![]() ![]() A commercial and traditional bonding agent, Chemosil (see Materials and Methods), is used as the reference system. The different bonding systems are compared in terms of reactivity toward the EPDM rubber, and the impact of the ability of the primary amines to covalently link the polymer films inter- and intramolecularly is discussed. The fracture toughness ( ) and cohesive-to-adhesive fracture ratio ( A r) are used to quantify the adhesive strength and performance of the joints. Bonding properties are evaluated by peel testing and subsequent three-dimensional (3D) scanning of the fractured surfaces. Samples are then installed in a sample holder and compression-molded with EPDM rubber covalently linking rubber and polymer brushes (see Figure S1, Supporting Information). The brush films are analyzed by ellipsometry, infrared reflectance–absorption spectroscopy (IRRAS), and X-ray photoelectron spectroscopy (XPS). First, PGMA and PDEAEMA polymer brushes are grown from stainless steel (SS) along with PGMA polymer brushes modified using either allylamine, diallylamine, or propylamine as the nucleophile. The PGMA brushes can subsequently be modified, exploiting the fact that nucleophiles such as amines, (17,18) thiols, (19) and azides (20) are able to open the oxirane ring.įigure 1 presents an overview of the steps involved in this work. (13−16) Specifically, poly(glycidyl methacrylate) (PGMA) and poly (PDEAEMA) polymer brushes may be grown from various surfaces using a controlled radical polymerization. (2,12) Several methods have been designed to ensure both durability and high grafting densities of polymer brushes generating a nanometer-thin primer layer. Anchoring of polymer brushes to metal surfaces is a versatile approach of making a metal compatible with a given coating. In this work, we used the controlled radical polymerization approach because the aim was to produce brushes covalently anchored to the substrate with good control of length and with minimal cross-linking of the brushes. Several methodologies can be applied for a surface-confined polymerization, that is, free radical polymerization (thermal, photochemical, or radiochemical), controlled radical polymerization, anionic polymerization, or electropolymerization. For these reasons, development of highly efficient thin-layer primer systems would be desirable. (10,11) The challenge with these primers is that they are applied in large amounts (at least a few micrometers in thickness) and are unable to establish covalent bonds all the way from the metal surface to the rubber. Solution-based organic primers and binders are widely employed, and components such as chlorinated polymers and poly(butadiene) are required (among a variety of other additives) to obtain strong adhesion. (9) Still, pretreatment of the metal is the most extensively used approach to enhance metal–rubber adhesion. Functionalization of rubber includes halogenation, cyclization, or copolymerization with polar monomers to increase the wettability. One interesting approach for handling the adhesion issue is through a chemical modification of either the rubber or the metal. (8) Unfortunately, most rubbers have a low wettability, and it is hard to create adhesion to metals, rendering interlocking designs the common solution. (5−7) What makes rubber particularly efficacious for such applications is its high elasticity and resistance to oxygen, ozone, ultraviolet light, and heat. Cross-linking of polymer brushes by intermolecular reactions by the primary amines proved to have a significant impact on the type of fracture (cohesive/adhesive) and the performance of the adhesives.Īdhesion of rubber to a metal is important for various purposes, including bridge bearings, mounts in car engines, tires, and so on. The obtained values of (15.4 ± 1.1 N mm –1) and A r (1.00 ± 0.01) matched those obtained for a micrometer-thick commercial bonding agent. For the nanometer-thin PGMA films modified with allylamine, in particular, full cohesive fracture was obtained. Two parameters, the fracture toughness ( ) and the cohesive-to-adhesive fracture ratio ( A r), were calculated to evaluate the strength and the performance of the coupling, respectively. The efficiency of the novel bonding solution was evaluated through peel experiments. All samples were compression molded with uncured ethylene-propylene-diene M-class rubber and dicumyl peroxide and vulcanized for 12 min at 170 ☌. Stainless steel (SS) surfaces were grafted with poly(glycidyl methacrylate) (PGMA) brushes that were post-modified using allylamine, diallylamine, and propylamine as reagents.
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