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. 2023 Feb 13;15(4):926.
doi: 10.3390/polym15040926.

Influence of Methacrylate and Vinyl Monomers on Radical Bulk Photopolymerization Process and Properties of Epoxy-Acrylate Structural Adhesives

Konrad Gziut  1 , Agnieszka Kowalczyk  1 , Beata Schmidt  1 , Tomasz J Idzik  2 , Jacek G Sośnicki  2
Affiliations

Influence of Methacrylate and Vinyl Monomers on Radical Bulk Photopolymerization Process and Properties of Epoxy-Acrylate Structural Adhesives

Konrad Gziut et al. Polymers (Basel). .

Abstract

In this paper, epoxy-acrylate structural adhesives tapes (SATs) were obtained from Bisphenol A-based liquid epoxy resin and epoxy acrylic resins (EARs). A new method of EARs preparation, i.e., the free radical bulk photopolymerization process (FRBP), was studied in detail. The influence of methacrylic monomers (methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, (2-acetoacetoxy)ethyl methacrylate) and vinyl monomers (N-vinylpyrrolidone and styrene) on the FRBP process of base monomers (i.e., butyl acrylate, glycidyl methacrylate and 2-hydroxyethyl acrylate) was investigated. The kinetics of photopolymerization process was monitored by photo-differential scanning calorimetry method. The properties of the obtained EARs (viscosity and average molecular weights), as well as monomers conversion using 1H NMR, were determined. It was revealed that styrene significantly decreases the photopolymerization rate and increases the final monomers conversion (+27%). However, the resulting tetrapolymers BA-co-GMA-co-HEA-co-STY have low molecular weights and low polydispersity (2.2). Methacrylate monomers with shorter aliphatic chains (<C4) also decrease the rate of photopolymerization due to the length of the aliphatic chain increasing. Surprisingly, the best results of adhesion to steel and shear strength were obtained for SAT based on epoxy acrylate resin with styrene (11 N/25 mm and 20.8 MPa, respectively). However, the thermomechanical properties of SAT with styrene were weaker than those with methacrylates.

Keywords: adhesion; epoxy acrylates; photopolymerization; polymer synthesis; structural adhesives; thermal analysis.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Preparation of epoxy acrylic resins via free-radical photopolymerization process.
Figure 2
Figure 2
Preparation of SATs and Al/SAT/Al joints.
Figure 3
Figure 3
The photopolymerization rates (a) and monomers conversions (b) of the base composition (reference sample) and the compositions with the additional comonomer.
Figure 4
Figure 4
Temperature during the bulk photopolymerization process in glass reactor.
Figure 5
Figure 5
Stacked plot of the proton nuclear magnetic resonance (1H NMR) spectra of epoxy acrylic resins. Peaks monitored for each monomer and the internal standard (naphthalene) are indicated.
Figure 6
Figure 6
DSC thermographs of the UV-crosslinked SATs (a) and SATs after UV-crosslinking and thermal curing (b).
Figure 7
Figure 7
Adhesion to steel of UV-crosslinked SATs.
Figure 8
Figure 8
Tack to steel of UV-crosslinked SATs.
Figure 9
Figure 9
Shear strength of thermally cured aluminum–SAT–aluminum overlap joints (a) and view of aluminum panels after shear strength test (b).
Figure 10
Figure 10
Storage modulus (E′) of thermally cured SATs.
Figure 11
Figure 11
Tangens delta (tan δ) of thermally cured SATs.
See this image and copyright information in PMC

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