Blends of modified epoxy resin and carboxyl‐terminated polybutadiene. I

Six blend samples were prepared by the physical mixing of epoxidized resole (EDR) with different weight ratios of carboxyl‐terminated polybutadiene (CTPB) liquid rubber ranging from 0 to 25 wt % in intervals of 5 wt %. The formation of various reaction products during the curing of unblended EDR and CTPB‐blended EDR were studied with Fourier transform infrared spectroscopy. The curing time at 100°C for the blend sample containing 15 wt % CTPB was the least among all of the blend samples. This blend sample, also, showed the highest initial degradation temperature, as obtained from thermogravimetric analysis thermograms, which indicated that it was the most thermally stable matrix system. The films of coatings based on the blend of EDR with 15 wt % CTPB offered the highest resistance toward different concentrations of acids and alkalis compared to the films having 5, 10, 20, and 25 wt % CTPB in the EDR/CTPB blends. Solvents showed almost the same behavior as acids and alkalis for these films except for hydrocarbon solvents such as mineral turpentine oil, toluene, and xylene. The resistance toward these solvents was poor and slightly inferior to those found with EDR unblended with CTPB. The tensile, flexural, and impact strengths of the molded specimens derived from the EDR/CTPB blends initially increased up to 15 wt % CTPB addition in the blend and then decreased, whereas the elongation at break remained constant for all blend compositions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1802–1808, 2006     

Synthesis and evaluation of liquid amine‐terminated polybutadiene rubber and its role in epoxy toughening

Epoxy resin is widely used for coatings, adhesives, castings, electrical insulation materials, and other applications. However, unsolved problems still remain in its applications. The main problem is low toughness: cured epoxy resin is rather brittle, with poor resistance to the propagation of cracks derived from the internal stress generated by shrinkage in the cooling process from cure temperature to room temperature. The objective of this study was to improve the flexibility and toughness of diglycidyl ether of bisphenol A based epoxy resin with a liquid rubber. For this purpose, amine‐terminated polybutadiene (ATPB) was synthesized. The product was characterized by Fourier transform infrared and NMR spectroscopy and elemental analysis. ATPB‐modified epoxy networks were made by curing with an ambient‐temperature curing agent, triethylene tetramine. We varied the epoxy/liquid rubber compositions to study the effect of toughener concentration on the impact and thermal properties. Higher mechanical properties were obtained for epoxy resins toughened with 1 phr ATPB. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2446–2453, 2005     

Adhesive properties of epoxy resin modified by end‐functionalized liquid polybutadiene

Adhesive properties of epoxy resin networks modified with different functionalized liquid polybutadiene were evaluated by using aluminum adherent. The end‐functionalized polybutadiene rubbers were hydroxyl‐ (HTPB), carboxyl‐ (CTPB), and isocyanate‐terminated polybutadiene (NCOTPB). The adhesive properties depend upon the morphology and the degree of interaction between the rubber–epoxy system. The most effective adhesive for Al–Al joint in both butt and single‐lap shear testing was epoxy resin–NCOTPB system. This system presents stronger rubber–epoxy interactions and a higher degree of rubber particle dispersion with particle size diameter in the nanoscale range. These characteristics were not important for improving the toughness of the bulk network but are fundamental for the improvement of adhesive strength. The effect of the pretreatment of the aluminum surface on the roughness was also evaluated by using profilometry analysis. The type of failure was also investigated by analyzing the adhered surfaces after fracture by scanning electron microscopy and profilometry. A proportion of cohesion failure higher than 90% was observed in all systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2370–2378, 2004     

Derivatization of carboxyl‐terminated polybutadiene for determining relative functionality distribution

A new and highly efficient method for determining relative carboxyl group distribution in carboxyl‐terminated polybutadiene has been developed using practical synthetic and analytical techniques. Using oxalyl chloride, samples of carboxyl‐terminated polybutadiene were rapidly transformed to acid chlorides that were then chemically derivatized with benzyl alcohol, 4‐nitrobenzyl alcohol, and 3,5‐dinitrobenzyl alcohol. This provided quick and quantitative conversion to the corresponding benzyl ester derivatives. Each new derivative was fully characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopy. The benzyl ester modified polymers were investigated in detail to determine their relative carboxyl group concentrations. To do this, gel permeation chromatography combined with ultra violet/refractive index dual detection was employed. The 4‐nitrobenzyl ester, having the highest extinction factor at 270 nm provided the best UV data for analysis. The ultra violet/refractive index data of four separate polymer samples were plotted as a function of molecular weight. The data were compared with a theoretical plot (carboxyl group = two for all molecular weights) to illustrate the relative carboxyl concentration over the entire molecular weight range. Supplemental characterization of the 4‐nitrobenzyl modified polymer was carried out using matrix‐assisted laser desorption ionization coupled with time of flight mass spectrometry. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties of epoxy resin modified with polycarbonate and reactive polybutadiene

Epoxy resin Epidian 5 cured with triethylene tetramine was modified with hydroxyl‐terminated polybutadiene (PB) and polycarbonate (PC). Compositions with different amount of modifiers were obtained and tested for their impact strength, flexural strength, as well as resistance to crack propagation. The latter was assessed by evaluating the critical stress intensity factor under three‐point bending mode using single‐edge notched specimens. Scanning electron microscopy was used to analyze the fractured sample surfaces. The obtained results revealed that the mechanical properties of epoxy resin were improved due to the formation of heterogeneous phase with rubber particles, which arrest the propagation of cracks. Moreover, synergism effect was observed with the hybrid composition containing 10% PC and 2.5% of reactive PB. The impact strength was higher by ～ 15% than the sum of impact strength of compositions containing only one modifier. Another hybrid composition with 2.5% PB and 2.5% PC also exhibited synergism effect with the flexural strain at break, the energy at break under flexure, as well as the brittle fracture energy estimated from the critical stress intensity factor measurements. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

环氧树脂的氨基硅油改性研究

利用氨基硅油对环氧树脂胶粘剂体系进行了改性,分析了氨基硅油与环氧树脂共聚反应温度、反应时间、环氧树脂与氨基硅油的配比、氨基硅油的氨值和黏度对改性胶粘剂力学性能的影响。结果发现,氨基硅油改性的环氧树脂其韧性大幅度提高。     

Enhanced Charpy impact strength of epoxy resin modified with vinyl‐terminated polydimethylsiloxane

This article deals with enhancement of the toughness of epoxy resin (ER) based on diglycidyl ether bisfenol A by either polydimethylsiloxane (PDMS) or vinyl‐terminated polydimethylsiloxane (VT‐PDMS). To improve the compatibility of these two phases, dicumylperoxide (DCP) was used as a compatibilizer. It was established that only specific composition of the components can lead to enhancement of ER toughness without significant reduction of storage modulus, T_g, and interphase adhesion. The highest impact strength was recorded for ER with VT‐PDMS (10 wt %) and DCP (2 wt %) due to increased interfacial compatibility between two phases, which was proved by ¹H NMR and dielectric spectroscopy. Critical ductile brittle transition occurring between 10 and 15 wt % of rubber was observed by both morphological and dynamic mechanical analysis studies. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45720.     

A toughened epoxy resin by silica nanoparticle reinforcement

Within this study the influence of adding 5 vol % of silica nanoparticles, obtained via a sol–gel process, on an Araldite‐F epoxy was investigated. To characterize toughening effects, compact tension specimens were used to obtain K_IC and G_IC. Additionally, tensile strength and E‐Modulus were measured as well as differential scanning calorimetry and dynamic mechanical thermal analysis were carried out to evaluate the influence on the thermal properties of the epoxy because of addition of the particles. Electronic microscopy was used to check dispersion quality and fracture surfaces, in transmission mode and scanning mode, respectively. The addition of 5 vol %. silica‐nanoparticles could improve the stiffness and the toughness of an epoxy resin at the same time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1849–1855, 2006     

Modification of aqueous polyurethane dispersions by polybutadiene

Aqueous polyurethane (PU) adhesives are nontoxic and nonflammable and do not pollute the air. However, they have low adhesive strengths compared to solvent‐based PU adhesives because of a low affinity with rubber substrates. In this study, PU adhesives were synthesized from isophorone diisocyanate with dimethylol propionic acid as the ionic center in the main chain, triethylamine as the neutralization agent, and hydrazine as the chain extender. The polyol was modified with hydroxyl‐terminated polybutadiene (HTPB) and hydroxyl‐terminated acrylonitrile–butadiene copolymer (HTBN). The effect of the HTPB and HTBN content on the adhesive strength was investigated. The effect of the prepolymer molecular weight was also investigated. Increases in the HTPB and HTBN contents led to an increase in the adhesive strength because of the increase of chemical affinity between the adhesive and the substrate. The adhesive strength increased as the prepolymer molecular weight increased. This was due to an increase in the tensile strength and modulus. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1062–1068, 2005     

Thermoresponsive crosslinked isocyanate‐free polyurethanes by Diels‐Alder polymerization

This new study is a continuation of our previous work on thermocleavable nonisocyanate polyurethanes (NIPUs), but it is focused on crosslinked networks. Two systems are studied: the first system involves a dicyclocarbonate adduct with a PPO‐bicyclocarbonate and a triamine as crosslinker. The second system involves a tetracyclocarbonate DA adduct as crosslinker with the same PPO‐bicyclocarbonate and a difunctional amine. Firstly, Diels‐Alder adducts are synthesized and characterized. Then they are copolymerized to yield two types of cleavable polymer networks. The thermal behavior of synthesized polymers is fully characterized. Finally, by SEC, it was demonstrated that the obtained NIPU polymer chains are sliced up by rDA reaction. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44408.     

The effect of hydroxyl‐terminated polybutadiene‐grafted carbon fiber on the impact performance of carbon fiber–epoxy resin composites

Carbon fiber (CF) containing 1.4 and 2.1 mmol/g of —COOH and —OH groups, respectively, was functionalized by using an excess of tolylene‐2,4‐diisocyanate. The NCO‐modified CF was submitted to a graft reaction with hydroxyl‐terminated polybutadiene (HTPB). The HTPB‐grafted carbon fiber was employed as reinforcing agent for epoxy resin‐based composites. The presence of the flexible HTPB at the interface between the fiber and the matrix resulted in a substantial improvement on impact strength. Additional improvement on toughness was achieved by using epoxy matrix containing dispersed phase of HTPB. The composite morphology was also studied by scanning electron microscopy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1424–1431, 1999     

Modification of cyanate ester resin by hydroxyl‐terminated liquid butadiene‐acrylonitrile rubber and free volume properties of their composites

The toughness of cyanate ester resin (CE) matrix is improved significantly with addition of hydroxyl‐terminated liquid butadiene‐acrylonitrile rubber (HTBN). The impact strength increased from 4.4 KJ/m² (pure CE) to 13.3 KJ/m² (CE/HTBN, HTBN 10 wt %). The curing behavior of the system is studied by differential scanning calorimetric and Fourier transform infrared spectroscope. The results showed that hydroxyl groups on the HTBN chains have slight activation effect to CE curing reaction at the beginning of the cure process. The toughening mechanism is mainly caused by the flexibilizing effects of the homogeneously dispersed HTBN molecules in the CE matrix. The toughening mechanism was demonstrated from the aspect of free volume using positron annihilation lifetime spectroscopy. With addition of HTBN, the mean free‐volume size of the composite is smaller than pure CE. The decrease in the mean free‐volume size of the system is mainly related to the partition effects of the finely dispersed HTBN molecules to the free‐volume holes of CE matrix. A dramatic increase in the interfacial area occurs in this highly miscible system. Good interfacial adhesion is also reflected from the higher I₂ of the composite. Therefore, more positrons annihilation in their free state occurs in the composites containing HTBN than pure CE. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Terminal functionalized hydroxyl‐terminated polybutadiene: An energetic binder for propellant

We report the functionalization of hydroxyl terminated polybutadiene (HTPB) backbone by covalently attaching 1‐chloro‐2, 4‐dinitrobenzene (DNCB) at the terminal carbon atoms of the HTPB. The modification of the HTPB by the DNCB does not alter the unique physico–chemical properties and the microstructure of the parent HTPB. IR, ¹H‐NMR, ¹³C‐NMR, size exclusion chromatography (SEC) and absorption spectroscopy studies prove that the DNCB molecules are covalently attached to the terminal carbon atoms of the HTPB. The π electron delocalization owing to long polymer chain, strong electron withdrawing effect of the DNCB molecule are the major driving forces for the covalent attachment of the DNCB at the terminal carbon atom of the HTPB. We are the first to observe the existence of intermolecular hydrogen bonding between the terminal hydroxyl groups of the HTPB. IR study shows that the attached DNCB molecules at the terminal carbon atoms of the HTPB breaks the intermolecular hydrogen bonding between the HTPB chains and forms a hydrogen bonding between the NO₂ groups of the DNCB and the OH groups of the HTPB. Absorption spectral study of the modified HTPB indicates the better delocalization of π electron of butadiene due to the strong electron withdrawing effect of the DNCB molecules. Theoretical calculation also supports the existence of hydrogen bonding between the OH and NO₂ groups. Theoretical calculation shows that the detonation performance of both the DNCB and the HTPB‐DNCB are promising. HTPB‐DNCB is the new generation energetic binder which has potential to replace the use of HTPB as binder for propellant.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Liquid crystalline epoxy resin modified cyanate ester/epoxy resin systems

Liquid crystalline epoxy resin (LCE) modify cyanate ester/epoxy resin blend systems were studied by scanning electron microscope, polarizing optical microscope, thermogravimetric analyzer, differential scanning calorimetry, thermal mechanical analysis, and rheometers. With the addition of LCE resin, the blends showed both an enhanced curing rate and increased glass transition temperature of cured samples. The phase structures of the blends changed from homogenous to liquid crystalline phase when the content of LCE was increased. At the same time, the mechanical properties were also improved and thermal expansion coefficients were lowed down. The thermal degradation temperatures showed little differences, while the residue char yields were slightly increased with the addition of LCE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Evaluation by various experimental approaches of the crosslink density of urethane networks based on hydroxyl‐terminated polybutadiene

Crosslink density (CLD) is an important characteristic for elastomeric polymer networks. The mechanical and viscoelastic properties of the elastomers are critically dependant on the CLD. Several methods have been adopted for its determination, but swelling and stress–strain methods continue to be more popular because of the convenience associated with these techniques. In this article, the determination of CLD of allophanate–urethane networks based on hydroxyl‐terminated polybutadiene and toluene diisocyanate with swelling and stress–strain methods is reported. The Flory–Rhener relationship was applied to calculate CLD from the swelling data. CLDs were also calculated from the initial slope of the stress–strain curve (Young's modulus), Mooney–Rivlin plots, equilibrium relaxation moduli, and dynamic mechanical properties. A comparison was drawn among the values obtained with the various methods. Although the CLD values obtained from Mooney–Rivlin plots were slightly lower than those obtained from swelling data, the values obtained with Young's modulus and storage modulus were considerably higher. The values obtained with swelling and equilibrium relaxation moduli data were very close to each other. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3129–3133, 2007     

Flexibility improvement of epoxy resin by chemical modification

Epoxy resin was chemically modified with carboxyl‐terminated poly(ethylene glycol) adipate (CTPEGA) and the modified epoxy networks were made by curing with an ambient‐temperature hardener. The modified epoxy networks containing various concentrations of CTPEGA were characterized for their tensile, flexural and impact properties. It was observed that the mechanical strength gradually decreases and the strain increases with increasing CTPEGA concentration. However, the toughness and impact strength gradually increase with increasing CTPEGA concentration, attain a maximum and then decrease. The optimum CTPEGA concentration was found to be 20 phr. Fracture surface analysis by scanning electron microscopy indicates massive plastic deformation in modified networks. Copyright © 2004 Society of Chemical Industry     

Structure and properties of polyurethane acrylate prepolymers based on hydroxy‐terminated polybutadiene

Precursors of polyurethane acrylate based on hydroxy‐terminated polybutadiene (HTPB) soft segments, different diisocyanate and hydroxy ethyl acrylate (HEA) as hard units, were synthesized in bulk or in solution in methyl methacrylate. During precursor synthesis (in bulk), microphase separation was observed by small‐angle X‐ray scattering (SAXS). Diffusing particles are around 50 Å in size and are assumed to be assembling of hard segments. From these morphologies, it can be deduced that some isocyanate groups were trapped/or buried in hard domains. At a larger scale, around millimeters, hard segment crystallites were observed. Properties such as molar masses, melting and glass‐transition temperatures, and viscosities were correlated with precursor structure and morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 225–233, 2002     

Mechanical and tribological properties of epoxy modified by liquid carboxyl terminated poly(butadiene-co-acrylonitrile) rubber

Diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin was modified using liquid carboxyl-terminated poly(butadiene-co-acrylonitrile) (CTBN) rubber. The liquid CTBN contents used ranged from 2.5 to 20 parts per hundred parts of resin (phr). Mechanical properties of the modified resins were evaluated and the microstructures of the fracture surfaces were examined using SEM technique. The changes in storage modulus and the glass transition temperature were also evaluated using dynamic mechanical analysis (DMA). The tribological tests were performed using a ball-on-disc tribometer. The worn surfaces and the ball counter-mates after tribological tests were investigated using optical microscope technique. The results revealed the influence of liquid CTBN content on mechanical and tribological properties, and also microstructure of the modified epoxy resins. Impact resistance increased whereas the storage modulus and the hardness decreased when the CTBN rubber was introduced to the epoxy network. The coefficient of friction of the CTBN-modified epoxy was lower than that of the neat epoxy. The CTBN content of lower than 10 phr was recommended for improving the wear resistance of epoxy resin. Changes in tribological properties of the CTBN-modified epoxy correspond well to those in mechanical changes, especially the toughness properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Toughening of epoxy resin using hydroxyl‐terminated polyesters

Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by relatively low toughness. Several approaches to improve epoxy resin toughness include the addition of fillers, rubber particles, thermoplastics, or their hybrids, as well as interpenetrating networks and flexibilizers, such as polyols. It seems that this last approach did not receive much attention. So in an attempt to fill this gap, the present work deals with the use of hydroxyl‐terminated polyester resins as toughening agents for epoxy resin. For this purpose, the modifier, that is, a hydroxyl‐terminated polyester resin (commercially referred to as Desmophen), which is a polyol, has been used at different concentrations. The prepared modified structure has been characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. Two types of Desmophen (800 and 1200) have been used as modifiers. The obtained results showed that hydroxyl‐terminated polyester improves the epoxy toughness. In fact, the impact strength increases with Desmophen content and reaches a maximum value of 7.65 J/m at 10 phr for Desmophen 800 and 9.36 J/m at 7.5 phr for Desmophen 1200, respectively. At a critical concentration (7.5 phr), Desmophen 1200 (with higher molecular weight, longer chains, and lower branching) leads to better results. Concerning K_c, the effect of Desmophen 800 is almost negligible; whereas a drastic effect is observed with Desmophen 1200 as K_c reaches a maximum of 2.41 MPa m^1/2, compared to 0.9 MPa m^1/2 of the unmodified epoxy prior to decreasing. This is attributed to the intensive hydrogen bonding between epoxy and Desmophen 1200, as revealed by FTIR spectroscopy. Finally, the SEM analysis results suggested that the possible toughening mechanism for the epoxy resin being considered, which might prevail, is through localized plastic shear yielding induced by the presence of the Desmophen particles. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 29–38, 1999     

Toughened epoxy-liquid polybutadiene networks cured with anhydride with outstanding thermal and mechanical properties

Toughened epoxy systems cured with anhydride-based hardener were successfully prepared by incorporating nonpolar liquid polybutadiene (PB) previously functionalized with isocyanate groups (PBNCO). The NCO groups in PBNCO react with the hydroxyl and/or epoxy groups of the matrix forming a ER-PB-ER triblock copolymer. The block copolymer is evidenced by transmission electron microscopy (TEM). In fact the modified epoxy resin (ER) networks presented domains with cocontinuous-like morphology, composed by PB and ER phases in nanomeric dimensions. The effect of PBNCO on the curing process of ER was studied by rheometry. Also the resulting networks were characterized by mechanical and dynamic mechanical properties, differential scanning calorimetry, and TEM. By adding an amount of rubber as high as 20 phr, a great improvement of toughness (around 140%) and impact resistance as well as a good transparency were achieved without significantly affecting the modulus and stiffness. Also the glass transition temperature (Tg) increased around 10°C with the presence of 5 phr of PBNCO. Even with the addition of 20 phr of rubber, the Tg of the system was superior than that found for the neat epoxy network. The outstanding physic-mechanical performance is attributed to the peculiar morphology.