An epoxy‐ended hyperbranched polymer as a new modifier for toughening and reinforcing in epoxy resin

Abstract

A new epoxy-ended hyperbranched polyether (HBPEE) with aromatic skeletons was synthesized through one-step proton transfer polymerization. The structure of HBPEE was confirmed by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) measurements. It was proved to be one high efficient modifier in toughening and reinforcing epoxy matrix. In particular, unlike most other hyperbranched modifiers, the glass transition temperature (T g ) was also increased. Compared with the neat DGEBA, the hybrid curing systems showed excellent balanced mechanical properties at 5 wt % HBPEE loading. The great improvements were attributed to the increased cross-linking density, rigid skeletons, and the molecule-scale cavities brought by the reactive HBPEE, which were confirmed by dynamical mechanical analysis (DMA) and thermal mechanical analysis (TMA). Furthermore, because of the reactivity of HBPEE, the hybrids inclined to form a homogenous system after the curing. DMA and scanning electron microscopy (SEM) results revealed that no phase separation occurred in the DGEBA/HBPEE hybrids after the introduction of reactive HBPEE. SEM also confirmed that the addition of HBPEE could enhance the toughness of epoxy materials as evident from fibril formation.

Epoxy/anhydride thermosets modified with end-capped star polymers with poly(ethyleneimine) cores of different molecular weight and poly(ε–caprolactone) arms

“…In order to determine the potential application of the prepared materials as coatings, the generation of thermal stress during cooling of neat and PEI250 and PEI8 formulations on steel as a rigid substrate were studied using the Benabdi and Roche methodology described in the experimental section [23]. In a previous work, we demonstrated that the intrinsic stress generated during curing of an epoxy system, due to rearrangement of molecular structure, and the thermal stress generated in the rubbery state, are much lower than the thermal stress generated on cooling down from the T g to room temperature [14,20], therefore in the present work we only calculate the thermal stress originated on cooling. Table 4 collects the thermal stress values, # th , calculated using Equations (7) and (8) increases slightly.…”

“…Effective toughening is believed to occur with an intermediate interfacial bonding, since an excessive adhesion can deteriorate the interfacial adhesion between the toughener phase and the matrix [36]. In previous works we observed that polymeric modifiers with excessive physical-chemical compatibility with the matrix led to their covalent incorporation into the network structure, preventing phase separation and producing very little toughness enhancement, whereas polymers that phase-separate during curing but with certain physical-chemical compatibility with the matrix led to the highest increase in impact strength [14]. Although it is not possible to know the amount of amine groups that react during curing, it is reasonable assuming the formation of some covalent bonds between the remaining amine groups at the core of the star polymer and the epoxy groups.…”

“…Recently, a significant toughening effect has been achieved without compromising other properties and processability by using dendritic polymers, especially if the structure and properties of the modifier have been tailored to enhance the physical and chemical interaction between them and the matrix. The improvement in toughness can be achieved by chemically induced phase separation (CIPS) or by in situ homogeneous reinforcing and toughening mechanism, but in both cases covalent linkages or a good compatibility between the modifier and the matrix are necessary [8][9][10][11][12][13][14][15][16]. The thermal stresses generated during cooling of thermosetting coatings applied over metal can be minimized by reducing the CTE and elastic modulus in the glassy state of the coating, as well as by decreasing its T g , which in certain applications may not be desired.…”

Effect of blending with polyamidoamine (PAMAM) dendrimer on the toughness of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)

“…In recent years, more attention has been paid to improve the resin properties of polymers by using with HBPs as a modifying agent. Studies [17][18][19] have indicated that if the terminal functional groups of a HBP are used as a proton donor or receptor to act on the resin, a hydrogen bonding effect is generated between the molecules of the blended polymers. Hydrogen bonding influences several properties of polymeric blends, such as the blending efficiency, glass transition temperature (T g ), melting point, crystallization, and surface energy.…”

Synthesis and characterization of amino-terminated hyperbranched polymer and its effect on impact resistance of epoxy resin thermosets

“…Hyperbranched polymers (HBPs) are a subfamily of dendritic polymers [15,16] and can be used as effective polymer modifiers of thermosetting materials especially epoxy resins [17], due to (1) their unique sphere structure networks, which makes them with low viscosity than linear polymer with the same molar mass [18] and can reduce the shrinkage of epoxy resins owing to the stretching after terminal groups interacting with other functional groups of epoxy resins and/or curing agents [19][20][21]; (2) their high density and versatile functional terminal groups such as hydroxyl, amine, epoxide groups, anhydride, carboxylic, and isocyanate, which can greatly enhance the compatibility between HBPs and epoxy matrixes; and (3) a lot amount of free volumes in their networks, which can sharply improve the toughness of epoxy resins when HBPs are used as modifiers [19,22]. H. Wu et al [23] reported that the viscosity difference caused by HBP end group was not due to the reaction between epoxide ring and the end groups of HBP but may be due to the lower viscosity of HBP with hydroxyl groups than that of HBP with acetyl groups.…”