Curing behavior and toughening performance of epoxy resins containing hyperbranched polyester

Abstract

The effects of the hyperbranched polyester with hydroxyl end groups (HBPE-OH) on the curing behavior and toughening performance of a commercial epoxy resin (diglycidyl ether of bisphenol A, DGEBA) were presented. The addition of HBPE-OH into DGEBA strongly increased its curing rate and conversion of epoxide group due to the catalytic effect of hydroxyl groups in HBPE-OH and the low viscosity of the blend at curing temperature. The improvements on impact strength and critical stress intensity factor (or fracture toughness, K 1c ) were observed with adding HBPE-OH. The impact strength was 8.04 kJ m À1 when HBPE-OH reached 15 wt% and the K 1c value was approximately two times the value of pure epoxy resin when HBPE-OH content was 20 wt%. The morphology of the blends was also investigated, which indicated that HBPE-OH particles, as a second phase in the epoxy matrix, combined with each other as the concentration of HBPE-OH increased. HBPE-OH has on average eight -OH end groups per molecule. DGEBA was supplied by Wuxi Resin Factory, China, with an epoxide value of 0.51-0.53 mmol g À1 . mPDA, as a curing agent, was supplied by Shanghai First Reagent Co., China. These materials were used as received without further purification. The chemical structures of the epoxy resin, hardener, and HBPE-OH are shown in Fig. 1.

Influence of end groups in hyperbranched polyesters used as modifiers in the characteristics of epoxy thermosets cured by adipic dihydrazide

“…The best formulation in terms Tomuta et al -eXPRESS Polymer Letters Vol.7, No.7 (2013) 595-606 Figure 6. Derivatives of the TGA curves in N 2 atmosphere for the thermosets obtained It is possible to prove that the modification of DGEBA/AH thermosets with all the HBPs synthesized improves this value, as it was reported in previous publications on epoxy/ amine or anhydride systems [28].…”

The Effect of the Degree of Branching in Hyperbranched Polyesters Used as Reactive Modifiers in Epoxy Thermosets

“…[21,24,25] On the contrary, cationic curing allows the reaction of hydroxyl-functional HBPs with epoxides to take place by means of the AM mechanism. This leads to chain transfer reactions that produce the covalent incorporation of hydroxyl-group containing structures to the epoxy matrix.…”

New Improved Thermosets Obtained From Diglycidylether of Bisphenol A and a Multiarm Star Copolymer Based on Hyperbranched Poly(glycidol) Core and Poly(methyl methacrylate) Arms

“…[ 8,9,29 ] However, until now, not many data are available concerning the effect of multiarm star polymers as modifi ers for epoxy resins on the impact strength. [ 25 ] The effect of adding PGOH-b -PMMA to the formulations in the impact strength is shown in Figure 6 A.…”