Low‐Temperature Cu(I)‐Catalyzed “Click” Reactions for Self‐Healing Polymers

Abstract

Systematic investigations on the Cu(I)-catalyzed "click" reaction between a three-arm star polymer and low-molecular-weight alkynes are described. Liquid trivalent alkynes ( 2 -7 ) are reacted either with monovalent azidotelechelic polyisobutylene 1b ( M n = 1900 g mol − 1 , PDI = 1.3) in solution, or with the trivalent azidotelechelic polyisobutylene 1a ( M n = 4000 g mol − 1 , PDI = 1.3). A signifi cant autoacceleration is observed leading to increased reaction rates of the mono-, di-, and trisubstituted alkynes. Reaction in the solvent-free state proved to be signifi cantly faster than reaction in solution. Upon testing various Cu(I) catalysts, CuBr(PPh 3 ) 3, tripropargylamine 2 emerges as the ideal component for a room-temperature "click" reaction with the threearm star polyisobutylene 1a .components displaying suffi cient (high) molecular mobility to allow subsequent formation of a supramolecular or covalent network. Thus, liquid components (DCPD or derivatives, liquid epoxides) or molecules with low molecular weights (corresponding to high mobility) are used preferentially, in order to keep the time scale of diffusion suffi ciently short as to allow physical contact between the interacting molecules. We recently have reported [ 13 ] on a chemical self-healing polymer (see Figure 1 ), where two reactive liquid (polymeric) components are embedded into separate capsules, subsequently reacting after rupture of the capsule by mechanical deformation and destruction. In contrast to similar systems reported in the literature, our approach uses the azide/alkyne "click" reaction [14][15][16] as the underlying chemical "addition" reaction to effect crosslinking between a multivalent (polymeric) liquid azide 1a and the trivalent alkynes 2 and 6 (see Scheme 1 ). To effect the encapsulation of polymer 1a , an emulsion method was developed, generating urea/formaldehyde capsules with incorporated (fl uorescently) labeled polymer. The two different capsules were then embedded into a polymeric matrix containing added Cu(I) catalyst and base, leading to effect a separate location of the capsules in the matrix, which release their contents after mechanically induced rupture and subsequent crosslinking reaction. The so-induced "click" reaction leads to a measureable reaction rate of several days at temperatures of 40 ° C. The present

Self-healing polymeric materials based on microencapsulated healing agents: From design to preparation

“…In a recent report, the authors further analyzed the reactivities of different alkynes using different Cu(I)-based catalysts [270]. A significant autoacceleration of the reaction was observed, leading to increased rates of the azide/alkyne "click" using mono-, di-, and trisubstituted alkynes.…”

Kinetic Study of the Thermal Polymerization Reactions between Diazide and Internal Diyne

“…Its application in numerous areas has highlighted the value of its benign reaction conditions, functional tolerance, simple workup, and purification procedures. Hence, these long‐neglected reactions were suddenly reestablished in organic synthesis and, in particular, have gained popularity in materials science nowadays .…”

Self-healing hyperbranched poly(aroyltriazole)s

“…Though the alkyne-azide click reactions have been used to prepare self-healing polymers, the focus was on the Cu( i )-catalyzed systems5051525354, which are heterogeneous due to the catalyst additives and make the healing process complicated. For example, Binder and coworkers have applied this reaction to prepare self-healing polymers but with the encapsulated-monomer strategy5051.…”

“…For example, Binder and coworkers have applied this reaction to prepare self-healing polymers but with the encapsulated-monomer strategy5051. In this contribution, we report an irreversible covalent-bonded self-healing system based on hb -PATAs.…”