Studies on sublimation of disperse dye out of dyed polymers. II. Rate of sublimation and amorphous transition of polypropylene

The diffusion coefficient D of disperse dyes through unmodified polypropylene (dyed at 120° and 137°C) was measured at 50°–160°C in the dry system. The diffusion transition points indicated by the breaks in the log D versus 1/T°K were obtained at about 70°, 90°, and 115°C. The 70° and 115°C transitions are in good accordance with the transition temperature of smectic into monoclinic phase and with the temperature of abrupt change in lattice expansion of monoclinic crystal, respectively. These phenomena were explained on the basis of the intimate correspondence between amorphous and crystalline transitions, as expressed by one of us for poly(ethylene terephthalate). The 115°C transition was confirmed by the same sort of diffusion transition occurring, expectedly, at 83°C in the case of polyethylene, an abrupt increase in lattice expansion of which had been found at about 80°C. The diffusion transitions were also confirmed by dilatometry and shrinkage measurement. The 90°C transition has never been reported and it cannot be explained at present.     

Visible dichroism of polypropylene–disperse dye system at high temperatures

The dichroism of polypropylene film dyed with C. I. Disperse Yellow 7 was investigated at various temperatures up to 160°C. The dichroic value D drops as the temperature is raised. So long as the amorphous structure does not change irreversibly, D changes reversibly with temperature. The experimental results agree qualitatively with those obtained on poly(ethylene terephthalate) in our previous paper, although the effect of temperature on the extent of the reversible change in D is larger in PP than in PET. The plot of D versus temperature exhibits breaks at 40°–50°C (T₀), 70°–80°C (T₁), and 115°–120°C (T₃). These temperatures agree with the transition points of polypropylene in the literature. From the change in the intrinsic dichroism D₀ with temperature, it is concluded that the decrease in D at high temperatures is due to the drop of D₀ caused by the disorientation of dye molecules in the amorphous region, while the amorphous polymer chain is not disoriented. Such a conclusion is supported by the fact that Δn of a heat-set specimen is kept constant during heating, in contrast to D.     

Visible dichroism of the poly(ethylene terephthalate)–disperse dye system at high temperatures

The dichroic behavior of PET film dyed at 70°C with Disperse Red 17 or Disperse Yellow 7 was investigated in the temperature range 20–200°C with a view to studying the changes in amorphous region of PET at high temperatures. The dichroic orientation factor D versus temperature plot is expressed by a straight line with negative slope; two breaks appear at 80 (T_g) and 120°C. So long as the amorphous structure does not change irreversibly, the values of D change reversibly with the temperature. Hence, if a change in D after heating is observed at room temperature, it is evidence that an irreversible change occurred in the amorphous structure during the heating. The break at 120°C is a new amorphous transition point of PET existing along with T_g, although the T_g can hardly be observed after the cold crystallization; some phenomena reported in the literature are proposed as evidence.     

Polymer welding relations investigated by a lap shear joint method

A lap shear joint method was used to study strength development during welding of polystyrene surfaces- The surfaces previously had not been in contact and care was taken to insure rapid wetting of the interface. The shear stress at failure, τ_f was measured at room temperature as a function of contact time, t, at constant welding temperatures up no 20°C above the glass transition temperature, T_g. The time dependence of welding could be well described by τ_fαt^1/4. This result is in agreement with predictions of the reptation molecular dynamics model applied to inter-diffusion at a symmetric amorphous polymer-polymer interface. The activation energy for the thermally activated increase in strength development was determined as E = 96 kcal/mol at T = 113.5°C, which compares with E = 93,2 kcal/mole as predicted by the W-L-F theory using C₁ = 13.7, C₂ = 50 and T_g = 100°C. The polystyrene samples had molecular weights, M_n = 143,000 and M_w = 262.000. The time to achieve complete healing, t_∞ ≈? 256 min at 118°C, was found to be of the same order of magnitude as the viscoelastic relaxation time and also with the time required for a polymer chain to diffuse a distance equal to its root mean square end-to-end vector.     

Simultaneous diffusion of a disperse dye and a solvent in PET film analyzed by rutherford backscattering spectrometry

Poly(ethylene terephthalate) (PET) is a difficult fiber to dye from an aqueous dyebath due to its high degree of crystallinity and lack of polar groups. One method used to increase the dyeing rate of the fibers is the addition of an organic solvent, called a dye carrier, to the aqueous bath. This study utilized Rutherford backscattering spectrometry and neutron activation analysis to examine both simultaneous diffusion and individual diffusion characteristics of a disperse dye and dye carrier into PET film. The dye exhibited Fickian diffusion above and below glass transition temperature (T_g) of the PET film both in the presence and absence of solvent. The presence of carrier in the dyebath was found to increase the diffusion coefficient of the dye at each temperature condition; increasing from 10⁻¹⁴ to 10⁻¹¹ cm²/s below T_g (65°C) and 10⁻¹² to 10⁻¹⁰ cm²/s above T_g (90°C). Bromobenzene exhibited case II diffusion below T_g of the film, which indicates that the solvent is swelling the near surface regions of the film. This increase in void volume resulted in an increased dye uptake when films dyed inthe presence of carrier were compared with those dyed without carrier. In fact, the penetration depth of the dye was found to be equivalent to that of the swollen region of the film (∼ 600 nm) after 15 s. Above T_g, the bromobenzene exhibited Fickian diffusion. The coupling of the increased thermal motion of the polymer at the higher temperature and the solvent effect increased dye uptake when compared either with dye uptake at the lower temperature or with uptake when no solvent was present. The application of the dye and solvent simultaneously did not affect the diffusion mechanism of either species, leading to the conclusion that there was no competition for specific sites between these two species in the PET film. Similar results were obtained for chlorobenzene when used as the dye carrier. © 1996 John Wiley & Sons, Inc.     

Detection of polymer transition temperatures by infrared absorption spectrometry

Infrared bands in the 900–1100 cm^?1 region are sensitive to thermal energy. These bands can result from intermolecular coupling, producing the crystal lattice, or from intramolecular coupling of the various atomic groups in a regular helix or coiled chain. In either case an increase in temperature will disrupt the coupling mode, resulting in a form of structural relaxation and a reduction in the integrated absorbance. It is proposed that the temperature at which the peak areas begin to decrease be assigned as the T_g. This is measured by continuously scanning a selected peak in the infrared spectrum of a polymer film while it is heated at a rate of about 1°C/min. Using this technique polyamides (nos. 6,66, and 610) exhibited transitions in the 30–50°C range, and by studying the increase in the free NH region (3440 cm^?1) of nylon 66 two other transitions were detected at 80 and 137°C; the latter represents a change in the nylon 66 crystal state. An amorphous film of poly(ethylene terephthalate) displayed a transition at 58–68°C (T_g) and at 85°C, which is the crystallization temperature. Films of poly(vinyl acetate) and polystyrene exhibited transitions at 25–37°C and at 70°C, respectively.     

The specific volume of poly(4-methylpentene-1) as a function of temperature (30°–320°C) and pressure (0–2000 kg/cm2)

The dependence of the specific volume of a commercial sample of poly(4-methylpentene-1) (Mitsui TPX, RT-20, abbr. PMP) on temperature (30°–320°C) and pressure (0–2000 kg/cm²) has been determined. Results are reported in tabular form and as approximate fits, making use of the Tait equation. The data show that the crystalline melting transition of this type of PMP is completed at 235°C under zero pressure and gives indication of a glass transition temperature T_g at about 20°C at p = 0. Its approximate pressure dependence is given by dT_g/dp ≈ 0.015°C kg^?1 cm². The zero pressure results on the melting and glass transitions are in agreement with DTA results. The p-v-T data, quenching experiments, and a determination of the crystalline unit cell (tetragonal, a = b = 18.70 Å, c = 13.54 Å) confirm earlier work indicating that the room-temperature crystalline specific volume of PMP is greater than the amorphous specific volume. This unusual density behavior persists to a temperature of 50–60°C at p = 0 and to temperatures as high as 230–240°C under a pressure of 2000 kg/cm².     

Poly(L‐Lactide), 8. High‐Temperature Hydrolysis of Poly(L‐Lactide) Films with Different Crystallinities and Crystalline Thicknesses in Phosphate‐Buffered Solution

Poly(L ‐lactide) (PLLA) films having different crystallinities (X_c's) and crystalline thicknesses (L_c's) were prepared by annealing at different temperatures (T_a's) from the melt and their high‐temperature hydrolysis was investigated at 97°C in phosphate‐buffered solution. The changes in remaining weight, molecular weight distribution, and surface morphology of the PLLA films during hydrolysis revealed that their hydrolysis at the high temperature in phosphate‐buffered solution proceeds homogeneously along the film cross‐section mainly via the bulk erosion mechanism and that the hydrolysis takes place predominantly and randomly at the chains in the amorphous region. The remaining weight was higher for the PLLA films having high initial X_c when compared at the same hydrolysis time above 30 h. However, the difference in the hydrolysis rate between the initially amorphous and crystallized PLLA films at 97°C was smaller than that at 37°C, due to rapid crystallization of the initially amorphous PLLA film by exposure to crystallizable high temperature in phosphate‐buffered solution. The hydrolysis constant (k) values of the films at 97°C for the period of 0–8 h, 0.059–0.085 h^–1 (1.4–2.0 d^–1), were three orders of magnitude higher than those at 37°C for the period of 0–12 months, 2.2–3.4×10^–3 d^–1. The melting temperature (T_m) and X_c of the PLLA films decreased and increased, respectively, monotonously with hydrolysis time, excluding the initial increase in T_m for the PLLA films prepared at T_a = 100, 120, and 140°C in the first 8, 16, and 16 h, respectively. A specific peak that appeared at a low molecular weight around 1×10⁴ in the GPC spectra was ascribed to the component of one fold in the crystalline region. The relationship between T_m and L_c was found to be T_m (K) = 467·[1–1.61/L_c (nm)] for the PLLA films hydrolyzed at 97°C for 40 h.     

The absorption behavior and crystallization of poly(aryl ether ketone) films

The absorption and subsequent desorption behaviors of amorphous polymer films of PEEK poly(ether ether ketone), PEEKK poly(ether ether ketone ketone), and PEKK poly(ether ketone ketone) in solvent of 1,2-dichloroethane (C₂H₄Cl₂) are investigated and compared. The equilibrium absorption weight (M_∞) of these polymers is related to their molecular ketone content or molecular chain rigidity and also to the experimental conditions. Especially, at a certain temperature, the molecular chains in the solvent can be polarized, which leads to producing greater M_∞ for polymer films; for example, at 60°C, M_∞ = 46% for PEEK and M_∞ = 65% for PEKK. The pseudodiffusion coefficients for PEEK, PEEKK, and PEKK all surpass the 6.0 × 10⁻¹² m² s⁻¹. The polymer's molecular polarization has been proved in concentrated sulfur acid. Results also show that amorphous resin's films become white and creeped in dichloroethane, which is more serious when metaphenyl links are introduced into PEEKK or PEKK molecular main chains. The residual solvent of 1% or so often exists in the films, even though a long desorption time (over 100 h) has been proceeded. Absorption has induced crystallization of amorphous polymer films, but this crystallization process is slightly different from that of the films crystallized from both the glassy state and the melting state in the solvent, which makes the amorphous interlayers grow progressively and more condensely; thus, the crystallized films will have higher T_g's than these crystallized under annealing condition. The morphology results have shown that the solvent-crystallized films are less toughened than the amorphous ones because of the intermediate layer between the induced crystallized area and the amorphous area in the core. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2065–2075, 1998     

Conformational transition characterization of glass transition behavior of polymers

The conformational transition behavior of polymer in the amorphous state has been investigated through molecular dynamics simulations across the glass transition temperature (T_g). We find that the conformational transition, a localized and short time dynamics feature, crosses over different barrier heights when the system transforms from the molten state into the glass state and the barrier height in the glass state is markedly lower than that above T_g. In addition to the overall transition behavior, the specific transitions between the rotational isomeric states (RIS) g⁺, t⁻, t⁺ and g⁻ are also investigated in detail. The populations of these specific transitions undergo considerable changes when the temperature decreases; meanwhile, the larger transition rates of the ending torsions get diminished. Besides the rate, the rotation degrees of the dihedrals during the transitions also change their distributions tremendously through T_g, below which most of the larger transition angles (50-100°) were inhibited remaining those sharply around 30°. This possibly explains why below T_g the conformational transition process has a lower effective barrier.     

Thermally stimulated current study on flexible siloxane-modified epoxy sheets

Copolymers prepared from the epoxy resin of ALBIFLEX and PMPS oligomer were evaluated with IR, ¹H-and ¹³C NMRs for structural determinations. The flexible epoxy resin as a model compound was examined by TSC with variations on the operational parameters t_p and V_p. Transitions denoted as T_g,δ, T_g,γ, T_g,β, T_g,α and T_g,ρ in increasing order of temperature were observed for these copolymers. As an example, ESAF-7430 copolymer showed these transitions at −138, −84, 26, 87, and 110 °C, respectively. Each transition except the T_g,ρ at 110 °C, has been correlated to a segment in the copolymeric structure. The result indicates that TSC provides clear molecular transitions at the temperature of the transition. The molecular transition of the grafted PMPS-siloxane segment in an epoxy matrix appeared at the −45 °C region as a broad, nearly flat peak as it filled the concave part of the TSC curve of the unmodified resin. The flexibility that the modified copolymers retained may be attributed to these sub-T_g transitions as observed in the TSC spectrum.     

Water sorption in amorphous poly(ethylene terephthalate)

The water sorption characteristics of poly(ethylene terephthalate) (PET) amorphous samples of 250 μm thickness have been studied at various temperatures in a saturated atmosphere. Concerning diffusivity, one can distinguish the following two domains characterized by distinct values of the activation energy: E_D ≈ 36 kJ mol⁻¹ at T > 100°C, and E_D ≈ 42 kJ mol⁻¹ at T < 60°C, with a relatively wide (60–100°C) intermediary domain linked to the glass transition of the polymer. The crystallization of this latter occurs in the time scale of diffusion above 80°C but doesn't change the Fickian character of sorption curves. The equilibrium concentration m_∞ is an increasing function of temperature, but the solubility coefficient S decreases sharply with this latter, with the apparent enthalpy of dissolution ΔH_s being of the order of −28 kJ mol⁻¹ at T < 80°C and −45 kJ mol⁻¹ at T > 80°C. Density measurements in the wet and dry states suggest that water is almost entirely dissolved in the amorphous matrix at T < 80°C but forms partially a separated phase at T > 80°C. Microvoiding can be attributed to crystallization-induced demixing. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1131–1137, 1999     

Proton spin–lattice and spin–spin relaxation times in isotactic polypropylene. II. Effects of stretching ratio and temperature

Proton spin–lattice, T₁, and spin–spin, T₂, relaxation times of uniaxially stretched polypropylene film were measured at 40°C using a wide line pulse spectrometer operating at 19.8 MHz. T_1l, the longer T₁, increases almost linearly with increasing stretching ratio, and T_2a, T₂ of the amorphous region, decreases gradually as the stretching ratio is increased. These results can be interpreted in terms of the increased constraints to molecular motion in the amorphous region. The fraction of the rigid protons in the sample, F_c, increases with increasing stretching ratio, while the crystallinity calculated from the density, X_d, does not change largely. The difference between F_c and X_d, therefore, increases as the stretching ratio is increased. This indicates that the physical structure of the highly stretched sample is far from the ideal two-phase model. The influence of the stretching temperature was also investigated. There are only slight increases in T_1l and in F_c for the samples stretched in a temperature range from 80°C to 150°C, whereas the considerable increase in T_2a occurs. The most notable change introduced at a high temperature stretching is the increase in the chain mobility in the amorphous region.     

Properties of syndiotacticity-rich poly(vinyl alcohol) thin film in water. IV. Elastic behavior of untreated thin film by repeated elongation and contraction in water

The activation energy ΔE_a for diffusion of water molecules into untreated thin film of poly(vinyl alcohol) (PVA_VTFA) derived from vinyl trifluoroacetate was estimated as 30.3 kcal/mol from the temperature dependence of the initiation time of swelling. The degree of equilibrium swelling increases with the increase in temperature in the range of 10–70°C, passing through the constant range between 30 and 50°C. Under the forced, repeated elongation and contraction for swollen PVA_VTFA thin film in water, the perfect elastic behavior is kept up to higher elongation with the increase in temperature and especially up to about three times equilibrium swelling length at 70°C. Young's modulus of swollen PVA_VTFA thin film in water was 6.47 × 10⁶ to 1.60 × 10⁶ dyn/cm² at 25–70°C. The molecular weight between junctions M_c increased with the increase in temperature; M_c was nearly equal to about one-sixth of the molecular weight of raw polymer M at 25°C and about one-third of M at 70°C. The interaction parameter between PVA_VTFA and water X₁, was 0.493–0.497 at 25–70°C.     

Characterization of optical properties of acrylate based adhesives exposed to different temperature conditions

Optical adhesives combine the traditional function of structural attachment with a more advanced function of providing an optical path between optical interconnects. This article aims to characterize refractive index and birefringence of such adhesives under environmental exposure to different temperature conditions. Optical time domain reflectometery (OTDR) and prism coupling methods were employed to measure optical properties of an optical adhesive. Thermo‐optic coefficient (dn/dT) of the adhesive was observed to decrease noticeably from ?2 × 10^?4°C^?1 to ?4 × 10^?4°C^?1 around the glass transition temperature (T_g ～ 78°C). It is observed that refractive indices for both T_E and T_M modes increase with increasing annealing temperature, but the birefringence (T_E ? T_M) is decreasing. This suggests that the material has become more isotropic due to the annealing. The environmental changes in optical properties of the adhesive are discussed in the light of Lorentz–Lorenz equations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 950–956, 2005     

Equilibrium disperse-dye sorption by isotactic polypropylene films of varied thermal histories

Spherulitic polypropylene (PP) films prepared by a melt-quenched process and then exposed to isothermal annealing treatments at various temperatures ranging from 120°C to 155°C have been dyed at 80°C with C.I. Disperse Yellow 7(Y-7) or p-aminoazobenzene. Different PP films as crystallized isothermally in the range of 60°C to 155°C have also been dyed with the same dyes. The equilibrium dye sorption (M_o) obtained for these films increased slightly with an increase in polymer volume crystallinity (C_u). Using fine structural data of these films, the change in M_o were analyzed in terms of the mosaic-block structural model; e.g., the values of M_o were divided into sorption by the amorphous end region (M_e) located between lamella surfaces and sorption by the amorphous side region (M_s) located between crystalline cores parallel to the molecular chain axis. The value of M_s increased with increasing C_v in both cases of the dyeing systems, while the value of M_e decreased monotonically in an opposite manner. The amorphous chains in the side region seem to have a strong affinity to a long rodlike dye molecule of Y-7; this feature is considered to be associated with the extended chain conformation of the side region which originates from distorted lattice chains.     

Dyeing mechanism and model of nylon 6 fiber dyeing in low‐temperature hydrogen peroxide–glyoxal redox system

This article reports the results of a study of nylon 6 fiber dyed in a low‐temperature hydrogen peroxide–glyoxal redox system. It was expected that the dyed fiber would have better dye fastness and higher economic value than would conventional fiber. In addition, this article presents the proposed mechanism for and model of a free‐radical dyeing system as well as a derived theoretical equation. From the experimental results, it was found that formation of covalent bonds by the coupling of the dye and the fiber radical in free‐radical dyeing was only 25%–40%, whereas with the conventional type of ionic dyeing, it was almost 60%–75%. Because the initiation efficiency of free‐radical formation is affected by many factors, such as the pH of the dye bath and the concentrations of the oxidant and reductant, the aims of this study were to investigate the formation of free radicals and the effects on dye uptake of the concentrations of dye, oxidant, and reductant and of the fiber amine end group. In addition, the dyeing properties of dyed fiber were investigated, and the dyeing order and rate constant of the rate equation were evaluated from the experimental data. From the experimental results, the following conclusions were drawn. (1) The hydrogen peroxide–glyoxal redox system produced many free radicals in the dye bath as temperature reached 70°C. (2) The amine end group in the nylon fiber was the main site of ionic and covalent bonding between nylon 6 fiber and dye. (3) The proposed model of free‐radical dyeing showed, from the fit of the experimental data into the equation and the evaluation of the equation parameters, that the order fit the theoretical value well, with the rate constant dependent on the dyeing conditions; at pH = 3, it could match the equation's best (rate equation of the proposed model: d[D]_R/dt = k_A[GO]¹[H₂O]^m[D]^1/2[F]^1/2). (4) The optimum dyeing conditions in the hydrogen peroxide–glyoxal redox system were: [H₂O₂] = 0.15–0.20M, [glyoxal] = 0.07–0.10M, pH = 3, dyeing temperature = 70°C, and dyeing time = 45–50 min. (5) The redox dyeing system had better dye fastness than did the conventional system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4197–4207, 2006     

Poly(ethylene terephtalate) films modified with N,N‐dimethylacrylamide: Incorporation of disperse dye

Poly(ethylene terephtalate), PET, can be modified with N,N‐dimethylacrylamide to obtain a better incorporation of disperse dye (Disperse Blue 79). Minimal variations in the decomposition at 10% level, melting, and glass transition temperatures, show that the thermal stability of modified PET films does not change when compared to nonmodified PET. The atomic force images show nanopeaks formation on the surface due to the modification. Modified PET films show a decrease in the contact angle and then, an increase in the superficial tension measurements, when compared to the value of 37 ± 1 dynes · cm⁻¹(nonmodified), with values liying in the range of 42–46 ± 0.5 dynes · cm⁻¹. The data obtained by photoacoustic spectroscopy (PAS) for dyed PET films show a dye peak at 580 nm. The data analysis of the peak area show that PET films modified with N,N‐dimethylacrylamide for 15 min at 85°C, dyed for 6 h at 85°C with a dye concentration of 0.333 g/L, incorporate three times more dye than the nonmodified films dyed in the same conditions. By the data obtained from PAS, it was possible to calculate the depth profile of dyeing with values around 54 μm. Factorial analyses show that the dyeing time was the most important variable. The major amount of incorporated dye was obtained by the following combination of variables: temperature and time of modifier treatment were, respectively, 72.5°C and 15 min; time and temperature of dyeing were, respectively, 90°C and 195 min for a dye concentration of 0.133 g/L. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 269–282, 2000     

Thermoreversible hydrogels. I. Synthesis and effect of a hydrophobic monomer on swelling behaviors of thermoreversible gels prepared by copolymerizing N-alkoxyalkylacrylamide with butyl acrylate

A series of copolymeric gels were prepared from N-alkoxyalkylacrylamide and n-butyl acrylate (BA) at various feed ratios. The effect of the content of BA in the copolymer on the gel behaviors is discussed. The respective crosslinked copolymer exhibits a gel transition behavior, collapsing and shrinking above gel transition temperature but swelling and reexpanding below gel transition temperature. By utilizing this character, these copolymeric gels could be used for drug release or drug delivery systems. The drug released from the copolymeric gels was plotted as M_t/M_∞ versus t, where M_t/M_∞ is the fraction of drug released at given time t. In this experiment, crystal violet and caffeine were chosen as model drugs. The deswelling-kinetics experiments with caffeine showed that a water pocket was formed within the gel matrix when the gel deswelled rapidly. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1477–1484, 1997     

Isothermal Cure of an Epoxy System Containing Tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM), a Multifunctional Novolac Glycidyl Ether and 4,4′-Diaminodiphenylsulphone (DDS): Vitrification and Gelation

Times to gelation and vitrification have been determined at different isothermal curing temperatures between 200 and 240°C for an epoxy/amine system containing both tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) and a multifunctional Novolac glycidyl ether with 4,4′-diaminodiphenylsulphone (DDS). The mixture was rich in epoxy, with an amine/epoxide ratio of 0·64. Gelation occurred around 44% conversion. Vitrification was determined from data curves of glass transition temperature, T_g, versus curing time obtained from differential scanning calorimetry experiments. The minimum and maximum values T_g determined for this epoxy system were T_g0=12°C and T_gmax=242°C. Values of activation energy for the cure reaction were obtained from T_g versus time shift factors, a_T, and gel time measurements. These values were, respectively, 76·2kJmol^-1 and 61·0kJmol^-1. The isothermal time–temperature–transformation (TTT) diagram for this system has been established. Vitrification and gelation curves cross at a cure temperature of 102°C, which corresponds to glass transition temperature of the gel. © of SCI.