Fast Dynamic Siloxane Exchange Mechanism for Reshapable Vitrimer Composites

Abstract

To develop siloxane-containing vitrimers with fast dynamic characteristics, different mechanistic pathways have been investigated using a range of catalysts. In particular, one siloxane exchange pathway has been found to show a fast dynamic behavior in a useful temperature range (180−220 °C) for its application in vitrimers. The mechanism is found to involve 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) as an organic catalyst in the presence of hydroxyl groups. Using this new mechanistic approach, vitrimers with ultrafast stress-relaxation characteristics (relaxation times below 10 s) have been prepared with a readily available epoxy resin and siloxane-amine hardener. Subsequently, the low viscosity siloxane-containing vitrimer resin enabled the preparation of glass fiber-reinforced vitrimer composites using an industrially relevant vacuum-assisted resin infusion technique. The resulting composite was successfully thermoformed into a new shape, which makes it possible to envision a second life for such highly engineered materials.

Self-Healable Covalently Adaptable Networks Based on Disulfide Exchange

“…Additionally, as the test temperature increased from 100 °C to 130 °C, the relaxation time decreased from 3487 s to 373 s for P3 ( Figure 5 c), and from 1110 s to 174 s for P4 ( Figure 5 d). To deeply study the energy required for the macroscopic flow of the material, the activation energy ( E a ) of polymer films was calculated using the Arrhenius equation: τ = τ 0 × exp ( E a / RT ) [ 48 , 49 , 50 , 51 ] and is shown in Figure 5 c,d. The E a of the polymer films was in the following order: P3 (94 kJ/mol) > P4 (72 kJ/mol) > P1 (61 kJ/mol) > P2 (51 kJ/mol), demonstrating that the disulfide bond decreased the activation energy for the same type of film system.…”

Vitrimer composites: current status and future challenges

“…So far, only one article related to composites has been published, referring to the use of siloxane exchange for making fibre-reinforced composites. 49 VIT (polymer engineering via molecular design: embedding electrical and optical properties into VITrimers) proposes to endow vitrimers with desirable optical and electrical properties which retain their properties after recycling, fulfilling the circular economy paradigm. Coordinated by the University of Parma, the project gathers 10 academic research groups from 3 different continents (Europe, America, and Asia) and 2 highly innovative companies.…”

“…It is a very appealing chemistry for dynamic materials as it has intrinsic characteristics such as high chemical and thermal stability. Although a typical silyl ether material exhibits slow exchange, 48 a recent discovery by Debsharma and co-workers reported much faster exchanges based on a new pathway involving siloxanes and a base catalyst: 1,5,7-triazabicyclo[4.4.0] dec-5-ene 49 (Fig. 2vi(a)).…”

“…Recently, a low-viscosity resin (300 mPa s) based on siloxane exchanges was especially designed for the preparation of glass fibre-reinforced composites. 49 The composite was prepared via infusion using the VARI technique (vacuum assisted resin infusion), which is a widely used technique for the manufacturing of wind turbine blades. The produced composite was fully transparent and appeared defect-free but some fibre wrinkling was observed in the longitudinal section.…”

Renewable Plant Oil-Based Polysiloxane Coatings with Efficient Frost Resistance and Anti-Icing Properties

“…Polysiloxanes as one of the common synthetic polymers are usually produced from feedstocks of limited petroleum-based resources. 14 The fast depletion of global nonrenewable fossil feedstocks gives rise to serious resource crisis and environmental concerns. Recently, the development of polymeric materials from biomass has been intensively pursued by scientists.…”