New thermosetting resins for high performance composites

Investigations leading to the development of a new family of heat-stable thermosets, the Xylok

1 Registered trademark.

resins, are outlined. These polymers are the condensation products of aralkyl ethers or halides with phenols, and in some instances other classes of aromatic, heterocyclic and organometallic compounds, in the presence of a Friedel-Crafts catalyst. They are fast curing and Xylok composites have been prepared with glass, asbestos and carbon fibre reinforcement, which give excellent high-temperature mechanical strength and strength retention on prolonged exposure up to 250°. A comparative evaluation of the mechanical and electrical properties of a series of glasscloth laminates prepared with various classes of thermosetting resins has shown the Xylok resins to give outstanding overall performance. In addition, the chemical and radiation resistance, and ablative, wear and frictional properties of the Xylok composites suggest that they will find use in chemical plant, aircraft aerospace and bearing applications. Asbestos flour-filled Xylok moulding compounds have been shown to give similar flow and curing characteristics to phenolic based products, but the mouldings are significantly more heat stable.     

Glass fiber-reinforced epoxy composites

Glass fiber-reinforced epoxy composites were prepared from the matrix resins tetraglycidyl diaminodiphenylmethane

1 Systematic name: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-4,4′-diaminodiphenylmethane.

(TGDDM) and tetraglycidyl bis(o-toluidino)-methane

2 Systematic name: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-4,4′-bis(o-toluidino)methane.

(TGMBT) using various amines like 4,4′-diaminodiphenylmethane (DDM), 4,4′-diaminodiphenylsulfone (DDS) and diethylene triamine (DETA) as curing agents. The fabricated laminates were evaluated for their mechanical and dielectrical properties and chemical resistance. The composites prepared using an epoxy fortifier (20 phr) showed significant improvement in the mechanical properties.     

The synthesis and properties of a cation-exchange resin prepared by the pyrolysis of starch in the presence of phytic acid

A black charcoal-like material having cation exchange and adsorption properties was prepared by the controlled pyrolysis of starch in the presence of a commercial phytic acid solution. Resins with binding capacities of 0.7–5.7 meq/g of calcium were prepared by varying the phytic acid to starch ratio, the temperature, or the duration of heating of the reaction mixture. SEM photomicrographs of some of these new materials showed that they are composed of particles similar in size and shape to the starting starch granules. These resins also removed atrazine from aqueous solutions. © 1995 John Wiley & Sons, Inc.

1 This article is a US Government work and , as such, is in the public domain in the United States of America.

     

Polyamine-modified urea–formaldehyde-bonded wood joints. III. Fracture toughness and cyclic stress and hydrolysis resistance

The objective of this study was to improve the durability and stability of urea–formaldehyde-bonded wood products by decreasing the internal stress developed during the resin cure and by improving the ability of the cured system to withstand cyclic stresses. Urea–formaldehyde resins were modified either by incorporating urea-capped di-and trifunctional amines into the resin structure or by using the hydrochloride derivatives of some of these amines as the curing agent, or by both methods. This study supplements our previous work by examining the effects of additional amines and subjecting bonded products to additional testing. Solid wood joints bonded with a variety (7 of 15) of modified adhesives had resistance to cyclic stress superior compared to that of joints bonded with unmodified urea–formaldehyde adhesive; at least three of the modified adhesives approached the behavior of phenol–formaldehyde-bonded joints. Resistance to moist heat aging, although still inferior to that of phenol–formaldehyde-bonded joints, was significantly improved for joints bonded with modified adhesives over joints made with unmodified resins. The fracture behavior of joints made with modified adhesives was different from that of joints made with unmodified resins. The fracture energy was greater for joints made with three of four modified adhesives than for joints made with unmodified resins. Modified adhesives produced particleboards made with enhanced cyclic stress resistance. Formaldehyde emission from particleboards made with resins modified with urea-terminated amines was less than emission from boards made with unmodified resins. However, emissions from particleboards made with amine hydrochlorides were not improved compared to those from boards made with an ammonium chloride curing agent. © 1993 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Porous bead aliphatic-aromatic methacrylate copolymers,I. Effect of polymerization conditions on porous structure formation of methyl methacrylate — di(methacryloyloxymethyl)naphthalene copolymers

The influence of inert porogenic mixture and monomer mixture composition and concentration on specific surface areas, pore size distribution, volumes of pores capable of capillary condensation of nitrogen and true density of copolymers were investigated for a new type of methacrylate monomer system: methyl methacrylate and di(methacryloyloxymethyl)naphthalene. The obtained copolymers exhibit similar character as it is typical for PPS

1 PPS = Porous by Precipitant and Solvent.

styrene-divinylbenzene resins.     

Behavior of amine-modified urea–formaldehyde-bonded wood joints at low formaldehyde/urea molar ratios

Urea–formaldehyde-bonded wood products are limited to interior nonstructural applications because of their poor durability under cyclic moisture or humid environments. The stability of solid-wood joints and particleboards can be enhanced by bonding with urea–formaldehyde adhesives modified with di- and trifunctional amines at an effective resin formaldehyde-to-urea mol ratio (F/U) of 1.6; however, particleboard formaldehyde emissions were not improved over those from boards made with unmodified adhesives and were unacceptably high. The relative effectiveness of selected modifications was investigated at resin form aldehyde-to-urea (F/U) molar ratios of 1.4 and 1.2 Solid-wood joints and particleboards made with modified adhesives, an unmodified adhesive, and a phenol formaldehyde (PF) resin were subjected to cyclic soak-dry (cyclic stress) treatments and moist-heat aging. Formaldehyde emissions from particleboards were also determined. At F/U 1.4, the resistance of solid-wood joints made with modified adhesives to cyclic stress and moist-heat aging was equal to that of PF-bonded joints and superior to that of joints bonded with unmodified adhesive. The resistance of particleboards made with modified adhesives was greater than that of boards made with unmodified adhesive but less than that of PF-bonded board. Solid-wood joints and particleboards made with F/U 1.4 resins performed better than did those made with F/U 1.2 resins. Particleboards made with F/U 1.2 resins had formaldehyde emissions well below the standard, and room temperature aging or bonding at high temperature reduced emissions substantially. © 1994 John Wiley & Sons, Inc. 1

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Skin and layer formation in films prepared from carbohydrates,poly(ethylene-co-acrylic acid), and polyethylene

Cornstarch, a canary dextrin, and a maltodextrin were compared in films blown from carbohydrates compounded with poly(ethylene-co-acrylic acid) (EAA), low-density polyethylene (LDPE), and aqueous ammonium hydroxide plasticizer. Dextrins or maltodextrins having dextrose equivalent values of one and greater caused dark-colored films with caramel odors, probably due to Maillard reactions. Blown films with hydrophobic skins and water sensitive cores were produced with the dextrinized carbohydrates, but not from natural cornstarch. Water sensitivity of films containing the dextrinized carbohydrate was reduced by recycling the films through the blown film die. A mechanism for development of the skins is proposed, as is a method for preparing thin semipermeable membranes. © 1993 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Cure of epoxy resins with aromatic amines: High heat-distortion studies

Castings having unexpectedly high heat-distortion temperatures result when certain treated resins of the EPON

1 EPON is a registered trademark of the Shell Oil Company.

828 type and about 75% of the stoichiometric amount of m-phenylenediamine, are postcured for 10–20 hr. at 175–200°C. The improvement in heat-distortion temperature is about 100°C., to values as high as 250°C. A recrystallized resin has given the highest values. Other glycidyl ethers of polyphenols have shown this phenomenon to a lesser degree, but other amine curing agents, including isomers and substitution products of m-phenylenediamine, have not. Some evidence of a new curing reaction has been developed, by NMR and pyrolysis studies of model compounds, which supports the postulate that the m-phenylenediamine is alkylated with a fifth epoxy group during the postcure, presumably at a ring carbon, resulting in greater crosslinking.     

Physical and mechanical properties of highly plasticized pectin/starch films

Blends of citrus pectin and high amylose starch plasticized with glycerine were investigated to determine the effect of compositional variables on film properties. Several films with representative compositions were made from sugar beet and almond pectin, and tested for comparison. The films were cast from water onto glass plates, dried, and removed. Mechanical analysis was done using a Rheometrics RSA II solids analyzer. Increasing the glycerine concentration led to decreases in static modulus, dynamic modulus, and tensile strength, but to increases in elongation. Increasing levels of starch in the blend lowered the effect of glycerine on mechanical properties. Oxygen permeability of the films was extremely low. Sugar-beet pectin and almond pectin gave films with mechanical properties comparable to those made with citrus pectin. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Grafting of methyl methacrylate on isoprene rubber

Methyl methacrylate has been grafted on artificial isoprene rubber (IR) latex, with use of redox initiation. The properties of latices containing up to 40 phr

1 Parts per hundred parts of rubber.

methyl methacrylate (MMA) as well as solid products containing up to 80 phr of this compound were studied. Compared with ungrafted IR latex with the same solids content, the grafted IR latices had a lower viscosity, owing to their particle size being larger. Vulcanised films obtained from the grafted latices showed a considerably higher modulus, particularly at large deformations, than those based on IR or blends of IR with polymethyl methacrylate. by incorporation of certain reinforcing white fillers in the MMA-grafted IR latices, a further increase in the modulus of the latex films was effected.     

The Effect of Asymmetric Heterocyclic Units on the Microstructure and the Improvement of Mechanical Properties of Three Rigid‐Rod co‐PI Fibers

Three kinds of rigid‐rod copolyimide (co‐PI) fibers are prepared by wet‐spinning of their precursor poly(amic acid)s, which are copolymerized from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), p‐phenylenediamine (PDA), and the third asymmetric heterocyclic diamines, including 2‐(4‐aminophenyl)‐5‐aminobenzoxazole (BOA), 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (PABZ), and 2,5‐bis(4‐aminophenyl)‐pyrimidine (PRM), respectively. The asymmetry is increasing in the order PRM < BOA ≈ PABZ. The introduction of asymmetric heterocyclic units results in mesomorphic order structure and decreases the size of microvoid of PI fiber, which apparently improves the toughness of PI fiber and shows positive effects on mechanical properties. The tensile strength and initial modulus of co‐PI fibers are in the ranges of 2.6–3.2 GPa and 91.8–133.5 GPa, respectively. The lowest asymmetry leads to the highest lateral order, crystal orientation, and initial modulus of BPDA/PDA/PRM co‐PI. Moreover, the introduction of asymmetric heterocyclic units can effectively improve compressive properties. BPDA/PDA/PABZ co‐PI fiber shows the highest loop strength and recoil compressive strength due to hydrogen bonding interactions. The highest orientation leads to the lowest transverse strength of BPDA/PDA/PRM co‐PI fibers, reducing the recoil compressive strength.

     

Preparation of polyimides derived from biphenyltetracarboxylic dianhydrides and aromatic diamines bearing alkylene spacers

Four series of aromatic polyimides (PIs V–VIII) composed of biphenyltetracarboxylic dianhydrides (BPDAs) and aromatic diamines bearing alkylene spacers were prepared by two methods. Most polymers could be readily prepared in a one‐step method for the combination of a‐BPDA with α,ω‐bis(3‐aminophenoxy)alkanes, a‐BPDA with α,ω‐bis(4‐aminophenoxy)alkanes, and s‐BPDA with α,ω‐bis(3‐aminophenoxy)alkanes. However, the polymerization of s‐BPDA with α,ω‐bis(4‐aminophenoxy)alkanes gave powders. On the other hand, all four monomer combinations afforded the desired polyamic acid solution in a two‐step method. These polymer solutions could be cast into tough and flexible films, which were characterized by their inherent viscosity, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical spectrometry measurements. The glass transition temperatures (T_gs) of the polymers were in the range of 110–240°C, but they were not clearly defined for PIs VIII and VI. The 5% weight loss temperatures were around 450°C for all prepared PIs. For PI VIII an “odd–even” behavior of the tensile properties of the films was detected, corresponding to the reported behavior of the melting temperatures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2404–2413, 1999     

Synthesis and properties of novel soluble fluorinated aromatic polyamides containing 4-benzoyl-2,3,5,6-tetrafluorophenoxy pendant groups

A new diaroyl chloride monomer, 5-(4-benzoyl-2,3,5,6-tetrafluorophenoxy)isophthaloyl dichloride (BTFPIPC), was prepared in a three-step synthesis. Six novel aromatic polyamides containing 4-benzoyl-2,3,5,6-tetrafluorophenoxy pendant groups were synthesized by low temperature polycondensation of BTFPIPC with six aromatic diamines in N,N-dimethylacetamide (DMAc). All these new polymers are amorphous and readily soluble in various dipolar solvents such as DMAc, N-methyl-2-pyrrolidinone (NMP), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) at room temperature. These polymers showed glass transition temperatures between 212 and 243 °C and 5% weight loss temperatures ranging from 439 °C to 456 °C. These polyamides could be cast into transparent, flexible and strong films from DMAc solution with tensile strengths of 73.5–85.4 MPa, tensile moduli of 2.06–2.72 GPa, and elongations at break of 6.4–9.3%. These new polyamide films exhibited low dielectric constants of 3.26–3.57 (1 MHz), lower water uptakes in the range of 1.27–2.28%, and excellent transparency with an ultraviolet-visible absorption cut-off wavelength in the 326–373 nm range. Primary characterization of these new polyamides shows that they might serve as new candidates for processable high-performance polymeric materials.     

Oxidative aging of thermoplastic polyimide films

Two linear polyimides were subjected to accelerated isothermal aging at temperatures between 300 and 400°C. Losses in toughness correlated well with changes in glass transition temperature (T_g) of the films, but not with weight loss. Both materials have extrapolated lifetimes of 100,000 h near their T_g's. © 1995 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Investigation of primers reducing the pink-ring formation in multilayer printed circuit boards

A rapid and easy screening test was applied to assess the capability of various formulated primers to reduce the defect of pink rings in multilayer printed circuit boards. The mixtures of silanes with multifunctional silanol groups (crosslinkers) and 3-glycidoxypropyl-trimethoxysilane

1 Systematic name: 3-(2,3-Epoxypropoxy)propyl-trimethoxysilane.

(referred to as silane C) or N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane

2 Systematic name: 3-[N-2-aminoethyl]aminopropyl-trimethoxysilane.

(silane B) were proved to be effective in reducing the pink rings. The performance of the mixed silanes using silane A and crosslinkers with aromatic groups were better than other formulated primers which was partly attributed to less amounts of hydrophilic groups and better integrity in the primer films. A developed primer consisting of siloxane compounds had the best performance. The online test confirmed the results from the screening test and demonstrated the feasibility of the designed screening test in assessing the performance of primers. The results of FTIR spectroscopy and thermogravimetric analyses confirmed that the effective primers coated on the copper oxides could improve the curing reaction and the thermal oxidative stability of the epoxy/CuO system.     

Effect of chemical structure of aromatic dianhydrides on the thermal, mechanical and electrical properties of their terpolyimides with 4,4′-oxydianiline

Aromatic terpolyimides were synthesized by the reaction of 3,3′,4,4′-oxydiphthalicdianhydride(ODPA), 3,3′,4,4′-biphenyldianhydride(BPDA) and 3,3′,4,4′-benzophenonetetracaboxylicdianhydride(BTDA) with 4,4′-oxydianiline(ODA) via thermal imidization with the view to enhance their tensile properties without compromising thermal properties compared to their homo and copolyimides. Their films were characterized by FTIR, TGA, DSC and XRD. Their FTIR spectra established formation of polyimide by the characteristic vibrations at 1375cm⁻¹(C-N stretch) and 1113 cm⁻¹(imide ring deformation). TGA results showed imidization of residual polyamide acid close to 250 °C and decomposition of polyimides at about 540 °C. XRD results showed amorphous nature for all terpolyimides. Their tensile strength and tensile modulus were higher than either homo or copolyimides. Incorporation of BPDA, without bridging groups between the aromatic rings into the backbone of ODPA/BTDA-ODA is suggested as the cause for such an enhancement. Such terpolyimide can find application as adhesives in making flexible single/multilayer polyimide metal-clad laminates in flexible printed circuits and tape automated bonding applications. In addition, the terpolyimide, BPDA/BTDA/ODPA-ODA (mole ratio 0.5:0.25:0.25:1), showed low dielectric constant (3.52) as BPDA could offer slight rigidity by which the orientation of polar groupings could be reduced.     

Polyphosphazene membranes. II. Solid-state photocrosslinking of poly[(alkylphenoxy)(phenoxy)phosphazene] films

The solid-state UV photocrosslinking mechanism and the properties of dense crosslinked films composed of poly [(methylphenoxy)(phenoxy)phosphazene], poly[(ethylphenoxy)(phenoxy)phosphazene], and poly[(isopropylphenoxy)(phenoxy)phosphazene] were investigated, where the alkyl substituent was in either the meta- or para-position. Solution-cast films containing dissolved benzophenone photoinitiator (at a concentration of 1–25 mol %) were crosslinked at either 25 or 70°C. The ordering of benzophenone disappearance during polymer irradiation was methylphenoxy > ethylphenoxy > isopropylphenoxy, indicating that the rate controlling step for photoinitiator disappearance was the consumption of benzophenone, either by benzopinacole formation (with the creation of a polymer crosslink) or by reaction of a benzophenone-derived ketyl radical with a polymer macro-radical. The presence of such a ketyl adduct in crosslinked ethylphenoxy/phenoxy and isopropylphenoxy/phenoxy phosphazene films was verified by solid-state NMR. The ordering of crosslinked polymer swelling (for a given initial benzophenone concentration) when films were equilibrated in dimethylacetamide (DMAc) was isopropylphenoxy/phenoxy > ethylphenoxy/phenoxy > methylphenoxy/phenoxy, indicating that steric effects of the alkyl group were playing a role during crosslink formation. The methylphenoxy/phenoxy phosphazenes were the best materials for crosslinking; the glass transition temperature increased by approximately 25°C (from −15 to 10°C) and the film swelling (in DMAc) decreased from infinity (complete solubilization) to 35% as the benzophenone concentration was increased from 0 to 25 mol %. © 1998 John Wiley & Sons, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America.

J Appl Polym Sci 68:827–836, 1998     

Effect of organosilica isomers on the interfacial interaction in polyimide/aromatic organosilica hybrids

We report the effect of organosilica precursor isomers on the interfacial interaction between polyimide and organosilica in polyimide/organosilica hybrid composite films. Poly(4,4′‐oxydianiline biphenyltetracarboxamic acid) (BPDA‐ODA PAA) was used as the polyimide precursor, while the organosilica was made using o‐substituted, m‐substituted, and p‐substituted phenyl organosilica precursor isomers. For the preparation of precursor hybrid films, BPDA‐ODA PAA and organosilica precursors were mixed and then the organosilica precursors were converted to corresponding organosilica via sol–gel process. Finally, these precursor films were converted to corresponding polyimide/organosilica hybrid films by the thermal imidization of BPDA‐ODA PAA, which results in poly(4,4′‐oxydianiline biphenyltetracarboximide) (BPDA‐ODA PI). The polyimide/organosilica hybrid films were characterized using three distinctive nuclear magnetic resonance spectroscopies (¹H NMR, ¹³C‐CPMAS‐NMR, and ²⁹Si‐MAS‐NMR), wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and peel strength measurement. We found that the m‐substituted phenyl organosilica shows poorer interfacial interaction with BPDA‐ODA PI than do the o‐ or p‐substituted phenyl organosilicas. It was observed, however, that the peel strength of the hybrid films against an aluminum substrate increased with increasing contents of organosilicas, regardless of the nature of the organosilica isomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2507–2513, 2007     

Thermal analysis of poly(phenylene sulfide) polymers. I: Thermal characterization of PPS polymers of different molecular weights

Thermal properties of Fortron®

1 ®Registered trademark of Hoechst Celanese Corporation.

poly(phenylene sulfide) (PPS) polymers of different molecular weights were studied by DSC. Crystallization studies revealed that the ability of these polymers to crystallize decreases with increasing molecular weight. The Avrami equation poorly describes the isothermal crystallization of PPS. Lamellar crystallization was observed for the lowest molecular weight sample. For the other, higher molecular weight polymers the Avrami exponent is always between 2 and 3, suggesting development of distorted spherulites with heterogeneous nucleation. The temperature dependence of the solid and melt heat capacities have been determined. The solid specific heat capacity did not exhibit a molecular weight dependence. The heat capacity increase at the glass transition, T_g, has been calculated to be 28.1 J°C^?1 mole^?1. The equilibrium melting point of PPS has been estimated to be 348.5°C using the Hoffman–Weeks method. The T_g of PPS increases with molecular weight. The T_g of the highest molecular weight evaluated is 92.5°C. A DMA relaxation peak corresponding to the onset of the phenylene ring rotation occurs at ?92°C. Only the highest molecular weight could be quenched to a completely amorphous state.