Synthesis of hydroxyl‐terminated poly(ether ether ketone) with pendenttert‐butyl groups and its use as a toughener for epoxy resins

Abstract

Hydroxyl-terminated poly(ether ether ketone) with pendent tert-butyl groups (PEEKTOH) was synthesized by the nucleophilic substitution reaction of 4,4 0difluorobenzophenone with tert-butyl hydroquinone with potassium carbonate as a catalyst and N-methyl-2-pyrrolidone as a solvent. Diglycidyl ether of bisphenol A epoxy resin was toughened with PEEKTOHs having different molecular weights. The melt-mixed binary blends were homogeneous and showed a single composition-dependent glass-transition temperature (T g ). Kelley-Bueche and Gordon-Taylor equations gave good correlation with the experimental T g . Scanning electron microscopy studies of the cured blends revealed a two-phase morphology. A sea-island morphology in which the thermoplastic was dispersed in a continuous matrix of epoxy resin was observed. Phase separation occurred by a nucleation and growth mechanism. The dynamic mechanical spectrum of the blends gave two peaks corresponding to epoxy-rich and thermoplastic-rich phases. The T g of the epoxy-rich phase was lower than that of the unmodified epoxy resin, indicating the presence of dissolved PEEK-TOH in the epoxy matrix. There was an increase in the tensile strength with the addition of PEEKTOH. The fracture toughness increased by 135% with the addition of high-molecular-weight PEEKTOH. The improvement in the fracture toughness was dependent on the molecular weight and concentration of the oligomers present in the blend. Fracture mechanisms such as crack path deflection, ductile tearing of the thermoplastic, and local plastic deformation of the matrix occurred in the blends. The thermal stability of the blends was not affected by blending with PEEKTOH.

Hydroxyl terminated poly(ether ether ketone) with pendant methyl group‐toughened epoxy clay ternary nanocomposites: Preparation, morphology, and thermomechanical properties

“…Data reveals that there is a marginal decrease in both tensile modulus and flexural modulus with the addition of PEEKMOH oligomer to the epoxy/DDS system. Similar observation was made by us earlier for epoxy-hydroxyl terminated tertiary butyl PEEK 24 and epoxy-hydroxyl terminated methyl PEEK systems. 23 It is known that the incorporation of clay into the epoxy matrix enhances tensile modulus and flexural modulus to a great extent.…”

“…However, no evidence of drastic increase in fracture toughness was reported in the open literature for epoxy clay nanocomposites. On the other hand, more than 100% increase in fracture toughness was observed by us 23,24 and others [26][27][28][29][30][31][32] for the thermoplastic-toughened epoxy systems. Frohlich et al 33 reported the improved toughness in rubber-toughened hybrid epoxy nanocomposites compared with nanocomposite without rubber.…”

“…It was reported that 4,4'-diamino diphenyl sulfone (DDS)-cured epoxy nanocomposites showed an exfoliated morphology with improved mechanical properties when dispersed through exerting shearing force on epoxy montmorillonite solution by ball milling. 19 The toughening effects of thermoplastic [21][22][23][24] and nanoclay 25 separately on the thermomechanical properties of epoxy systems have been studied enormously. However, no evidence of drastic increase in fracture toughness was reported in the open literature for epoxy clay nanocomposites.…”

Thermoplastic toughened layered silicate epoxy ternary nanocomposites—Preparation, morphology, and thermomechanical properties

“…The phase separation that occurred by nucleation and growth mechanism was due to off-critical composition of the thermoplastic in liquid epoxy as calculated by Flory-Huggins model [57]. Similar observations were made by us earlier for PEEK-MOH-and PEEKTOH [hydroxyl terminated poly(ether ether ketone) with pendant tertiary butyl groups] toughened epoxy systems [8,12]. Here gelation followed by vitrification occurred after the phase separation.…”

“…However, their brittle nature due to its high cross-link density and poor resistance to crack propagation limits the applications in advanced aerospace structures. To overcome this problem various Engineering thermoplastics like polyether sulfone [2,3], polycarbonate [4,5], polyethylene tere phthalate [6,7], poly ether ether ketone/hydroxyl terminated poly (ether ether ketone) with pendant methyl groups (PEEKMOH) [8,9], Poly ether ether ketone/hydroxyl terminated poly ether ether ketone with pendant tertiary butyl groups [10][11][12][13] or poly (cyanoarylene ether)/hydroxyl terminated poly arylene ether nitrile with pendant tertiary butyl groups [14,15] have been used as a toughness modifiers for epoxy resin without sacrificing other thermomechanical properties. However no evidence of improvement in modulus, gas barrier property and in coefficient of thermal expansion (CTE) was reported in the literature.…”