Phase‐separation process in a poly(methyl methacrylate)‐modified epoxy system: A novel approach to understanding the effect of the curing temperature on the final morphology

In this study, the physical and chemical changes of a poly(methyl methacrylate) (PMMA)‐modified epoxy system were examined to understand the effect of the curing conditions on its final morphology. The curing process of the PMMA–epoxy reactive system was complementarily analyzed by Fourier transform infrared spectroscopy in the near range (FT‐NIR) and fluorescence spectroscopy. The relationships among (1) the chemical conversion of the curing reaction, (2) the first moment of the fluorescence emission band (〈ν〉) arising from a chromophore chemically bonded to the epoxy reactive system, (3) the phase‐separation process, and (4) the dynamics of the epoxy thermoset during its curing process are discussed. From a chemical point of view, FT‐NIR did not reveal any significant change in the curing reaction with the presence of 2 wt % PMMA. However, in terms of physical changes, the analysis of the fluorescence response clearly showed variations in the curing reaction due to the presence of the thermoplastic polymer. Also, fluorescence allowed the estimation of the glass‐transition temperature of the system with curing when the reaction was diffusion‐controlled, whereas Fourier transform infrared spectroscopy was not sensible enough. In the second part of this study, scanning electron microscopy images of the PMMA‐modified epoxy system were analyzed to understand the effect of the temperature on the final morphology when the amount of thermoplastic was below the critical volume fraction. A linear dependence between the inverse of the mean area of the thermoplastic‐rich domains and the inverse of the absolute temperature was obtained. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Epoxy curing reaction studied by using two‐dimensional correlation infrared and near‐infrared spectroscopy

The isothermal curing process of bisphenol A epoxy resin with polyamine reagent (1,6‐diaminohexane) was monitored in situ by using temperature‐controlled Fourier‐transform infrared (FTIR) and Fourier‐transform near infrared (FTNIR) spectroscopy to elucidate the relative changes in functional groups during the curing reaction. It was shown that generalized two‐dimensional correlation spectroscopy can provide new information about the mechanisms and kinetics of the curing process, and the band assignments for complex NIR spectrum associated with this system. The sequential order of relative changes in functional groups during the curing process was examined by generalized 2D correlation spectroscopy and NIR‐IR hetero‐correlation spectroscopy, and the details of the complex epoxy curing reaction involving both primary and secondary amino group were revealed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preirradiation‐induced emulsion graft polymerization of glycidyl methacrylate onto poly(vinylidene fluoride) powder

An epoxy‐group‐containing monomer, glycidyl methacrylate (GMA), was grafted onto poly(vinylidene fluoride) powder via preirradiation‐induced emulsion graft polymerization. The existence of graft chains was proven by chemical structure characterization with Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy analysis. The degree of grafting was calculated by means of fluorine content analysis. A kinetic study indicated that, with the emulsion graft polymerization system, the GMA conversion rate was high, exceeding 80%. The variation in the molecular weight of the grafted polymer was measured by gel permeation chromatography, and its crystallinity was investigated with differential scanning calorimetry. The epoxy groups in graft chains were found to be suitable for further chemical modification. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Consistent model predictions for isothermal cure kinetics investigation of high performance epoxy prepregs

An accurate kinetics model is essential for understanding the curing mechanism and predicting the end properties of polymer materials. Graphite/epoxy AS4/8552 prepreg is a recent high‐performance thermosetting composite modified with thermoplastic, which is being used in the manufacture of aircraft and military structures. The isothermal cures of this system along with another thermoplastic toughened high‐performance prepreg, the T800H/3900‐2 system, were investigated by real‐time Fourier transform infrared (FTIR) spectroscopy. The cure rate was quantitatively analyzed based on the concentration profiles of both the epoxy and primary amine groups. Three autocatalytic models were used to determine kinetics parameters for both composite systems. The model which utilizes an empirical term, the final relative conversion (at different isothermal curing temperatures), describes the experimental data of both systems more satisfactorily than the model which applies a diffusion factor. The modeling results suggest that the curing of epoxy within both prepregs can be assumed to be a second order process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Fiberoptic intrinsic fluorescence for in-situ cure monitoring of amine cured epoxy and composites

The cure reactions of epoxy-diamine and its composites are monitored in-situ using the intrinsic fluorescence of the aromatic diamine, diaminodiphenyl sulfone (DDS). With a fiberoptic fluorimeter, in-situ cure monitoring was performed via a single fiber, distal-end probe, in neat epoxy as well as in commercial grade prepregs containing graphite fibers and DDS curing agent. The prepregs were investigated during multiply lamination in an oven. The fluorescence excitation spectra were obtained by emitting at 420 nm with a scan range of 320 to 400 nm, and the DDS peak position was determined as a function of cure time and temperature. The DDS spectra show a progressive red shift up to 24 nm when the primary amine is reacted with epoxide to become the secondary and the tertiary amines. The spectral shift of the DDS is also correlated with the extent of epoxide reaction determined by the Fourier transform infrared (FTIR) spectroscopy. Both data exhibit a linear relation, consistent with the behavior of the DDS peak shift, which increases linearly with the amine reaction. The excitation spectra also show a temperature dependency such that the amount of red shift increases with the measurement temperature in a manner that can be described by an exponential function. The temperature effects also depend on the state of cure in the sample. The temperature correction can be made by the application of an empirically developed equation. Thus, a direct comparison can be made among the on-line data obtained under varying conditions of cure, by reducing the spectral data to any reference temperature. This intrinsic fluorescence technique is much simpler than the previously reported extrinsic fluorophore technique, which requires the addition of an extrinsic fluorophore and an internal dye, and can be applied to any commercial prepregs containing DDS, thus making it a very powerful and widely applicable monitoring tool for composite processing.     

Synthesis and characterization of novel poly(phenylene sulfide) containing a chromophore in the main chain

A kind of novel poly(phenylene sulfide)s (PPSs) containing a chromophore group were synthesized by the reaction of dihalogenated monomer and sodium sulfide (Na₂S.xH₂O) via nucleophilic substitution polymerization under high pressure. The polymers were characterized by Fourier transform infrared spectroscopy, ultraviolet spectroscopy, fluorescence spectroscopy, XRD, DSC, TGA, mechanical testing and dissolvability experiments. The intrinsic viscosity of the polymers obtained with optimum synthesis conditions was 0.22 ? 0.38 dl g^?1 (measured in 1‐chloronaphthalene at 208 °C). These polymers were found to have good thermal performance with a glass transition temperature (T_g) of 90.5 ? 94.6 °C and initial degradation temperature (T_d) of 475–489 °C, showing improved thermal properties compared with homo‐PPS. At the same time the resultant resins had a high tensile strength of 67.5 ? 74.1 MPa and compressive strength of 70.7 ? 85.4 MPa. Additionally, these polymers exhibited a weak UV ? visible reflectivity minimum at 450–570 nm, and the fluorescence spectra of the polymers showed maximum emission around nearly 370 nm. Also they showed excellent chemical resistance and another special property ? bright shiny colors changed into different colors in acid solution. © 2014 Society of Chemical Industry     

Preparation and characterization of poly(vinyl chloride)‐graft‐acrylic acid membrane by electron beam

Poly(vinyl chloride) (PVC) was irradiated by electron beam in vacuum at 20 KGy to produce living free radicals, and then reacted with acrylic acid (AA) in solution to obtain the PVC‐g‐AA copolymers. The copolymers were characterized by Fourier transform infrared spectroscopy. Porous membranes were prepared from copolymers by the phase inversion technique. The morphology of PVC‐g‐AA membranes was studied by field emission scanning electron microscopy. The mean pore size and pore size distribution were determined by a mercury porosimeter. The mean pore size was 0.19 μm, and the bulk porosity was 56.02%. The apparent static water contact angle was 89.0°. The water drop penetration rate was 2.35 times to the original membrane. The maximum stress was 4.10 MPa. Filtration experiments were carried out to evaluate the fouling resistance of the PVC‐g‐AA membrane. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Study on the curing reaction,dielectric and thermal performances of epoxy impregnating resin with reactive silicon compounds as new diluents

Two silicon compounds including (3‐glycidoxypropyl)trimethoxysilane (A187) and (3‐glycidoxypropyl)methyldiethoxysilane (W78) were used and studied as reactive diluents for aluminum (III) acetylacetonate (Alacac) accelerated epoxy/anhydride impregnating resin systems. The dielectric performances were studied and characterized by the dielectric dissipation factor, dielectric constant, volume resistivity, and breakdown strength. The curing behaviors and thermal properties of the cured impregnants were studied by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetry. The activation energies of different epoxy formulations were determined with Kissinger method. The results showed that W78 was effective to decrease the viscosity and had little influence on the curing reaction. The cured sample of 15 parts‐of‐W78‐containing‐epoxy resin/methyl‐hexahydrophthalic anhydride (MHHPA) accelerated by Alacac exhibits good dielectric and heat resistant performances with a dielectric dissipation factor below 0.04 at 155°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Monitoring of lamination processes in an autoclave with fiber-optic infrared spectroscopy

Curing reactions of certain laminates involve a series of chemical structure changes which occur with increasing temperature and/or pressure. This paper describes the use of a midinfrared chalcogenide fiber to monitor the lamination of polymer prepregs in an autoclave. The fiber optic was used both as a wave guide and as a sensing element for acquiring evanescent wave spectra. The spectra were measured by embedding the fiber optic in a polymer prepreg package. The polymer prepregs studied include epoxy, polyimide, and bismaleimide triazine (BT) resins. The degree of cure and an understanding of the kinetic processes were obtained from the absorbance changes in specific bands. This in situ sampling technique demonstrates a new area of Fourier transform infrared (FTIR) spectroscopy for following the formation of polymeric bonds. © 1995 John Wiley & Sons, Inc.     

Degradation of poly(vinyl chloride) in the presence of 9-(2,3-epoxypropane)carbazole studied by means of TGA/FTIR

Blends containing poly(vinyl chloride) and 9-(2,3-epoxypropane)carbazole in different weight ratios were subjected to investigations using thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The effect of additive on the polymer degradation process was studied. It was found that 9-(2,3-epoxypropane)carbazole causes an increase in the onset temperature of hydrogen chloride emission by about 20–25°C. Finally, the mechanisms of stabilization were proposed. © 1995 John Wiley & Sons, Inc.     

Immobilization of lipase on a polymeric microsphere with an epoxy group prepared by radiation‐induced polymerization

A polymeric microsphere (PM) with an epoxy group was prepared by the radiation‐induced polymerization of glycidyl methacrylate and diethylene glycol dimethacrylate in reaction conditions with variations in solvents, irradiation dose, and monomer composition. The epoxy group of the PM was analyzed by solid‐state ¹³C‐NMR, Fourier transform infrared spectroscopy (FTIR), Fourier transform Raman spectroscopy, and elemental analysis (EA) after amination. In EA after amination, the epoxy group content was in the range 0.20–0.50 mmol/g. The lipase was immobilized to the epoxy group of the PM in experimental conditions with variations in the pH and the epoxy group content. The activity of the lipase‐immobilized PM was in the range 148–342 unit/mg min. The activity of lipase‐immobilized PM increased in accordance with the epoxy group content. The lipase‐immobilized PM was also characterized by FTIR and EA. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1153–1161, 2003     

Synthesis and fluorescence properties of star‐shaped polymers carrying two fluorescent moieties

A well‐defined fluorescent star‐shaped polymer containing two different fluorescent functionalities one in the main chain and another in the end group was designed and synthesized by combining atom transfer radical polymerization (ATRP) and azide‐alkyne click reaction. The star polymer with four arms was prepared from copolymerization of methyl methacrylate and 4‐(2‐(9‐anthryl))‐vinyl‐styrene using ATRP. Subsequently the end group was modified with another fluorescent moiety by click coupling. The structure of all the intermediate and final products was established through NMR spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, UV?visible spectroscopy and fluorescence spectroscopy. The novel hybrid polymer exhibits an attractive high fluorescence at 494 nm and over a broad range which was a combination of both the fluorescence moieties. © 2013 Society of Chemical Industry     

High‐performance biobased epoxy derived from rosin

Great achievements have been made in the research of biobased thermoplastic polymers, but the progress concerning thermosetting resins has been minor. In particular, research on high‐performance thermosetting polymers from renewable feedstock has not been reported elsewhere. A novel biobased epoxy was synthesized from a rosin acid. Its chemical structure was confirmed using ¹H NMR, ¹³C NMR and Fourier transform infrared spectroscopy. The results indicated that the rosin‐based epoxy possessed high glass transition temperature (T_g = 153.8 °C), high storage modulus at room temperature (G′ = 2.4 GPa) and good thermal stability. A rosin‐based epoxy with excellent properties was achieved. The results suggest it is possible to develop high‐performance thermosetting resins from renewable resources. Copyright © 2010 Society of Chemical Industry     

Preparation and properties of halogen‐free flame‐retarded phthalonitrile–epoxy blends

Halogen‐free flame‐retarded blends composed of 2,2‐bis[4‐(3,4‐dicyanophenoxy) phenyl] propane (BAPh) and epoxy resin E‐44 (EP) were successfully prepared with 4,4′‐diaminodiphenyl sulfone as a curing additive. The structure of the copolymers was characterized by Fourier transform infrared spectroscopy, which showed that epoxy groups, a phthalocyanine ring, and a triazine ring existed. The limiting oxygen index values were over 30, and the UL‐94 rating reached V‐0 for the 20 : 80 (w/w) BAPh/EP copolymers. Differential scanning calorimetry and dynamic rheological analysis were employed to study the curing reaction behaviors of the phthalonitrile/epoxy blends. Also, the gelation time was shortened to 3 min when the prepolymerization temperature was 190°C. Thermogravimetric analysis showed that the thermal decomposition of the phthalonitrile/epoxy copolymers significantly improved with increasing BAPh content. The flexible strength of the 20:80 copolymers reached 149.5 MPa, which enhanced by 40 MPa compared to pure EP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of poly(ether sulfone)‐graft‐polydimethylsiloxane copolymers

Novel poly(arylene ether sulfone) (PAES) polymers containing polydimethylsiloxane (PDMS) side chains were synthesized and characterized with NMR and Fourier transform infrared spectroscopy. The thermal properties of the copolymers were evaluated with differential scanning calorimetry and thermogravimetric analysis. The polymers showed perfect thermal stability, as the decomposition temperatures were all above 380°C, and exhibited glass‐transition temperatures in the range 130–188°C. Furthermore, the surface properties of the copolymers were evaluated by X‐ray photoelectron spectroscopy and contact angle analysis. The results show that the hydrophobic abilities of the graft copolymer surfaces were improved significantly compared to PAES through the introduction of the PDMS chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Tailored thermal and mechanical properties of epoxy resins prepared using multiply hydrogen‐bonding reactive modifiers

In this study, we synthesized a phosphorus‐containing triply functionalized reactive modifier, DOPO‐tris(azetidine‐2,4‐dione), and a phosphorus‐free doubly functionalized reactive modifier, bis(azetidine‐2,4‐dione), and embedded them into epoxy resin systems. We characterized these synthesized reactive modifiers using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, elemental analysis, and mass spectrometry. During the thermosetting processes, we reacted the epoxy curing agents 4,4‐diaminodiphenylmethane and tris(4‐aminophenyl)amine with the multiply hydrogen‐bonding reactive modifiers and epoxy monomers. The introduction of the DOPO segment, strongly hydrogen bonding malonamide linkages, and hard aromatic groups into the backbones of the synthesized reactive modifiers resulted in epoxy networks exhibiting tailorable crosslinking densities, flexibilities, glass transition temperatures, thermal decomposition temperatures, and flame retardancies. Furthermore, dynamic mechanical analyses indicated that intermolecular hydrogen bonding of these reactive modifiers enhanced the thermal and physical properties of their epoxy resins through the formation of unique pseudocrosslinked polymer networks. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Cure monitoring of aerospace epoxy resins and prepregs by Fourier transform infrared emission spectroscopy

Spectral analysis of the infrared radiation emitted from thin films of resin transferred from the surface of high performance aerospace carbon fibreepoxy composite prepregs and heated to the cure temperature allows the cure chemistry and kinetics to be monitored in real time. Quantitative spectra with excellent signal-to-noise ratio are obtained by heating a thin resin film on a platinum hotplate fitted to the external optics of a Fourier transform infrared (FTIR) spectrometer and referencing the resulting emission (with the platinum emission subtracted) to a graphite black body at the same temperature. The resulting spectra are identical to absorption spectra and the quantitative features of the analysis are demonstrated by the appearance of isosbestic points during the curing reactions, so indicating that concentration profiles of the reacting species may be obtained. From the initial rate of amine and epoxy consumption, activation energies of 75kJ mol⁻¹ were obtained for both functional groups in the uncatalysed resin 4,4′-tetraglycidyl diamino diphenyl methane (TGDDM) with 27% 4,4′-diaminodiphenylsulfone (DDS), while values of 74 and 89kJ mol⁻¹ were obtained for amine and epoxy consumption from the TGDDM/DDS prepreg catalysed with boron trifluoride monoethylamine (Hercules 3501–6), consistent with homopolymerization occurring in the prepreg as well as amine–epoxy addition. Analysis of the FTIR emission at 177°C of resin from prepreg aged up to 90h at 23°C and 55% relative humidity shows a lowering of epoxy and amine concentration and a higher rate of cure, consistent with the formation of catalytic species. This technique may be used to monitor changes in surface properties such as tack and resin transfer, in addition to changes in the cure profile of the aged epoxy propreg.     

Synthesis,thermal properties,and flame retardance of phosphorus‐containing epoxy‐silica hybrid resins

A novel epoxy resin modifier, phosphorus‐containing epoxide siloxane (DPS) with cyclic phosphorus groups in the Si O network, was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with polyhedral‐oligomeric siloxanes, which was synthesized by the sol–gel reaction of 3‐glycidoxypropyltrimethoxysilane. DPS was confirmed by Fourier transform infrared and ²⁹Si NMR measurement, and then was employed to modify epoxy resin at various ratios, with 4,4‐diaminodiphenyl‐methane as a curing agent. In order to make a comparison, DOPO‐containing epoxy resins were also cured under the same conditions. The resulting organic–inorganic hybrid epoxy resins modified with DPS exhibited a high glass transition temperature (T_g), a good thermal stability, and a high limited oxygen index. In addition, the tensile strength of cured products was also rather desirable. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Surface properties of lithospermum‐containing multiple phase emulsion systems

In this study, we employed a one‐step emulsion process—rather than the traditional, relatively difficult two‐step process—to obtain multiple phase emulsion systems containing the Chinese herbal medicine lithospermum. We characterized these systems in terms of their contact angles, surface tensions, fluorescence, and stability and analyzed them using polarized microscopy, atomic force microscopy, and attenuated total reflection Fourier transform infrared spectroscopy. Our one‐step emulsion process involved mixing lithospermum at various concentrations with three different emulsifiers to control the properties of the emulsion systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of phosphorous‐containing poly(epichlorohydrin) and polyurethane from a novel synthesis route

Phosphorylation of poly(epichlorohydrin) (PECH) was successfully performed via reacting the P? H bond of 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with the pendent chloromethyl groups of PECH. From this reaction, phosphorus‐containing PECH with hydroxyl terminal groups was obtained. This compound was further reacted with toluene‐2,4‐diisocyanate to form a phosphorous‐containing polyurethane. The performance of the phosphorylation reaction and the structure of the resulting polymers were characterized by Fourier transform infrared spectroscopy, phosphorous‐31 nuclear magnetic resonance (³¹P NMR) spectroscopy, and elemental analysis. The phosphorylated PECH and polyurethane were characterized by thermogravimetric analysis (TGA), which showed weight loss retardation behavior under air at high temperature at >500 °C and high char yield at 700 °C. Both of the synthesized polymers are potentially useful as multifunctional modifiers for epoxy resins and for improving the toughness and flame retardancy of the resins. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2254–2259, 2002