Synthesis and properties of phthalonitrile-terminated oligomeric poly(ether imide)s containing phthalazinone moiety

Three novel series of soluble and curable phthalonitrile-terminated oligomeric poly(ether imide)s containing phthalazinone moiety were synthesized from an excess amount of three dianhydrides and phthalazinone-based diamine, followed by reacting with 4-(3-aminophenoxy)phthalonitrile (APPh) in a two-step, one-pot reaction, respectively. The phthalonitrile oligomers containing phthalazinone moiety were cured in the presence of 4,4′-diaminodiphenylsulfone (DDS). The oligomers and the crosslinked polymers were characterized by DSC, FT-IR and elemental analysis. These phthalonitrile oligomers containing phthalazinone groups were found to be soluble in some aprotic solvents, such as chloroform, pyridine, m-cresol and N-methyl-2-pyrrolidone (NMP). The crosslinked polymers were insoluble in all solvents. The thermal properties of the oligomers and the crosslinked polymers were evaluated using DSC and TGA analysis. The phthalonitrile oligomers showed high glass transition temperatures (T_gs) in the range of 214-256 °C and high decomposition temperatures with 10% weight loss (T_d10%) ranging from 523 to 553 °C. The crosslinked polymers showed excellent thermal stability with the 10% weight loss temperatures ranging from 543 to 595 °C, but did not exhibit a glass transition temperature upon heating to 350 °C.     

苯乙炔封端的BTDA系列酰亚胺预聚体的研究

合成了具有苯侧基的二胺单体1,4-双(4'-氨基苯氧基)-2-(苯基)苯(p-TPEQ), 并与3,3',4,4'-苯酮四羧酸二酐(BTDA)进行缩聚反应, 分别以4-苯乙炔苯酐(PEPA)和4-苯乙炔-1,8-萘二甲酸酐(PENA)作为封端剂, 合成了两个系列的苯乙炔封端的酰亚胺预聚体. DSC测试结果表明, 此类预聚体具有比PETI-5更宽的加工窗口; 利用所合成的预聚体制成了具有较高热分解温度热固性交联PI薄膜. 结果表明, PI预聚体加工性能良好, 其交联后具有优异的力学和热学性能; 同时PEPA封端的预聚体树脂具有比PENA封端的树脂更为优异的综合性能.     

High Tg nematic thermosets: Synthesis, characterization and thermo-mechanical properties

In this paper the synthesis and characterization of a new family reactive nematic oligomers based on 4-hydroxybenzoic acid (4-HBA) will be presented. We modified the backbone using para- and meta-substituted aromatic monomers such as terephthalic acid (TA), isophthalic acid (IA), hydroquinone (HQ), resorcinol (RS), 4,4′-bisphenol (BP) and 3-hydroxybenzoic acid (3-HBA). All oligomers, with a target M_n of 5000 and 9000 g mol⁻¹, were end-capped with reactive phenylethynyl functionalities and synthesized using standard melt condensation techniques. Curing of the phenylethynyl reactive functionalities proceeds through chain extension and crosslinking, depending upon the temperature and time and can be carried out between 310 and 400 °C. Fully cured nematic thermosets could be obtained with glass-transition temperatures previously not accessible (T_g > 400 °C). The cured polymers exhibit excellent tensile properties, i.e. tensile strength (83 MPa) and elongation at break (9%). This approach allows us to prepare all-aromatic polymers with a combination of useful properties such as ease of processing, high T_g’s, and excellent mechanical properties.     

Phenylethynyl terminated oligoimides derived from 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride and their adhesive properties

A series of phenylethynyl terminated oligoimides based on 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), m-phenylene diamine (m-PDA) or/and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) with calculated molecular weight of 5000 g mol⁻¹ were synthesized. The effect of molecular structure on solubility and melt viscosity of oligoimides as well as the thermal properties of cured polyimide resins was investigated. Experimental results indicated that the oligoimides have good solubility in strong polar solvents to afford homogeneous solutions with the solid content as high as 50 wt%. The oligoimides exhibited better solubility and lower minimum melt viscosity at relatively lower temperature with the incorporation of flexible 6FAPB. These oligoimides could be thermally cured at 320-380 °C to give thermosetted resins. The cured resins have good thermal stability with the glass transition temperatures of 278-329 °C and the onset decomposition temperatures higher than 500 °C. Adhesive properties of polyimides adhered to stainless steel at various conditions were evaluated by lap shear strength test. It was found that the LSS at room temperature increased with the molar ratio of 6FAPB increasing. The polyimides with combination of rigid and flexible structures exhibited good adhesive properties. With the increasing of curing temperature, the lap shear strength of polyimides at elevated temperature maintained at a high level due to the formation of strong bond.     

Synthesis and properties of novel fluorinated epoxy resins based on 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane

A novel fluorinated epoxy resin, 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane (BGTF), was synthesized through a four-step procedure, which was then cured with hexahydro-4-methylphthalic anhydride (HMPA) and 4,4′-diaminodiphenyl-methane (DDM). As comparison, a commercial available epoxy resin, bisphenol A diglycidyl ether (BADGE), cured with the same curing agents was also investigated. We found that the BGTF gave the exothermic starting temperature lower than BADGE no mater what kind of curing agents applied, implying the reactivity of the former is higher than the latter. The fully cured fluorinated BGTF epoxy resins have good thermal stability with glass transition temperature of 170-175 °C and thermal decomposition temperature at 5% weight loss of 370-382 °C in nitrogen. The fluorinated BGTF epoxy resins also showed the mechanical properties as good as the commercial BADGE epoxy resins. The cured BGTF epoxy resins exhibited improved dielectric properties as compared with the BADGE epoxy resins with the dielectric constants and the dissipation factors lower than 3.3 and dissipation 2.8 × 10⁻³, respectively, which is related to the low polarizability of the C-F bond and the large free volume of CF₃ groups in the polymer. The BGTF epoxy resins also gave low water absorption because of the existence of hydrophobic fluorine atom.     

Novel organosoluble and colorless poly(ether imide)s based on 1,1-bis[4-(3,4-dicarboxyphenoxy)phenyl]cyclohexane dianhydride and trifluoromethyl-substituted aromatic bis(ether amine)s

A series of novel fluorinated poly(ether imide)s (IV) having inherent viscosities of 0.70-1.08 dL/g were prepared from 1,1-bis[4-(3,4-dicarboxyphenoxy)phenyl]cyclohexane dianhydride (I) and various trifluoromethyl (CF₃)-substituted aromatic bis(ether amine)s II_a-g by a standard two-step process with thermal and chemical imidization of poly(amic acid) precursors. These poly(ether imide)s showed excellent solubility in many organic solvents and could be solution-cast into transparent, flexible, and tough films. These films were essentially colorless, with an ultraviolet-visible absorption edge of 375-380 nm and a very low b^∗ value (a yellowness index) of 5.5-7.3. They also showed good thermal stability with glass-transition temperatures of 207-269 °C, 10% weight loss temperatures in excess of 474 °C, and char yields at 800 °C in nitrogen more than 62%. In comparison with analogous V series poly(ether imide)s without the -CF₃ substituents, the IV series polymers showed better solubility, lower color intensity, and lower dielectric constants.     

Study on thermal cure and heat-resistant properties of N-(3-acetylenephenyl)maleimide monomer

N-(3-acetylenephenyl)maleimide (3-APMI), was synthesized by reacting 3-aminophenylacetylene (3-APA) with maleic anhydride by the usual two-step procedure that included ring-opening addition to give maleamic acid, followed by cyclodehydration to maleimide. Structure of the monomer was confirmed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), elemental analysis (EA) and mass spectrum (MS). Thermal cure of the monomer was investigated by differential scanning calorimetry (DSC) and FTIR, then processing parameters and cure kinetics parameters were determined. The results showed that the monomer possesses excellent reactivity, whose cure peak temperature was 197.9 °C and cure reaction was almost complete after 4 h cure at 200 °C. Thermal properties of the cured monomer were determined by dynamic mechanical analysis (DMA) and the results show that glass transition temperature (represented by onset temperature of storage modulus) is high up to 460 °C. The results of thermogravimetry analysis (TGA) reveal that the cured monomer possessed excellent thermal stability, whose 10% weight loss temperature (T_10%) is 515.6 °C and char yield at 800 °C is 59.1%. All these characteristics make the 3-APMI monomer be an ideal candidate for matrix of thermo-resistant composites.     

Synthesis and characterization of a novel arylacetylene oligomer containing POSS units in main chains

A novel arylacetylene oligomer containing octamethyl POSS units in main chains was prepared from difluoride octamethyl POSS (diexo-(CH₃)₈Si₈O₁₁F₂) and diethynylbenzene (DEB) by Grignard reaction and characterized by FT-IR, NMR, WAXD, GPC, DSC, and TGA. The curing reaction kinetic of the oligomer was studied by Kissinger and Ozawa methods and the kinetic parameters were obtained. The cured polymer had good thermal and thermal-oxidative properties. TGA analyses demonstrated that the thermal decomposition temperature (T_d5) of the cured polymer in nitrogen and air were 503 and 479 °C, respectively.     

Synthesis and thermal properties of bisphthalonitriles containing aromatic ether nitrile linkages

Low-melting bisphthalonitrile oligomers with variable length of aromatic ether nitrile linkages (nPEN-BAPh) was firstly synthesized and the length of the linkages (n) was controlled by mole ratio of 2, 6-dichlorobenzonitrile and bisphenol A. The oligomers were characterized by FTIR and NMR spectra, and detailed study showed that the linkages were constructed in the backbone of nPEN-BAPh. The FTIR showed, with the curing reaction progressed, the characteristic peak of nitrile at 2230 cm⁻¹ disappeared while the characteristic peak of phthalocyanine ring at 3290, 1010 cm⁻¹ and triazine ring at 1360 cm⁻¹ appeared. The melting and polymerization temperature of the oligomers was around 60 °C and 220 °C, respectively. So a large processing window was obtained. The char yields of completely cured materials were above 65% at 800 °C in nitrogen and over 70% at 600 °C in air. All materials exhibited excellent thermal and thermo-oxidative stability.     

Poly(ester imide)s possessing low coefficients of thermal expansion (CTE) and low water absorption (III). Use of bis(4-aminophenyl)terephthalate and effect of substituents

A variety of poly(ester imide)s (PEsIs) were prepared using bis(4-aminophenyl)terephthalate (BPTP) and substituted BPTP (BPTP series) for applications to novel base film materials in flexible printed circuit boards (FPC). BPTP series were all highly reactive with various tetracarboxylic dianhydrides and led to considerably high molecular weights of PEsI precursors. The thermally imidized BPTP-based PEsI films achieved lower extents of water absorption (W_A) than the corresponding 4-aminophenyl-4′-aminobenzoate (APAB)-based PEsI systems while keeping other target properties, in particular, the linear coefficient of thermal expansion (CTE) much lower than that of copper foil as a conductive layer in FPC. The lower W_A is attributed to the decreased imide contents in the structure by using BPTP. The considerably low CTE can be explained in terms of intimate stacking between the p-aromatic ester fragments with an extended conformation. The BPTP-based PEsI system also exhibited a considerably low dissipation factor (tan δ = 1.91 × 10⁻³) at a high-frequency electric field of 18.3 GHz, comparable to a liquid-crystalline polyester. An effect of substituents on the film properties was also investigated in this work. Incorporation of methyl substituents on BPTP was very effective for property improvement, whereas methoxy substituents on BPTP, as well as methyl substituents onto hydroquinone bis(trimellitate anhydride) (TAHQ), showed a trend to significantly increase the CTE. Copolymerization with an adequate amount of a typically flexible monomer, 4,4′-oxydianiline (4,4′-ODA), allowed the CTE matching with copper foil and the film toughness improvement at the same time. The PEsI copolymer prepared from TAHQ (10 mmol) with methyl-substituted BPTP (7 mmol) and 4,4′-ODA (3 mmol) achieved excellent combined properties, namely, a very high T_g at 410 °C, a slightly lower CTE (10.0 ppm/K) than that of copper foil, suppressed water absorption (0.35%), an extremely low linear coefficient of humidity expansion (CHE = 3.4 ppm/RH%), and good film toughness (the elongation at break, ε_b = 50.7%). Thus, BPTP- and methyl-substituted BPTP-based PEsI systems can be promising candidates as a next generation of FPC base film materials.     

Novel aromatic poly(amide-hydrazide)s based on the bipyridine. Part I: Synthesis, characterization and thermal stability

A series of new poly(amide-hydrazide)s were obtained by the direct polycondensation of 5-amino 5′-carbohydrazido-2,2′-bipyridine with commercially available diacids by means of triphenyl phosphite and pyridine in the N-methyl-2-pyrrolidone (NMP) solutions containing dissolved LiCl. The resulting hydrazide containing polymers exhibited inherent viscosities in the 0.42-0.64 dL/g range. All copolymers were soluble in polar solvents such as NMP and dimethyl sulfoxide (DMSO). Most of the amorphous hydrazide copolymers formed flexible and tough films by solvent casting. The poly(amide-hydrazide)s had glass-transition temperatures (T_g) between 178 and 206 °C. All hydrazide copolymers could be thermally converted into the corresponding poly(amide-oxadiazole) approximately in the region of 300-400 °C, as evidenced by the DSC thermograms. The oxadiazole polymers and copolymers showed a dramatically decreased solubility and higher T_g when compared to their respective hydrazide prepolymers. They exhibited T_gs of 197-248 °C and were stable up to 450 °C in air or nitrogen.     

Preparation and properties of a high temperature, flexible and colorless ITO coated polyimide substrate

A new high temperature, flexible and colorless indium-tin-oxide (ITO) coated plastic substrate has been prepared from a thermally stable, high glass transition temperature (T_g) and colorless polyimide film. The polyimide was synthesized from 3,3′-diaminodiphenylsulfone (3,3′-DDS) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) monomers. Its heat distortion temperature was 278 °C. The ITO was deposited on the polyimide film using the magnetron-sputtering process. After annealing at 250 °C under nitrogen for 1 h, the resistivity of the ITO film was 4.0 × 10⁻⁴ Ω cm, and its transmittance was 83.5%. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to observe the surface and morphology of the ITO film. UV-visible spectroscopy and the four-probe method were used to study their optical and electrical properties. The high performance ITO-plastic substrate can be used in the next generation flat panel displays.     

Synthesis of new polyazines by 1,4 photochemical or anionic polymerization of 1,2-diaza-1,3-butadienes

Photochemical and anionic polymerizations of 1,2-diaza-1,3-butadienes are described. Photochemical polymerization was smoothly performed by irradiation of some 1-aminocarbonyl-1,2-diaza-1,3-butadienes with high pressure mercury arc (λ = 300 nm) in the presence of allyltributylstannane. Molecular weights (M_w) in the range 14.6-559 × 10² g/mol were obtained. The TGA curve revealed a first weight loss starting at about 200 °C of some 85%, and a second starting at about 300 °C. The DSC showed the glass transition (T_g) at about −34 °C. Anionic polymerization was performed by treatment of some 1-alkoxycarbonyl-1,2-diaza-1,3-butadienes with n-butyllithium. Molecular weights (M_w) in the range 8.44-242 × 10² g/mol were obtained.     

Preparation and thermal stability of boron-containing phenolic resin/clay nanocomposites

In order to further improve thermal stability of the phenolic resins, we combined boron and clay with phenolic resins to prepare nanocomposites (BH-B, BP-B, and BE-B series). Boron-containing phenolic resin/clay (montmorillonite) nanocomposites were prepared using in situ polymerization of resol-type phenolic resins. Montmorillonite (MMT) was modified by benzyldimethylhexadecylammonium chloride (BH), benzyldimethyphenylammonium chloride (BP), and benzyltriethylammonium chloride (BE). X-ray diffraction measurements and transmission electron microscope (TEM) observations showed that clay platelets were partially exfoliated after complete curing of the phenolic resins. Thermogravimetric analysis showed that thermal decomposition temperatures (T_d) and residual weight at 790 °C of cured boron-containing nanocomposites were much higher than the corresponding nanocomposites without boron. For example, the rise in decomposition temperature of BE-B10% is about 42 °C (from 520 to 566 °C), whereas the increase in char yields is 6.4% (from 66.2% to 72.6%). However, the boron-containing composites were more prone to absorb moisture (ca. 9-14%) than boron-free ones (ca. 3-4%), which was attributed to unreacted or partially reacted boric acid during preparation process.     

Synthesis and characterization of poly(thioether ether sulfone imide)s derived from isomeric bis(chlorophthalimide)s and bis(4-mercaptophenyl) sulfone

A series of isomeric bis(chlorophthalimide)s (BCPIs) were conveniently prepared from 3-chlorophthalic anhydride, 4-chlorophthalic anhydride, and mixtures thereof. Polymerization of BCPIs with bis(4-mercaptophenyl) sulfone (BMPS) proceeded smoothly in the presence of tributylamine, from which a class of isomeric poly(thioether ether sulfone imide)s (PTESIs) with inherent viscosities of 0.45-0.82 dL/g were obtained. The solubility, thermal stability, and mechanical properties of these polymers were characterized. Compared to the PTESIs derived from single BCPIs, i.e., 3,3′-, 3,4′-, or 4,4′-BCPIs, the PTESIs derived from mixed BCPIs showed better solubility and higher storage modulus. These PTESIs also demonstrated good thermal stability, giving only 5% weight loss at temperature of 490 °C in nitrogen atmosphere. The glass transition temperatures (T_gs) of these isomeric PTESIs were between 242 and 265 °C, and were increased with increasing of the ratio of 3-chlorophthalimide unit in the polymer backbone.     

Synthesis of phenol-formaldehyde resol resins using organosolv pine lignins

Lignin was extracted from white pine sawdust by organosolv-extraction using hot-compressed ethanol-water co-solvent. The optimum conditions for extracting lignin from the pine sawdust were found to be at 180 °C with ethanol-water solvent (1:1 wt/wt), where the lignin yield attained ca. 26% with a purity of ca. 83%. The lignin under such conditions was oligomers with a broad molecular weights distribution: M_n of 537, M_w of 1150 and polydispersity of 2.14. Bio-based phenol-formaldehyde resol resins were synthesized using the resultant lignin as the replacement of petroleum-based phenol at varying ratios from 25 to 75 wt.% by condensation polymerization catalyzed by sodium hydroxide. Upon heating the lignin-phenol-formaldehyde resols could solidify with a main exothermic peak at around 150-175 °C, typical of the conventional phenolic resol resins, and a secondary peak at 135-145 °C, likely due to the exothermic reactions between the free formaldehyde with phenol or lignin to form methylophenols. The replacement of phenol with lignin at a large ratio deferred the curing process, and the introduction of lignin in the resin formula decreased the thermal stability of the resin, leading to a lowered decomposition temperature and a reduced amount of carbon residue at elevated temperatures. For practical applications, it is suggested that the replacement ratio of phenol with lignin be less than 50 wt.%. The thermal stability can however be improved by purifying the lignin feedstock before the resin synthesis.     

Free radical copolymerization of methyl substituted stilbenes with maleic anhydride

Stilbene-maleic anhydride is a well-known donor-acceptor comonomer pair which undergoes free radical copolymerization to form an alternating copolymer. A series of methyl substituted stilbenes were synthesized and copolymerized with maleic anhydride. A conversion versus time study was undertaken to understand the methyl substituent effect on copolymerization rates. Methyl substituents on the phenyl ring of stilbene can change the reactivity of stilbene by changing the resonance stability of the propagating radical and steric hindrance in the propagation step and thereby change the copolymerization rate. Methyl substituted stilbene-maleic anhydride copolymers were determined by quantitative ¹³C 1D NMR to be alternating copolymers. Size exclusion chromatography (SEC) measurements showed that the weight-average molecular weights of these copolymers varied from 3000 to over 1,000,000 g/mol. Interchain aggregation was observed in poly((E)-4-methylstilbene-alt-maleic anhydride) by dynamic light scattering (DLS). The SEC trace for poly((E)-4-methylstilbene-alt-maleic anhydride) exhibited bimodal peaks. No glass transition temperature or crystalline melting temperature was observed between 0 °C and 250 °C by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) showed that these polymers have 5% weight loss around 290 °C.     

A novel ternary polymer electrolyte for LMP batteries based on thermal cross-linked poly(urethane acrylate) in presence of a lithium salt and an ionic liquid

A new ternary polymer electrolyte based on thermally cross-linked poly(urethane acrylate) (PUA), lithium bis(trifluoromethansulfonyl)imide (LiTFSI) and the ionic liquid N-butyl-N-methylpyrrolidinium TFSI (PYR₁₄TFSI) was developed and tested for application in LMP batteries. The polymer electrolyte was a transparent yellow self-standing material with quite good mechanical properties, i.e., comparable to that of a flexible rubber. The room temperature ionic conductivity of the dry polymer electrolyte was found to be as high as 0.1 mS cm⁻¹ for the compound containing 40 wt% of ionic liquid (PYR₁₄TFSI) and a O/Li ratio of 15/1 (Li⁺ from LiTFSI). The thermal analysis of the new cross-linked electrolyte showed that it was homogeneous, amorphous and stable over a wide temperature range extending from −40 °C to 100 °C. The homogeneity of the polymer electrolyte was also confirmed by SEM analysis.     

Cationic concentration effects on electron beam cured of carbon-epoxy composites

Electron beam (e-beam) curing is a technology that offers advantages over the thermal curing process, that usually requires high temperature and are time-consuming. E-beam curing is faster and occurs at low temperatures that help reduce residual mechanical stresses in a thermoset composite. The aim of the present study is to analyze the effects of cationic initiator (diaryliodonium hexafluoroantimonate) ranged from 1 to 3 wt% in DGEBA (diglycidyl ether of bisphenol A) epoxy resin when cured by a 1.5 MeV electron beam. The specimens were cured to a total dose of 200.4 kGy for 40 min. Analyses by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) show that the e-beam irradiated samples with 2 wt% cationic initiator were 96% cured obtained a glass transition temperature (tan δ) of 167 °C. The same epoxy resin, thermally cured for 16 h with an anhydride hardener, reached a T_g (tan δ) of 136 °C. So, the irradiated sample had its T_g increased approximately 20% and the curing process was much less time consuming.     

Design and characterization of thermosetting polyimide structural adhesive and composite matrix systems

Fully cyclized, organo soluble, phenylethynyl-terminated, ether-imide oligomers of 2–10,000 g/mol (M_n) were prepared by the reaction of 2,2′-bis[4-(3,4-dicarboxyphenoxy)phenyl]-propane dianhydride (bisphenol-A dianhydride, BPADA) with a stoichiometric excess of either para, meta, or isomeric mixtures of phenylene diamine and phenylethynylphthalic anhydride (4-PEPA) endcapper. High para-containing oligomers produced semicrystalline powders, but the all meta isomer was completely amorphous. The lower molecular weight oligomers displayed an attractive low viscosity melt and were cured to very high gel content networks at 350–380°C for 30–90 min. The cured 3000 g/mol oligomers showed a (DSC) glass transition temperature (T_g) of 267°C and produced tough, solvent-resistant films. Excellent adhesion to surface-treated titanium alloys was achieved, as judged by single-lap shear measurements. Resin infusion molding was conducted, which permitted low-void, graphite-fabric composite panels to be prepared. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2943–2954, 1997