Vitrimers: A new class of polymeric materials with exchangeable covalent bonds

Document Type : compile

Authors

1 Faculty of Polymer Processing, Iran Polymer and Petrochemical Institute, Tehran, Iran.

2 Iran Polymer and Petrochemical Institute

3 Professor of Polymer Engineering at Iran Polymer & Petrochemical Institute

Abstract

Classically, polymers are subdivided into two main classes according to their thermal behavior: thermoplastics and thermosets. Vitrimers are a new class of polymers that combine the desired mechanical/chemical properties of thermosets with the reprocessability of thermoplastics. They are covalent networks with the ability to change their topology through reversible bond exchange reactions. The viscoelastic behavior of vitrimers is described using two transition temperatures. The first one is the usual glass transition temperature, Tg, between the glassy and rubbery state of polymer networks. The second transition temperature derives from the network cross-link exchange reactions. Hence, a transition from viscoelastic solid to viscoelastic liquid occurs at a temperature denoted as the topology freezing transition temperature. When vitrimers are heated above the topology freezing transition temperature, they can slightly flow like thermoplastics. In this state, total crosslink density remains constant, but the rate of bond exchange increases with temperature. This leads to a gradual decrease in viscosity with temperature, which differs from the relatively abrupt drop in viscosity associated with the melting transition of thermoplastic materials. Based on the viscoelastic behavior of vitrimers, they are capable to provide unique properties such as repairing, reshaping, and recycling. However, these materials have limitations such as low scalability, high cost, and low mechanical properties. In this paper, after explaining the above-mentioned issues, two applications of vitrimers in the preparation of reversible adhesives and durable prepregs are investigated.

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Articles in Press, Accepted Manuscript
Available Online from 20 June 2024

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