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Low-temperature curable negative-tone photosensitive polyimide (n-LTPI) viscous solutions were prepared by dissolving photo-crosslinkable poly (amic ester) (pc-PAE) resin, photophotocrosslinker, photoinitiator, and the heteroaromatic base as curing catalysts, and other additives in organic solvents. Among them, the pc-PAE resin was synthesized by polycondensation of aromatic diacid chloride and diester of 2-ethoxymathacrylate, aromatic diamines in aprotic solvents. After being spun-coated on a silicon wafer surface, soft-baked, exposed to UV light, and developed, the n-LTPI with 2% of imidazole (IMZ) as a curing catalyst produced high-quality photo-patterns with line via resolution of 5 μm at 5 μm film thickness. The photo-patterned polymer films thermally cured at 230 °C/2 h in nitrogen showed 100% of the imidization degree (ID) determined by in situ FT-IR spectroscopy. The thermally cured polymer films exhibited great combined mechanical and thermal properties, including mechanical properties with tensile strength of as high as 189.0 MPa, tensile modulus of 3.7 GP, and elongation at breakage of 59.2%, as well as glass transition temperature of 282.0 °C, showing great potential in advanced microelectronic packaging applications. [ABSTRACT FROM AUTHOR]

To improve the processability and thermal stability of polyimide, a series of novel phenylethynyl-endcapped oligoimides (PEPA-oligoimides) with calculated molecular weights ( M C) were successfully prepared from thermal imidization of 4,4'-(9-fluorenylidene) dianiline (BAFL) as fluorenyl diamine, 4,4′-oxy-diphthalic anhydride (ODPA) as aromatic dianhydride and 4-phenylethynylphthalic anhydride (4-PEPA) acted as reactive end-capping reagent at elevated temperatures. Experiment results indicated that the oligoimides were the mixtures of PEPA-endcapped oligomers with different degrees of polymerization characterized by MALDI-TOF mass spectra. The influence of chemical structures on the melt processabilities of the oligoimides, the thermal, dielectric and mechanical properties of the thermoset resins was studied. The typical oligoimide resin owned minimum melt viscosity of 0.2 Pa·s at around 310 °C and wide melting processing window, suitable for resin transfer molding (RTM). Besides, its corresponding thermal-cured polyimide resin possessed glass transition temperature ( T ) as high as 514 °C. The dielectric constants of polyimide resins decreased from 3.15 to 2.80 by reducing the M C. The mechanical properties of the polyimide neat resins were improved gradually with increasing M C. Finally, the carbon fiber/polyimide (C/PI) composite laminates showed excellent mechanical strength retention rate at 350 °C, might be long-term served at extremely high temperature in aerospace and aviation field. [ABSTRACT FROM AUTHOR]

An anhydride monomer containing ether oxide bridge, 7-oxa-bicyclo[2,2,1]hept-5-ene-2,3-dicarboxylic anhydride (ONA), was successfully synthesized by Diels-Alder reaction of furan and maleic anhydride. The ONA was also studied as an end-cap for the polymerization of monomer reactant (PMR) type polyimides. Three molecular weight levels of the ONA end-capped PMR resins were evaluated. The effects of process conditions of these novel PMR resins on thermal and mechanical properties were investigated. It was demonstrated that the imidized prepolymers using the end-cap have good processability, and the cured polyimide specimens exhibited good thermal stability. The initial decomposition temperature, T ( ca. 580°C) and glass transition temperature, T (330°C) of the novel resin (PI-20), prepared under optimum process conditions, compare favorably with the T ( ca. 620°C) and T ( ca. 348°C) of the state-of-the-art resin (PI′-20), respectively. [ABSTRACT FROM AUTHOR]

Phenylethynyl-endcapped imideoligomers (oligomides) with low melt viscosities and high glass transition temperatures (Tg) were prepared by the high temperature polycondensation of 2,3,3′,4′-biphenyltetracarboxcylic anhydride (a-BPDA), 4,4′-methylenebis(2,6-dimethylaniline) (MBDA) and 4-phenylethynyl-phthalic anhydride (4-PEPA). Experimental results indicated that the oligomides were mixtures of biphenylethynyl-endcapped imide oligomers with different degrees of polymerization (DP = 0, 1, 2, 3, 4), corresponding to the molecular weights (Mn) of 737 to 2787 determined by MALDI-TOF. The melt viscosities of the oligomide were reduced by lowering the calculated molecular weight (Calc’d Mn). The thermally cured polyimide neat resins showed glass transition temperatures (Tg) of > 400 °C and 5% weight loss temperature (T5) of > 499 °C. It was also found that the mechanical properties of the thermally cured polyimide neat resins were dependent on the Calc’d Mn values of the oligomide, and improved gradually with increasing Calc’d Mn. [ABSTRACT FROM AUTHOR]

New polyphenylquinoxalines (PPQs) containing methyl substituents have been synthesized and characterized. The PPQs were prepared by the polycondensation of a newly-developed aromatic tetraketone, 4,4' -bis(4-benzilyloxy)-3,3',5,5' -tetramethylbiphenyl (III) and aromatic tetraamines. Compared with the non-methyl-substituted PPQs derived from 1,4-bis (4-benzilyloxy)benzene (I) and 4,4' -bis(4-benzilyloxy)biphenyl (II), the obtained polymers exhibited better solubility. They were soluble not only in the common m-cresol and chloroform, but in polar aprotic solvent N-methyl-2-pyrrolidinone (NMP). The polymers showed glass transition temperatures of 325°C for PPQ-IIIa (from III and 3,3',4,4' -tetraaminobiphenyl) and 287°C for PPQ-IIIb (from III and 3,3',4,4' -tetraaminodiphenyl ether), which were much higher than their analogues. The PPQs exhibited good thermal stability up to 470°C in nitrogen and good optical transparency at 450 nm with a thickness of around 10 μ m. The refractive indices and birefringences of the PPQs were in the range of 1.6998-1.7739 and 0.0002-0.0007, respectively. [ABSTRACT FROM AUTHOR]

With the goal of improving processability of imide oligomers and achieving of high temperature carbon fiber composite, a series of Thermosetting Matrix Resin solutions (TMR) were prepared by polycondensation of aromatic diamine (3,4′-oxybisbenzenamine, 3,4-ODA) and diester of biphenylene diacid (BPDE) using monoester of 4-phenylethynylphthalic acid (PEPE) as end-capping agent in ethyl alcohol as solvent to afford phenylethynyl-endcapped poly(amic ester) resins with calculated molecular weight (Calc'd Mw) of 1500–10,000. Meanwhile, a series of reactive diluent solutions (RDm) with Calc'd Mw of 600–2100 were also prepared derived from aromatic diamine (4,4′-oxybisbenzenamine, 4,4-ODA), diester of asymmetrical biphenylene diacid (α-BPDE) and monoester of 4-phenylethynylphthalic acid (PEPE) in ethyl alcohol. Then, the TMR solution was mixed with the RDm solution at different weight ratios to afford a series of A-staged thermosetting blend resin (TMR/RDm) solutions for carbon fiber composites. Experimental results demonstrated that the thermosetting blend resins exhibited improved melt processability and excellent thermal stability. After being thermally treated at 200 °C/1 h, the B-staged TMR/RDm showed very low melt viscosities and wider processing window. The minimum melt viscosities of ≤50 Pa·s was measured at ≤368 °C and the temperature scale at melt viscosities of ≤100 Pa·s were detected at 310–390 °C, respectively. The thermally cured neat resins at 380 °C/2 h showed a great combination of mechanical and thermal properties, including tensile strength of 84.0 MPa, elongation at breakage of 4.1%, and glass transition temperature (Tg) of 423 °C, successively. The carbon fiber reinforced polyimide composite processed by autoclave technique exhibited excellent mechanical properties both at room temperature and 370 °C. This study paved the way for the development of high-temperature resistant carbon fiber resin composites for use in complicated aeronautical structures. [ABSTRACT FROM AUTHOR]

A new type of aromatic tetraamine containing biphenyl moiety in the side chain was synthesized via a modified Chichibabin's reaction. 3-Nitro-4-acetamidoacetophenone was reacted with 4-phenyl benzaldehyde in the presence of ammonium acetate to obtain 2,6-bis(3′,4′-diaminophenyl)-4-biphenyl pyridine (DPPA). A series of polypyrrolones (PPys) were prepared using tetraamine and various aromatic dianhydrides via a two-step cyclization procedure. All the PPys show excellent high temperature stabilities with the initial decomposition temperatures of 530–549°C and residual weight ratio of 49%–80% at 750°C in nitrogen. The polymers exhibit no apparent glass transition temperatures (Tgs) except PPy-1 (Tg = 327°C), which is derived from tetraamine DPPA and 2,2-bis[4-(3′,4′-dicarboxyphenoxy)-phenyl]propane dianhydride (BPADA). In addition, the polymers have acceptable mechanical properties with the tensile strength of 65–94 MPa. The PPy films show excellent hydrolysis-resistance in alkaline aqueous medium and could maintain most of the properties even after boiling in 10% aqueous sodium hydroxide solution for a week. [ABSTRACT FROM AUTHOR]