Reaction kinetics modeling and thermal properties of epoxy–amines as measured by modulated‐temperature DSC. I. Linear step‐growth polymerization of DGEBA + aniline

A mechanistic approach including both reactive and nonreactive complexes can successfully simulate both nonreversing (NR) heat flow and heat capacity (C_p) signals from modulated‐temperature DSC in isothermal and nonisothermal reaction conditions for different mixtures of diglycidyl ether of bisphenol A + aniline. The reaction of the primary amine with an epoxy–amine complex initiates cure (E_1A1 = 80 kJ mol^?1), whereas the reactions of the primary amine (E_1OH = 48 kJ mol^?1) and secondary amine (E_2OH = 48 kJ mol^?1) with an epoxy–hydroxyl complex are rate determining from about 2% epoxy conversion on. The reliability of the proposed mechanistic model was verified by experimental concentration profiles from Raman spectroscopy. When cure temperatures are chosen inside or below the full cure glass‐transition region, vitrification takes place partially or completely, respectively, as can be concluded from the magnitude of the stepwise decrease in C_p. The effect of the epoxy conversion (x) and mixture composition on thermal properties such as the glass‐transition temperature (T_g), the change in heat capacity at T_g [ΔC_p(T_g)], and the width of the glass transition region (ΔT_g) are considered. The Couchman relationship, in which only T_g and ΔC_p(T_g) of both the unreacted and the fully reacted systems are needed, was evaluated to predict the T_g– x relation by using simulated concentration profiles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2798–2813, 2004     

Use of temperature‐modulated DSC in kinetic analysis of a catalysed epoxy–anhydride system

The curing kinetics of a catalysed epoxy‐anhydride system was studied by temperature‐modulated differential scanning calorimetry. The chemical‐controlled regime was analysed by empirical kinetic equations. The diffusion‐controlled regime was detected by the diffusion factor, DF(α,T), which was calculated from the ratio of the experimental rate to the chemical reaction rate. DF(α,T) was compared with a mobility factor, MF(α,T), which was obtained by measuring the modulus of the complex heat capacity |C_p*|. The equivalence of the two factors allowed the diffusion‐controlled regime to be studied using the |C_p*| signal. However, the results obtained in the epoxy–anhydride system showed a limitation to the method, and this is discussed in terms of the modulation period necessary for the variation in MF(α,T) to occur in the same conversion interval as does DF(α,T). Copyright © 2004 Society of Chemical Industry     

Thermal analysis of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) irradiated under vacuum

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) was irradiated by ⁶⁰Co γ‐rays (doses of 50, 100 and 200 kGy) under vacuum. The thermal analysis of control and irradiated PHBV, under vacuum was carried out by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile properties of control and irradiated PHBV were examined by using an Instron tensile testing machine. In the thermal degradation of control and irradiated PHBV, a one‐step weight loss was observed. The derivative thermogravimetric curves of control and irradiated PHBV confirmed only one weight‐loss step change. The onset degradation temperature (T_o) and the temperature of maximum weight‐loss rate (T_p) of control and irradiated PHBV were in line with the heating rate (°C min^?1). T_o and T_P of PHBV decreased with increasing radiation dose at the same heating rate. The DSC results showed that ⁶⁰Co γ‐radiation significantly affected the thermal properties of PHBV. With increasing radiation dose, the melting temperature (T_m) of PHBV shifted to a lower value, due to the decrease in crystal size. The tensile strength and fracture strain of the irradiated PHBV decreased, hence indicating an increased brittleness. Copyright © 2004 Society of Chemical Industry     

High‐Performance Small‐Amount Fe2O3‐Doped (K,Na)NbO3‐Based Lead‐Free Piezoceramics with Irregular Phase Evolution

[(K_0.43Na_0.57)_0.94Li_0.06][(Nb_0.94Sb_0.06)_0.95Ta_0.05]O₃ + x mol% Fe₂O₃ (KNLNST + x Fe, x = 0~0.60) lead‐free piezoelectric ceramics were prepared by conventional solid‐state reaction processing. The effects of small‐amount Fe₂O₃ doping on the microstructure and electrical properties of the KNLNST ceramics were systematically investigated. With increasing Fe³⁺ content, the orthorhombic‐tetragonal polymorphic phase transition temperature (T_O‐T) of KNLNST + x Fe ceramics presented an obvious “V” type variation trend, and T_O‐T was successfully shifted to near room temperature without changing T_C (T_C = 315°C) via doping Fe₂O₃ around 0.25 mol%. Electrical properties were significantly enhanced due to the coexistence of both orthorhombic and tetragonal ferroelectric phases at room temperature. The ceramics doped with 0.20 mol% Fe₂O₃ possessed optimal piezoelectric and dielectric properties of d₃₃ = 306 pC/N, k_p = 47.0%, = 1483 and tan δ = 0.023. It was revealed that the strong internal stress in the KNLNST + x Fe ceramics with higher Fe³⁺ contents (x = 0.40, 0.60) stabilized the orthorhombic phase, leading to the irregular “V” type rather than the usually observed monotonic phase transition with composition change in the ceramics.     

Synthesis of a novel phosphorus‐containing dicyclopentadiene novolac hardener and its cured epoxy resin with improved thermal stability and flame retardancy

A novel phosphorus‐containing dicyclopentadiene novolac (DCPD‐DOPO) curing agent for epoxy resins, was prepared from 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and n‐butylated dicyclopentadiene phenolic resin (DCPD‐E). The chemical structure of the obtained DCPD‐DOPO was characterized with FTIR, ¹H NMR and ³¹P NMR, and its molecular weight was determined by gel permeation chromatography. The flame retardancy and thermal properties of diglycidyl ether bisphenol A (DGEBA) epoxy resin cured with DCPD‐DOPO or the mixture of DCPD‐DOPO and bisphenol A‐formaldehyde Novolac resin 720 (NPEH720) were studied by limiting oxygen index (LOI), UL 94 vertical test and cone calorimeter (CCT), and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. It is found that the DCPD‐DOPO cured epoxy resin possess a LOI value of 31.6% and achieves the UL 94 V‐0 rating, while its glass transition temperature (T_g) is a bit lower (133 °C). The T_g of epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 increases to 137 °C or above, and the UL 94 V‐0 rating can still be maintained although the LOI decreases slightly. The CCT test results demonstrated that the peak heat release rate and total heat release of the epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 decrease significantly compared with the values of the epoxy resin cured by NPEH720. Moreover, the curing reaction kinetics of the epoxy resin cured by DCPD‐DOPO, NPEH720 or their mixture was studied by DSC. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44599.     

Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/poly (L‐lactide) blend

Reaction after mixing of liquid epoxidized natural rubber/poly(L ‐lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L ‐lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (T_g) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while T_g and melting temperature (T_m) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high‐resolution solid‐state ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermogravimetric analysis of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

The thermal degradation of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (T_o) was derived by T_o = 0.97B + 259, where B represents the heating rate (°C/min). The temperature at which the weight loss rate was maximum (T_p) was T_p = 1.07B + 273, and the final temperature (T_f) at which degradation was completed was T_f = 1.10B + 280. The percentage of the weight loss at temperature T_p (C_p) was 69 ± 1% whereas the percentage of the weight loss at temperature T_f (C_f) was 96 ± 1%. In the thermal degradation of P(HB‐HV) (7:3), T_o = 0.98B + 262, T_p = 1.00B + 278, and T_f = 1.12B + 285. The values of C_p and C_f were 62 ± 7 and 93 ± 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB‐HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (T_o, T_p, andT_f) by 7–12°C (measured at B = 20°C/min). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2237–2244, 2001     

Time–temperature–transformation (TTT) cure diagrams: Relationship between Tg and the temperature and time of cure for a polyamic acid/polyimide system

Glass transition temperatures (T_g) were obtained vs. isothermal temperature (T_cure) and time of cure for a polyamic acid/polyimide system. A time–temperature–transformation (TTT) isothermal cure diagram was constructed to include the time to vitrification and iso-T_g curves. As for expoxies, the relationship between T_cure and the time to vitrification is S-shaped. Plots of T_g vs. T_cure show that solvent evaporation and chemical reaction are controlled by vitrification.     

Continuous heating transformation (CHT) cure diagram of an aromatic amine/epoxy system at constant heating rates

The overall reaction kinetics of a high-T_g tetrafunctional aromatic diamine/difunctional epoxy system (maximum glass transition temperature, T_g∞ = 182°C), which can satisfactorily describe the rate of the reaction in both kinetically and diffusion-controlled regimes, had been determined earlier from isothermal conversion/T_g data by differential scanning calorimetry (DSC). The mathematical expression of the kinetics, together with the unique one-to-one relationship between T_g and chemical conversion, is used to calculate the material's T_g vs. time under heating at constant rates. For a heating scan from below T_g0 (the glass transition temperature of the unreacted material), initial devitrification corresponds to the reaction temperature (T_cure) first passing through the T_g of the reacting material; vitrification corresponds to T_g becoming equal to the increasing T_cure after initial devitrification; and finally, upper devitrification corresponds to T_g eventually falling below the rising T_cure. The results of the calculation correlate well with the available experimental data of the dynamic mechanical behavior of the material during temperature scans at constant rates that were obtained by the torsional braid analysis (TBA) technique. T_g is calculated to remain slightly higher than T_cure after vitrification due to the influence of diffusion control, the difference being greater for lower heating rates. The limiting heating rate with no initial devitrification and that with no vitrification are also calculated.     

Synthesis and characteristics of a novel aliphatic polycarbonate,poly[(propylene oxide)‐co‐(carbon dioxide)‐co‐(γ‐butyrolactone)]

A novel aliphatic polycarbonate, poly[(propylene oxide)‐co‐(carbon dioxide)‐co‐(γ‐butyrolactone)] [P(PO? CO₂? GBL)], was synthesized by the copolymerization of carbon dioxide, propylene oxide (PO) and γ‐butyrolactone (GBL). The resulting copolymers were determined by FTIR and NMR spectral analysis with viscosity‐average molecular weights (M_v) from 50 000 to 120 000 g mol^?1. According to elemental analysis, the calculated data of elemental contents in P(PO? CO₂? GBL)44 were close to the found data. The result showed that GBL was inserted into the backbone of poly[(propylene oxide)‐co‐(carbon dioxide)] successfully. GBL offered an ester structural unit that gave the copolymer better degradability. The correlations between reaction conditions and properties were studied. When GBL content increased, the M_v and the glass transition temperature (T_g) of the copolymers improved relative to an identical copolymer without GBL. Prolonging the reaction time of the copolymerization resulted in increases in M_v and T_g. P(PO? CO₂? GBL) exhibited a high T_g above 40 °C. The rate of backbone degradation increased with increasing GBL content. Copyright © 2005 Society of Chemical Industry     

Free‐standing hybrid anion‐exchange membranes for application in fuel cells

A series of free‐standing hybrid anion‐exchange membranes were prepared by blending brominated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (BPPO) with poly(vinylbenzyl chloride‐co‐γ‐methacryloxypropyl trimethoxy silane) (poly(VBC‐co‐γ‐MPS)). Apart from a good compatibility between organic and inorganic phases, the hybrid membranes had a water uptake of 32.4–51.8%, tensile strength around 30 MPa, and T_d temperature at 5% weight loss around 243–261°C. As compared with the membrane prepared from poly (VBC‐co‐γ‐MPS), the hybrid membranes exhibited much better flexibility, and larger ion‐exchange capacity (2.19–2.27 mmol g^?1) and hydroxyl (OH^?) conductivity (0.0067–0.012 S cm^?1). In particular, the hybrid membranes with 60–75 wt % BPPO had the optimum water uptake, miscibility between components, and OH^? conductivity, and were promising for application in fuel cells. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improved thermal stability of the piezoelectric properties of (Li,Ag)‐co‐modified (K,Na) NbO3‐based ceramics prepared by spark plasma sintering

High‐performance lead‐free piezoelectric ceramics 0.94(K_0.45Na_0.55)_1?xLi_x(Nb_0.85Ta_0.15)O₃–0.06AgNbO₃ (KNNLTAg‐x) were successfully prepared by spark plasma sintering technique. The doping effect of Li on the structural and electrical properties of KNNLTAg‐x (x=0, 0.02, 0.04, 0.06, 0.08 and 0.10) ceramics was studied. The lattice structure, ferroelectric and piezoelectric properties of the KNLNTAg‐x ceramics are highly dependent on the Li doping level. In particular, the Li dopant has a great impact on both Curie temperature T_c and orthorhombic‐tetragonal transition temperature T_O‐T. The 4% Li‐doped sample exhibited relatively high T_O‐T of 95°C, leading to a stable dynamic piezoelectric coefficient (d₃₃*) of 220‐240 pm/V in a broad temperature range from 25°C to 105°C. Additionally, the 2% Li‐doped sample shows a high d₃₃* of 320 pm/V at 135°C, suggesting its great potential for high‐temperature applications.     

Novel anion‐exchange organic‐inorganic hybrid membranes prepared through sol‐gel reaction and UV/thermal curing

Anion‐exchange organic‐inorganic hybrid membranes were prepared through sol‐gel reaction and UV/thermal curing of positively charged alkoxysilane and the alkoxysilane containing acrylate or epoxy groups. Properties of prepared hybrid membranes were varied by control of the molar ratio of the precursors. It was shown that the thermal degradation temperatures (T_d) of the membranes were in the range of 212–226°C, water uptakes in the range of 9.6–14.6% and IEC values in the range of 0.9–1.6 mmol g^?1. The hybrid membranes show high permeability to anions, as reflected by the high static transport number (t_?) of the anion (Cl^?). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Non‐Isothermal Decomposition Kinetics,Heat Capacity,and Thermal Safety of 2‐Nitroimino‐5‐Nitro‐Hexahydro‐1,3,5‐Triazine (NNHT)

The kinetic equation describing the thermal decomposition reaction of NNHT obtained by TG‐DTG data, integral isoconversional non‐linear method and integral method of treating TG‐DTG curves is . The specific heat capacity (C_p) of NNHT was determined with the continuous C_p mode of the microcalorimeter. The equation of C_p (T) was obtained. The standard molar heat capacity of NNHT was 218.41 J mol⁻¹ K⁻¹ at 298.15 K. With the help of the onset temperature (T_e) and maximum peak temperature (T_p) from the non‐isothermal DTG curves of NNHT at different heating rates (β), the apparent activation energy (E_K and E_O), and the pre‐exponential constant (A_K) of the thermal decomposition reaction obtained by Kissinger’s method and Ozawa’s method, C_p obtained by microcalorimetry, density (ρ) and thermal conductivity (λ), the decomposition heat (Q_d, taking half‐explosion heat), Zhang‐Hu‐Xie‐Li’s formula, Smith’s equation, Friedman’s formula, Bruckman‐Guillet’s formula, and Wang‐Du’s formulas, the values (T_e0 and T_p0) of T_e and T_p corresponding to β→0, thermal explosion temperature (T_be and T_bp), adiabatic time‐to‐explosion (t_TIad), 50 % drop height (H₅₀) of impact sensitivity, critical temperature of hot‐spot initiation (T_cr), thermal sensitivity probability density function [S(T)] versus temperature (T) relation curves for spheroidic NNHT with radius of 1 m surrounded with ambient temperature of 300 K, peak temperature corresponding to the maximum value of S(T) versus T relation curve ( ), safety degree (SD), and critical ambient temperature(T_acr) of thermal explosion of NNHT are calculated. The following results of evaluating the thermal safety of NNHT are obtained: T_SADT=T_e0=453.34 K, T_SADT=T_p0=454.86 K, T_be=462.68 K, T_bp=467.22 K, t_TIad=1.03 s, H₅₀=17.69 cm, T_α=461.4 K. SD=72.74 %, P_TE=27.26 %, and T_acr=321.96 K.     

The role of the ratio (PEG:PPG) of a triblock copolymer (PPG‐b‐PEG‐b‐PPG) in the cure kinetics,miscibility and thermal and mechanical properties in an epoxy matrix

The aim of this study was to evaluate the role of different poly(ethylene glycol):poly(propylene glycol) (PEG:PPG) molar ratios in a triblock copolymer in the cure kinetics, miscibility and thermal and mechanical properties in an epoxy matrix. The poly(propylene glycol)‐block‐poly(ethylene glycol)‐block‐poly(propylene glycol) (PPG‐b‐PEG‐b‐PPG) triblock copolymers used had two different molecular masses: 3300 and 2000 g mol^?1. The mass concentration of PEG in the copolymer structure played a key role in the miscibility and cure kinetics of the blend as well as in the thermal–mechanical properties. Phase separation was observed only for blends formed with the 3300 g mol^?1 triblock copolymer at 20 wt%. Concerning thermal properties, the miscibility of the copolymer in the epoxy matrix reduced the T_g value by 13 °C, although a 62% increase in fracture toughness (K_IC) was observed. After the addition of PPG‐b‐PEG‐b‐PPG with 3300 g mol^?1 there was a reduction in the modulus of elasticity by 8% compared to the neat matrix; no significant changes were observed in T_g values for the immiscible system. The use of PPG‐b‐PEG‐b‐PPG with 2000 g mol^?1 reduced the modulus of elasticity by approximately 47% and increased toughness (K_IC) up to 43%. Finally, for the curing kinetics of all materials, the incorporation of the triblock copolymer PPG‐b‐PEG‐b‐PPG delayed the cure reaction of the DGEBA/DDM (DGEBA, diglycidyl ether of bisphenol A; DDM, Q3‐4,4′‐Diaminodiphenylmethane) system when there is miscibility and accelerated the cure reaction when it is immiscible. All experimental curing reactions could be fitted to the Kamal autocatalytic model presenting an excellent agreement with experimental data. This model was able to capture some interesting features of the addition of triblock copolymers in an epoxy resin. © 2018 Society of Chemical Industry     

Curing kinetics and thermal property characterization of a bisphenol‐S epoxy resin and DDS system

The kinetics of the cure reaction for a system of bisphenol‐S epoxy resin (BPSER), with 4,4′‐diaminodiphenyl sulfone (DDS) as a curing agent was investigated with a differential scanning calorimeter (DSC). Autocatalytic behaviour was observed in the first stages of the cure which can well be described by the model proposed by Kamal, using two rate constants, k₁ and k₂, and two reaction orders, m and n. The overall reaction order, m + n, is in the range 2∼2.5, and the activation energy for k₁ and k₂ was 86.26 and 65.13 kJ mol⁻¹, respectively. In the later stages, a crosslinked network was formed and diffusion control was incorporated to describe the cure. The glass transition temperature (T_g) of the BPSER/DDS samples partially cured isothermally was determined by means of torsional braid analysis (TBA) and the results showed that the reaction rate increased with increasing T_g, in terms of rate constant, but decreased with increasing conversion. It was also found that the  SO₂ group both in the epoxy resin and in the hardener increases the T_g values of the cured materials compared with that of BPAER. The thermal degradation kinetics of this system was investigated by thermogravimetric analysis (TGA). It illustrated that the thermal degradation of BPSER/DDS has nth order reaction kinetics. © 2000 Society of Chemical Industry     

Nonlinear phase‐separation behavior of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride) blends

The nonlinear phase‐separation behavior of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride) (PMMA/SMA) blends over wide appropriate temperature and heating rate ranges was studied using time‐resolved small‐angle laser light scattering. During the non‐isothermal process, a quantitative logarithm function was established to describe the relationship between cloud point (T_c) and heating rate (k) as given by T_c = Alnk + T₀, in which the parameter A, reflecting the heating rate dependence, is much different for different compositions due to phase‐separation rate and activation energy difference. For the isothermal phase‐separation process, an Arrhenius‐like equation was successfully applied to describe the temperature dependence of the apparent diffusion coefficient (D_app) and the relaxation time (τ) of the early stage as well as the late stage of spinodal decomposition (SD) of PMMA/SMA blends. Based on the successful application of the Arrhenius‐like equation, the related activation energies could be obtained from D_app and τ of the early and late stages of SD, respectively. In addition, these results indicate that it is possible to predict the temperature dependence of the phase‐separation behavior of binary polymer mixtures during isothermal annealing over a range of 100 °C above the glass transition temperature using the Arrhenius‐like equation. © 2012 Society of Chemical Industry     

Temperature‐insensitive piezoelectricity in lead‐free NaNbO3‐based ceramics

In this work, we report a lead‐free piezoelectric ceramic of (0.9‐x)NaNbO₃‐0.1BaTiO₃‐xBaZrO₃, and the effects of BaZrO₃ on the phase structure, microstructure, electrical properties and temperature stability are investigated. A morphotropic phase boundary‐like region consisting of rhombohedral (R) and tetragonal (T) phases is constructed in the compositions with x = 0.035‐0.04. More importantly, in situ temperature independence of the piezoelectric effect {piezoelectric constant (d₃₃) and strain} can be achieved below the Curie temperature (T_c). Intriguingly, the electric field‐induced strain is still observed at T ≥ T_c due to the combined actions of the electrostrictive effect and the electric field‐induced phase transition. We believe that NaNbO₃‐based ceramics of this type have potential for applications in actuators and sensors.     

A novel dazzling Eu3+‐doped whitlockite‐type phosphate red‐emitting phosphor for white light‐emitting diodes

A series of novel red‐emitting Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors were successfully synthesized using the high‐temperature solid‐state reaction method. The crystal structure, photoluminescence spectra, thermal stability, and quantum efficiency of the phosphors were investigated as a function of Eu³⁺ concentration. Detailed analysis of their structural properties revealed that all the phosphors could be assigned as whitlockite‐type β‐Ca₃(PO₄)₂ structures. Both the PL emission spectra and decay curves suggest that emission intensity is largely dependent on Eu³⁺ concentration, with no quenching as the Eu³⁺ concentration approaches 100%. A dominant red emission band centered at 611 nm indicates that Eu³⁺ occupies a low symmetry sites within the Ca₈ZnLa(PO₄)₇ host lattice, which was confirm by Judd‐Ofelt theory. Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors exhibited good color coordinates (0.6516, 0.3480), high color purity (~96.3%), and high quantum efficiency (~78%). Temperature‐dependent emission spectra showed that the phosphors possessed good thermal stability. A white light‐emitting diode (LED) device were fabricated by integrating a mixture of obtained phosphors, commercial green‐emitting and blue‐emitting phosphors into a near‐ultraviolet LED chip. The fabricated white LED device emits glaring white light with high color rendering index (83.9) and proper correlated color temperature (5570 K). These results demonstrate that the Ca₈ZnLa_1?xEu_x(PO₄)₇ phosphors are a promising candidate for solid‐state lighting.     

Differential scanning calorimetry of copolymer of isotactic polypropylene backbone with grafted poly(ethylene‐co‐propylene) branches

A series of graft polymers having polypropylene (PP) backbone and poly(ethylene‐co‐propylene) (EPR) side chains was prepared. PP backbone molecular weight (M_n) was 28–98 kg/mol, EPR side chain M_n was 2.6–17 kg/mol, and EPR content was 0–16 wt %. In this work, thermal analysis of the copolymers was performed using differential scanning calorimetry (DSC). Nonisothermal crystallization was performed at different cooling rates. The DSC thermograms revealed multiple melting peaks for slowly cooled samples, most likely the result of the melting of thinner tangential lamellae followed by the melting of thicker radial lamellae. Equilibrium melting temperature (T_m⁰) was determined using the linear Hoffman–Weeks method. Another approach was also used for determining T_m⁰: melting temperature (T_m) and crystallization temperature (T_c) were plotted as functions of logarithmic cooling rate. Linear relationships were observed for all samples with the cross points as T_m⁰'s. As cooling rate decreased, T_c, T_m, and enthalpy of fusion (ΔH_f) increased. T_m and T_m⁰ increased with increasing PP M_n. T_c and T_m were unaffected by the grafting of EPR onto the PP backbone. T_m⁰ and ΔH_f decreased as EPR content increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3380–3388, 2006