Click polymer networks

Keywords Click reaction Crosslinked hydrogels Smart polymers Amphiphilic polysaccharides Supramolecular hydrogels Star polymers Ordered polysaccharides Interpenetrating polymer networks Antibiofilm... 

A new and elegant solvent-free approach to main chain LCEs was found by Yang et al. [39] who, based on the work on linear LC polymers by Lub et al. [40 2], made use of the photo-induced addition of thiols and olefins (click-chemistry) to synthesize nematic polymer networks. Starting from a mixture of the mesogen, a tetrafunctional crosslinker and a photo-initiator networks with a around 170 °C were obtained by UV crossUnking (Scheme 8). 

Several chemically degradable triazole-based polymer networks (e.g., 72) were reported by Finn and coworkers [70]. The network was constructed by the click cross-linking of a linear a,0)-bifunctional diazide polymer 73 cOTitaining a double bond in the polymer main chain with either a triacetylene 74 or a tetraacetylene 75... 

Scheme 9.2 Possible architectures accessible by click chemistry, (a) Block copolymers, (b) star-shaped polymers, (c) cyclic polymers, (d) graft polymers, (e) backbone modification, (f-h) network formation using...

The copper-catalyzed azide/alkyne click reaction has found the broadest application in the modification of ROMP polymers, with the first reported example in 2004 by Binder and Kluger [13]. Since then, the copper-catalyzed click reaction has been used for the preparation of block copolymers [24, 29, 37], stars [18, 26], cycles [23], networks [25], and graft copolymers [27, 28, 38, 56, 57], as well as for end- [16] and side-chain-functionalized polymers [13, 17, 19-22, 48]. The most often used catalysts and bases for the azide/alkyne click reaction include copper(l) iodide, copper(l) bromide, trisftriphenylphosphine) copper(l) bromide, or copperfll) sulfate/sodium ascorbate as catalyst and diisopropylethylamine (DIPEA), pentamethyldiethylenetriamine (PMDETA), or 2,2 -bipyridine (bPy) as base. 

Madsen FB, Dimitrov I, Daugaard AE et al (2013) Novel cross-linkers for PDMS networks for controlled and well distributed grafting of fimctionalMes by click chemistry. Polym Chem... 

Johnson, J.A., Firm, M.G., Koberstein, J.T., and TUrro, N.J. (2008) Construction of Unear polymers, dendrimers, networks, and other polymeric architectures by copper-catalyzed azide-alkyne cycloaddition click chemistry. Macromolecular Rapid Communications, 29,1052. 

CCS can be introduced into injectable materials by separately modifying soluble polymer chains with a pair of molecules that have specific affinity to each other. When these modified polymeric chains are injected simultaneously to the cross-linking site, they undergo rapid cross-linking to give rise to a covalent cross-linked network. The most commonly used pairs of molecules with specific affinities towards each other are iV-hydr-oxysuccinimide (-NHS) to amine (-NH2), 1,4-addition of a doubly stabilized carbon nucleophile to an a,p-unsaturated carbonyl compound (Michael-type addition reaction), and alkyne to azide (click chemistry). In these types of reactions, the rate, stability, and kinetics of network formation are solely dependent upon the strength of the affinity of one molecule to its counterpart. 

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