Abstract
New modifiers (i.e., acrylic syrups; ASs) of epoxy-resin-based thermally curable structural self-adhesive tapes (SATs) were prepared via a free radical bulk polymerization (FRBP) of n-butyl acrylate, butyl methacrylate, glycidyl methacrylate, and hydroxybutyl acrylate. In the process, two kinds of UV-photoinitiators (i.e., monoacylphosphine oxide/Omnirad TPO and bisacylphosphine oxide/Omnirad 819) and various mixing speed of the monomers mixture (200–1000 rpm) were applied. The TPO-based syrups exhibited a lower copolymers content (10–24 wt%), dynamic viscosity (<0.1 Pa·s), molecular weights (Mn and Mw, and polydispersity (1.9–2.5) than these with Omnirad 819. Additionally, the higher mixing speed significantly reduced monomers conversion and viscosity of ASs as well as molecular weights of the acrylate copolymers. These parameters influenced the properties of thermally uncured (e.g., adhesion) and thermally cured SATs (shear strength of aluminum/SAT/aluminum overlap joints). Better self-adhesive features were observed for SATs-TPO (based on ASs with lower monomers conversion, Mn and Mw); however, a slightly higher shear strength was noted for the thermally cured SAT-819 (ASs with higher monomers conversion, Mn and Mw). An impact of polydispersity of the acrylate copolymers as well as crosslinking degree of thermally cured SATs on the mechanical strength was also revealed.
Highlights
Epoxy resins (ERs) are widely used in coatings, adhesives, fiber-reinforced composites, electrical cast insulations, and other applications [1,2,3]; their high crosslinking density leads to low-impact and crack-propagation resistance of the materials
Acrylate copolymers can be incorporated into ERs in the form of hybrid nanoparticles consisting of an inorganic core and a reactive methacrylate-based shell
The following components were used for the preparation of the acrylic syrups (ASs): nbutyl acrylate (BA), butyl methacrylate (BMA), 2-hydroxyethyl acrylate (HEA) (BASF, Ludwigshafen, Germany), and glycidyl methacrylate (GMA) (Dow Europe, Horgen, Germany)
Summary
Epoxy resins (ERs) are widely used in coatings, adhesives, fiber-reinforced composites, electrical cast insulations, and other applications [1,2,3]; their high crosslinking density leads to low-impact and crack-propagation resistance of the materials. Many attempts have been made to improve these features, i.e., chemical and physical modification, including the incorporation of solid polymers or inorganic micro-and nanoparticles [4,5,6,7,8,9]. Copolymers of butyl acrylate (BA) and glycidyl methacrylate (GMA), prepared via an in situ polymerization process, were tested as impact modifiers of ERs [11]. Acrylate copolymers can be incorporated into ERs in the form of hybrid nanoparticles consisting of an inorganic core (silica or aluminum oxide) and a reactive methacrylate-based shell. Applications of epoxyacrylate copolymers (based on BA, GMA, and 2-hydroxyethyl acrylate) prepared by a conventional radical polymerization process in an organic solvent [16,17,18,19] or by bulk photopolymerization [20] are known
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