyamides and polyurethanes, we can control tensile strength (stress at break) over a range of 18 to 31 MPa (25).…”

“…Here, we show that chemospecificity in mixed-polymer recycling is enabled through molecular engineering of polydiketoenamines (PDKs) (24,25), where fast-and slow-to-depolymerize PDK chemistries incorporated into either mixed-polymer or mixed-material products allow each PDK variant to be selectively deconstructed in space and time simply by varying the depolymerization temperature under acidic conditions (Fig. 1A).…”

Reprocessable, Reworkable, and Mechanochromic Polyhexahydrotriazine Thermoset with Multiple Stimulus Responsiveness

“…through the reversible depolymerization or exchange reactions of their dynamic cross-links [ 3 , 9 , 10 , 11 ]. So far, a number of CANs based on Michael addition [ 12 , 13 , 14 ], Diels-Alder reaction [ 15 , 16 ], disulfide exchange [ 17 , 18 , 19 ], imine metathesis [ 20 , 21 , 22 ], transesterification [ 23 , 24 , 25 ], olefin metathesis [ 26 , 27 ], silyl ether transalkoxylation [ 28 , 29 ], diketoenamine exchange [ 30 , 31 ], and dioxaborolane metathesis [ 32 , 33 ] have been proposed in the literature. Besides recyclability, many other adaptive properties of CANs were also investigated, such as reconfigurability [ 34 , 35 ], shape memory [ 36 , 37 ], and network topological transformation [ 18 , 25 , 38 ].…”