Photopolymerization and toughening performance in polypropylene of hyperbranched polyurethane acrylate

A novel UV-curable hyperbranched polyurethane acrylate (HUA) was synthesized and found to polymerize rapidly in the presence of 5 wt.% benzophenone in N₂ under UV exposure. The photopolymerization kinetics of HUA was studied by differential photocalorimetry (DPC). Its toughening effect for polypropylene (PP) was investigated by tensile and impact tests of the UV irradiated PP/HUA blends. The morphological structures and thermal behavior were determined by polarized optical microscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The obtained results demonstrate that (1) the maximum photopolymerization rate increases with raising temperature up to 140 °C, whereas decreases at above 150 °C. The activation energy of 19 kJ mol⁻¹ for the photopolymerization was obtained at below 140 °C from the Arrhenius plot, while it is negative at above 150 °C. (2) The incorporation of 5 wt.% HUA greatly improved the notched impact strength of PP matrix with a slight improvement in the tensile strength and without obvious decline in breaking elongation. These results correlate well with SEM observation. (3) During the UV irradiation of PP/HUA blends, PP can be crosslinked/grafted with the cured HUA particles, resulting in the increase of the impact strength of PP matrix. (4) The cured HUA particles in the PP/HUA blends act as heterogeneous nucleation agent for PP, which results in the decrease of spherulite size and less perfection of PP crystals.     

Crystallization kinetics of polypropylene with hyperbranched polyurethane acrylate being used as a toughening agent

The crystallization kinetics of polypropylene (PP) with hyperbranched polyurethane acrylate (HUA) being used as a toughening agent was studied by isothermal and nonisothermal differential scanning calorimetry (DSC). The presence of a small amount of HUA (2-7%) remarkably influences the crystallizability of PP. An addition of HUA leads to an increase in the number of effective nuclei, thus resulting in an increase of crystallization rate and a stronger trend of instantaneous three-dimensional growth. For isothermal crystallization, Avrami exponents were determined to be about 2.97 for pure PP and 3.51 for the HUA/PP blend containing 5% HUA (HUA-PP). The half crystallization time (t_1/2) of pure PP was measured to be 8.43 min, while being 3.28 min for HUA-PP at the crystallization temperature of 132 °C. The nonisothermal crystallization kinetics of HUA/PP blends was analyzed by Avrami, Ozawa and Kissinger methods. It has also been proved that an addition of HUA could increase the crystallization rate of PP. Moreover, the crystallization activation energies of pure PP and HUA-PP were estimated by Kissinger and Friedman methods.     

Synthesis and properties of a novel hyperbranched polyphosphate acrylate applied to UV curable flame retardant coatings

A series of hyperbranched polyphosphate acrylates (HPPAs) being used for UV curable flame retardant coatings were prepared by the reaction of tri(acryloyloxyethyl) phosphate (TAEP) with piperazine at given ratios, and characterized using FTIR, ¹H NMR and GPC measurements. HPPA was blended with TAEP in different ratios to obtain a series of UV curable resins. Their maximum photopolymerization rates and final unsaturation conversion (P^f) in the cured films at the presence of a photofragmenting initiator were investigated. The results showed that the P^f increased along with HPPA content and the pure HPPA has the maximum value of 82.1% in the photo-DSC analysis. The data from dynamic mechanical thermal analysis showed that HPPA has good miscibility with TAEP. The crosslinking density and T_g of the cured film decrease along with the content of HPPA in the blend. The mechanical properties of the cured films were also investigated. Less than 20% HPPA addition improved both the tensile strength and elongation at break without damaging the modulus. The HPPA₂₀TAEP₈₀ film with 20% HPPA addition has the highest tensile strength of 31.7 MPa and an elongation at break two times that of cured TAEP. The flame retardancy of the UV cured films was investigated by the limiting oxygen index (LOI). The cured TAEP/HPPA samples greatly expanded when burning, and the degree of expansion increased along with HPPA content. However, the LOI values decreased from 47.0 to 34.0 along with HPPA content, which can be ascribed to that the flame retardancy of TAEP is mainly acting in the gas phase, whereas HPPA mainly acting in condensed phase, and the gas phase mechanism holds the dominant effect while their blends are burning.     

Photopolymerization of waterborne polyurethane acrylate dispersions based on hyperbranched aliphatic polyester and properties of the cured films

A series of novel waterborne hyperbranched polyurethane acrylates for aqueous dispersions (WHPUD) based on hydroxy-functionalized hyperbranched aliphatic polyester Boltorn H20 were investigated and used as UV curable oligomers. The aqueous dispersions were electrostatically stabilized with carboxyl groups incorporated into their structures, which were neutralized by triethylamine. The photopolymerization kinetics of these WHPUDs was studied with respect to polymerization rates and unsaturation conversions in the presence of a photoinitiator using differential scanning calorimetry. The polymerization rates of the resins under UV irradiation and the gel contents in the cured films showed an increasing trend with higher concentration of acrylate functionality, which is in favor of the theory of radical chain polymerization. The mechanical and thermal behaviors of UV cured films of aqueous dispersions were evaluated by tensile testing and dynamic mechanical thermal analysis (DMTA). The results of DMTA investigations indicated that the glass transition temperature shifted to higher temperature as the content of the hard segment consisting of IPDI-HEA increased. Moreover, the storage modulus and pendulum hardness also increased with increasing the hard segment content. As the degree of neutralization increased, the T_g and tensile strength decreased, whereas, the elongation at break increased.     

Blends of different linear polyamides with hyperbranched aromatic AB2 and A2 + B3 polyesters

To explore the possible applications of hyperbranched polymers for modifying linear polyamides, two hyperbranched aromatic polyesters characterized as high T_g polymers possessing phenolic end groups were used in melt mixing with partly aromatic polyamide and commercially available aliphatic polyamide‐6, respectively. Different amounts of both hyperbranched polyesters (from 1 wt % up to 20 wt %) were added to the polyamides, and the influence of these hyperbranched polyesters on the properties of the polyamides was investigated. The hyperbranched polyester based on an AB₂ approach was found to be the most effective modifier. A significant increase of the glass transition temperature of the final blend was detected. However, a remarkable reduction of crystallinity as well as complex melt viscosity of those blends was also observed. The use of an A₂+B₃ hyperbranched polyester as melt modifier for the polyamides was less effective for changing the thermal properties, and the complex melt viscosity of the final material increased since heterogeneous blends were formed. In contrast to that, generally, the addition of the AB₂ hyperbranched polyester to the polyamides resulted in homogeneous blends with improved T_g and processability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3558–3572, 2009     

Synthesis,rheological, and thermal properties of waterborne hyperbranched polyurethane acrylate dispersions for UV curable coatings

A series of waterborne hyperbranched polyurethane acrylate (WHUAs) ionomers used for ultraviolet curable waterborne coatings were synthesized. The average particle size of aqueous dispersion ranged between 48.2 and 75.3 nm at 0.05% concentration determined by laser light scattering. The effects of end group of WHUAs on rheological properties were investigated. WHUAs have much lower viscosity than EB2002, commercial linear waterborne polyurethane acrylate. Moreover, the glass transition temperature (T_g) evaluated by differential scanning calorimetry of samples showed that the influence of end capping by hard segment consisting of toluene diisocyanate–hydroxyethyl acrylate is significant due to the increase of crosslink density. All cured WHUA have higher glass transition temperatures than those of cured EB2002. The results of thermogravimetric analysis for cured WHUA films indicated good thermal stability with no appreciable weight loss until 200°C, and that an increase in the hard segment content provoked the increases in thermal degradation temperature. The activation energies were calculated by Flynn–Wall method to be 91.3, 114.3, and 139.7 kJ mol⁻¹ for cured WHUA62, WHUA44, and WHUA26, with the individual ratios of 6:2, 4:4, and 2:6 for salt-like group to double bond at the terminals, compared with 81.1 kJ mol⁻¹ of EB2002 in N₂ atmosphere, respectively.     

Membrane preparation from hyperbranched perfluorinated polymers

In this research, membrane formation with hyperbranched perfluorinated polymers (HBFP) was investigated. To create a tough membrane, HBFP was blended and crosslinked with a tougher linear polymer. Blending only or crosslinking only was not sufficient to create a tough membrane, but combining blending with crosslinking was successful. Miscibility, phase separation, and thermal and mechanical properties were evaluated for a variety of systems. By using a toughening linear polymer with lower polarity, reduced phase separation and improved mechanical properties were seen. Overall, imidazole‐containing HBFPs produced the clearest and toughest blends. These new hyperbranched ionomers and copolymers are strong candidates for future use in anhydrous proton exchange membranes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 961–972     

Mechanical properties of gradient copolymers of styrene and n‐butyl acrylate

The mechanical properties of linear and V‐shaped compositional gradient copolymer of styrene and n‐butyl acrylate with composition of around 55 wt % styrene were investigated by comparing with their block copolymer counterparts. Compared with their block copolymer counterparts, the gradient copolymers showed lower elastic modulus, much larger elongation at break, and similar ultimate tensile strength at room temperature. This performance could be ascribed to that the local moduli continuously change from the hardest nanodomains to the softest nanodomains in the gradient copolymer, which alleviates the stress concentration during tensile test. Compared with the V‐shaped gradient (VG) copolymer, the linear gradient copolymer showed much higher elastic modulus but lower elongation at break. The mechanical properties of the gradient copolymers were more sensitive to the change in temperature from 9 °C to 75 °C. With recovery temperature increased from 10 °C to 60 °C, the strain recovery of VG copolymer would change steadily from 40% to 99%. However, the elastic recovery of linear and triblock copolymer was poor even at 60 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 860–868     

Preparation and cryogenic mechanical properties of epoxy resins modified by poly(ethersulfone)

A thermoplastic, poly(ethersulfone) (PES) was used to modify a bisphenol‐F based epoxy resin cured with an aromatic diamine. The initial mixtures before curing, prepared by melt mixing, were homogeneous. Scanning electron microscopy (SEM) micrographs of solvent‐etched fracture surfaces of the cured blends indicated that phase separation occurred after curing. The cryogenic mechanical behaviors of the epoxy resins were studied in terms of tensile properties and Charpy impact strength at cryogenic temperature (77 K) and compared to their corresponding behaviors at room temperature (RT). The addition of PES generally improved the tensile strength, elongation at break, and impact strength at both RT and 77 K except the RT tensile strength at 25 phr PES content. It was interesting to observe that and the maximum values of the tensile strength, elongation at break, and impact strength occurred at 20 phr PES content where a co‐continuous phase formed. Young's modulus decreased slightly with the increase of the PES content. Moreover, the tensile strength and Young's modulus at 77 K were higher than those at RT at the same composition, whereas the elongation at break and impact strength showed the opposite results. Finally, the differential scanning calorimetry analysis showed that the glass transition temperature (T_g) was enhanced by the addition of PES. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 612–624, 2008     

Synthesis and crosslinking of hyperbranched poly(n‐nonyl acrylate) to form organogels

(2‐Bromo‐n‐nonan‐1‐oxycarbonyl)ethyl acrylate was synthesized as an inimer for self‐condensing vinyl polymerization (SCVP) to produce hyperbranched poly(n‐nonyl acrylate), either as a homopolymer or as a copolymer with n‐nonyl acrylate. The inimer was homopolymerized and copolymerized by atom transfer radical polymerization (ATRP) and activator generated by electron transfer ATRP to produce soluble polymers with broad polydispersities (up to ? = 9.91), which is characteristic of hyperbranched polymers produced by SCVP. The resulting hyperbranched (co)polymers were crosslinked by atom transfer radical coupling in both one‐pot and two‐step procedures. The radical–radical crosslinking reaction is extremely efficient, resulting in hard plastic particles from the homopolymer of (2‐bromo‐n‐nonan‐1‐oxycarbonyl)ethyl acrylate synthesized in bulk. Crosslinked organogels that swell in tetrahydrofuran were formed when the rate of crosslinking decreased using acetonitrile solutions. Dynamic shear and stress relaxation experiments demonstrated that the dry network behaves as a covalently crosslinked soft gel, with a glass transition at ?50 °C according to differential scanning calorimetry. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2399–2410     

Bio‐based hyperbranched polyurethane/clay nanocomposites: adhesive,mechanical, and thermal properties

The unison of vegetable oil‐based hyperbranched polymers with nanotechnology can unhook myriad of avant‐garde applications of such materials. Thus Mesua ferrea L. seed oil‐based hyperbranched polyurethane (HBPU)/clay nanocomposites and their performance, with special reference to adhesive strength, are reported for the first time. The nanocomposites of the hyperbranched polyurethane with organically modified nanoclay were obtained by ex situ solution technique and cured by bisphenol‐A‐based epoxy with poly(amido amine) hardener system. The partially exfoliated and well‐distributed structure of nanoclay was confirmed by XRD, SEM, and TEM studies. FTIR spectra indicate the presence of H‐bonding between nanoclay and the polymer matrix. Two times improvement in the adhesive strength and scratch hardness, 10 MPa increments in the tensile strength and 112°C more thermo‐stability have been observed without much affecting the impact resistance, bending, and elongation at break of the nanocomposites compared to the pristine epoxy modified HBPU system. Thus, the resulted nanocomposites are promising materials for different advanced applications including adhesive. Copyright © 2009 John Wiley & Sons, Ltd.     

Transparent and ductile poly(lactic acid)/poly(butyl acrylate) (PBA) blends: Structure and properties

Poly(butyl acrylate) was prepared by the free radical polymerization of butyl acrylate as an initiator in the presence of 2,2′-Azoisobu-tyronitrile (AIBN) and the average molecular weight, polydispersity and thermal stability were evaluated. PLA and PBA were melt blended using a Haake Rheometer, and the light transmission, thermal properties, dynamic rheological properties, mechanical properties, phase morphology of blends and toughening mechanism were investigated. Dynamic rheology, SEM and DSC results show that the PLA is partial miscible with PBA. The PBA component improved the crystallization ability of PLA and the crystallinity of PLA increased with content of PBA (<15 wt.%). With the increase of PBA, the tensile strength and modulus of the blend decreased slightly while the elongation at break and toughness were dramatically increased. With the addition of PBA, the failure mode changes from brittle fracture of neat PLA to ductile fracture of the blend. Rheological results revealed the complex viscosity and melt elasticity of the blends decreased with increasing content of PBA and phase segregation occurred at loading above 11 wt.% PBA. UV–vis light transmittance showed that PLA/PBA blends with a high transparency, and the transmittance decreased with the amount of PBA.     

Effects of hyperbranched poly(ester‐silane) as a coupling agent on the mechanical behavior of glass bead filled epoxy resin

Hyperbranched poly(ester‐silane)s (HPE‐Si, including HPE‐Si4 and HPE‐Si8) were synthesized for glass bead filled epoxy resins. The grafting reaction and the degree of grafting of HPE‐Si onto the surface of glass beads were characterized by Fourier transform infrared photoacoustic spectroscopy (FT‐IR‐PAS) and thermogravimetric analysis (TGA) measurements. The degree of grafting was calculated to be in the range 1.0–4.2% for different HPE‐Si treatments. The tensile strength and modulus of glass bead filled epoxy resins were found to increase with increasing filler content. Moreover, HPE‐Si4 series have the highest tensile strength and modulus at the same glass bead size and volume fraction in the composites compared with HPE‐Si8 series. The fracture toughness (K_1c) of specimens with different glass bead sizes (4.8 and 2.0 μm) has the same trend that changes with the filler content and the modification of the surface of glass beads. The investigation of the toughening mechanism using Irwin's model through the yield stress measurements suggest that the toughening mechanism for small glass bead filled resins does not involve matrix plasticity, whereas the toughening mechanism involving matrix shear banding for large glass bead filled resins with higher filler content (up to 10 wt%) was proposed. The morphology of the filled resins studied by scanning electron microscopy (SEM) showed that the interface compatibility between the glass beads and epoxy matrix was greatly improved by the treatment with HPE‐Si. Copyright © 2005 John Wiley & Sons, Ltd.     

Phase separation,porous structure,and cure kinetics in aliphatic epoxy resin containing hyperbranched polyester

Thermosetting blends of an aliphatic epoxy resin and a hydroxyl‐functionalized hyperbranched polymer (HBP), aliphatic hyperbranched polyester Boltorn H40, were prepared using 4,4′‐diaminodiphenylmethane (DDM) as the curing agent. The phase behavior and morphology of the DDM‐cured epoxy/HBP blends with HBP content up to 40 wt % were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The cured epoxy/HBP blends are immiscible and exhibit two separate glass transitions, as revealed by DMA. The SEM observation showed that there exist two phases in the cured blends, which is an epoxy‐rich phase and an HBP‐rich phase, which is responsible for the two separate glass transitions. The phase morphology was observed to be dependent on the blend composition. For the blends with HBP content up to 10 wt %, discrete HBP domains are dispersed in the continuous cured epoxy matrix, whereas the cured blend with 40 wt % HBP exhibits a combined morphology of connected globules and bicontinuous phase structure. Porous epoxy thermosets with continuous open structures on the order of 100–300 nm were formed after the HBP‐rich phase was extracted with solvent from the cured blend with 40 wt % HBP. The DSC study showed that the curing rate is not obviously affected in the epoxy/HBP blends with HBP content up to 40 wt %. The activation energy values obtained are not remarkably changed in the blends; the addition of HBP to epoxy resin thus does not change the mechanism of cure reaction of epoxy resin with DDM. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 889–899, 2006     

Thermal properties and toughness performance of hyperbranched‐polyimide‐modified epoxy resins

An amine‐terminated hyperbranched polyimide (HBPI) was prepared by the condensation polymerization of a commercially available triamine monomer with a dianhydride monomer. The effects of the HBPI content on the thermal and mechanical interfacial properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resins were investigated with several techniques. The thermogravimetric analysis results showed that the thermal stability of the DGEBA/HBPI blends did not obviously change as the HBPI content increased. The glass‐transition temperature (T_g) of the DGEBA/HBPI blends increased with the addition of HBPI. Improvements in the critical stress intensity factor (K_IC) and impact strength of the blends were observed with the addition of HBPI. The K_IC value and impact strength were 2.5 and 2 times the values of the neat epoxy resins with only 4 wt % HBPI. The fractured surfaces were studied with scanning electron microscopy to investigate the morphology of the blends, and they showed that shear deformation occurred to prevent the propagation of cracks in the DGEBA/HBPI blends. These results indicated that a toughness improvement was achieved without a decrease in the thermal stability or T_g. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3348–3356, 2006     

Synthesis and photoinitiating behavior of hyperbranched polymeric photoinitiators bearing coinitiator amine

A series of benzophenone (BP)‐terminated hyperbranched polyester (BoltornTM P1000), bearing amine moieties as synergists by reacting with piperidine, were synthesized as yellowish liquids with low viscosity, and used as polymeric photoinitiators (HPPIs). For comparison, acrylate groups were introduced to the terminals of hyperbranched polyester for obtaining a polymerizable photoinitiator. The chemical structures were characterized by FTIR and ¹H NMR spectroscopy. HPPIs and BP exhibited the similar absorptions by UV–vis spectroscopy. The photoinitiating behavior of HPPIs with trimethylolpropane triacrylate (TMPTA) as a trifunctional monomer was investigated by using photo‐DSC analysis. The results indicated that the maximum photopolymerization rate and unsaturation conversion of TMPTA initiated by HPPIs were both lower than that by BP. Among them, the HPPI with double tertiary amine moiety of BP moiety was found to be the most efficient photoinitiator. Additionally, the films cured with bisphenol A epoxy acrylate EB605 initiated by HPPIs were uniform and possessed high T_g from DMTA. Copyright © 2010 John Wiley & Sons, Ltd.     

UV-cured hyperbranched polyester polythiol(H20-SH)-epoxy acrylate networks: Preparation,thermal and mechanical properties

A hyperbranched polyester polythiol(H20-SH) was synthesized and characterized by FTIR spectral analysis, ¹H-NMR spectral analysis and GPC analysis. H20-SH was added into the formulation of UV-curable epoxy acrylate networks based on thiol-acrylate chemistry. The effects of H20-SH on polymerization kinetics, thermal and mechanical properties of thiol-epoxy acrylate networks were investigated by Real-time infrared spectroscopy, dynamic mechanical analysis (DMA), thermogravimetric (TGA), tensile test and water absorption characterization. Results show that epoxy acrylate resin with the addition of H20-SH massively reduces oxygen inhibition, improves the uniformity of cured films and enhances the tensile strength of the films. However, the thermal stability and glass transition temperature (T_g) decreases with the increasing amount of H20-SH.     

Hyperbranched Acrylated Aromatic Polyester Used as a Modifier in UV-Curable Epoxy Acrylate Resins

The viscosity,the shrinkage degree and the photopolymerization rate of the epolxy acrylate(EB600) blended with hyperbranched acrylated aromatic polyester(HAAPE) were investigated.The addition of HAAPE into EB600 largely reduces the viscosity of the blend formulation and the shrinkage degree.For example,EB600 resin with 50% weight fraction of HAAPE has the 1250 cps of the viscosity and 2.0% of shrinkage degree,while the pure EB600 resin has 3000 cps of the viscosity and 10.5% of shrinkage degree.The photopolymerization rate of the resin is also promoted by HAAPE addition.The good miscibility between HAAPE and EB600 was also observed from the dynamic mechanical analysis.The tesile,flexural and compressive strength,and the thermal properties of the UV cured films are greatly improved.     

The influence of N‐vinyl pyrrolidone on polymerization kinetics and thermo‐mechanical properties of crosslinked acrylate polymers

Polymerization of multifunctional acrylate monomers generates crosslinked polymers that are noted for their mechanical strength, thermal stability, and chemical resistance. A common reactive diluent to photopolymerizable formulations is N‐vinyl pyrrolidone (NVP), which is known to reduce the inhibition of free radical photopolymerization by atmospheric oxygen. In this work, the copolymerization behavior of NVP was examined in acrylate monomers with two to five functional groups. At concentrations as low as 2 wt %, NVP increases the polymerization rate in copolymerization with multifunctional acrylate monomer. The relative rate enhancement associated with adding NVP increases dramatically as the number of acrylate double bonds changes from two to five. The influence of NVP on polymerization kinetics is related to synergistic cross‐propagation between NVP and acrylate monomer, which becomes increasingly favorable with diffusion limitations. This synergy extends bimolecular termination into higher double bond conversion through reaction diffusion controlled termination. Copolymerizing concentrations of 5–30 DB% NVP with diacrylate or pentaacrylate monomer also increases Young's modulus and the glass transition temperature (T_g) in comparison to neat acrylate polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4062–4073, 2007     

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

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. Copyright © 2008 John Wiley & Sons, Ltd.