Latent Thermal Catalyst Research Articles

DABCO-Intercalated α-Zirconium Phosphate as a Latent Thermal Catalyst in the Reaction of Urethane Synthesis

The mixture of hexamethylene diisocyanate (HDI) and butanol (BuOH) with the intercalation compound of 1,4-diazabicyclo[2.2.2]octane (DABCO) with α-zirconium phosphate (α-ZrP) has been evaluated as a latent thermal catalyst at varying temperatures. α-ZrP·DABCO did not show activity at 25 °C, but showed a high level of activity at a higher temperature of 80 °C. To clarify the reaction behavior of HDI-BuOH with α-ZrP·DABCO, a viscosity value of 1200 mPa·s·g/cm2 was reached at 80 °C for 30 min. To investigate the deintercalation behavior of DABCO from the α-ZrP interlayer, it was investigated in BuOH and in HDI, respectively, under heated conditions. Interestingly, XRD patterns showed a reduction in α-ZrP·DABCO for the interlayer distance due to the deintercalation of DABCO in BuOH, while no changes associated with the deintercalation of DABCO were observed in HDI. Butanol was found to be important for the deintercalation of DABCO. To examine the reactivity of bifunctional monomers, the reaction of 1,4-butanediol (1,4-BDO) and HDI with α-ZrP·DABCO were investigated to show good reactivity at 80 °C and stability at 40 °C.

DBU-intercalated γ-titanium phosphate as a latent thermal catalyst in the reaction of glycidyl phenyl ether (GPE) and hexahydro-4-methylphthalic anhydride (MHHPA).

The capabilities and performance of γ-titanium phosphate (γ-TiP) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a latent thermal catalyst were investigated by the copolymerization of glycidyl phenyl ether (GPE) and hexahydro-4-methylphthalic anhydride (MHHPA) at different temperatures for a period of one hour. Polymerization was not observed until the reactants were heated to 100 °C. Upon increasing the temperature to 120 °C, the conversion in the presence of γ-TiP·DBU as a catalyst showed 98% conversion in 1 h. The thermal stability of GPE and MHHPA reacted in the presence of γ-TiP·DBU at 40 °C for 144 h resulted in less than 7% conversion of GPE. The conversion of GPE did not show a significant increase at 40 °C.

DBU-Intercalated α-Zirconium Phosphates as Latent Thermal Catalysts in the Reaction of Hexamethylene Diisocyanate and Phenol

The catalytic activity of 1,8-diazabicyclo [5,4,0]undec-7-ene-intercalated α-zirconium phosphates (α-ZrP·DBU) as thermal latent catalysts in the reaction of hexamethylene diisocyanate (HDI) and phenol was investigated. α-ZrP intercalation compounds with varying amounts of DBU (α-ZrP·xDBU, where x = 0.58, 0.44, 0.22, and 0.10) were prepared. The reaction of HDI and phenol with α-ZrP·DBU was carried out at varying temperatures for 30 min periods. The α-ZrP·DBU showed high catalytic activity in the reaction of HDI-phenol under heating conditions. The α-ZrP·DBU extended the pot lifetimes at 25 °C.

Imidazole derivatives as thermal latent catalyst for thiol-michael reaction thermosetting resins

Imidazole is an excellent nucleophilic initiator in thiol-Michael addition reaction of thiol and vinyl sulfone at room temperature. To delay the gelation of the monomer mixture, thermal latent curing agents based on imidazole are designed and the latency and curing efficiency towards thiol-vinyl sulfone system are evaluated. N-carbonylated imidazole derivatives are non-nucleophilic towards Michael reaction with vinyl sulfone. However, during curing at elevated temperature (>80 °C), thiol monomer thiolyze imidazole derivative and the released imidazole acts as a nucleophilic initiator. It is found that the viscosity at room temperature of thiol-vinyl sulfone system with 2b or 2d imidazole derivatives increases slowly up to over 10 h, which permits sufficient time for processing such as mixing, degassing and injection into the mold. In the application of 2b or 2d in network polymerization of polythiol and divinyl sulfone, both catalysts have excellent curing ability with a 98% and 95% thiol conversion, respectively within 7 h at 100 °C. Using 2b or 2d, transparent thiol-vinyl sulfone resins with a refractive index of 1.57 and an Abbe number of 47.78 are successfully produced.

Imidazoles-Intercalated α-Zirconium Phosphate as Latent ThermalCatalysts in the Curing Reaction of Epoxy-Thiol System

Imidazoles-Intercalated α-Zirconium Phosphate as Latent ThermalCatalysts in the Curing Reaction of Epoxy-Thiol System

Thermal and Mechanical Interfacial Behaviors of Graphene Oxide-Reinforced Epoxy Composites Cured by Thermal Latent Catalyst.

A series of composites was prepared from a diglycidyl ether of bisphenol A (DGEBA) with different graphene filler contents to improve their mechanical performance and thermal stability. Graphene oxide (GO) and GO modified with hexamethylene tetraamine (HMTA) were selected as reinforcing agents. As a latent cationic initiator and curing agent, N-benzylepyrizinium hexafluoroantimonate (N-BPH) was used. The effect of fillers and their contents on the mechanical properties and thermal stability of the composites were studied. Fracture toughness improved by 23% and 40%, and fracture energy was enhanced by 1.94- and 2.27-fold, for the composites containing 0.04 wt.% GO and HMTA-GO, respectively. The gradual increase in fracture toughness at higher filler contents was attributed to both crack deflection and pinning mechanisms. Maximum thermal stability in the composites was achieved by using up to 0.1 wt.% graphene fillers.

Effect of Ozone Treatment on Fracture Toughness of Single-Walled Carbon Nanotubes-Reinforced Epoxy Resin Initiated by a Thermal Latent Catalyst

Effect of Ozone Treatment on Fracture Toughness of Single-Walled Carbon Nanotubes-Reinforced Epoxy Resin Initiated by a Thermal Latent Catalyst

DABCO- and DBU-intercalated α-zirconium phosphate as latent thermal catalysts in the copolymerization of glycidyl phenyl ether (GPE) and hexahydro-4-methylphthalic anhydride (MHHPA)

The latent catalytic abilities of tertiary amines-intercalated α-zirconium phosphate [(α-ZrP·amine): 1,4-diazabicyclo[2,2,2]octane (α-ZrP·DABCO) and 1,8-diazabicyclo[5,4,0]undec-7-ene (α-ZrP·DBU)] were examined by copolymerization of glycidyl phenyl ether (GPE) and hexahydro-4-methylphthalic anhydride (MHHPA) at varying temperatures for 1h periods. Polymerization was not observed until the reactants were heated to 100°C or above. Upon increasing the temperature, the conversion factors of GPE increased such that, at 140°C, both conversions were over 90% for α-ZrP·DABCO and α-ZrP·DBU. The thermal stabilities of GPE and MHHPA with the catalysts at 40°C for 144h were tested: GPE with α-ZrP·DBU achieved conversions of 9%. The reaction in the presence of α-ZrP·DABCO did not proceed at 40°C for 144h.

Cationic Catalyst as Latent Curing Agent for Epoxy Resin

1-Benzyl-3-methyl-imidazolium hexafluoroantimonate (BMH) was newly synthesized and characterized with FT-IR, 1H-NMR. We synthesized catalysts fulfill requirements for a rapid cure at a moderately elevated temperature in curing the epoxy resin for neat diglycidyl ether bisphenol A (DGBEA). The cure behavior of this resin was investigated at elevated temperature and cure temperature in the presence of 0.5, 1.0, 2.0 wt% of 1-benzyl-3-methyl-imidazolium hexafluoroantimonate (BMH) by mean of differential scanning calorimeter (DSC). Chemical conversion as function of temperature and amount of BMH (0.5, 1.0, 2.0 wt%) were determined from DSC. It was found that BMH were superior latent thermal catalyst for catinonic curing which have a good thermal stability.

Gallium(iii) xanthate as a novel thermal latent curing agent for an epoxy resin composite

The latent thermal curing catalyst “Ga(iii) xanthate” for an epoxy resin/phenol composite, and its curing behaviour are reported.

A Study on the Preparation of the Eco-friendly Carbon Fibers-Reinforced Composites

In this work, the effect of catalysts on the mechanical properties of carbon fibers-reinforced epoxy matrix composites cured by cationic latent thermal catalysts, i.e., N-benzylpyrazinium hexafluoroantimonate (BPH) was studied. Differential scanning calorimetry was executed for thermal characterization of the epoxy matrix system. Mechanical interfacial properties of the composites were studied by interlaminar shear strength (ILSS), critical stress intensity factor (KIC), and specific fracture energy (GIC). As a result, the conversion of neat epoxy matrix cured by BPH was higher than that of one cured by diaminodiphenyl methane (DDM). The ILSS, KIC, GIC, and impact strength of the composites cured by BPH were also superior to those of the composites cured by DDM. This was probably the consequence of the effect of the substituted benzene group of BPH catalyst, resulting in an increase in the cross-link density and structural stability of the composites studied.

Thermal and Mechanical Properties of Epoxy/Polyurethane Blend System Initiated by Cationic Latent Thermal Catalyst

In this work, the blend of diglycidylether of bisphenol A (DGEBA) and modified polyurethane (PU) was prepared and characterized the cure behavior and mechanical interfacial properties. The N-benzylpyrazinium hexafluoroantimonate was used as a cationic initiator for cure, and the content of PU was varied within 0~20 phr. The cure behavior and mechanical interfacial properties were studied by DSC and the critical stress intensity actor (KIC) measurements. Also thermal stabilities were carried out by TMA and TGA analyses. It is found that the cure activation energy (Ea) was slightly increased on increasing the PU content, and a maximum value was noted at 10 phr PU. The mechanical interfacial properties measured from KIC showed a similar behavior with the results of conversion. These results were probably due to the increase of the hydrogen bonding between the hydroxyl groups of DGEBA and isocyanate groups in PU.

Rheological and mechanical properties of DGEBA-S epoxy copolymer initiated byN-benzylquinoxalinium hexafluoroantimonate

The rheological and mechanical properties of the DGEBA-S epoxy copolymer initiated by N-benzylquinoxalinium hexafluoroantimonate (BQH) as a cationic latent thermal catalyst were investigated. The rheological properties of the DGEBA-S/BQH system were investigated using a rheometer under isothermal conditions, and the mechanical properties of the casting specimens, involving flexure and impact tests, were also performed. The crosslinking activation energy and mechanical properties of the DGEBA-S/BQH system were higher than those of the DGEBA/BQH system. This could be attributed to the introduction of sulfone groups with a polar nature to the main chain of the epoxy resins which led to a decrease of molecular motion and an improvement in the toughness of the cured epoxy copolymers. Copyright © 2005 Society of Chemical Industry

Effect of Biodegradable Epoxidized Castor Oil on Physicochemical and Mechanical Properties of Epoxy Resins

AbstractSummary: Biobased epoxy materials were prepared from diglycidyl ether of bisphenol A (DGEBA) and epoxidized castor oil (ECO) initiated by a latent thermal catalyst. The physicochemical and mechanical interfacial properties of the DGEBA/ECO blends were investigated. As a result, the thermal stability of the cured epoxy blends showed a maximum value in the presence of 10 wt.‐% ECO content, which was attributed to the excellent network structure in the DGEBA/ECO blends. The storage modulus and glass transition temperature of the blends were lower than those of neat epoxy resins. The mechanical interfacial properties of the cured specimens were significantly increased with increasing the ECO content. This could be interpreted in terms of the addition of larger soft segments of ECO into the epoxy resins and thus reducing the crosslinking density of the epoxy network, which results in increasing toughness in the blends.KIC values of the DGEBA/ECO blends as a function of ECO content.magnified imageKIC values of the DGEBA/ECO blends as a function of ECO content.

Rheological and mechanical properties of epoxy/polyurethane blends initiated by N‐benzylpyrazinium hexafluoroantimonate salt

AbstractIn this work the cure behavior and rheological and mechanical interfacial properties of the diglycidylether of bisphenol A (DGEBA)/polyurethane (PU) blend system, initiated by 1 wt % N‐benzylpyrazinium hexafluoroantimonate as a latent thermal catalyst, were investigated. To characterize the mechanical interfacial properties of the system, the critical stress intensity factor (KIC) was calculated with a single‐edge‐notched beam (SEN) beam fracture toughness test. And an impact test was performed at room and cryogenic temperatures to determine the performance of PU at room and low‐temperatures, respectively. As a result, the Ec of the blend system was increased with increasing PU content, showing a maximum value at 30 wt % PU, which was in good agreement with the mechanical properties of the blend system. Consequently, these results could be explained by the improvement that occurred in intermolecular hydrogen bonding between the hydroxyl group in EP and the isocyanate group in PU, resulting in increased compatibility of the components within the interpenetrating polymer networks. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3841–3848, 2004

Studies on epoxy resins cured by cationic latent thermal catalyst at elevated temperature

AbstractIn this work, the effect of the catalyst content was investigated in terms of the thermal and mechanical properties of epoxy resins at elevated temperature. A synthesized cationic latent thermal catalyst, N‐benzylpyrazinium hexafluoroantimonate (BPH), was used to cure epoxy resins. The content of catalyst added was 0.5, 1, 2, 3 and 5 wt% and the heating time was varied from 0 to 1024 h. As a result, the mechanical properties, including flexural strength, elastic modulus in flexure and impact strength, as well as thermal‐oxidative resistance, showed a maximum value in the presence of 1 wt% BPH. With increasing elapsed time, up to 4 h, the thermal and mechanical properties of the specimens were improved. These results show that the internal structure of the epoxy system was stabilized, and post‐curing for a longer period of time, resulted in improved thermal and mechanical behaviour of the cast specimens. Copyright © 2004 Society of Chemical Industry

Effect of the substituted benzene group on thermal and mechanical properties of epoxy resins initiated by cationic latent catalysts

AbstractEpoxy resins (DGEBA) were cured by cationic latent thermal catalysts, that is, N‐benzylpyrazinium hexafluoroantimonate (BPH) and N‐benzylquinoxalinium hexafluoroantimonate (BQH) to investigate the effect of substituted benzene group on cure kinetics and mechanical properties of epoxy system. Differential scanning calorimetry (DSC) was undertaken for activation energy of the system. It was also characterized in terms of flexural, fracture toughness, and Izod impact strengths for the mechanical tests. As a result, the cure reaction of both epoxy systems resulted in an autocatalytic kinetic mechanism accelerated by hydroxyl groups. Also, the conversion and cure activation energy of the DGEBA/BQH system were higher than those of DGEBA/BPH system. The mechanical properties of the DGEBA/BQH system were also superior to those of the DGEBA/BPH system, as well as the morphology. This was probably due to the consequence of the effect of the substituted benzene group of the BQH catalyst, resulting in increasing the crosslinking density and structural stability in the epoxy system studied. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2419–2429, 2004

Physical and Mechanical Interfacial Properties of Epoxy Copolymers Initiated by Latent Thermal Catalysts

AbstractSummary: The epoxy copolymers containing sulfone groups, diglycidyl ether of bisphenol‐A – Bisphenol‐S (DGEBA‐S) were synthesized by a hot‐melt method. The thermal properties of the epoxy systems initiated by two cationic latent catalysts, i.e., N‐benzylpyrazinium hexafluoroantimonate (BPH) and N‐benzylquinoxalinium hexafluoroantimonate (BQH), were investigated by using a dynamic DSC, DMA, and TGA. The mechanical properties were measured by single‐edge‐notched (SEN) beam fracture toughness tests. As a result, the thermal stability and mechanical interfacial properties of the DGEBA‐S/catalyst system were found to be higher than those of the DGEBA/catalyst. This was probably due to the fact that the introduction of sulfone groups with a polar nature to the main chain of the epoxy resins led to an improvement of thermal stability and toughness of the cured epoxy copolymers.Conversion of the epoxy/catalyst systems as a function of curing temperature.imageConversion of the epoxy/catalyst systems as a function of curing temperature.

Synthesis and Thermal Properties of Epoxidized Vegetable Oil

AbstractSummary: The novel potential epoxy resins, epoxidized soybean oil (ESO) and epoxidized castor oil (ECO), were synthesized and characterized. The cationic polymerization of ESO and ECO with a latent thermal catalyst, N‐benzylpyrazinium hexafluoroantimonate (BPH), was initiated at 80 and 50 °C, respectively. The cured ECO samples showed a higher Tg and lower coefficient of thermal expansion than those of ESO, due to the higher intermolecular interaction in the ECO/BPH system.Relationships between ESO or ECO conversion and temperature in the polymerization with 1 wt.‐% BPH for 2 h.imageRelationships between ESO or ECO conversion and temperature in the polymerization with 1 wt.‐% BPH for 2 h.

Influence of Catalyst Content on the Thermal and Mechanical Properties of Epoxy Resins Initiated by a Cationic Latent Thermal Catalyst at Elevated Temperatures

AbstractThe effect of catalyst content on the thermal and mechanical properties of diglycidyl ethers of bisphenol A (DGEBA)/BPH system was investigated at elevated temperatures. The contents of the catalyst, N‐benzylpyrazinium hexafluoroantimonate (BPH), examined were 0.5, 1, and 3 wt.‐% and the elapsed heating time was varied from 0 to 1 024 h. As a result, the thermal‐oxidative resistance and mechanical properties, including flexural strength, elastic modulus in flexure, and impact strength showed a maximum value at 1 wt.‐% BPH. By increasing the elapsed time to 4 h, the thermal and mechanical properties of the specimens were also improved. These results showed that the internal structure of the epoxy system was stabilized and post‐cured as the elapsed time increased, resulting in an improvement of the thermal and mechanical properties of the specimens.Impact strength of the DGEBA/BPH system as a function of BPH content and elapsed heating time.magnified imageImpact strength of the DGEBA/BPH system as a function of BPH content and elapsed heating time.