Morphology, toughness mechanism, and thermal properties of hyperbranched epoxy modified diglycidyl ether of bisphenol A (DGEBA) interpenetrating polymer networks

Abstract

New hyperbranched poly(trimellitic anhydride-triethylene glycol) ester epoxy (HTTE) is synthesized and used to toughen diglycidyl ether of bisphenol A (DGEBA) 4,4(-diaminodiphenylmethane (DDM) resin system. The effects of content and generation number of HTTE on the performance of the cured systems are studied in detail. The impact strength is improved 2--7 times for HTTE/ DGEBA blends compared with that of the unmodified system. Scanning electron microscopy (SEM) of fracture surface shows cavitations at center and fibrous yielding phenomenon at edge which indicated that the particle cavitations, shear yield deformation, and in situ toughness mechanism are the main toughening mechanisms. The dynamic mechanical thermal analyzer (DMA) analyses suggest that phase separation occurred as interpenetrating polymer networks (IPNs) for the HTTE/DGEBA amine systems. The IPN maintains transparency and shows higher modulus than the neat epoxy. The glass transition temperature (T g ) decreases to some extent compared with the neat epoxy. The T g increases with increase in the generation number from first to third of HTTE and the concentrations of hard segment. The HTTE leads to a small decrease in thermal stability with the increasing content from TGA analysis. The thermal stability increases with increase in the generation number from first to third. Moreover, HTTE promotes char formation in the HTTE/DGEBA blends. The increase in thermal properties from first to third generation number is attributed to the increase in the molar mass and intramolecular hydrogen bridges, the increasing interaction of the HTTE/ DGEBA IPNs, and the increasing crosslinking density due to the availability of a greater number of end hydroxyl and end epoxide functions.

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

“…Several authors reported that the addition of HBPs reduced the T g of the modified thermosets due to the aliphatic nature of the HBPs studied. [1,2,31,32] In the present study, the presence of aromatic structures and the covalent linkage of phenolic groups to the epoxy matrix help the T g of the materials to be practically maintained, but in general a slight decrease is observed on increasing the proportion of modifier. On decreasing the DB of the GBPEX this value also decreases due to the reduction of covalent bonding of the modifier to the epoxy matrix.…”

Properties and morphology of interpenetrating polymer networks based on poly(urethane-imide) and epoxy resin

“…[26][27][28][29] But for poly(urethane-imide) modified epoxy resin, the T max1 of epoxy resin at 202.0 o C disappeared while shift to higher temperature. It suggests that there is no dehydration of hydroxyl occurs due to the reaction of -NCO of the polyurethane and -OH of epoxy resin, which is also consistent with the IR analysis.…”

Tailored thermal and mechanical properties of epoxy resins prepared using multiply hydrogen‐bonding reactive modifiers

“…[2][3][4][5] The most feasible approach of improving the properties of epoxy resins is incorporating general additive or reactive-type compounds within them. Three approaches have been adopted in previous studies to eliminate the brittleness of epoxy resins while ensuring high impact strengths and elongations after curing: (1) adding or in situ formation of rubber or thermoplastic particles into the epoxy matrix (these materials act merely as additives), [6][7][8] (2) introducing long-chain molecules into the epoxy resins during the curing process, 9,10 and (3) increasing the crosslinking density or enhancing the strength and number of intermolecular forces. 5,[11][12][13] The major problem encountered with the first two methods are incompatibility between the modifiers and epoxy resins which leading to the decrease of glass transition temperatures (T g ) and phase separation.…”