Reversible TAD Chemistry as a Convenient Tool for the Design of (Re)processable PCL‐Based Shape‐Memory Materials

Abstract

A chemically cross-linked but remarkably (re)processable shape-memory polymer (SMP) is designed by cross-linking poly(ε-caprolactone) (PCL) stars via the efficient triazolinedione click chemistry, based on the very fast and reversible Alder-ene reaction of 1,2,4-triazoline-3,5-dione (TAD) with indole compounds. Typically, a six-arm star-shaped PCL functionalized by indole moieties at the chain ends is melt-blended with a bisfunctional TAD, directly resulting in a cross-linked PCL-based SMP without the need of post-curing treatment. As demonstrated by the stress relaxation measurement, the labile character of the TAD-indole adducts under stress allows for the solid-state plasticity reprocessing of the permanent shape at will by compression molding of the raw cross-linked material, while keeping excellent shape-memory properties.

Click chemistry strategies for the accelerated synthesis of functional macromolecules

“…Bis-TAD reagents have also been envisaged for crosslinking polymers either along the backbone or through the side chains. [174][175][176][177][178][179][180][181] The thermal reversibility of the TAD-ene reaction with indole derivatives permits the network made by this chemistry to be healable and remoldable. 179 The high efficiency of TAD-based click chemistry allows surface modification to be completed within minutes, 182,183 while the TAD transclick reaction enables the preparation of rewritable polymer brush micropatterns.…”

“…This is an opportunity as main reaction partner of TAD are alkene and electron rich aromatic systems, which are abundant in both natural and synthetic polymers. TAD crosslinking applications can therefore involve (i) Alder-ene reaction with polymer containing isolated alkene 180,492,493 or indole, 177,178 (ii) DielsÀAlder reaction 494 with polymer containing conjugated diene, 174,180,181,494,495 and (iii) electrophilic aromatic substitution with phenol in polypeptide containing tyrosine derivatives. 172 The reversible bond between indole and TAD in Alder-ene reaction has inspired the "transclick" concept.…”

A Metallosupramolecular Shape‐Memory Polymer with Gradient Thermal Plasticity

“…The recently emerged thermal plasticity, which is achieved by dynamic covalent bond exchange in a SMP network, allows fabrication of highly complexed permanent shapes without being limited by traditional molding techniques. Since its discovery, a variety of dynamic covalent bonds have been demonstrated for achieving thermal plasticity in SMPs, including transesterification, transcarbamoylation, reversible TAD (1,2,4‐triazoline‐3,5‐dione) chemistry, and Diels–Alder reactions …”

“…[1] This progress has centered around the reversibility of the morphing, [5] versatility in temporary shape fixing, [6] and new stimulation mechanisms. [7] Innovations involving permanent shapes have been scarce,d espite the fact that practical applications often demand complexed permanent geometries.T he recently emerged thermal plasticity, [8] which is achieved by dynamic covalent bond exchange in aSMP network, allows fabrication of highly complexed permanent shapes without being limited by traditional molding techniques.Since its discovery,avariety of dynamic covalent bonds have been demonstrated for achieving thermal plasticity in SMPs,i ncluding transesterification, [8a] transcarbamoylation, [8c,9] reversible TAD (1,2,4-triazoline-3,5-dione)c hemistry, [10] and Diels-Alder reactions. [11] Theabove developments pose interesting challenges with respect to the preparation of SMP networks:1 )using noncovalent supramolecular bonds instead of dynamic covalent bonds to achieve thermal plasticity;2 )designing network thermal plasticity in as patio-selective manner that would further extend the shape morphing versatility.R egarding point one,the challenge lies in the fact that most supramolecular bonds,while intrinsically dynamic,donot simultaneously offer high bond strength and thermal switchability.A n exception is the metal-ligand interaction (or metallobond), [12] which is not only switchable but also possesses bond strength rivaling typical covalent bonds.B ecause of these features,metal-ligand interactions have shown distinct advantages in designing self-healing polymers.…”

Thermally amendable tailor‐made acrylate copolymers via RAFT polymerization and ultrafast alder‐ene “click” chemistry

“…The major demerit of such reactions is many of these processes (e.g., DA reaction) are time‐consuming and require elevated temperatures for completion of the reaction. The introduction of 1,2,4‐triazoline‐3,5‐dione (TAD) chemistry in macromolecular system attracted the attention of polymer chemists, as the TAD reactions are very fast and occurred within few seconds even at milder reaction conditions. Recently we reported the preparation of thermoreversible self‐healable polymer based on homopolymer of 2‐hydroxyethylmethacrylate (HEMA) via RAFT polymerization and Alder‐ene reaction using a TAD derivative.…”