Cationic electron‐beam curing of a high‐functionality epoxy: effect of post‐curing on glass transition and conversion

This paper reports on the cationic electron‐beam curing of a high‐functionality SU8 epoxy resin, which is extensively used as a UV‐curing negative photoresist for micro‐electronics machine systems (MEMS) applications. Results show that elevated post‐curing treatment significantly increased both the conversion and the glass transition. The degree of conversion and the glass transition temperature were measured by using Fourier‐transform infrared (FTIR) spectroscopy and modulated differential scanning calorimetry (MDSC^®), respectively. The glass transition temperature (T_g), which has been observed to be dependent on the degree of conversion, reaches a maximum of 162 °C at 50 Mrad and post‐curing at 90 °C. The degradation pattern of the cured resin does not show much variation for exposure at 5 Mrad, but does show significant variation for 50 Mrad exposure at various post‐curing temperatures. A degree of conversion of more than 0.8 was achieved at a dosage of 30 Mrad with post curing at 80 °C, for the epoxy resin with an average functionality of 8 a feature simply not achievable when using UV‐curing. Copyright © 2004 Society of Chemical Industry     

Cure kinetics for the ultraviolet cationic polymerization of cycloliphatic and diglycidyl ether of bisphenol‐A (DGEBA) epoxy systems with sulfonium salt using an auto catalytic model

This paper investigates the cure kinetics for the ultraviolet (UV) cationic polymerization for both a cycloaliphatic and diglycidyl ether of bisphenol‐A (DGEBA) epoxy system, using the photoinitiator triarylsulfonium hexafluoroantimonate salt. Using an autocatalytic kinetic cure model, the reaction rate values for both cycloaliphatic and DGEBA epoxy systems were determined for different photoinitiator amount (wt %) added, and at different UV exposure temperatures. The value for the cycloaliphatic epoxy increased significantly with addition of the sulfonium salt, reaching a limiting maximum after 2%. The value for the DGEBA epoxy system also increased, to a limiting maximum after 3%. Addition of the sulfonium salt significantly lowered the activation energy for the cycloaliphatic epoxy at all levels of addition, with the reduction proportional to the amount of salt added. In contrast, the sulfonium salt did not have a major effect on the DEGBA until the addition of at least 3% of the salt. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1587–1591, 2002     

Relationship between viscoelastic properties and gelation in the epoxy/phenol‐novolac blend system with N‐benzylpyrazinium salt as a latent thermal catalyst

A study of viscoelastic properties and gelation in epoxy/phenol‐novolac blend system initiated with 1 wt % of N‐benzylpyrazinium hexafluoroantimonate (BPH) as a latent cationic thermal initiator was performed by analysis of rheological properties using a rheometer. Latent behavior was investigated by measuring the conversion as a function of curing temperature using traditional curing agents, such as ethylene diamine (EDA) and nadic methyl anhydride (NMA) in comparison to BPH. In the relationship between viscoelastic properties and gelation of epoxy/phenol‐novolac blend system, the time of modulus crossover was dependent on high frequency and cure temperature. The activation energy (E_c) for crosslinking from rheometric analysis increased within the composition range of 20–40 wt % phenol‐novolac resin. The 40 wt % phenol‐novolac (N40) to epoxy resin showed the highest value in the blend system, due to the three‐dimensional crosslinking that can take place between hydroxyl groups within the phenol resin or epoxides within the epoxy resin involving polyaddition of the initiator with BPH. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2299–2308, 2001     

Synthesis,reactivity, and properties of new diaryliodonium salts as photoinitiators for the cationic polymerization of epoxy silicones

Diaryliodonium tetrakis (pentafluorophenyl) borate salts generate a higher reactivity than any other known diaryliodonium salt. The photochemical properties of diaryliodonium tetrakis (pentafluorophenyl) borate salts were compared to those of the diaryliodonium hexafluoroantimonate salt. The results show that these new salts are the most reactive photoinitiators in this family. In addition, diaryliodonium tetrakis (pentafluorophenyl) borate salts are soluble in low polarity media, such as epoxy silicone oils, which are rich in epoxy groups and insensitive to humidity. These salts have the advantage not to contain a heavy metal (such as antimony). The new properties generated by the use of the tetrakis (pentafluoropheyl) borate anion make the future of the cationic photopolymerization promising. © 1996 John Wiley & Sons, Inc.     

Cationic photopolymerization of 3‐benzyloxymethyl‐3‐ethyl‐oxetane

The cationic photopolymerization of 3‐benzyloxymethyl‐3‐ethyl‐oxetane (MOX104) initiated by triphenylsulfonium hexafluoroantimonate under UV light was conducted. The kinetics were investigated by real‐time Fourier transform IR spectroscopy and the mechanical and thermal properties of poly(MOX104) were examined by dynamic mechanical analysis and TGA. To adjust the properties of the polymer, different initiator concentrations and comonomer composition were applied. The results showed that the conversion of MOX104 was improved significantly from 17% to almost 90% by adding a certain amount of 3,4‐epoxycyclohexane carboxylate or diglycidyl ether of bisphenol A epoxy resin, while not much effect was observed by adding 1,4‐butanediol diglycidyl ether. Moreover, the glass transition temperature, decomposition temperature and Young's modulus of poly(MOX104) were improved by adding different amounts of diglycidyl ether of bisphenol A epoxy resin. © 2016 Society of Chemical Industry     

Preparation and characterization of siliconized epoxy/bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenyl methane) intercrosslinked matrices for engineering applications

Novel hybrid intercrosslinked networks of hydroxyl‐terminated polydimethylsiloxane‐modified epoxy and bismaleimide matrix systems have been developed. Epoxy systems modified with 5, 10, and 15 wt % of hydroxyl‐terminated polydimethylsiloxane (HTPDMS) were developed by using epoxy resin and hydroxyl‐terminated polydimethylsiloxane with γ‐aminopropyltriethoxysilane (γ‐APS) as compatibilizer and dibutyltindilaurate as catalyst. The reaction between hydroxyl‐terminated polydimethylsiloxane and epoxy resin was confirmed by IR spectral studies. The siliconized epoxy systems were further modified with 5, 10, and 15 wt % of bismaleimide (BMI). The matrices, in the form of castings, were characterized for their mechanical properties. Differential scanning calorimetry and thermogravimetric analysis of the matrix samples were also performed to determine the glass‐transition temperature and thermal‐degradation temperature of the systems. Data obtained from mechanical studies and thermal characterization indicate that the introduction of siloxane into epoxy improves the toughness and thermal stability of epoxy resin with reduction in strength and modulus values. Similarly the incorporation of bismaleimde into epoxy resin improved both tensile strength and thermal behavior of epoxy resin. However, the introduction of siloxane and bismaleimide into epoxy enhances both the mechanical and thermal properties according to their percentage content. Among the siliconized epoxy/bismaleimide intercrosslinked matrices, the epoxy matrix having 5% siloxane and 15% bismaleimide exhibited better mechanical and thermal properties than did matrices having other combinations. The resulting siliconized (5%) epoxy bismaleimide (15%) matrix can be used in the place of unmodified epoxy for the fabrication of aerospace and engineering composite components for better performance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 38–46, 2001     

UV intensity,temperature and dark-curing effects in cationic photo-polymerization of a cycloaliphatic epoxy resin

A difunctional cycloaliphatic epoxy monomer was cationically photo-polymerized in the presence of a diaryliodonium salt photoinitiator and an isopropyl thioxanthone photosensitizer at different temperatures and UV intensities. The photo-polymerization kinetics and structure formation were analysed using photo-DSC, IR spectroscopy and photo-rheology. An autocatalytic relation was used to model the conversion state with Arrhenius and power-law relationships for temperature and light intensity dependence. Conversion was found to depend on sample thickness, following the Beer–Lambert law. Photo-rheology measurements showed that the system vitrified before gelation at ambient temperature, and after gelation at high temperature under intense UV illumination. Time temperature transformation and time intensity transformation diagrams were built. Moreover, isothermal dark-curing enabled significant conversion increases up to the occurrence of vitrification, while thermal post-curing above T_g led to conversion as high as 71%. Thermo-mechanical measurements enabled to quantify T_g and the effects of the increase in conversion provided by thermal post-curing.     

Ultraviolet‐curing behavior of an epoxy acrylate resin system

Ultraviolet (UV)‐curing behavior of an epoxy acrylate resin system comprising an epoxy acrylate oligomer, a reactive diluent, and a photoinitiator was investigated by Fourier transform infrared (FTIR) spectroscopy. The conversion changes of the resin system containing 20 phr of 1,6‐hexanediol diacrylate as a reactive diluent and 2‐hydroxy‐2‐methyl‐1‐phenyl‐propan‐1‐one as a photoinitiator were measured under different UV‐curing conditions. The fractional conversion was calculated from the area of the absorption peak for the vinyl group vibration occurring at 810 cm^?1. The effects of photoinitiator concentration, total UV dosage, one‐step or stepwise UV irradiation, UV intensity, atmosphere, and temperature on the curing behavior of the resin system were investigated. The conversion of the resin system increased rapidly at the initial stage of the UV‐curing process but increased very slowly after that. The final conversion of the resin system was mainly affected by total UV dosage. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1180–1185, 2005     

Rheological characterization of UV‐curable epoxy systems: Effects of o‐Boehmite nanofillers and a hyperbranched polymeric modifier

An organo‐modified Boehmite (o‐Boehmite) was used to prepare nanocomposite UV‐curing coatings, based on a cycloaliphatic epoxy resin (3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate). A hyperbranched polymer (HBP) based on highly branched polyester, was also added to the resin, with the aim to modify its reactivity, such as a possible route to increase the toughness of the resin. Different amounts of the nanofiller and the HBP, ranging from 5 up to 20 wt % of resin, were dispersed into the resin in the presence of triarylsulfonium hexafluoroantimonate, as a photoinitiator for the UV curing of the resin. The rheological behavior of the formulations produced was studied as function of the shear rate and of the content of each filler using a cone and plate rheometer. A general increase in viscosity was observed with increasing the volume fraction of each filler and a moderate pseudoplastic behavior was observed when o‐Boehmite filler was added. A non‐Newtonian behavior was observed with the incorporation of the HBP. The viscosity of the epoxy/boehmite resin mixtures was analyzed as function of the nanofiller volume fraction. In the case of epoxy/hyperbranched resin mixtures, the Cross equation was used to predict the viscosity of each formulation as a function of the shear rate and an appropriate relationship to predict the viscosity of each formulation as a function of the filler volume fraction, was determined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study of the cationic photopolymerization kinetics of cyclic acetals

Summary Photocationic polymerization for three cyclic acetals, namely 1,3-dioxolane, 1,3-dioxepane and 1,3,6-trioxocane, respectively, has been studied. Several cationic photo-initiators (diaryliodonium or triarylsulfonium salts, and one arene-metal complex) have been used. Differential scanning photo-calorimetry (DPC) has been employed to record the dependence conversion versus time. DPC thermogrames, in turn, have been utilized to calculate the propagation reaction constants as well as the corresponding activation energies. The values for the propagation constants at 30°C are 1.6·10² L/mol·s for 1,3-dioxolane, using a diaryliodonium salt as photoinitiator, 1.6·10³ L/mol·s for 1,3-dioxepane and 6.1·10³ L/mol·s for 1,3,6-trioxocane, respectively, in the presence of a triarylsulfonium salt as photoinitiator. The activation energies are in the range of 9.6÷19.6 kcal/mole. Received: 19 July 2000/Revised version: 8 November 2001/ Accepted: 8 November 2001     

A novel dry photopolymer for volume‐phase holograms

A novel photopolymer for the fabrication of high‐resolution volume‐phase holograms, which primarily are used for holographic optical elements, is reported. This photopolymer consists of a thermosetting resin as a polymeric binder, a polyfunctional monomer, a photoinitiator, and a sensitizing dye. The chemistry to form images is based on the polymerization of an acrylic monomer initiated by radical species while making the holographic exposure, and accelerated diffusion transfer of the polymerized monomer with postexposure baking, and of a bisphenol‐type epoxy resin as a binder initiated by cations with UV exposure, which are generated through photodecomposition of a diaryliodonium salt‐sensitized 3‐ketocoumarin dye. Exposure of these photopolymer films to an Ar⁺ laser beam emitting 514.5 nm light at 60–150 mJ/cm² and subsequent heat treatment resulted in a refractive index alteration according to the light intensity. With this dry process, high diffraction efficiency and heat‐stable holograms can be formed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2189–2200, 2000     

Cure properties of methacrylate‐type prepolymer that include cyclohexane moiety

New methacrylate‐type prepolymers including a cyclohexane moiety, which may be used as binder resins for the color filter resist of liquid crystal display, were synthesized by the reaction with methacrylic acid (MA) and epoxy resins. Their photo‐ and thermal cure properties were investigated using Fourier transform infrared spectroscopy and DSC, respectively. Their photocure reaction rates and the extent of reaction conversion increased with the concentration of photoinitiator and intensity of UV irradiation. An increase of photocure reaction temperature was attributed to the increase of photocure reaction rate and the degree of reaction conversion for EHPE‐3150‐MA prepolymer. Thermal stability was studied by observing changes in the transmittance of the photocured polymer film upon heating. The polymer was extremely stable, showing almost no transmittance change in the visible range even after being heated at 250°C for 1 h. We also investigated thermal cure reaction using a DSC technique. An autocatalytic kinetic reaction occurs in these systems, and the kinetic parameters of all systems were reported in terms of a generalized kinetic equation that considered the diffusion term. It can be shown that the reaction conversion rate of NC‐9110‐MA is faster than that of EHPE‐3150‐MA, regardless of the kind of thermal initiator. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 43–52, 2004     

Curing kinetics of UV‐initiated cationic photopolymerization of divinyl ether photosensitized by thioxanthone

Photodifferential scanning calorimetry was used to investigate the photocuring kinetics of UV‐initiated cationic photopolymerizations of 1,4‐cyclohexane dimethanol divinyl ether (CHVE) monomer with and without a photosensitizer, 2,4‐diethylthioxanthone (DETX), in the presence of a diaryliodonium‐salt photoinitiator. Two kinetics parameters, the rate constant (k) and the order of the initiation reaction (m), were determined for the CHVE system with different amounts of added DETX photosensitizer (0–1 wt %) and at different isothermal temperatures (25–55°C) using an autocatalytic kinetics model. The photosensitized CHVE system exhibited much higher k and m values than did the nonphotosensitized system, which was attributable to the effects of photosensitization. Furthermore, the values of k and m for both CHVE systems increased significantly with increasing isothermal temperature because of a thermal contribution toward increasing the mobility of active species. The addition of DETX lowered the activation energy for the UV‐curable vinyl ether system. The collision factor for the system with DETX was higher than that obtained for the system without DETX, indicating that the reactivity of the former was greater than that of the latter because of the photosensitization effect. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1345–1351, 2005     

Electron Beam Curing of the System Cycloaliphatic Diepoxide‐Epoxidized Natural Rubber‐Glycidyl Methacrylate in Presence of Cationic Initiators

Electron beam curing of the system cycloaliphatic diepoxide‐epoxidized natural rubber‐glycidyl methacrylate containing a cationic initiator was carried out. Storage modulus, glass transition temperature and pendulum hardness were measured as function of EB dose, photoinitiator concentration, content of epoxidized natural rubber, post cure temperature and post cure time. At electron beam doses larger than 100 kGy a highly cross‐linked polymer network is generated which shows a two phase morphology. Microscale elastomeric domains are incorporated into a continuous epoxy resin phase. Dynamical mechanical analysis and pendulum hardness measurement show that an increase of the ENR ratio leads to a more elastic polymer network. Post curing results in increased glass transition temperatures. This EB cured polymer system is believed to provide both toughness and favorable viscoelastic properties to be used as component of EB curable composites.     

Low‐temperature photopolymerization and post‐cure characteristics of acrylates

Near‐infrared spectroscopy was used to investigate the post‐cure characteristics of acrylates polymerized from ? 75 °C up to room temperature. The results obtained showed that the double bond conversion increased with increasing initiator concentration. Post‐cure was much more striking for samples cured at lower temperatures. The chemical structure of monomer and photoinitiator had a great effect on the post‐cure process. The greater the functionality, the lower the final double bond conversion and the more distinct the post‐cure effect. Copyright © 2006 Society of Chemical Industry Society of Chemical Industry     

Crosslinking of mixtures of diglycidylether of bisphenol‐A with 1,6‐dioxaspiro[4.4] nonan‐2,7‐dione initiated by tertiary amines: III. Effect of hydroxyl groups on network formation

BACKGROUND: Blends of epoxy resin oligomers, diglycidylether of bisphenol‐A (DGEBA), and a bislactone, 1,6‐dioxaspiro[4.4]nonan‐2,7‐dione (s(γBL)), were anionically copolymerized using two tertiary amines as anionic initiators. Their curing rheology and gelation behaviour were studied to provide a more comprehensive knowledge of the curing of these previously studied systems. RESULTS: The activation energy for gelation was found to be similar to that previously measured using differential scanning calorimetry and appeared to increase in the presence of the bislactone. The reaction rate during copolymerization of DGEBA with s(γBL) was slower than DGEBA homopolymerization alone because the alkoxide attack on the epoxide is faster than the reaction of the carboxylate ion and the epoxy group. The effect of the initiator type on the gel conversion was small and was presumably due to differences in the kinetic chain length caused by amine regeneration from the quaternary amine. For the same initiator and at a constant ratio of DGEBA/s(γBL), an increase in the hydroxyl concentration of the DGEBA oligomer raised the gel conversion. For a DGEBA oligomer with low hydroxyl levels, an increase in the concentration of s(γBL) increased the gel conversion; however, for a DGEBA oligomer with high hydroxyl levels, increasing s(γBL) concentration decreased the gel conversion. CONCLUSION: These results are interpreted in terms of the effect of initiation rate and chain transfer rate on the kinetic chain length. The glass transition temperature of the gel was found to be controlled by the fraction of the aliphatic s(γBL) and the amount of plasticizing sol in the matrix. Copyright © 2009 Society of Chemical Industry     

Preparation and characterization of siliconized epoxy‐1,2‐bis(maleimido)ethane intercrosslinked matrix materials

Novel intercrosslinked networks of siliconized epoxy‐1,2‐bis(maleimido)ethane matrix systems are developed. The siliconization of epoxy resin is carried out by using 5–15% hydroxyl‐terminated poly(dimethylsiloxane) with γ‐aminopropyltriethoxysilane as a crosslinking agent and dibutyltin dilaurate as a catalyst. The siliconized epoxy systems are further modified with 5–15% 1,2‐bis(maleimido)ethane and cured by using diaminodiphenylmethane. The prepared neat resin castings are characterized for their mechanical properties. Mechanical studies indicate that the introduction of siloxane into these epoxy resins improves the toughness with a reduction in the stress–strain values, whereas incorporation of bismaleimide (BMI) into the epoxy resin improves the stress–strain properties with a lowering of the toughness. The introduction of both siloxane and BMI into the epoxy resin influences the mechanical properties according to their content percentages. Differential scanning calorimetry (DSC), thermogravimetry, and heat distortion temperature analyses are also carried out to assess the thermal behavior of the matrix materials that are developed. DSC thermograms of the BMI modified epoxy systems show unimodal reaction exotherms. The glass‐transition temperature, thermal degradation temperature, and heat distortion temperature of the cured BMI modified epoxy and siliconized epoxy systems increase with increasing BMI content. The water absorption behavior of the matrix materials is also studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3808–3817, 2003     

The electron beam-induced cationic polymerization of epoxy resins

The rapid, efficient electron beam-induced cationic polymerization of multifunctional epoxy monomers has been carried out in the presence of diaryliodonium and triarylsulfonium salts. These polymerizations take place at low doses (1–3 Mrad), which make them attractive for commercial applications. The factors that contribute to the high reactivity of these monomers are discussed.     

Effects of the electron‐beam absorption dose on the glass transition,thermal expansion,dynamic mechanical properties,and water uptake of polycardanol containing epoxy groups cured by an electron beam

In this study, the glass transition, thermal expansion, dynamic mechanical properties, and water‐uptake behaviors of diepoxidized polycardanol (DEPC) cured by electron‐beam radiation in the presence of cationic photoinitiators were investigated. How the type and concentration of cationic photoinitiators and the electron‐beam absorption dose influenced the properties of the cured DEPC was also studied. Two types of cationic photoinitiators, triarylsulfonium hexafluorophosphate (simply referred to as phosphate type or P‐type) and triarylsulfonium hexafluoroantimonate (simply referred to as antimonate type or Sb‐type), were used. Electron‐beam absorption doses of 200, 300, 400, and 600 kGy were applied to the uncured diepoxidized cardanol (DEC) samples, respectively. It was revealed that the Sb‐type photoinitiator was preferable to the electron‐beam curing of DEC; this led to a lower photoinitiator concentration and/or a lower electron‐beam absorption dose compared to that in the phosphate‐type photoinitiator. As a result, the variations in the glass‐transition temperature, coefficient of thermal expansion, storage modulus, and water uptake of the cured DEPC were quite consistent with each other. We found that the optimal conditions for the enhanced properties of DEPC by electron‐beam curing were an Sb‐type photoinitiator at 2 wt % and an electron‐beam absorption dose of 600 kGy. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42570.     

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