Generic, Metal-Free Cross-Linking and Modification of Silicone Elastomers Using Click Ligation

Abstract

Silicone elastomers are widely used in a variety of biomaterials applications. Their high hydrophobicity can, in some cases, compromise their utility. There exist few convenient, efficient and metal-free processes to introduce hydrophilic groups onto the elastomer surface. We describe the utilization of the metal-free click reaction between azido-and alkynyl-modified silicones to both cross-link and functionalize silicone elastomers. Initial crosslinking at, optionally, reduced or elevated temperatures depending on the alkyne used, results in elastomers whose moduli and tackiness can be controlled by manipulation of cross-link density through use of different chain length constituents: the systematic capping of azides on the azide-rich partner provides a level of control of both cross-linking and residual functionality after cross-linking. The residual azides or alkynes resulting from nonstoichiometric mixing of the starting materials can be used for sequential functionalization of the elastomer as shown through the improved wettability that results from the grafting of alkyne-functional PEG to azide-rich silicone elastomers: contact angles decrease from ∼105°for the pure silicone elastomers to 85°for the aziderich silicone elastomer, and to as low as 41°for the PEG-modified product. It is possible to modify the entire elastomer body or only the surface by judicious choice of the solvent used for the hydrophilic modification.

Thermally controlled silicone functionalization using selective Huisgen reactions

“…All materials were used as received. 1,3-Bis(azidopropyl)tetramethyldisiloxane 1 [6], benzyl propiolate 3 [15], benzyl propiolamide 5 [16], propargyl-terminated disiloxane 12 [17], and benzyl azide [18] were prepared according to literature procedures.…”

“…The analogous amide 6 was prepared by the DCC amidation of commercial 3-aminopropylmethylbis(trime thylsiloxy)silane 10 with propiolic acid. Terminal alkynes, amides 11 and esters 12 [17], respectively, were prepared using analogous carbodiimide coupling chemistry with a, x-difunctional disiloxanes (Fig. 1C).…”

Surface modification of silicone via colloidal deposition of amphiphilic block copolymers

“…9,10 Alternatively, the biomaterial can be modified only at its surface, without altering its bulk properties. For example, protein-repellent and biocompatible groups have been introduced on PDMS surfaces with a number of macromolecular structures, which include poly(ethylene glycol) (PEG), [11][12][13][14][15][16][17] poly(2-methacryloyloxyethyl phosphorylcholine), [18][19][20] poly(3-sulfopropyl methacrylate), 21 poly(N-vinylpyrrolidone) 22 and poly(2-hydroxyethyl methacrylate). 23 Here, we have focused on a different hydrophilic structure that provides the advantageous combination of abundance of groups for chemical functionalization and the potential of a "stealth" behaviour: poly(2,3-dihydroxypropyl methacrylate), more commonly referred to as poly(glycerol monomethacrylate) (PGMMA), which features two vicinal alcohols on each repeating unit.…”

“…As for the functionalization, we have discarded the covalent attachment, either in a "grafted to" 11,17 or in a "grafted from"…”

Amphiphilic thermoset elastomers from metal-free, click crosslinking of PEG-grafted silicone surfactants

“…30 This strategy was used to create thermoset elastomers (hereafter referred to as elastomers) containing excess reactive groups (azido-or alkynyl-) that could subsequently graft hydrophilic macromolecules and polymers (such as alkynyl-PEG) to create a more hydrophilic elastomer surface. 31 It was also demonstrated that alkynyl-PEG could be grafted onto an azido-functional PDMS backbone using the metal-free strategy at less than stoichiometric ratios, preserving reactive groups for controlled sequential functionalization. 32 Herein, we report an extension of the metal-free methodology for the preparation of amphiphilic silicone-PEG networks that involves first creating PDMS-g-PEG surfactants containing reactive azido groups that can subsequently be used to crosslink alkyne-terminated PDMS.…”