Mapping crosslinking reaction–structure–property relationship in polyether‐based vinylogous urethane vitrimers

Abstract

Vitrimers with dynamic covalent bonds are sustainable alternatives for traditional thermosetting polymers. The variations of building block alter the properties of vitrimers, but obstruct detailed structure–property correlations. Besides, a recognizable crosslinking reaction is responsible for the network structures of vitrimers. Herein, we investigated the effects of building block variations (i.e., the content of crosslinker, and the type and molar mass of polymer matrix) on the crosslinking kinetics, as well as on the static and dynamic properties using polyether‐based vinylogous urethane vitrimers as model system. The kinetics of crosslinking tracked by in situ FTIR provides an insightful understanding on the vitrimer yield and formation rate under conditions. And the apparent rate coefficient (k) was linearly correlated to the crosslinking density (νe) in case of different polymer matrixes being used. In addition, based on the classical theoretical models we also realized the correlations between the static property (i.e., glass transition temperature, Tg) and νe, as well as the dynamic property (i.e., topology freezing temperature, Tv) and νe. Tg has been found to be exclusively positively related to νe, while Tv is jointly determined by νe and the content of free amine. This strategy to establish reaction–structure–property relationship bridged by the crosslinking density will guide the preparation of novel, tailor‐made sustainable polymeric materials.

Structure and Dynamics of Associative Exchange Dynamic Polymer Networks

“…Likewise, an apparent activation energy E a was calculated by the temperature dependence of relaxation time λ , that is, E a = 76.6 kJ/mol, which was closed to the value calculated from (82.8 kJ/mol in Figure d). The apparent activation energies of the dynamic vinylogous urethane exchange reaction (from the terminal relaxation time) are comparable with other vinylogous urethane vitrimers calculated from experiments or computational studies (∼55–102 kJ/mol). ,,,− …”

“…It is well known that the dynamics of CANs play a critical role in the processing and application of polymers, − which primarily rely on the effect of catalysts, sorts of linkages, , crosslinking degree, , and polymer matrix. , Current studies in the dynamics of CANs mainly focus on the dissociative state of reaction kinetics and molecular dynamics. For dissociative CANs, the bond exchange mechanism and dynamics have been clearly resolved due to the uncomplicated reactions, in which only one state exists, that is, dissociation-disconnect. ,− For instance, Pratchayanan et al prepared Diels–Alder (DA) crosslinked poly­(caprolactone) networks and studied the DA dissociation kinetics by correlating stress relaxation with the rate of retro-DA reaction.…”

Closed-Loop Recyclable Vinylogous Carbamothioate-Based Covalent Adaptable Networks

“…CANs containing VC dynamic covalent bonds were synthesized by cross-linking 2,2′-(ethylenedioxy)­diethanethiol-acetoacetate (EDT-AA) with tris­(2-aminoethyl)­amine (TREN), and the same procedure was performed to produce VU-based CANs as a control by replacing EDT-AA with triethylene glycol-acetoacetate (TEG-AA) (Figure A). The proportion of primary amine groups in the synthesis of CANs was 1.1 times that of acetoacetate groups to ensure efficient transamination of VC and VU moieties, according to our previous work . FTIR-ATR results of both CANs show that the characteristic absorption peaks of acetoacetate (1717 and 1741 cm –1 ) disappear, and the absorption peaks of VC (1572 and 1602 cm –1 ) and VU (1588 and 1646 cm –1 ) bonds are newly generated corresponding to VC and VU bonds, respectively, demonstrating that the curing is fully completed (Figure B).…”

“…The proportion of primary amine groups in the synthesis of CANs was 1.1 times that of acetoacetate groups to ensure efficient transamination of VC and VU moieties, according to our previous work. 46 FTIR-ATR results of both CANs show that the characteristic absorption peaks of acetoacetate (1717 and 1741 cm −1 ) disappear, and the absorption peaks of VC (1572 and 1602 cm −1 ) and VU (1588 and 1646 cm −1 ) bonds are newly generated corresponding to VC and VU bonds, respectively, demonstrating that the curing is fully completed (Figure 3B). Additionally, the absorption peak of C−S is detected at 838 cm −1 for the VCbased CAN.…”

Sustainable Polyurethane Networks with High Self‐Healing and Mechanical Properties Based on Dual Dynamic Covalent Bonds

“…[54] With the weight percentage of BDB/HTPB increasing, the crossing density firstly is increased and then is decreased as shown in Figure 3b, possibly because too much free -SH to decrease the crosslinking density, similar to the reported work. [55] At the ratio of HPS/HTPB = 5 and the weight percentage of BDB/HTPB = 20%, the crossing density is the highest of 16.9 × 10 −4 mol cm −3 as listed in Table 1. Meanwhile, compared with HHMB with duel dynamic covalent bonds, the HHMB-0-20 (0:1) with single boronic ester bonds show a lower crossing density of 5.2 × 10 −4 mol cm −3 , as shown in Figure 3a.…”