A series of inherently heat-sealable copolyimides (CPIs) with high glass transition temperatures were synthesized from 2,3,3′,4′-oxydiphthalic anhydride (aODPA) and bicomponent diamines, 4,4′-oxydianiline (ODA) and para-phenylenediamine (PDA). The PI chain rigidity was manipulated by the regulation of the diamine ratio, and its effects on the heat sealability and thermal resistance of the derived CPI films were investigated in detail. The results show that these films are in possession of both good heat sealability and thermal resistance due to the synergetic effect of the asymmetry of aODPA and the rigidity of PDA. It is also found that there exists one critical PDA content that distinguishes the heat-sealing behaviors of the CPI films, and the relevant mechanism was established. Especially for CPI-5, the heat-sealing strength is up to 350 N m⁻¹ simultaneously with a relatively high T_g of 310°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43058.

A series of novel quartz-fiber-cloth-reinforced polyimide substrates with low dielectric constants were successfully prepared. For this purpose, the A-stage polyimide solution was first synthesized via a polymerization-of-monomer-reactant procedure with 2,2′-bis(trifluoromethyl)benzidine and 3,3′,4,4′-oxydiphthalic anhydride as the monomers, and cis−5-norbornene-endo-2,3-dicarboxylic anhydride as the endcap. Then, an A-stage polyimide solution (TOPI) was impregnated with quartz-fiber cloth (QF) to afford the prepregs, which were thermally molded into the final substrate composites. The influence of the curing temperature and the resin content on the mechanical properties of the composite were examined. The composites exhibited a high glass-transition temperature over 360°C, a low and steady dielectric constant below 3.2 at a test frequency of 1–12 GHz, and a volume resistance over 1.8 × 10¹⁷ Ω cm. Meanwhile, they also showed a high mechanical strength with flexural and impact strengths in ranges 845–881 MPa and 141–155 KJ/m², respectively. The excellent mechanical and thermal properties and good dielectric properties indicated that they are good candidates for integrated circuit packaging substrates. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42358.

Two novel aromatic tetraamines containing bulky lateral phenyl unit and multiple trifluoromethyl groups, 1,1-bis[4-(3′,4′-diaminophenoxy)phenyl]-1-(3″-trifluoromethylphenyl)−2,2,2-trifluoroethane (6FTA) and 1,1-bis[4-(3′,4′-diaminophenoxy)phenyl]-1-[3″,5″-bis(trifluoromethyl)phenyl]-2,2,2-trifluoroethane (9FTA) were synthesized and characterized. A series of fluorinated aromatic polybenzimidazopyrrolones (polypyrrolones, PPys) were synthesized via a two-step polycondensation procedure. The inherent viscosities of the precursors, poly(amide amino acid) (PAAA), ranged from 0.39 dL/g to 0.54 dL/g. All the FPPys were amorphous. The freestanding FPPy films could be prepared, which exhibited good thermal stability with the glass transition temperature of 315–389°C, the temperatures of 5% weight loss (T_5%) of 497–535°C in nitrogen and residual weight retention at 700°C over 60%. All the FPPy films exhibited excellent alkaline-hydrolysis resistance which retained their original shapes and toughness after boiling 7 days in 10% sodium hydroxide solution. Also after boiling 8 h in 10% sodium hydroxide solution, the tensile strength could retain as high as 56% of the original values. The alkaline-hydrolysis resistance was much better than the polyimides which had similar chemical structures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40041.

A novel phosphorous-silicone-nitrogen ternary flame retardant (FR), [(1,1,3,3-tetramethyl-1,3-disilazanediyl)di-2,1-ethanediyl]bis(diphenylphosphine oxide) (PSiN) was synthesized with high yield via a one-step procedure by the reaction of diphenylphosphine oxide and vinyl-terminated silazane with triethylborane as the catalyst. The chemical structure of the target compound was confirmed by nuclear magnetic resonances, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and Flourier transform infrared measurements. The developed PSiN FR was applied in the flame retardancy of o-cresol novolac epoxy (CNE)/phenolic novolac (PN) hardener system. Effects of PSiN on the processability, thermal properties, especially the flame retardancy properties of the composites were investigated. Experimental results revealed that addition of PSiN improved the flowability of the CNE/PN systems, while the thermal stability of the epoxy thermosets was maintained. Meanwhile, the incorporation of PSiN was in favor of the formation of char during the thermal degradation process of the epoxy thermosets. The limited oxygen index of the epoxy system increased along with the PSiN content. An UL 94 V-0 FR rating was achieved when the weight content of PSiN in the epoxy composites reached 20 wt %. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40412.

Closed-cell polyimide rigid foams with different Calculated Molecular Weight (Calc'd M_n) and foam density (ρ) have been prepared by thermal foaming of nadimide-endcapped imideoligomers (NAIO) powder. The NAIO powder was obtained by thermally treating of a PMR poly(amide ester) solution derived from the reaction of diethyl ester of 2,3,3′,4′-biphenyltetracarboxylic dianhydride (α-BPDE) and p-phenylenediamine (p-PDA) using monoethyl ester of cis-5-norbornene- endo-2,3-dicarboxylic acid (NE) as reactive endcapping agent in ethyl alcohol. Effect of Calc'd M_n and foam density (ρ) on mechanical and thermal properties of the polyimide rigid foams have been systematically investigated. It was found that the thermal foaming properties of NAIO powders were affected by the Calc'd M_n. The appreciate Calc'd M_n could yield polyimide foams with both high closed-cell content (C_c) (>80%) and outstanding mechanical properties. Moreover, the thermal properties were reduced by increasing of Calc'd M_n and the mechanical properties improved gradually by increasing foam densities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3282–3291, 2013

Poly(etherimide)s (PEIs) with different chemical structures were synthesized and characterized, which were employed to toughen epoxy resins (EP/PEI) and carbon fiber-reinforced epoxy composites (CF/EP/PEI). Experimental results revealed that the introduction of the fluorinated groups and meta linkages could help to improve the melt processability of EP/PEI resins. The EP/PEI resins showed obviously improved mechanical properties including tensile strength of 89.2 MPa, elongation at break of 4.7% and flexural strength of 144.2 MPa, and good thermal properties including glass transition temperature (T_g) of 211°C and initial decomposition temperature (T_d) of 366°C. Moreover, CF/EP/PEI-1 and CF/EP/PEI-4 composites showed significantly improved toughness with impact toughness of 13.8 and 15.5 J/cm², respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

A novel fluorinated epoxy compound, 4,4′-bis(2,3-epoxypropoxy-phenyl)-1-(3-trifluoromethylphenyl)-2,2,2-trifluoroethane (BEF), was synthesized starting from the coupling of phenol with 3′-trifluoromethyl-2,2,2-trifluroacetophenone catalyzed by Lewis acid to yield an intermediate compound, which was then converted to the fluorinated epoxy by epoxidation with epichlorohydrin. BEF could be thermally cured with organic anhydride or aromatic amine as curing agents to produce thermally cured epoxy resins. Experimental results demonstrated that the thermally cured fluorinated epoxy resins showed good thermal stability with decomposition temperature at 5% weight loss of 342–364°C in nitrogen, high glass transition temperature (T_g) of 165–171°C (determined by DMA), and outstanding mechanical properties with flexural strengths of 79–119 MPa, flexural moduli of 2085–2130 MPa. The thermally cured fluorinated epoxy resins also exhibited excellent electric insulating properties with volume resistivity of 1.59–9.23 × 10¹⁶ Ω cm and surface resistivity of 4.81 × 10¹⁵–7.70 × 10¹⁶ Ω. The dielectric constants at 1 MHz were measured in the range of 3.1–3.4 and the dielectric dissipation factor (tan δ) in the range of 1.38–2.48 × 10⁻³. It was found that the fluorinated epoxy resins have improved electric insulating and dielectric properties as well as lower moisture adsorption compared with the corresponding commercial Bisphenol A type epoxy resins. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Novel-fluorinated poly(etherimide)s (FPEIs) with controlled molecular weights were synthesized and characterized, which were used to toughen epoxy resins (EP/FPEI) and carbon fiber-reinforced epoxy composites (CF/EP/FPEI). Experimental results indicated that the FPEIs possessed outstanding solubility, thermal, and mechanical properties. The thermally cured EP/FPEI resin showed obviously improved toughness with impact strength of 21.1 kJ/m² and elongation at break of 4.6%, respectively. The EP/FPEI resin also showed outstanding mechanical strength with tensile strength of 91.5 MPa and flexural strength of 141.5 MPa, respectively. The mechanical moduli and thermal property of epoxy resins were not affected by blending with FPEIs. Furthermore, CF/EP/FPEI composite exhibited significantly improved toughness with Mode I interlaminar fracture toughness (G_IC) of 899.4 J/m² and Mode II interlaminar fracture toughness (G_IIC) of 1017.8 J/m², respectively. Flexural properties and interlaminar shear strength of the composite were slightly increased after toughening. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

A novel fluorinated biphenyl-type epoxy resin (FBE) was synthesized by epoxidation of a fluorinated biphenyl-type phenolic resin, which was prepared by the condensation of 3-trifluoromethylphenol and 4,4′-bismethoxymethylbiphenyl catalyzed in the presence of strong Lewis acid. Resin blends mixed by FBE with phenolic resin as curing agent showed low melt viscosity (1.3–2.5 Pa s) at 120–122°C. Experimental results indicated that the cured fluorinated epoxy resins possess good thermal stability with 5% weight loss under 409–415°C, high glass-transition temperature of 139–151°C (determined by dynamic mechanical analysis), and outstanding mechanical properties with flexural strength of 117–121 MPa as well as tensile strength of 71–72 MPa. The thermally cured fluorinated biphenyl-type epoxy resin also showed good electrical insulation properties with volume resistivity of 0.5–0.8 × 10¹⁷ Ω cm and surface resistivity of 0.8–4.6 × 10¹⁶ Ω. The measured dielectric constants at 1 MHz were in the range of 3.8–4.1 and the measured dielectric dissipation factors (tan δ) were in the range of 3.6–3.8 × 10⁻³. It was found that the fluorinated epoxy resins have improved dielectric properties, lower moisture adsorption, as well as better flame-retardant properties compared with the corresponding commercial biphenyl-type epoxy resins. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A series of molecular-weight-controlled imide resins end-capped with phenylethynyl groups were prepared through the polycondensation of a mixture of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 1,3-bis(4-aminophenoxy)benzene with 4,4′-oxydiphthalic anhydride in the presence of 4-phenylethynylphthalic anhydride as an end-capping agent. The effects of the resin chemical structures and molecular weights on their melt processability and thermal properties were systematically investigated. The experimental results demonstrated that the molecular-weight-controlled imide resins exhibited not only meltability and melt stability but also low melt viscosity and high fluidability at temperatures lower than 280°C. The molecular-weight-controlled imide resins could be thermally cured at 371°C to yield thermoset polyimides by polymer chain extension and crosslinking. The neat thermoset polyimides showed excellent thermal stability, with an initial thermal decomposition temperature of more than 500°C and high glass-transition temperatures greater than 290°C, and good mechanical properties, with flexural strengths in the range of 140.1–163.6 MPa, flexural moduli of 3.0–3.6 GPa, tensile strengths of 60.7–93.8 MPa, and elongations at break as high as 14.7%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Two series of melt-processable polyimides were prepared from 4,4′-bis(3-amino-5-trifluoromethylphenoxy)biphenyl (m-6FBAB) and 4,4′-bis(4-amino-5-trifluoromethylphenoxy) biphenyl (p-6FBAB) with various aromatic dianhydrides. The effects of the chemical structures of the polyimides on their properties, especially the melt processability and organic solubility, were investigated. The experimental results demonstrate that some of the fluorinated aromatic polyimides showed good melt processability at elevated temperatures (250–360°C) with relatively low melt viscosities and could be melt-molded to produce strong and tough polyimide sheets. Meanwhile, the polyimides showed excellent organic solubility in both polar aprotic solvents and common solvents to give stable polyimide solutions with high polymer concentrations and relatively low viscosities. Thus, we prepared high-quality polyimide films by casting the polyimide solutions on glass plates followed by baking at relatively low temperatures. The polyimides derived from m-6FBAB showed better melt processability and solubility than the p-6FBAB based polymers. The melt-processable polyimides showed a good combination of thermal stability and mechanical properties, with decomposition temperatures of 547–597°C, glass-transition temperatures in the range 205–264°C, tensile strengths of 81.3–104.9 MPa, and elongations at break as high as 19.6%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A series of novel phenylethynyl-endcapped polyimide oligomers were prepared by polycondensation of an aromatic diamine mixture of 1,3-bis(4-aminophenoxy) benzene (1,3,4-APB) and 3,4′-oxydianiline (3,4′-ODA) with different aromatic dianhydrides including 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-(hexafluoro isopropylidene)diphthalic anhydride (6FDA), 4,4′-oxydiphthalic anhydride (ODPA), and 4,4′-[2,2,2-trifluoro-1-(3′,5′-bis-(trifluoro-methyl)phenyl)ethylidene]diphthalic anhydride (9FDA) in the presence of 4-phenyl-ethynylaniline (PEA) as endcapping agent in aprotic solvent at elevated temperature. The chemical structures, thermal behavior, and melt rheological properties of the synthesized polyimide oligomers were investigated. Experimental results indicated that the fluorinated polyimide oligomers derived from 6FDA (PI-2) and 9FDA (PI-4) are amorphous solid resins and exhibited lower melt viscosities than those prepared from the unfluorinated aromatic dianhydrides such as BPDA and ODPA. The BPDA-based polyimide oligomers with a molar ratio of 1,3,4-APB/3,4′-ODA = 50:50 (PI-5) showed lower melt viscosity than those derived from a mixture of 1,3,4-APB and 3,4′-ODA with molar ratios of 75:25 and 100:0, respectively. In addition, the melt viscosity of the polyimide oligomers increased obviously with increasing of the polymer calculated molecular weights. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers