Abstract
In this study, we used diglycidyl ether bisphenol A (DGEBA) as a matrix, the ABA block copolymer poly(ethylene oxide–b–propylene oxide–b–ethylene oxide) (Pluronic F127) as an additive, and diphenyl diaminosulfone (DDS) as a curing agent to prepare flexible epoxy resins through reaction-induced microphase separation (RIMPS). Fourier transform infrared spectroscopy confirmed the existence of hydrogen bonding between the poly(ethylene oxide) segment of F127 and the OH groups of the DGEBA resin. Small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy all revealed evidence for the microphase separation of F127 within the epoxy resin. Glass transition temperature (Tg) phenomena and mechanical properties (modulus) were determined through differential scanning calorimetry and dynamic mechanical analysis, respectively, of samples at various blend compositions. The modulus data provided evidence for the formation of wormlike micelle structures, through a RIMPS mechanism, in the flexible epoxy resin upon blending with the F127 triblock copolymer.
Highlights
Epoxy resins have good mechanical integrity, high thermal stability, ready processability, good chemical resistance to solvents and moisture, and exceptional adhesion to many materials
We used Fourier transform infrared (FTIR) spectroscopy to ascertain whether hydrogen bonding was occurring within the (DGEBA + diphenyl diaminosulfone (DDS))/F127 blend system
The broad peak centered at 3480 cm–1 for diglycidyl ether bisphenol A (DGEBA) became broader when it was blended with F127 at increasing DGEBA concentrations, suggesting that hydrogen bonding was occurring between the OH groups of DGEBA and the ether groups of both the poly(ethylene oxide) (PEO) and PPO segments
Summary
Epoxy resins have good mechanical integrity, high thermal stability, ready processability, good chemical resistance to solvents and moisture, and exceptional adhesion to many materials. Many attempts have been made to enhance the toughness of crisp epoxy resins through the self-assembly of amphiphilic block copolymers that form ordered or disordered nanostructures within thermoset polymers [14,15,16,17,18]. These amphiphilic block copolymers often contained block segments that are miscible and immiscible with epoxy resin; for example, Materials 2016, 9, 449; doi:10.3390/ma9060449 www.mdpi.com/journal/materials. We used Fourier transform infrared (FTIR) spectroscopy to investigate the hydrogen bonding interactions within these flexible epoxy resins; small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) to examine their microphase separation behavior; and differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) to study their mechanical and thermal properties
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