The curing of epoxy resins with aminophenoxycyclotriphosphazenes

Aminophenoxycyclotriphosphazenes have been used as curing agents for epoxy resins. The thermal curing was performed in stages at 120–125 and 175–180°C followed by postcuring at 225°C to give tough brown polymers. The thermal curing reaction was monitored using FTIR and differential scanning calorimetry. Thermogravimetric analysis of the cured resins has shown thermal stability up to 350–340°C. The char yield obtained in nitrogen at 800°C was about 55–42% and in air at 700°C was about 40–32%. Graphite cloth laminates were prepared. The mechanical properties evaluated were found superior to those of commonly used epoxy resin systems. These resins are useful for making fire- and heat-resistant composites, laminates, molded parts, and adhesives.     

Dimensionally and thermally stable polymer,containing disordered graphitic structure and adamantane

In an attempt to develop a low‐k interlayer dielectric, adamantane‐diphenyldiethynyl moiety containing oligomer is prepared. Oligomerization of 1,3,5,7‐tetrakis[3/4‐ethynylphenyl]adamantane ( 4 ) is accomplished by a Glaser–Hay oxidative coupling with 1,3,5‐triethynylbenzene and phenylacetylene end‐capping agent. The CHCl₃ soluble oligomer is then thermally treated by step‐curing at 200, 300, 380, and 450 °C for 30 min at each temperature under nitrogen flow to render a shiny void‐free black polymer. TGA analysis indicates that the polymer is stable under nitrogen up to 500 °C with a marginal decomposition up to 800 °C. Solid‐state ¹³C NMR, Raman scattering, and FTIR are used to characterize the structure of the polymer. The polymer consists of amorphous carbon networks with the adamantane moieties and nanosized graphitic regions (clusters), which are generated from the thermal crosslinking of the diphenyldiethynyl units. It shows a remarkably low linear coefficient of thermal expansion (～25 ppm/°C), presumably due to the presence of the disordered graphitic structure. Its high density (～1.21 g/cm³), refractive index (～1.80 at 632 nm), and Young's modulus (～17.0 GPa) are also consistent with the interpretation. This study reveals important details about the effect of microscopic structure on the macroscopic properties of the highly crosslinked polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6909–6925, 2006     

Alkaline-developable positive-type photosensitive polyimide with high mechanical strength and high resolution based on chain extendable poly(amic acid), thermally degradable cross-linker and photoacid generator

A positive-type photosensitive polyimide ( PSPI ) based on a chain extendable poly(amic acid) ( PAA ), a thermally degradable cross-linker 1,3,5-tris[(2-vinyloxy)ethoxy]benzene ( TVEB ), and a photoacid generator (PAG) (5-propylsulfonyloxyimino-5H-thiophene-2-ylidene)-(2-methylphenyl)acetonitrile ( PTMA ) has been developed. The chain extendable PAA was prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride ( BPDA ) and 4,4′-oxydianiline ( ODA ) and end-capped with di-tert-butyl dicarbonate ( DIBOC ) in N-methyl-2-pyrrolidone (NMP), which has a controlled molecular weight for developing in a 2.38 wt% tetramethyl ammonium hydroxide aqueous solution ( TMAH _aq ) and undergoes a chain extending reaction during curing stage. The photosensitive resist solution was formulated with the polymerization solution (30 wt% in NMP), TVEB (15 wt% for the polymer), and PAG (4.5 wt% for the polymer). The PSPI showed a sensitivity of 47 mJ cm⁻² and a contrast of 5.8 when exposed to 365-nm light, followed by postexposure baking at 90 °C for 10 min and development with the 2.38 wt% TMAH _aq at room temperature. A fine-positive image with 3-μm line-and-space patterns was obtained on a 3-μm thick film exposed to UV light at 365 nm in the contact-printed mode. After thermal curing at 350 °C for 1 hr, the resulting PSPI features excellent mechanical strength and elongation.     

Synthesis and Characterization of Poly(allyl methacrylate) Obtained by Free Radical Initiator

Allyl methacrylate was polymerized in CCl₄ solution by α,α′‐azoisobutyronitrile at 50, 60, and 70°C. The kinetic curves were auto‐accelarated types at 60 and 70°C, but almost linear at 50°C. Arrhenius activation energy was 77.5 kJ/mol. The polymer was insoluble in common organic solvents. It was characterized by FT‐IR, NMR, DSC, TGA and XPS methods. About 98–99% of allyl side groups were remained as pendant even after completion of the polymerization. The spectroscopic and thermal results showed that polymerization is not a cyclopolymerization type, but may have end group cyclization. The high molecular weight is the main cause of a polymer being insoluble even in the early stage of the polymerization. Molecular weight of 1.1×10⁶ for a soluble polymer fraction was measured by light scattering method. The Tg of polymer was 94°C, and after curing at 150–200°C, increased to 211°C. The thermal pyrolysis of polymer at about 350°C gave an anhydride by linkage type degradation, and side group cyclization. The XPS analysis showed the presence of radical fragments of AIBN (initiator) and CCl₄ (solvent) associated with oligomers.     

Thermal curing and water re‐exposure of silane–PVA/PVAc complex film on glass fiber surface

Because glass fiber reinforced composites are in industrial demand, chemistry and topography of the glass fiber sizing are of interest. Silane–PVA/PVAc (polyvinyl alcohol/polyvinyl acetate) complex film on the glass fiber surface is studied during thermal curing and water re‐exposure by using atomic force microscopy. The complex film consists of silane with the honeycomb structure film and PVA/PVAc with the hexagonal close pack structure of ellipsoidal shaped microspheres (270 × 620 nm). The thermal curing at 100 °C is leading to the evaporation of water contained in the microspheres. Because of water evaporation, the average roughness value of 1‐min thermal curing decreases from initial 7.3 to only 2.7 nm. Such a collapse of microsphere is followed by an intermixing between silane film and PVA/PVAc microspheres leading to a change of silane honeycomb structure along with silane tips. The average value of the silane honeycomb structure wall width decreases from 144 nm to 54 nm, for curing times of 15 and 30 min, respectively. A re‐exposure to an aqueous environment after 100 °C curing leads to almost completely restored microspheres regarding shape and size. The average complex film thickness increases from 180 nm for thermal curing for 30 min to 225 nm for water re‐exposed film. Interestingly, the pits in the microsphere structure are observed presumably because of the tips from intermixing. The thermal curing at 200 °C enhances the intermixing, and after 15 min, an intramixing is suggested to occur between PVAc core and PVA shell of the microsphere. The water re‐exposure after 15 min of 200 °C curing leads to a re‐containing of water but without restored microsphere structure; Because of the intramixing, leaving the silane–PVA/PVAc film is not complex anymore. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis, cure kinetics, and thermal properties of a novel boron–silicon hybrid polymer

A novel boron–silicon hybrid polymer (PASB) was synthesized from polycondensation between phenylboron dichloride and dichloromethylsilane with Grignard reagent. The structure of PASB was characterized using fourier transform infrared spectra, ¹H-NMR, ¹³C-NMR, and gel permeation chromatography. The curing behavior of PASB was investigated by means of non-isothermal differential scanning calorimetry and the kinetic parameters were determined by the Kissinger’s and Ozawa’s methods, respectively. The results showed that both the methods for calculating the activation energy value gave fairly close results of 104.4 and 107.7 kJ mol^?1, respectively. A reasonable curing cycle for the resin system was also established, which suggested that it was reasonable to choose a curing temperature between T _i0 (452.0 K) and T _f0 (554.0 K). These results can provide theoretical guidance reference for determining the curing of the resin system. The thermal stability of cured PASB resin was studied by means of thermogravimetric analysis under nitrogen atmosphere and the temperature of 5 % mass loss (Td₅) was 610.1 °C, the residue at 1,000 °C was 87.8 %, which showed that the cured PASB resin exhibited excellent thermal properties and made it potentially useful as high performance matrix resin and precursor for ceramics.     

Biaspartimide-diamines as Curing Agents for Epoxy Resins

Various 4,4′ -bis(N²-[4-(4-aminophenoxy)phenyl]aspartimido)diphenylmethane-type bisaspartimide-diamines have been used as solventless curing agents for epoxy resins. The thermal curing was performed at 170, 190, and 230°C to give a tough brown polymer. Thermogravimetric analysis of the polymer obtained showed thermal stability up to 330°C and char yields of 45% in N₂ at 800°C and 12% in air at 700°C. The thermal curing reaction was monitored using FT-IR. The synthesized polymers are useful for making composites, laminates, and adhesives.     

Room temperature processable heat‐resistant epoxy‐oxazolidone‐based syntactic foams

Syntactic foams based on oxazolidone‐modified epoxy resin using glass microballoons as reinforcing filler with varying densities were processed. The influence of various grades of microballoons and their concentration on the mechanical, thermal, thermomechanical, and flammability characteristics were investigated. The effect of temperature on the compressive strength with density was monitored in detail. By incorporating the microballoons, T_g of the syntactic foam increased from 90 °C to 115 °C. Thermal conductivity was found to decrease from (0.064 to 0.056 W/(m·K)) in conjunction with decreasing resin to filler ratio. In the case of composites filled with K25 alone, the creation of large voids due to less effective packing between the microballoons led to lower thermal conductivity. The specific heat of the different composites was in the range of 0.32 to 0.44 cal/g/°C, and the coefficient of thermal expansion was in the range of 13.2 to 17.4 × 10⁻⁶/°C with limiting oxygen index of 28% to 33%.     

Thermal expansion and compressibility in the chain direction of a polydiacetylene single crystal

An x-ray back-reflection rotating camera has been used to measure the lattice constant, thermal expansion, and compressibility in the polymer chain direction of a polydiacetylene, poly[bis(p-toluene sulfonate) of 2,4-hexadiyne 1,6-diol]. The thermal expansion coefficient of the polymer chain is small and positive (0.9 ± 0.2 × 10^?6 °K^?) at 300°K, but negative below about 70°K. Application of 3.43 kbar hydrostatic pressure at 299°K changed the unit cell dimension in the polymer chain direction by less than 10 ppm.     

Poly(urethane Methacrylate) Thermo-Setting Resins Studied by Thermogravimetry and Thermomechanical Analysis

Two different poly(urethane acrylate) resins (one with a trimer: PUA1, the second with a dimer: PUA2) prepared [1] by photo curing reaction are investigated by means of thermogravimetry and thermomechanical measurements. The lack of mass loss found up to 300°C for both systems shows their good thermal stability. Beyond this temperature, two mass losses occur consecutively. This mass loss already studied by TG-FTIR coupled measurements for PUA1 resin has been attributed to the degradation of carbonyl groups [1]. The extension to PUA2 and the comparison between the mass loss magnitude and the relative contain in acrylate of the resins leads to attribute the first degradation to the degradation of the acrylate fraction. The degradation of dimer based resin occurs earlier and with a faster kinetic than the trimer based resin. The variations of linear expansion and penetration coefficients measured by thermomechanical analysis (penetration probe) in the glassy state and in the glass transition temperature domain (the onset glass transition temperatures measured by DSC at 20°C min^–1 are respectively equal to 111 and 107°C for PUA1 and PUA2, the transitions, not well defined, extending over 30°C), show that despite of a weaker compactness, the trimer based resin is more rigid than the dimer one. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electron delocalization contribution to single crystal thermal expansion of a polydiacetylene

The thermal expansion contribution due to temperature-dependent π-electron delocalization is evaluated from spectral measurements on a single crystal polydiacetylene (poly-2,4-hexadiyne-1,6-diol bisphenylurethane). The observed temperature independence of backbone associated vibrations (less than ±1 cm^?1 change in ν_C?C and ν_C?C between 25 and 90°C) implies that thermal conformational fluctuations and equilibrium defect formation (which produce a negative thermal expansion coefficient) do not measurably affect π-electron delocalization. The separation of equilibrium defects is either much longer than that of nonequilibrium defects or much longer than required to appreciably limit π-electron delocalization in an effectively defect-free polymer. Arguments presented indicate that, in the experimental temperature interval, the observed thermal expansion coefficient in the chain direction is over an order of magnitude larger than the delocalization-associated contribution.     

Synthesis and characterization of oligosalicylaldehyde-based epoxy resins

The synthesis of a new epoxy resin of oligosalicylaldehyde by the reaction with epichlorohydrin is reported. New resin’s epoxy value and chlorine content were determined and found to be 25% and 1%, respectively. The characterization of the new resin was instrumented by FTIR, ¹H NMR, scanning electron microscopy, and thermal gravimetric analyses. TGA results showed that the cured epoxy resin has a good resistance to thermal decomposition. The mass losses of cured epoxy resin were found to be 5%, 10%, 50% at 175°C, 240°C, and 400°C, respectively. On the curing procedure the resin was cured with polyethylenepolyamine at 25 °C for 8 h and 100°C for 1.5 h. The FTIR spectrum of new epoxy resin gave the peak of oxirane ring at ṽ = 918 cm⁻¹. In memory of Professor Dr. Adalet R. Vilayetoğlu     

Functionalized monomers based on N-(4-hydroxy phenyl)maleimide

N-(4-Hydroxy phenyl)maleimide (HPMI) is functionalized with acryloyl, methacryloyl, allyl, propargyl and cyanate groups and the structures of the materials are characterized by FTIR, ¹H NMR and ¹³C NMR. Thermal curing behaviours of the monomers and thermal stabilities of the polymers are studied using thermal analysis. Introduction of polymerizable groups shifts the curing exotherm to low temperatures, and the curing behaviour is dictated by the polymerizable substituent present in the aromatic ring. Polymer from acryloyl-functionalized monomer shows the highest thermal stability (402 °C), whereas the highest char value (49 % at 700 °C) is noted for the polymer obtained from propargyl-functionalized monomer. Polymers derived from functionalization of HPMI with acryloyl and methacryloyl showed better thermal stabilities. Thermosets formed by the thermal polymerization of HPMI functionalized with propargyl and cyanate groups showed higher char values at 700 °C in nitrogen atmosphere.     

Synthesis and characterization of a novel polytriazole resin with low‐temperature curing character

A novel low‐temperature curing polytriazole resin was prepared from a triazide and a tetraalkyne and characterized. The resin can be cured at 70°C. The glass transition temperature T_g and thermal decomposition temperature T_d5 of the cured resin with the molar ratio of azide to alkyne group [A]/[B] = 1.0:1.0 reached 324 and 355°C, respectively. The study on the curing kinetics of the resin shows that the apparent activation energy of the curing reaction is 93 kJ mol^?1. The flexural strength of the cured resin reached 137.6 MPa at room temperature and 102.6 MPa at 185°C. Copyright © 2007 John Wiley & Sons, Ltd.     

Determination of the glass transition temperature in thin polymeric films used for microelectronic packaging by temperature-dependent spectroscopic ellipsometry

We characterized the glass transition temperature T_g of thin polyimide films by temperature-dependent spectroscopic ellipsometry and compared the results to DSC measurements of the bulk polymer. The effect of the curing temperature on T_g and the thermal expansion α(T) was analyzed. An improved ellipsometric data evaluation was used to get most precise and reliable T_g data. T_g increased with increasing curing temperature, while the bulk T_g was considerably lower than the thin film T_g. Both observations are attributed to the temperature sensitive release of the imidization by-product 2-hydroxyethyl methacrylate (HEMA) and crosslinker components as well as decomposition products from the material. Variation in the curing temperatures of 230–380 °C led to an increase in the T_g of 34 °C.     

Approach to improving the toughness of TGMDA/DDS epoxy resin by blending with thermoplastic polymer powders

A series of hot-melt processable thermosetting compositions was prepared by blending N,N,N′,N′-tetraglycidyl-4,4′ -diaminodiphenyl-methane/4,4′-diaminodiphenylsulfone (TGMDA/DDS) epoxy resin and thermoplastic polymer powders with average particle size below 30 μm. The basic thermoplastic polymers were either a high T_g amorphous cardo polyimide (T_g=350°C) or commercial semicrystalline PA6 and PA12 polyamides. The resulting heterogeneous mixtures showed viscosity values below 5000 cps suitable for prepregging process. After cure, phase-separated morphologies were maintained with a rather limited interphase miscibility as demonstrated by thermomechanical analysis. Scanning electron microscope examination of fracture surfaces pointed out a strong adhesion between the powder particles and the surrounding polyepoxy network, particularly for the potentially reactive polyamide structures. Moreover, as shown by differential scanning calorimeter analysis, the crystallinity ratio of the PA6 and PA12 powders was lowered due to melting during thermal polymerization. The fracture toughness properties of the powder-containing materials were compared with those of a fully miscible cardo polyimide–TGMDA/DDS blend coming from an homogeneous resin composition. The best improvement in fracture energy was obtained for the powder-modified resins. The most effective composition filled with 16 wt% of powdered polyimide exhibited a fourfold increase in G_IC (388 J/m² versus 100 J/m²) without compromising the epoxy thermomechanical stability (T_g=227°C versus 223°C).     

Fire- and heat-resistant matrix resins based on ethynyl-substituted aromatic cyclotriphosphazenes

A novel class of fire- and heat-resistant matrix resins has been synthesized by thermal polymerization of ethynyl-substituted aromatic cyclotriphosphazenes. Thermal polymerization of new tris[4-(4′-ethynylbenzanilido)phenoxy]tris(phenoxy) cyclotriphosphazene ( III ) and tris[4-(4′-ethynylphthalimido)phenoxy]tris(phenoxy)cyclotriphosphazene ( VII ) at 250°C for 1–1.5 h gave tough polymers. The thermal stabilities of the polymers were evaluated in nitrogen and in air by thermogravimetric analysis (TGA). The synthesised polymers were stable to 400–410°C and showed char yield of 78–65% at 800°C in nitrogen and of 78–69% at 700°C in air. The ethynyl-substituted polymer precursor ( III ) was synthesised by the reaction of tris(4-aminophenoxy)tris(phenoxy)cyclotriphosphazene ( I ) with 4-ethynylbenzoyl chloride. The polymer precursor ( VII ) was synthesised by a solution condensation of I with 4-ethynylphthalic anhydride followed by in situ thermal cyclodehydration at 150°C. The structure of polymer precursors was characterized using proton nuclear magnetic resonance (¹H-NMR), infrared (IR) spectroscopy, and elemental analysis. The curing of polymer precursors was monitored by differential scanning calorimetery (DSC) and IR spectroscopy. The synthesised matrix resins are potential candidates for the development of heat- and fire-resistant fiber-reinforced composites. © 1993 John Wiley & Sons, Inc.     

Bismaleimides chain-extended by imidized benzophenone tetracarboxylic dianhydride and their polymerization to high temperature matrix resins

Heat-resistant polymers were obtained by thermal polymerization of several bismaleimides or their substituted derivatives. The chain of the polymer precursors was extended by incorporation of imidized benzophenone tetracarboxylic dianhydride between the maleimide rings in order to impart a degree of flexibility in the polymers. The bismaleimides and their corresponding tetraamic acids were characterized by infrared (IR) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The differential thermal analysis (DTA) thermograms of the monomers showed exotherms at 200–340°C attributed to the thermally induced polymerization reactions. The influence of different substituents in the maleic double bond on the curing temperature was investigated. The thermal stability of the cured resins was evaluated by thermogravimetric analysis (TGA) and isothermal gravimetric analysis (IGA). They were stable up to 367–433°C both in nitrogen and air atmosphere and afforded 57–68% char yield at 800°C under anaerobic conditions. The structure of the aromatic and aliphatic diamines utilized for imidization was correlated with the thermal stability of the cured resins. The bismaleimide derived from p-phenylenediamine gave the most heat-resistant resin because of its higher rigidity.     

Synthesis of a novel epoxy resin containing naphthalene moiety and properties of its cured polymer with phenol novolac

A new epoxy resin (Bis-ENA) containing naphthalene structure linked with a 1,4-bis(isopropylidene)phenylene was synthesized and was confirmed by elemental analysis, infrared spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. To estimate the effect of naphthalene moiety on the cured polymer, an epoxy resin (Bis-EP) having phenyl moiety was synthesized, and curing behaviors of Bis-ENA and Bis-EP with phenol novolac were evaluated by differential scanning calorimetry. The incorporation of naphthalene structure into the resin backbone increased the curing temperature and reduced the curing reactivity. Thermal properties of the cured polymers obtained from Bis-ENA and Bis-EP with phenol novolac were examined by thermomechanical analysis and dynamic mechanical analysis. Mechanical properties and moisture resistance were evaluated by flexural strength, flexural modulus, and moisture absorption measurements. The cured polymer obtained from Bis-ENA showed higher glass transition temperature, higher flexural modulus, lower thermal expansion, and lower moisture absorption than that from Bis-EP. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3063–3069, 1999     

Thermal stability of flexible polyurethane foams containing modified layered double hydroxides and zinc borate

Abstract

Flexible polyurethane foams (FPUFs) have been modified to contain layered double hydroxides (LDHs) by dihydrogen phosphate (H₂PO₄ ^?). The thermal stability of the prepared foams has been characterized using thermogravimetric analysis (TGA) at 5, 10, 20, 30, and 40?°C/min heating rates. The experimental data indicate that the temperature range for the two pyrolysis stages of FPUF is about 212–350?°C and 350–565?°C, respectively. Integral programmed decomposition temperature (IPDT) has been calculated according to the measured data, which was found that the IPDT of the modified FPUF was increased to 526?°C. Additionally, the thermal stability of FPUF composite has been also evaluated by the activation energy (E) on the basis of the pyrolysis kinetics of FPUF composites during thermal decomposition using Coats–Redfern integral method. These results manifest that the presence of intercalated LDHs enhances the thermal stability of FPUF.