Selective repartition of in situ generated silica produced during the evolution of an epoxide network from a homogeneous precursors mixture and effects on properties

Phase separation of organic networks derived from mixtures of reactive monomers and/or oligomers can take place through the formation of IPNs or precipitation of particles. The latter systems are widely used as a means of increasing the fracture toughness of thermosetting resins, and particularly for products obtained from mixtures of epoxy resins and functionalized aliphatic oligomers. In the present work several mixtures comprised of difunctional epoxy resins, silane functionalized perfluoroether oligomers, prehydrolyzed tetraethoxysilane, and an aromatic amine hardener were examined in a variety of compositions and preparative procedures. The aims were to control the kinetics of phase separation and the repartition of the different components in the two phases, so that the silica domains could be preferentially located within the precipitated soft particles. It was found that the silane functionalization of the perfluoroether oligomer provided an effective mechanism for the localization of the siloxane networks within the precipitated particles. However, phase separation by the precipitation of particles would only take place for systems in which the perfluoroether oligomer could be reacted with an excess of epoxy resin prior to adding the alkoxysilane solution and the hardener. Moreover, it was difficult to achieve the total localization of the siloxane component into the perfluoroether network. The siloxane species remaining dissolved in the resin gave rise to severe embrittlement of the products through reactions with the epoxy chains. Using mixtures of suitably functionalized perfluoroether oligomers it was possible to produce the conditions by which the localization of the silica domains into the precipitated particles could be maximized. This has resulted also in the formation of graded interphase regions and to a global improvement in mechanical properties, manifested as a concomitant increase in modulus, strength, and toughness. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1279–1290, 2004     

Reactive blending approach to modify spin‐coated epoxy film: Part I. Synthesis and characterization of star‐shaped poly(ϵ‐caprolactone)

To effectively modify the properties of an epoxy, branched oligomers were synthesized from ?‐caprolactone (CL) and end‐functionalized to realize network precursors that can be reactively blended with the epoxy. The ring‐opening polymerization (ROP) of the CL in the presence of polyglycerol (PGL) initiator (3.9 and 9.1 mol %) and Sn(II) 2‐ethylhexanoate catalyst yielded oligomers with hydroxyl end‐groups, which were converted to carboxylic acid functionality by reaction with succinic anhydride. The functionalized oligomers had a four‐armed structure and the molecular weight of the oligomers could be controlled by the ratio of CL to PGL in the feed. To achieve an adequately crosslinked network in the reactive blending, a dual‐catalyzed reaction scheme was employed. First the oligomer was incorporated into the epoxy matrix in an imidazole‐catalyzed reaction and then the crosslinking was completed with an acid‐catalyzed ROP of the residual epoxies. Investigations showed that toughened coatings could be prepared from the inherently brittle epoxy through proper choice of the blending ratio of oligomer to epoxy. The blending increased surface hydrophobicity at high concentrations of functionalized oligomer, but did not have an adverse effect on the inherently advantageous endothelial cell spreading. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3677–3688, 2006     

Phase separation in epoxy resin‐reactive dendritic hyperbranched polymer blends

Equilibrium phase diagrams in composition‐conversion space have been calculated for stoichiometric blends of an epoxy resin with a diamine hardener and dendritic hyperbranched polymers, to which various numbers of epoxy groups have been grafted. An attempt has been made to incorporate both the effects of the polydispersity of the resin and the reactivity of the functionalized hyperbranched polymers for any given value of the interaction parameter. However, if the reactivities of all the epoxy groups are comparable, the presence of a highly functionalized modifier is expected to lead to a reduction of the gel point conversion and a narrowing of the composition‐conversion window available for cure induced phase separation. The experimental cloud point data are consistent with the model, although they sugget that the functionalized hyperbranched polymers may be significantly less reactive than the resin. Moreover, in the present system, the influence of functionalization on the phase behavior is also strongly linked to the accompanying changes in the interaction parameter.     

Blends of epoxy resin with amine‐terminated polyoxypropylene elastomer: Morphology and properties

A liquid diglycidyl ether of bisphenol A (DGEBA) epoxy resin is blended in various proportions with amine‐terminated polyoxypropylene (POPTA) and cured using an aliphatic diamine hardener. The degree of crosslinking is varied by altering the ratio of diamine to epoxy molecules in the blend. The mixture undergoes almost complete phase separation during cure, forming spherical elastomer particles at POPTA concentrations up to 20 wt %, and a more co‐continuous morphology at 25 wt %. In particulate blends, the highest toughness is achieved with nonstoichiometric amine‐to‐epoxy ratios, which produce low degrees of crosslinking in the resin phase. In these blends, the correlation between G_IC and plateau modulus (above the resin T_g), over a wide range of amine‐to‐epoxy ratios, confirms the importance of resin ductility in determining the fracture resistance of rubber‐modified thermosets. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 427–434, 1999     

Polyurethane/Polysiloxane Ceramer Coatings: Evaluation of Corrosion Protection

A series of polyurea and polyurethane ceramer coatings were formulated using hexamethylene diisocyanate (HDI) isocyanurate, alkoxysilane‐functionalized HDI isocyanurate, tetraethyl orthosilicate (TEOS) oligomers and cycloaliphatic polyesters. The coatings were prepared as a function of alkoxysilane‐functionalized HDI isocyanurate and TEOS oligomers concentration. Also, the effect of acid catalyst was investigated. The corrosion resistance of polyurea or polyurethane ceramer coating systems were evaluated using a prohesion chamber on aluminium alloy 2024‐T3 substrate. The polyurethane ceramer coatings were compared with the chromate pretreatment and the epoxy‐polyamide primer containing the chromate pigment. In addition to prohesion, the interface between the coating and substrate was characterized using X‐ray photoelectron spectroscopy (XPS). The prohesion data showed that the corrosion was inhibited by the TEOS oligomers. However, high concentrations of TEOS oligomers and acid catalyst produced blistering in the polyurea/polysiloxane ceramer coatings. The prohesion data also showed that the corrosion protection of ceramer coatings performed as well as the chromate pretreatment and competitively with the epoxy primer. From the XPS and prohesion data, a self assembling silicon oxide layer at the metal‐coating interface was proposed.     

Morphology and mechanical properties of epoxy resins containing functionalized perfluoroether oligomers

Chain extended perfluoroether oligomers were found to be miscible with bisphenol epoxy resins at all concentrations. These were evaluated as modifiers for anhydride cured resin systems, taking advantage of the carboxylic acid functionality at the chain ends. By altering the mixing and curing procedure different two-phases morphologies could be obtained varying from fine co-continuous networks, which produced transparent castings, to opaque systems consisting of precipitated heterogeneous particles. While the T_g and flexural modulus were found to be slightly lower than the control cure resin, the addition of the fluoroligomer modifier produced large increases in flexural strength, ductility, and fracture toughness. Samples with an IPN type morphology were found to exhibit an increase in ductility after aging at 200°C for three weeks proportionally to the concentration of fluoroligomer used.     

Dielectric monitoring of curing of liquid oligomer‐modified epoxy matrices

Dielectric measurements were performed in ‘real‐time’ at several temperatures to follow polymerization reactions on blends of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin with 4, 4′‐diaminodiphenylmethane (DDM) hardener and different amounts of polyoxypropylenetriamine (POPTA) oligomer. These systems exhibit phase separation induced by molar mass increasing through curing of the resin. Monitoring of phase separation and vitrification (related to the α‐relaxation) was performed by this technique. The results are compared with those for the unmodified resin–hardener mixture. The change of the main α‐relaxation with cure time, cure temperature, and amount of modifier was measured for the mixtures. This change of the main relaxation through curing in the frequency domain was indicative of the cure reaction advancement, because of its dependence on the viscosity of the medium. The change of the ionic conductivity during curing was also analysed, showing its dependence upon cure temperature. © 2001 Society of Chemical Industry     

Adhesive Properties of Epoxy Resin with Chromic Hardener

Cohesive and adhesive properties have been compared of epoxy resins crosslinked either with chromic‐based hardener or with conventional amine‐type hardener. Higher cohesive parameters, such as yield strength, Young's modulus and impact resistance were observed for the material cured with chromic hardener. The adhesive strength of metal‐metal joints (steel‐aluminium) has been also found to be higher for chromic hardener containing epoxy compared to conventional curing systems. The time dependencies of adhesive strength after thermal treatment at 140°C of the joints showed a higher thermal resistance of the epoxy with chromic hardener when compared to the amine cured resin.     

Toughening of epoxy resin systems using low‐viscosity additives

This study has evaluated three low‐viscosity epoxy additives as potential tougheners for two epoxy resin systems. The systems used were a lower‐reactive resin based upon the diglycidyl ether of bisphenol A (DGEBA) and the amine hardener diethyltoluene diamine, while the second epoxy resin was based upon tetraglycidyl methylene dianiline (TGDDM) and a cycloaliphatic diamine hardener. The additives evaluated as potential tougheners were an epoxy‐terminated aliphatic polyester hyperbranched polymer, a carboxy‐terminated butadiene rubber and an aminopropyl‐terminated siloxane. This work has shown that epoxy‐terminated hyperbranched polyesters can be used effectively to toughen the lower cross‐linked epoxy resins, i.e. the DGEBA‐based systems, with the main advantage being that they have minimal effect upon processing parameters such as viscosity and the gel time, while improving the fracture properties by about 54 % at a level of 15 wt% of additive and little effect upon the T_g. This result was attributed to the phase‐separation process producing a multi‐phase particulate morphology able to initiate particle cavitation with little residual epoxy resin dissolved in the continuous epoxy matrix remaining after cure. The rubber additive was found to impart similar levels of toughness improvement but was achieved with a 10–20 °C decrease in the T_g and a 30 % increase in initial viscosity. The siloxane additive was found not to improve toughness at all for the DGEBA‐based resin system due to the poor dispersion within the epoxy matrix. The TGDDM‐based resin systems were found not to be toughened by any of the additives due to the lack of plastic deformation of the highly cross‐linked epoxy network Copyright © 2003 Society of Chemical Industry     

Novel amine terminated elastomeric oligomers and their effects on properties of epoxy resins as a toughener

The objective of this study was to investigate the effects of amine terminated elastomeric epoxy tougheners on the mechanical and thermal properties of diglycidyl ether of bisphenol A based epoxy resin. The amine terminated polycaprolactone (PCL) (1) and PCL‐PDMS‐PCL (2) based oligomers were synthesized and characterized by FTIR spectroscopy. The stoichiometrical amount of the reactive oligomers as toughener, reactive epoxy resin and the curing agent, 4,4′‐diaminodiphenyl sulfone (DDS) were mixed and degassed. The homogenous mixtures were cured at 120°C into the preheated molds. The mechanical and thermal characterizations of toughened epoxy resin system were evaluated. It has been shown that the mechanical and thermal properties of toughened epoxy system vary as a function of the chemical structure and the concentration of rective oligomers. Higher mechanical properties were obtained for epoxy resin toughened by PCL‐PDMS‐PCL (2) based oligomer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of aliphatic amine epoxy hardener on the adhesive properties of blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with epoxy resin

The adhesive properties have been investigated in blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with diglycidyl ether of bisphenol A and three different aliphatic amine epoxy hardener. The adhesives properties are evaluated in steel alloy substrate using single‐lap shear test. The copolymers are initially miscible in the stoichiometric blends of epoxy resin and hardener at room temperature. Phase separation is noted in the course of the polymerization reaction. Different morphologies are obtained according to the amine epoxy hardener. The most effective adhesive for steel–steel joints in single‐lap shear test is the blends using 1‐(2‐aminoethyl)piperazine (AEP) as hardener. This system shows the biggest lap shear strength. However, the modified adhesives show a reduction in the mechanical resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Conductive epoxy/amine system containing polyaniline doped with dodecylbenzenesulfonic acid

We developed a conductive epoxy/amine system containing polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA). The curing behaviors of diglycidyl ether of bisphenol A with triethylenetetramine (TETA), PAni.DBSA, and both amine compounds at different concentrations were investigated by differential scanning calorimetry (DSC). Epoxy/TETA systems containing PAni.DBSA presented two distinct exothermic peaks at 90°C due to the cure by TETA as a hardener and at 236°C related to PAni.DBSA as the curing agent. The presence of PAni.DBSA in the systems constituted by epoxy/hardener in stoichiometric proportions resulted in a decrease in the glass‐transition temperature of the epoxy matrix, as indicated by DSC and dielectric analyses. Electrical conductivity was determined in the epoxy/amine networks, with the TETA concentration kept constant and also in stoichiometric proportions of mixed hardener (TETA + PAni.DBSA) to epoxy resin. The last condition resulted in a higher electrical conductivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4059–4065, 2006     

Miscibilization of telechelic fluoroalkeneoxide oligomers in epoxy resins and effects on morphology and physical properties

Hydroxyterminated fluoroalkene oxide oligomers were reacted with chlorendic anhydride and subsequently with ?-caprolactone to produce carboxyterminated perfluoroethers prepolymers that were totally miscible with diglycidylether of bisphenol A. Curing the epoxy resin mixtures with hexahydrophthalic anhydride hardener and benzyl dimethylamine catalyst produced transparent products exhibiting a two-phase co-continuous morphology. Prereacting the fluoroalkeneoxide prepolymers with an excess of epoxy resin prior to the addition of hardener and catalyst, resulted in opaque products displaying a two-phase dispersed particles morphology. The dynamic mechanical spectra of the cured products confirmed the absence of any significant short-range network miscibility and revealed substantial enhancements in β-relaxations in all cases, which are normally associated with microdispersed morphologies. Both systems exhibited much higher flexural strength and ductility than the equivalent unmodified epoxy resins even at very low levels of addition. 3.5–5.0%. The surface energy was found to be much lower than that exhibited by the unmodified resin system, and the reduction in water absorption was relatively small. The above effects were much more pronounced for products exhibiting a particulate morphology than for systems that exhibited a co-continuous morphology. © 1994 John Wiley & Sons, Inc.     

Epoxidized natural rubber/epoxy blends: Phase morphology and thermomechanical properties

Epoxidized natural rubbers (ENRs) were prepared. ENRs with different concentrations of up to 20 wt % were used as modifiers for epoxy resin. The epoxy monomer was cured with nadic methyl anhydride as a hardener in the presence of N,N‐dimethyl benzyl amine as an accelerator. The addition of ENR to an anhydride hardener/epoxy monomer mixture gave rise to the formation of a phase‐separated structure consisting of rubber domains dispersed in the epoxy‐rich phase. The particle size increased with increasing ENR content. The phase separation was investigated by scanning electron microscopy and dynamic mechanical analysis. The viscoelastic behavior of the liquid‐rubber‐modified epoxy resin was also evaluated with dynamic mechanical analysis. The storage moduli, loss moduli, and tan δ values were determined for the blends of the epoxy resin with ENR. The effect of the addition of rubber on the glass‐transition temperature of the epoxy matrix was followed. The thermal stability of the ENR‐modified epoxy resin was studied with thermogravimetric analysis. Parameters such as the onset of degradation, maximum degradation temperature, and final degradation were not affected by the addition of ENR. The mechanical properties of the liquid‐natural‐rubber‐modified epoxy resin were measured in terms of the fracture toughness and impact strength. The maximum impact strength and fracture toughness were observed with 10 wt % ENR modified epoxy blends. Various toughening mechanisms responsible for the enhancement in toughness of the diglycidyl ether of the bisphenol A/ENR blends were investigated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39906.     

Syntheses of regular copolyamides using triphenyl phosphite and pyridine

In this article, a method of preparing of regular copolyamide (co‐PA) in a reactor using triphenyl phosphite/pyridine as the activating agent was investigated. In two‐step reactions of copolymers prepared from two kinds of dicarboxylic acids and one kind of diamine, oligomer PAs containing amine end groups were first synthesized; then, the second dicarboxylic acid was added to the same reactor to polymerize high molecular weight and regular co‐PAs. However, when oligomers having carboxylic acid end groups were first prepared and another kind of diamine was added, the degree of polymerization was low. The reason proposed was that if the oligomer has an amine end group, it would coexist with the activating agent without deactivating; if the end group was the carboxylic acid end group, deactivation would occur. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 116–122, 2000     

Morphology of epoxy resin modified with silyl‐crosslinked urethane elastomer

Silyl‐crosslinked urethane elastomer modifying epoxy resin has drawn much interest. Here the triethoxysilyl‐terminated polycaprolactone elastomer (PCL‐TESi) modifying diglycidylether of bisphenol A epoxy resins (DGEBA) system was chosen, and then the effect of the type of curing agent on the phase structure of the studied epoxy resin system was investigated. The modified systems were obtained with different phase structures by varying the formulations of the curing agent. It was experimentally shown that with the addition of aminosilane (KBE‐9103), the crosslinked density was greatly increased. The cured system also showed from SEM and TEM analysis that addition of KBE‐9103 increased the compatibility between the PCL‐TESi and DGEBA, which made the ductility of the system decrease, but also indicated from TEM that addition of much KBE‐9103 made the reacted silicone particles coagulate each other. The state of phase separation from TEM in the cured system was theoretically explained. These would serve the deeper studies of the mechanism of silyl‐crosslinked urethane elastomer modifying epoxy resin in the future. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 611–619, 2005     

Curing characteristics of epoxy resin systems that include a biphenyl moiety

The curing characteristics of epoxy resin systems that include a biphenyl moiety were investigated according to the change of curing agents. Their curing kinetics mainly depend on the type of hardener. An autocatalytic kinetic reaction occurs in epoxy resin systems with phenol novolac hardener, regardless of the kinds of epoxy resin and the epoxy resin systems using Xylok and DCPDP (dicyclopentadiene‐type phenol resin) curing agents following an nth‐order kinetic mechanism. The kinetic parameters of all epoxy resin systems were reported in terms of a generalized kinetic equation that considered the diffusion term. The fastest reaction conversion rate among the epoxy resin systems with a phenol novolac curing agent was obtained in the EOCN‐C epoxy resin system, and for systems with Xylok and DCPDP hardeners, the highest reaction rate values were obtained in NC‐3000P and EOCN‐C epoxy resin systems, respectively. The system constants in DiBenedetto's equation of each epoxy resin system with different curing agents were obtained, and their curing characteristics can be interpreted by the curing model using a curing agent as a spacer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1942–1952, 2002     

用液态含羧基丙烯酸酯低聚物改性环氧树脂

采用溶液聚合法合成了以丙烯酸丁酯、丙烯腈为主链结构的液态含羧基丙烯酸酯低聚物,用其对环氧树脂进行增韧改性,讨论了丙烯腈、丙烯酸以及丙烯酸酯低聚物质量分数对改性环氧树脂力学性能的影响,并研究了改性环氧树脂的微观形态和动态力学性能。结果表明,丙烯酸酯低聚物质量分数为5％时,丙烯酸丁酯／丙烯腈／丙烯酸（质量比）为75／20／5的改性环氧树脂的拉伸强度比纯环氧树脂提高4．3％;丙烯酸酯低聚物质量分数为10％时,该改性环氧树脂的冲击强度比纯环氧树脂提高近4倍,同时体系的耐热性能保持不变;环氧树脂改性体系呈两相结构,丙烯酸酯低聚物质量分数达到30％时,对环氧树脂的增韧效果变差;随着丙烯酸酯低聚物质量分数的增加,改性环氧树脂的玻璃化转变温度先升高后降低,其质量分数不超过10％时,改性环氧树脂的玻璃化转变温度高于纯环氧树脂。     

Effects of perfluoroether concentration and curing protocol on morphology and mechanical properties of toughened TGDDM/MNA resin systems

Previous published work has shown that hydroxyl terminated perfluoroether oligomers can be suitably modified and functionalised to make them miscible with epoxy resins in the uncured state. The reaction conditions can adjusted to induce phase separation either through spinodal decomposition to produce an IPN type morphology, or by nucleation and growth if a dispersed-particle microstructure is required.In the present work we examine the relative toughening enhancement efficiency of the two possible heterophase morphologies. Both systems show a sigmoidal increase in fracture toughness, with increasing concentration of the perfluoroether modifier. However, this takes place at much lower modifier concentrations for the systems with a particulate morphology (about 3.5% w/w) than for IPN systems (about 7.5% w/w). The maximum fracture toughness achievable for the two systems, on the other hand, is very similar and coincides with the concentration at which co-continuous phases are formed.These differences in morphology, however, are not reflected in the variation of modulus and compressive yield strength with increasing concentration of perfluoroether modifier, in so far as both systems exhibit a gradual and small reduction in property with increasing concentration. Furthermore, the dynamic mechanical spectra of the two systems are very different, but the changes resulting from increasing the concentration of toughening agent are relatively small in either case.Nanoindentation tests indicate that it is the local plasticity, brought about by the presence of the softer perfluoroether phase, which is responsible for the enhancement of fracture toughness. This is corroborated by AFM examinations, which reveal local plastic deformations in the regions surrounding the softer particles.     

硫醇固化剂的合成和应用

硫醇固化剂与环氧树脂的配合物可低温快速固化,广泛应用于胶粘剂领域,目前尚依赖进口。为促进硫醇固化剂的国产化,对硫醇固化剂的制备方法和应用进行了研究。实验表明,选用β-巯基丙酸与季戊四醇在酸性催化剂存在下酯化,然后再与环氧树脂进行扩链反应,可以制得黏度和使用配比均适用的硫醇固化剂,总产率为95%以上。用此固化剂与环氧树脂及叔胺混合后,能在5℃以下数分钟内固化。该合成方法工艺简单,易于控制,制得的硫醇固化剂黏度适中,与环氧树脂相溶性好,低温固化快,固化物无色透明等超过了进口产品。