Facile Access to Disulfide/Thiol Containing Poly(glycidyl methacrylate) Brushes as Potential Rubber Adhesive Layers

Abstract

Creating interchain cross-links can improve the stability and robustness of polymer brushes. Unfortunately, the synthetic strategies required for this are often tedious and time-consuming, making their scale-up difficult, if not impossible. Herein, we utilize polysulfides to cross-link poly­(glycidyl methacrylate) (PGMA) brushes grafted from stainless steel in a fast and simple step, converting the PGMA brush to a strong nanoscale adhesive layer for bonding stainless steel and ethylene–propylene–diene M-class rubber (EPDM). The polymer brush is cross-linked in aqueous solution, and the polysulfides are made from inexpensive and widely available reagents. The cross-linking introduces 10.9% sulfur in the film according to X-ray photoelectron spectroscopy, and Raman spectroscopy showed bands ascribed to S n (n ≥ 2) species. The polysulfide cross-links may be cleaved using dithiothreitol, resulting in an uncross-linked, thiol-functionalized polymer-brush coating. When used as an adhesive layer for bonding steel and EPDM rubber, the cross-linked polymer film displays higher fracture toughness (comparable to a commercial bonding agent) than the uncross-linked film and gives cohesive failure rather than the adhesive failure seen in the latter case. We anticipate that the industrial scale-up of the procedure using, e.g., dip coating, is straightforward considering that it uses inexpensive chemicals, is oxygen tolerant, takes place in aqueous solution, and can be accomplished within half a minute.

Enzymatic and Chemical Approaches for Post‐Polymerization Modifications of Diene Rubbers: Current state and Perspectives

“…Thiol-based reactions are the most popular click chemistry methodology applied to rubbers and comprise a family of reactions like the thiol-ene, [96] thiol-yne, [119,120] thiol-halogen, [121] thiol-epoxy, [122][123][124][125] thiol-isocyanate, [126] which are often described as thiol-X reactions. Thiol additions can also proceed through Michael additions in the presence of catalyst.…”

Polymer Brush Coating and Adhesion Technology at Scale

“…In some cases, a post-polymerization modification of the polymer brushes is necessary to introduce the reactive handles, because the presence of these functional groups in the monomer is incompatible with the ATRP reaction. Poly(glycidyl methacrylate) (PGMA) has been utilized for post-polymerization modifications in a wide array of systems, because the epoxide groups are compatible with the ATRP process and react readily with nucleophiles such as thiols [ 42 ], polysulfides [ 43 ], azides [ 36 ], and amines [ 44 ]. Functional groups introduced in the polymer brush in the post-polymerization modification may react and form covalent bonds to the adherend e.g., at elevated temperatures or with pressure in a molding process.…”

“…In a recent associated work by Buhl et al, a post-polymerization modification of PGMA brushes with sodium polysulfides was exploited to form sulfide cross-linked polymer brushes, which during overmolding and vulcanization with sulfur-cured EPDM rubber, reacted and formed cross-links ( Figure 2 ) [ 43 ]. Notably, the post-polymerization modification was extremely fast (<30 s) and was conducted in an aqueous solution.…”

“… Illustration of ( A ) sulfide cross-linked polymer brushes and ( B ) uncross-linked thiol-containing polymer brushes both with C–S bonds to EPDM rubber, adapted from Buhl et al [ 43 ]. …”

Adhesion Promoting Copolymer of Acetate-Protected Vinyl Catechol with Glycidyl Methacrylate: Unraveling Deprotection, Adsorption, and Adhesion Behaviors on Metal Substrates

“…Several surface treatment methods have been reported to strengthen the interfacial interactions between epoxy adhesives and adherends. − For example, cleaning surfaces through plasma/UV irradiation can form hydroxyl groups and effectively increase the wettability of adhesives on the adherend surfaces. , Nevertheless, the improved interactions remain to be the secondary bonding interactions such as van der Waals bonds or hydrogen bonds, which are inherently weak (10–50 kJ/mol), and the improved wettability is usually not maintained for a long period when stored under the ambient conditions . In contrast, coating a thin primer layer on the adherend surface containing reactive functional groups such as amine or epoxide units is a feasible and commonly used approach to form stronger primary bonding (300–500 kJ/mol) for epoxy/amine-based adhesive systems. , …”