Stainless steel (SS)
surfaces were grafted with poly(glycidyl methacrylate)
(PGMA) brushes that were post-modified using allylamine, diallylamine,
and propylamine as reagents. Likewise, poly[2-(diethylamino)ethyl
methacrylate] brushes were synthesized. All samples were compression
molded with uncured ethylene-propylene-diene M-class rubber and dicumyl
peroxide and vulcanized for 12 min at 170 °C. The efficiency
of the novel bonding solution was evaluated through peel experiments.
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. For
the nanometer-thin PGMA films modified with allylamine, in particular,
full cohesive fracture was obtained. 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. 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.
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.
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