Morphology control in polysulfone‐modified epoxy resins by demixing behavior

Polysulfone (PSu) was used as a modifier of epoxy/aromatic diamine formulations. Two epoxy monomers, based on diglycidyl ether of bisphenol A (DGEBA), were used. The cure agent was 4,4′‐diaminodiphenylsulfone. PSu was miscible with DGEBA, as shown by the existence of a single glass‐transition temperature within the whole composition range. The effect of PSu addition on the cure kinetics was investigated. The reaction rate of the epoxy–amine species was slightly lower in the presence of PSu. The morphology was analyzed by optical and scanning electron microscopy. A range of microstructures were obtained by control over the cure temperature, the amount of PSu incorporated, and the molecular weights of the epoxy resins. The variations in the morphology resulted from the different stages of demixing, which were arrested because of the different developments of the viscosity of the system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 405–412, 2003     

Blends of liquid crystalline polyester–polyurethane and epoxy: Preparation and properties

A novel liquid crystalline polyester–polyurethane (LCPU) that contains polyester mesogenic units was synthesized in the present work. Through a careful investigation of the structure and morphology of the LCPU, it was found that the home‐synthesized LCPU is a highly birefringent thermotropic nematic liquid crystal. After being blended with bisphenol‐A epoxy, the liquid crystalline polymer can, simultaneously, improve the impact strength and the glass transition temperature as well as the tensile strength and the tensile modulus of the blends. It was proved to be an efficient toughening agent for epoxy without the expense of other properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 783–787, 2003     

Modification of the thermal properties and crystallization behaviour of poly(ethylene terephthalate) by copolymerization

Poly(ethylene terephthalate) (PET) is a widely used polyester, which can be crystallized from the melt over a wide range of supercooling conditions or, alternatively, quenched into the amorphous state and, subsequently, crystallized by thermal treatment above the glass‐transition temperature. It is well known that the crystallization of PET can be hindered by means of copolymerization or reactive blending. The incorporation of comonomeric units into the polymer backbone leads to an irregular chain structure and thereby inhibits regular chain packing for crystallization. The crystallization of PET copolyesters is strongly influenced by the chain microstructure regarding comonomer distribution, randomness and length of the crystallizable ethylene terephthalate sequences. This paper is mainly devoted to the thermally induced crystallization behaviour of PET and to reviewing the efforts that have been made in the last decade to modify the glass‐transition and melting temperatures, the crystallinity and the crystallization rate of this polyester. Furthermore, some illustrative experimental data obtained from isothermal and non‐isothermal crystallization of PET are included in this study. © 2003 Society of Chemical Industry     

Effect of side‐chain length of succinic anhydride on coefficient of thermal expansion behavior of epoxy resins

The effect of an alkenyl side‐chain of succinic anhydride (SA) on the thermal behavior and the coefficient of thermal expansion (CTE) of diglycidylether of bisphenol A (DGEBA) epoxy resins was studied. The number of carbons in the side‐chain of SA was varied from 6 to 14 and N,N‐Dimethylbenzylamine was used as an accelerator. As a result, the reactivity of SA with epoxide groups was decreased on increasing the length of the alkenyl side‐chain of SA. The thermal stabilities of cured DGEBA/SA samples were approximately constant with varying alkenyl side‐chain of SA. Also, the CTE of the systems was increased as the length of the alkenyl side‐chain of SA increased. This could be attributed to the increased motion of the chain segments in the epoxy network structure induced by the longer alkenyl side‐chain of SA. The effect of amount anhydride, thermoplastics, and fillers on the CTE of the epoxy resins was also discussed. Copyright © 2006 Society of Chemical Industry     

Cationic photopolymerization of bisphenol A diglycidyl ether epoxy under 385 nm

The cationic photopolymerization of bisphenol A diglycidyl ether epoxy (DGEBA) at λ = 385 nm was conducted by the combination of a cationic photoinitiator PAG30201 (Bis (4‐isobutylphenyl) iodonium hexafluorophosphate) and a photosensitizer PSS303 (9,10‐dibutoxy‐9,10‐dihydroanthrance). The kinetic characterization was investigated by real‐time Fourier transform infrared spectroscopy. The enhancement of epoxy conversion of DGEBA was achieved by increasing temperature, adding alcohols, active monomers and radical photoinitiators. As a result, in the presence of 2 wt % PAG30201 and 1.2 wt % PSS303, the epoxy rings conversion of DGEBA has reached to more than 70% from 55.9% at room temperature; it could be increased to almost 80% if heated to 60°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3698–3703, 2013     

Dynamic mechanical properties of sandwich‐structured epoxy beam composites containing poly(ethyleneterephthalate)/poly(ethyleneglycol) copolymer with shape memory effect

To make smart vibration‐controlling composite laminate, a few poly(ethylene terephthalate) (PET) and poly(ethylene glycol) (PEG) copolymers with shape memory ability were prepared. After selecting the best composition of PET–PEG copolymer in mechanical properties, a crosslinking agent such as glycerine, sorbitol, or maleic anhydride (MA) was included for crosslinked copolymer, followed by analysis of its effect on mechanical, shape memory, and damping properties. The highest shape recovery was observed for copolymer with 2.5 mol % of glycerine, and the best damping effect indicating vibration control ability was from copolymer with 2.5 mol % of sorbitol. With the optimum copolymers in hand, sandwich‐structured epoxy beam composites fabricated from an epoxy beam laminate and crosslinked PET–PEG copolymer showed that impact strength increased from 1.9 to 3.7 times depending on the type of copolymer, and damping effect also increased as much as 23 times for the best case compared to epoxy laminate beam alone. The resultant sandwich‐structured epoxy beam composite can be utilized as structural composite material with vibration control ability, and its glass transition temperature can be controlled by adjustment of PET, PEG, or crosslinking agent composition. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3141–3149, 2003     

Effect of backbone moiety in epoxies on thermal conductivity of epoxy/alumina composite

We chose two commercial epoxies, bisphenol A diglycidyl ether (DGEBA) and 3,3′,5,5′‐tetramethyl‐4,4′‐biphenol diglycidyl ether (TMBP), and synthesized one liquid crystalline epoxy (LCE), 4′4′‐bis(4‐hydroxybenzylidene)‐diaminophenylene diglycidyl ether (LCE‐DP) to investigate the effect of backbone moiety in epoxies on the thermal conductivity of epoxy/alumina composite. The DGEBA structure shows an amorphous state and the TMBP structure displays a crystal phase, whereas the LCE‐DP structure exhibits a liquid crystalline phase. The curing behaviors of them were examined employing 4,4′‐diaminodiphenylsulfone (DDS) as a curing agent. The heat of curing of epoxy resin was measured with dynamic differential scanning calorimetry (DSC). Alumina (Al₂O₃) of commercial source was applied as an inorganic filler. Thermal conductivity was measured by laser flash method and compared with value predicted by two theoretical models, Lewis‐Nielsen and Agari‐Uno. The results indicated that the thermal conductivity of the LCE‐DP structure was larger than that of the commercial epoxy resins such as TMBP and DGEBA and the experimental data fitted quite well in the values estimated by Agari‐Uno model. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Mechanical properties of an epoxy resin toughened by polyester

The epoxy resins were toughened by 4–24 phr polyester with average molecular weight 1.9×10⁴ g/mol in this investigation. The mechanical properties were examined and dynamic mechanics analyses were performed for the epoxy resins before and after the modification. The toughening mechanism of polyester to epoxy resin is discussed in light of the scanning electronic microscopy observation of the fracture surfaces. The results showed that the impact strength and tensile strength of the modified epoxy resin were remarkably greater than those of the unmodified cured epoxy resin. The most suitable composition for the modified epoxy resin was the addition of 16 phr polyester, which led to 138 and 46% increments in the impact strength and the tensile strength, respectively. And the mechanical properties depended greatly on the congregating state of polyester added. The polyester dispersing in the epoxy matrix was amorphous when its addition was less than or equal to 12 phr, and was sphere crystals when the addition was over 16 phr. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3384–3389, 2003     

Solvent‐induced modifications in polyester yarns. II. Structural and thermal behavior

The structural and thermal behaviors of polyester yarns treated with trichloroacetic acid–chloroform (TCAC) mixture were investigated by differential scanning calorimetric analysis (DSC), wide‐angle X‐ray scattering (WAXS), infrared spectroscopy (IR), and scanning electron microscopy (SEM). The effects of TCAC treatment on original fine filament (FFP) and microdenier (MDP) polyester yarns and on heat‐set polyester yarns were studied. It was found that the glass transition temperature of TCAC‐treated polyester yarns decreases with an increase in treatment concentration due to the plasticization effect, which is remarkable even at lower treatment concentration. The TCAC treatment on polyester yarns resulted in the formation of new crystallites in the extended noncrystalline domains of PET as well as growth and perfection of these new crystallites and the preexisting crystals. Further, the DSC thermograms revealed that TCAC treatment with 3% concentration could be able to overcome the structural changes in PET produced by heat setting at 180°C. The substantial changes in noncrystalline and crystalline domains observed were related to the mechanical properties of yarns. From the WAXS studies, an increase in crystal size and lateral order of TCAC‐treated polyester yarns was noted. The most distinct changes brought about by TCAC treatment include overall orientation determined by the trans–gauche ratio from IR measurements. The removal of oligomers and smoothening out of the fiber surface by TCAC treatment were observed from SEM studies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1555–1566, 2003     

Development of Biobased Epoxy Matrices for the Preparation of Green Composite Materials for Civil Engineering Applications

Epoxy matrices are successfully used for structural strengthening in civil engineering applications by means of carbon fiber reinforced polymers (CFRPs). In the context of sustainable development, the aim of this study is to develop biobased epoxy matrices as an alternative to the traditional petroleum‐based epoxy matrices used in CFRPs. This study focuses on two biobased epoxy monomers: a diglycidyl ether of bisphenol A (DGEBA) and a sorbitol polyglycidyl ether (SPGE). These monomers are reacted with a biobased curing agent, a phenalkamine (PhA), derived from cardanol. After in‐depth characterization of the chemical structures of the three monomers, the reactivity of both systems, DGEBA‐PhA and SPGE‐PhA, is studied using differential scanning calorimetry and rheology. The properties of the networks are characterized via dynamic mechanical analysis and water uptake measurements for polymers with partial or full conversion of epoxy groups, which are obtained by crosslinking at room temperature or at high temperature, respectively. The results reveal that the two systems are good candidates for the preparation of green composite materials as they meet the requirements necessary for manufacturing composites in civil engineering applications.     

Synthesis,thermal behavior,and cone calorimetry of organophosphorus epoxy materials

An organophosphorus epoxy resin with diglycidyl ether of bisphenol A (DGEBA), which has improved fire performance, was synthesized from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and DGEBA. The epoxy resin was then cured with an isomeric mixture of 3,5‐diethyltoluene‐2,4‐diamine and 3,5‐diethyltoluene‐2,6‐diamine. The reaction kinetics were measured by Fourier transform IR, ¹H‐NMR, and differential scanning calorimetry. The effect of the incorporation of a phosphorus species into the epoxy network structures was also measured using thermogravimetric, thermal conductivity, and dynamic mechanical thermal analyses. The fire performance was measured using cone calorimetry, which showed that a significant improvement was achieved by the addition of only 1–4% phosphorus into the epoxy backbone. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3696–3707, 2003     

Miscibility study on blend of thermotropic liquid crystalline polymers and polyester

The miscibility of thermotropic liquid crystalline polymers (TLCPs) and polyester blends was investigated with thermal and morphological analyses, as well as transesterification. TLCPs composed of 80 mol % para‐hydroxybenzoate (PHB) and 20 mol % poly(ethylene terephthalate) (PET) or 60 mol % PHB and 40 mol % PET, and polyesters such as PET and poly(ethylene 2,6‐naphthalate) (PEN) were melt blended in an internal mixer. DSC analyses were performed to investigate the thermal transition behavior and to obtain thermodynamic parameters. All the blends showed only a single glass‐transition temperature, which means they are partially miscible in the molten state. The Flory–Huggins interaction parameter was calculated employing the Nishi–Wang approach, and negative values were obtained except for the P(HB8‐ET2)/PEN blends. Transesterification was investigated using ¹H‐NMR, and the change of chemical shift compared to pure PET or P(HB‐ET)s was observed in the P(HB‐ET)/PET blends. An intermediate chemical shift value (4.83 ppm) was observed in the P(HB6‐ET4)/PEN blends, which indicates transesterification occurred. The fractured surface morphology of scanning electron micrographs showed that the interfaces between the LC droplets and matrix were not distinct. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1842–1851, 2003     

Epoxy resin containing the poly(sily ether): Preparation,morphology, and mechanical properties

The poly(sily ether) with pendant chloromethyl groups (PSE) was synthesized by the polyaddition of dichloromethylsilane (DCM) and diglycidylether of bisphenol A (DGEBA) with tetrabutylammonium chloride (TBAC) as a catalyst. This polymer was miscible with diglycidyl ether of bisphenol A (DGEBA), the precursor of epoxy resin. The miscibility is considered to be due mainly to entropy contribution because the molecular weight of DGEBA is quite low. The blends of epoxy resin with PSE were prepared through in situ curing reaction of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐diaminodiphenylmethane (DDM) in the presence of PSE. The DDM‐cured epoxy resin/PSE blends with PSE content up to 40 wt % were obtained. The reaction started from the initial homogeneous ternary mixture of DGEBA/DDM/PSE. With curing proceeding, phase separation induced by polymerization occurred. PSE was immiscible with the 4,4′‐diaminodiphenylmethane‐cured epoxy resin (ER) because the blends exhibited two separate glass transition temperatures (T_gs) as revealed by the means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). SEM showed that all the ER/PSE blends are heterogeneous. Depending on blend composition, the blends can display PSE‐ or epoxy‐dispersed morphologies, respectively. The mechanical test showed that the DDM‐cured ER/PSE blend containing 25 wt % PSE displayed a substantial improvement in Izod impact strength, i.e., epoxy resin was significantly toughened. The improvement in impact toughness corresponded to the formation of PSE‐dispersed phase structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 505–512, 2003     

Cationic copolymerization of epoxy siloxane monomer with liquid poly‐butadiene and its light emitting diode encapsulation

A novel epoxy siloxane hybrid was prepared using epoxy siloxane monomers of 1,3‐bis[2‐(3‐{7‐oxabicyclo[4.1.0]heptyl})ethyl]‐tetramethyldisiloxane (BEPDS) with hydroxyl terminated hydrogenated polybutadiene (GI‐1000), in different proportions. Apparent polymerization reactivity was decreased with increasing GI‐1000 concentration but the normalized reactivity per epoxy group was slightly increased due to reaction between hydroxyl group and epoxy group. Increasing GI‐1000 concentration showed significant flexibility improvement in epoxy siloxane hybrid. At 30 wt % of GI‐1000 addition, glass transition temperature was decreased from 116 to 21°C and shore D hardness was decreased from 75 to 46.5% weight loss temperature of these epoxy siloxane hybrid was decreased with increasing GI‐1000 concentration, whereas thermal discoloration was increased. LED encapsulation with this epoxy siloxane demonstrated no crack when GI‐1000 was 30 wt % or more. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

Homopolymerization of epoxy monomers initiated by 4‐(dimethylamino)pyridine

The anionic epoxy homopolymerization initiated by tertiary amines, imidazoles, and ammonium salts is a complex reaction exhibiting two undesired characteristics for practical applications: (a) slow reaction rates with long induction periods, and (b) short primary chains due to the high rate of chain transfer reactions. Therefore, these systems have not found an important place in commercial applications. In this study, it is shown that using 4‐(dimethylamino)pyridine (DMAP) as initiator of the polymerization of phenyl glycidyl ether (PGE) or diglycidyl ether of bisphenol A (DGEBA) enables to obtain high polymerization rates and longer primary chains than those generated using typical initiators. A critical molar ratio DMAP/epoxy groups was necessary to attain complete conversion. Networks resulting from the DMAP‐initiated homopolymerization of DGEBA exhibited a high crosslink density and corresponding high values of the glass transition temperature (T_g = 160°C) and of the rubbery elastic modulus (higher than 100 MPa). An intense brown color of reaction products, associated with an absorption band with a maximum at 360 nm, was ascribed to the presence of initiator fragments with conjugated double bonds in chain ends. These results might revalorize the anionic homopolymerization of epoxy monomers for commercial applications. POLYM. ENG. SCI. 46:351–359, 2006. © 2006 Society of Plastics Engineers     

Transesterification in homogeneous poly(ε‐caprolactone)–epoxy blends

Transesterification has been investigated in poly(ε‐caprolactone) (PCL)–epoxy blends. In the hot melt process, the hydroxyl on diglycidyl ether of bisphenol‐A (DGEBA) monomers is too low to give a noticeable transesterification reaction. In the postcure process, model reactions reveal that the hydroxyls from a ring‐opening reaction are able to react with the esters of PCL. In the meantime, the PCL molecular weight decrease and its distribution becomes broader. Nuclear magnetic resonance spectra reveal that fraction of the tertiary hydroxyls converts to secondary hydroxyls. In the cured DGEBA–3,3′‐dimethylmethylene‐di(cyclohexylamine)–PCL blend, a homogeneous morphology is achieved. PCL segments are grafted onto the epoxy network after postcuring and result in the lower T_g observed in the differential scanning calorimetry thermogram. A higher transesterification extent also results in broader transition peaks by dynamic mechanical analysis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 75–82, 1999     

Fabrication of barium titanate nanoparticles‐epoxy resin composite films and their dielectric properties

A method for fabricating epoxy resin films dispersing the surface‐modified barium titanate (BT) particles (BT‐epoxy resin composite films) are proposed. BT particles with a size of 7.8 nm and a crystal size of 8.6 nm were synthesized with a complex alkoxide method. To introduce epoxy groups on the BT particle surface, the BT particles were surface‐modified with 2‐(3,4‐epoxycyclohexyl)‐ethyltrimethoxysilane. A precursor solution, which was prepared by prereacting 2,2‐bis(4‐glycidyloxyphenyl)propane (BGPP) and phthalic anhydride in 4‐butyrolactone and adding the surface‐modified BT particles to the prereacting solution, was spin‐coated on glass substrates to fabricate the composite films. An increase in BT volume fraction in film increased dielectric constant of the composite film while keeping dissipation factor below 0.03. The dielectric constant attained 10.8 at a BT volume fraction of 30% in film that was around twice higher than pure epoxy resin film. POLYM. COMPOS., 31:1179–1183, 2010. © 2009 Society of Plastics Engineers     

Toughening of recycled poly(ethylene terephthalate) with a maleic anhydride grafted SEBS triblock copolymer

Toughening of recycled poly(ethylene terephthalate) (PET) was carried out by blending with a maleic anhydride grafted styrene‐ethylene/butylene‐styrene triblock copolymer (SEBS‐g‐MA). With 30 wt % of the SEBS‐g‐MA, the notched Izod impact strength of the recycled PET was improved by more than 10‐fold. SEM micrographs indicated that cavitation occurred in just a small area near the notch root. Addition of 0.2 phr of a tetrafunctional epoxy monomer increased the recycled PET melt viscosity by chain extension reaction. Different from the positive effect of the epoxy monomer in toughening of nylon and PBT with elastomers, the use of the epoxy monomer in the recycled PET/SEBS‐g‐MA blends failed to further enhance dispersion quality and thus notched impact strength. This negative effect of the epoxy monomer was attributed to the faster reactivity of the epoxy group with maleic anhydride of the SEBS‐g‐MA than with the carboxyl or hydroxyl group of recycled PET. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1462–1472, 2004     

A comparative study of structure–property relationships in highly oriented thermoplastic and thermotropic polyesters with different chemical structures

Structure and properties of commercially available fully oriented thermoplastic and thermotropic polyester fibers have been investigated using optical birefringence, infrared spectroscopy, wide‐angle X‐ray diffraction and tensile testing methods. The effect of the replacement of p‐phenylene ring in poly(ethylene terephthalate) (PET) with stiffer and bulkier naphthalene ring in Poly(ethylene 2,6‐naphthalate) (PEN) structure to result in an enhanced birefringence and tensile modulus values is shown. There exists a similar case with the replacement of linear flexible ethylene units in PET and PEN fibers with fully aromatic rigid rings in thermotropic polyesters. Infrared spectroscopy is used in the determination of crystallinity values through the estimation of trans conformer contents in the crystalline phase. The analysis of results obtained from infrared spectroscopy data of highly oriented PET and PEN fibers suggests that trans conformers in the crystalline phase are more highly oriented than gauche conformers in the amorphous phase. Analysis of X‐ray diffraction traces and infrared spectra shows the presence of polymorphic structure consisting of α‐ and β‐phase structures in the fully oriented PEN fiber. The results suggest that the trans conformers in the β‐phase is more highly oriented than the α‐phase. X‐ray analysis of Vectran® MK fiber suggests a lateral organization arising from high temperature modification of poly(p‐oxybenzoate) structure, whereas the structure of Vectran® HS fiber contains regions adopting lateral chain packing similar to the room temperature modification of poly(p‐oxybenzoate). Both fibers are shown by X‐ray diffraction and infrared analyses to consist of predominantly oriented noncrystalline (63–64%) structure together with smaller proportion of oriented crystalline (22–24%) and unoriented noncrystalline (12–15%) structures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 142–160, 2006