Kinetics and mechanistic investigation of epoxy–anhydride compositions cured with quaternary phosphonium salts as accelerators

Mechanism and curing kinetics of bisphenol A epoxy resin–iso‐methyltetrahydrophthalic anhydride compositions using quaternary phosphonium salts as accelerators were investigated by differential scanning calorimetry (DSC) and electrospray mass‐spectrometry (ESI‐MS). The DSC method was applied to investigate curing kinetics and apparent activation energy values for the overall curing process. The DSC results showed that some of the phosphonium salts lead to a lower activation energy, that means they are more effective accelerators for the curing of epoxy–anhydride systems. The mechanism of curing was studied by ESI‐MS using the model reaction of epichlorohydrin (E) with phthalic anhydride (PA) in the presence of phosphonium salts or 2‐methylimidazole. Products containing the alkyl moiety of the phosphonium salt in form of alkyl esters could be identified. This suggests that the phosphonium salts activate the anhydride by electrophilic attack. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1088–1097     

From curing kinetics to network structure: A novel approach to the modeling of the network buildup of epoxy–anhydride thermosets

The curing kinetics and network buildup during curing of epoxy–anhydride formulations using tertiary amines as initiators are reviewed in this work. A mechanism‐based kinetic and structural model has been defined, showing better prediction capabilities than previous living polymerization and simple regeneration models. The curing kinetics have been analyzed using differential scanning calorimetry (DSC), and the gelation during curing has been determined by combined thermomechanical analysis and DSC. The effect of initiator content and epoxy equivalent weight are taken into account. The network buildup has been modeled using a stochastic network buildup model based on the random combination of primary chains generated by the kinetic model. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 61–75     

Cure behavior and thermal degradation mechanisms of epoxy and epoxy–cyanate resins

The cure reactions of tetraglycidyl methylene diamine (TGMDA) epoxy cured with tetrasubstituted aromatic diamine on one hand and diglycidyl ether of bisphenol A and diglycicyl ether tetrabromobisphenol A epoxies cured with methylene bis (phenyl‐4‐cyanate) on the other hand are reported. Systematic Fourier transform infrared (FTIR) spectroscopy studies of the cure reaction of epoxy and epoxy–cyanate during thermal cycles are presented. FTIR studies indicate that the reaction of TGMDA monomer is total but the network contains a large amount of primary amine. The cyanate monomer reacts rapidly to form triazine structures. Then the epoxy monomers homopolymerize and crosslink with free cyanate groups. The gas chromatography/mass spectrometry study of volatile products evolved during the polymer thermal degradation shows the dehydration of the epoxy network and the decomposition of the amine structure. The FTIR and solid‐phase ¹³C nuclear magnetic resonance analysis revealed that the ether functions and the amine groups are temperature sensitive but the triazine structure is not. Copyright © 1999 John Wiley & Sons, Ltd.     

Do epoxy–amine networks become inhomogeneous at the nanometric scale?

Epoxy–amine networks are known to be homogeneous. However, using new analysis tools that allow the observation scale to be reduced to a nanometric level, some authors have stated the opposite. In this work, the network morphology has been studied with atomic force microscopy in the tapping mode as a function of the hardener nature and the stoichiometry of the reactive blend. A very homogeneous epoxy network topography, similar to that of an amorphous thermoplastic, has been obtained. For comparison, a truly heterogeneous network topography, like that of unsaturated thermosets cured by free‐radical mechanisms, has been imaged. For the observation of surfaces on a scale smaller than a nanometer, caution must be taken:(1) the tips must be freshly cleaned so that distortion on the image is prevented and (2) the surfaces must be very flat so that the phase contrast is not influenced significantly by differences in the sample topography. This works gives guidelines on using atomic force microscopy in the tapping mode for epoxy–amine network characterization and discusses epoxy–amine network homogeneity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2422–2432, 2003     

Synthesis of novel boron‐containing epoxy–novolac resins and properties of cured products

Epoxy–novolac resins were synthesized by modifying a commercial novolac resin with epichlorohydrin. These epoxy–novolac resins were characterized and further modified with different contents of bis(benzo‐1,3,2‐dioxa‐borolanyl)oxide or bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxa‐borolanyl)oxide. The boron‐containing epoxy–novolac resins were autocatalytically crosslinked or crosslinked with BF₃MEA and their thermal stability and flame retardancy were determined by thermogravimetric analysis and limiting oxygen index (LOI) values. These LOI values for the bis(benzo‐1,3,2‐dioxa‐borolanyl)oxide derivatives were higher than the boron‐free novolac resins, which shows the benefit of the presence of boron. To test the role of boron in the enhancement of flammability, scanning electronic microscopy and energy‐dispersive X‐ray spectroscopy images were made. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6332–6344, 2006     

Phase separation induced by a chain polymerization: Polysulfone-modified epoxy/anhydride systems

The reaction-induced phase separation in a blend of a commercial polysulfone (PSu) with diepoxide-cyclic anhydride monomers, was studied. The diepoxide was based on diglycidylether of bisphenol A (DGEBA) and the hardener was methyl tetrahydrophthalic anhydride (MTHPA), used in stoichiometric proportion. Benzyldimethylamine (BDMA) was used as initiator. PSu had no influence on the polymerization kinetics, the gel conversion, and the overall heat of reaction per epoxy equivalent. A kinetic model including initiation, propagation, and termination steps was used to estimate the distribution of linear and branched species in the first stages of the chain-wise copolymerization. This distribution, together with the PSu distribution, were taken into account in a thermodynamic model of the blend. The interaction parameter was fitted from experimental determinations of conversions at the start of phase separation, obtained under different conditions. The thermodynamic model was used to explain the complex morphologies developed in materials containing different PSu concentrations as well as their dynamic mechanical response. The shift in glass transition temperatures was explained by the fractionation of different species during the phase separation process. Phase inversion produced a significant decrease of the elastic modulus in the glassy state and a thermoplastic-like behavior of the material in the rubbery region. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1349–1359, 1998     

Simultaneous interpenetrating polymer networks based on epoxy–acrylate combinations

Simultaneous interpenetrating polymer networks (SINs) based on epoxy/poly(n-butyl acrylate) systems were synthesized at 120°C. The polymerization kinetics were studied both in situ by Fourier Transform Infrared Spectroscopy (FT–IR). Three key events occurred during the polymerization, namely the gelation of the network I, gelation of the network II, and phase separation of one polymer from the other. Thus, metastable phase diagrams describing the relations between the three events were constructed. Three-dimensional tetrahedrons characterizing the four-component system (the two monomers and the two polymers) allow the visualization of these three key events and also define some critical points, for example, the loci of the points where simultaneous gelation of the two networks occurs. The inside of the tetrahedron was also investigated using partially reacted model compounds. These tetrahedrons can be used as guidelines for setting up a synthesis strategy leading to desired morphologies. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1973–1984, 1997     

Novel quaternary ammonium borates as latent catalysts for epoxy–phenolic resins

Novel tetrabutylammonium tetrakis(substituted benzoyloxy)borate salts ( 1a – 1d ) were synthesized by the reaction of tetrabutylammonium tetraphenylborate and corresponding substituted benzoic acids. Polyaddition reactions of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐bisphenol F (44BPF) or bisphenol F (BPF‐D) with the ammonium borates were investigated as model reactions of epoxy/phenol–novolac resin systems with respect to the thermal latency and storage stability of the catalyst. The polyaddition of DGEBA/44BPF with the ammonium borates in diglyme at 150 °C for 6 h proceeded up to 84–94% conversions and gave polymers with number‐average molecular weights of 3750–5750, whereas the polyaddition at 80 °C for 6 h gave less than 9% conversions. The catalytic activity of ammonium borates 1a – 1d depended on the substituent of the phenyl group of the borates, and the order of activity was 1b (p‐OMe) > 1a (? H) > 1c (p‐NO₂) > 1d [3,5‐(NO₂)₂]. The ammonium borate catalyst with the substituent that yielded lower acidity of the corresponding substituted benzoic acid tended to reveal higher activity. In comparison with tetrabutylammonium bromide (TBAB) as a conventional ammonium salt, 1a – 1d revealed better thermal latency. The storage stability of DGEBA/BPF‐D with the ammonium borate catalysts in bulk at 40 °C was better than that with TBAB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2689–2701, 2002     

Synthesis and cationic photopolymerization of epoxy‐functional siloxane monomers and oligomers

A series of difunctional silicon‐containing monomers were prepared with a novel method consisting of the monohydrosilation of an α,ω‐difunctional Si? H‐terminated siloxane with a vinyl‐functional epoxide or oxetane followed by the dehydrodimerization of the resulting Si? H‐functional intermediate. This method used simple, readily available starting materials and could be conducted as a streamlined one‐pot, two‐step synthesis. This novel method was also applied to the synthesis of several epoxy–silicone oligomers. The reactivities of these new monomers and oligomers were examined with Fourier transform real‐time infrared spectroscopy and optical pyrometry. Those monomers containing epoxycyclohexyl groups displayed excellent reactivity in cationic ring‐opening polymerization in the presence of lipophilic onium salt photoinitiators. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3056–3073, 2003     

Thermal latency of novel chelating borate catalysts as latent catalysts for epoxy–phenolic resins

Novel quaternary ammonium bis(2‐oxybenzoyloxy)borate salts ( 1a – 1c ) or quaternary ammonium bis(1,2‐benzenedioxy)borate salts ( 2a and 2b ) with tetra‐n‐butylammonium (TBA⁺), tetra‐n‐octylammonium (TOA⁺), or bis(triphenylphosphoranylidene)ammonium (PNP⁺) cations were synthesized as latent catalysts of epoxy/phenol–novolac resins by the complexation between boric acid and salicylic acid or catechol, followed by neutralization with quaternary ammonium hydroxide. Polyaddition reactions of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐bisphenol F (44BPF) or bisphenol F (BPF‐D) with the ammonium borates were investigated as model reactions of epoxy/phenol–novolac resin systems with respect to the thermal latency and storage stability of the catalyst. The polyaddition of DGEBA/44BPF with 1a – 1c in diglyme at 150 °C for 6 h proceeded up to 85–96% conversions and gave polymers with number‐average molecular weights of 4180–10,500, whereas the polyaddition at 80 °C for 6 h gave less than 8% conversions. However, the polyaddition with 2a containing TBA⁺ cation proceeded to only a 32% conversion at 150 °C for 6 h in diglyme and to a 64% conversion even at 180 °C for 6 h in triglyme and only gave low molecular weight oligomers, and no reaction proceeded in the polyaddition at 80 °C. However, polyaddition with 2b containing PNP⁺ cation proceeded up to a 96% conversion at 150 °C for 6 h in diglyme and gave a higher molecular weight polymer with a number‐average molecular weight of 8050, whereas the polyaddition at 80 °C for 6 h gave only a 5% conversion. The catalytic activity of ammonium borates 1a – 1c and 2a and 2b depended on the borate anion structure: 1a and 1c with bis(2‐oxybenzoyloxy)borate anion revealed higher activity than 2a and 2b with bis(1,2‐benzenedioxy)borate anion, respectively. In comparison with tetra‐n‐butylammonium bromide (TBAB) as a conventional ammonium salt or tetra‐n‐butylammonium tetrakis(benzoyloxy)borate (TBA‐TBB), 1a – 1c and 2b revealed better thermal latency. The catalytic activity of ammonium borates also depended on the bulkiness of the ammonium cation, and the order of activity was 1c (PNP⁺) > 1b (TOA⁺) ≧ 1a (TBA⁺) and 2b (PNP⁺) > 2a (TBA⁺). The storage stability of DGEBA/BPF‐D with the ammonium borate catalysts 1a – 1c and 2a and 2b in bulk at 40 °C was much better than that with TBAB and TBA‐TBB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2702–2716, 2002     

Synthesis and micellization of amphiphilic poly(sebacic anhydride)–poly(ethylene glycol)–poly(sebacic anhydride) block copolymers

Amphiphilic biodegradable block copolymers [poly(sebacic anhydride)–poly(ethylene glycol)–poly(sebacic anhydride)] were synthesized by the melt polycondensation of poly(ethylene glycol) and sebacic anhydride prepolymers. The chemical structure, crystalline nature, and phase behavior of the resulting copolymers were characterized with ¹H NMR, Fourier transform infrared, gel permeation chromatography, and differential scanning calorimetry. Microphase separation of the copolymers occurred, and the crystallinity of the poly(sebacic anhydride) (PSA) blocks diminished when the sebacic anhydride unit content in the copolymer was only 21.6%. ¹H NMR spectra carried out in CDCl₃ and D₂O were used to demonstrate the existence of hydrophobic PSA domains as the core of the micelle. In aqueous media, the copolymers formed micelles after precipitation from water‐miscible solvents. The effects on the micelle sizes due to the micelle preparation conditions, such as the organic phase, dropping rate of the polymer organic solution into the aqueous phase, and copolymer concentrations in the organic phase, were studied. There was an increase in the micelle size as the molecular weight of the PSA block was increased. The diameters of the copolymer micelles were also found to increase as the concentration of the copolymer dissolved in the organic phase was increased, and the dependence of the micelle diameters on the concentration of the copolymer varied with the copolymer composition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1271–1278, 2006     

Acrylonitrile–maleic anhydride copolymer membrane (II): effects of post‐treatment1

The effects of post‐treatment (including thermal treatment and base treatment) on the structure and performance of acrylonitrile–maleic anhydride (AN‐MA) copolymer membrane were investigated. The water flux decreased gradually (except the deviations when the temperature of thermal treatment was 50 °C or the time of thermal treatment was 50 min but rejection of bovine serum albumin increased slowly with increasing temperature or prolonging the time of thermal treatment. “The swelling effect of water in network” was proposed to explain the deviations. AN‐MA copolymer membrane is not resistant to a base. However, the performance of the membrane can be adjusted by treatment with a dilute base solution. Copyright © 2000 John Wiley & Sons, Ltd.     

High‐Performance Exfoliated Poly(propylene)/Clay Nanocomposites by In Situ Polymerization with a Novel Z–N/Clay Compound Catalyst

Highly exfoliated poly(propylene) (PP)/clay nanocomposites with obvious improvements in both the tensile strength and toughness have been prepared by a novel TiCl₄/MgCl₂/imidazolium‐modified montmorillonite (IOHMMT) compound catalysts. Through this approach, in situ propylene polymerization can actually take place between the silicate layers and lead not only to PP with a high isotacticity and molecular weight, but also to a highly exfoliated structure even at high clay content levels (as high as 19 wt.‐%).

     

Acrylonitrile–maleic anhydride copolymer membrane (I): effects of casting conditions

The effects of casting conditions, including casting solution (composition and temperature) and coagulation conditions (pre‐evaporation time, temperature and concentration of coagulation bath) on the structure and performance of acrylonitrile–maleic anhydride copolymer membrane have been investigated. The results showed that the water flux decreased gradually while the rejection of bovine serum albumin (BSA) decreased as the concentration of copolymer increased. When the total solid concentration was kept unchanged, the water flux increased with additive polyvinylpyrrolidone (PVP), the rejection did not decrease until the ratio of PVP/copolymer was 60%. When the content of copolymer in the casting solution was kept constant, the water flux decreased rapidly while the rejection increased a little (compared with the case of no additive) as the ratio of PVP/copolymer increased. As to the temperature of casting solution, the water flux had a maximum at 45 °C and the rejection had a maximum and a minimum at 45 and 55 °C, respectively. The water flux had a maximum value when the pre‐evaporation time was 40 sec. The rejection of BSA was almost unchanged when the pre‐evaporation time was less than 40 sec. and then decreased and reached a minimum value at 60 sec. As the temperature of coagulation bath increased, the water flux reached a maximum at 35 °C while the rejection increased uniformly. With increasing the concentration of DMSO in the coagulation bath, the water flux decreased gradually and got to a minimum at 50 wt% as the concentration of dimethylsulfoxide in the coagulation bath increased, but no apparent effect on the rejection was observed. Copyright © 2000 John Wiley & Sons, Ltd.     

NMR study of the synthesis of 17O‐enriched acetic acid by hydrolysis of acetic anhydride with 17O‐enriched water

¹⁷O‐enriched acetic acid (2.5% in ¹⁷O) was synthesized by hydrolysis of acetic anhydride with ¹⁷O‐enriched water. The reaction was monitored by ¹⁷O and ¹H NMR spectroscopy. Acetic anhydride, ¹⁷O‐enriched in both the ether and the carbonyl oxygens, was observed as an intermediate. This can be ascribed to competition between acetic acid and water for nucleophilic attack on acetic anhydride. Copyright © 2003 John Wiley & Sons, Ltd.     

Preparation and properties of poly(styrene-co-maleic anhydride)/silica hybrid materials by the in situ sol–gel process

Poly(styrene-co-maleic anhydride)/silica hybrid material has been successfully prepared from styrene–maleic anhydride copolymer and tetraethoxysilane (TEOS) in the presence of a coupling agent (3-aminopropyl)triethoxysilane (APTES) by an in situ sol–gel process. It was observed that the gel time of sol–gel solution was dramatically influenced by the amount of APTES. The hybrid material exhibits optical transparency almost as good as both silica gel and the copolymer. The covalent bonds between organic and inorganic phases were introduced by the aminolysis reaction of the amino group with maleic anhydride units of copolymer to form a copolymer bearing trimethoxysilyl groups, which undergo hydrolytic polycondensation with TEOS. The differential scanning calorimetry (DSC) showed that the glass transition temperature of the hybrid materials increases with increasing of SiO₂ composition. Photographs of scanning electron microscopy (SEM) and atomic force microscopy (AFM) inferred that the size of the inorganic particles in the hybrid materials was less than 20 nm. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1607–1613, 1998     

Preparation and properties of nanocomposites based on acrylonitrile–butadiene rubber,styrene–butadiene rubber,and polybutadiene rubber

Nanocomposites were prepared with different grades of nitrile rubber with acrylonitrile contents of 19, 34, and 50%, with styrene–butadiene rubber (23% styrene content), and with polybutadiene rubber with Na‐montmorillonite clay. The clay was modified with stearyl amine and was characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The XRD studies showed an increase in the gallery gap upon the modification of the filler by stearyl amine. The intercalation of the amine chains into the clay gallery gap was confirmed by the presence of some extra peaks (2928, 2846, and 1553 cm^?1) in the FTIR spectra. The clay–rubber nanocomposites were characterized by TEM and XRD. The mechanical properties were studied for all the compositions. An improvement in the mechanical properties with the degree of filler loading up to a certain level was observed. The changes in the mechanical properties, with changes in the nature and polarity of the rubbers, were explained with the help of XRD and TEM results. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1573–1585, 2004     

Facile synthesis of core‐shell organic–inorganic hybrid nanoparticles with amphiphilic polymer shell by one‐step sol–gel reactions

Organic–inorganic hybrid core‐shell nanoparticles with diameters ranging from 100 to 1000 nm were prepared by a one‐pot synthesis based on base catalyzed sol–gel reactions using tetraethoxysilane and a triethoxysilane‐terminated polyethylene‐b‐poly(ethylene glycol) as reactants. Data from TEM, TGA, and solid‐state NMR analysis are in agreement with the formation of core‐shell nanoparticles with an inorganic‐rich core and an external shell consisting of an amphiphilic block copolymer monolayer. The influence of the organic–inorganic ratio, solution concentration, and postcuring temperature on core and shell dimensions of the nanospheres were investigated by TEM microscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1699–1709, 2008     

Design of the ultimate behavior of tetrafunctional epoxies modified with polysulfone by controlling microstructure development

The reaction-induced phase separation in a tetrafunctional epoxy–cyclic anhydride system modified with polysulfone (PSF) was followed by optical microscopy (OM), light scattering (LS), and scanning electron microscopy (SEM). The selected system was N,N,N′,N′-tetraglycidyl-4,4′-diamino diphenylmethane cured with methyl tetrahydrophthalic anhydride, in the presence of variable PSF concentrations. The different experimental techniques allow us to establish the phase separation mechanism. For modifier concentrations close to the critical point, 10 and 15 wt % PSF, phase separation proceeded by spinodal demixing (SD). For a modifier concentration much lower than the critical point, 5 wt % PSF, phase separation occurred via the nucleation and growth (NG) mode. For 7.5 wt % PSF, depending on the cure temperature, SD or NG was observed. Dynamic mechanical behavior of the resulting materials had been discussed based on fractionation of different species during the phase separation process. The fracture toughness increased significantly when bicontinuous (10 wt % PSF) or phase-inverted (15 wt % PSF) structures were generated. For mixtures containing 15 wt % PSF, the dependence of fracture toughness on the stoichiometric ratio (anhydride groups/epoxy groups) was analyzed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2711–2725, 1999