Novel acetylene‐terminated polyimide oligomers with excellent processability and high toughness of films

A series of acetylene‐terminated imide oligomers based on 2,3,3′,4′‐Diphenyl ether tetracarboxylic acid dianhydride (a‐ODPA), 3,4′‐Oxydianiline (3,4′‐ODA), and 3‐Ethynylaniline (3‐EA) with different molecular weights were synthesized by using acetic anhydride and triethylamine as dehydrating agent. Their main structure was confirmed by Fourier transform infrared spectroscopy (FT‐IR). Thermal curing processing was characterized by FT‐IR and differential scanning calorimetry (DSC). All the uncured imide oligomers showed excellent solubility (more than 30 wt %) in organic solvent such as N,N‐dimethylacetamide (DMAc) and N‐methyl‐2‐pyrrolidone (NMP). These imide oligomers also possessed a very low viscosity, thus provided better processing window. These oligomers were formulated into thermosetting films by thermal crosslinking of the ethynyl groups. The properties of cured films were evaluated by dynamic mechanical thermal analysis (DMA), thermogravimetric analysis (TGA), and tensile measurement. The glass transition temperature (T_g) and elongation at break of the cured films were found to be almost >260°C and >9.2%, respectively. The cured films in air resulted in higher thermal stability than those under N₂ atmosphere. Experimental results suggested that the introduction of asymmetric and flexible ether‐hinge with 3‐EA in polyimide oligomers can improve the processability of the imide oligomers and the toughness for a cured sample without sacrificing their thermal‐oxidative stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42537.     

Synthesis of polyimides with low viscosity and good thermal properties via copolymerization

Novel polyimides were successfully synthesized through copolymerization of diamine monomers p‐phenylenediamine (p‐PDA) and 4,4'‐diaminodiphenylmethane (MDA) with different proportions and 2,3,3',4'‐biphenyltetracarboxylic dianhydride (a‐BPDA) using 4‐phenylethynylphthalic anhydride (4‐PEPA) as an end‐capping agent. The melt rheological properties, thermal properties, and crystallinity of PI oligomers were investigated via rheometer, dynamic mechanical analysis (DMA), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). The results indicate that melt viscosity and solubility of the PI oligomers were improved, but the glass transition temperature (T_g) and crystallinity decreased with the increasing molar ratio of MDA. PI oligomer 3 with the molar ratio of MDA/p‐PDA = 2/1 shows a lower minimum melt viscosity (66 Pa.s) at 313°C and better solubility in aprotic solvents. The corresponding PI‐3 exhibits a high glass transition temperature of 406°C and excellent thermal stability. This copolyimide shows good processability and thermal properties, and could become a good candidate of matrix resins for high performance composites in aerospace field. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41303.     

Synthesis of soluble and thermally stable polyimides from 3,5‐diamino‐N‐(4‐(8‐quinolinoxy) phenyl) aniline and various dianhydrides

Three novel polyimides (PIs) having pendent 4‐(quinolin‐8‐yloxy) aniline group were prepared by polycondensation of a new diamine with commercially available tetracarboxylic dianhydrides, such as pyromellitic dianhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride, and bicyclo[2.2.2]‐oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride. These PIs were characterized by FTIR, ¹H NMR, and elemental analysis; they had high yields with inherent viscosities in the range of 0.4–0.5 dl g⁻¹, and exhibited excellent solubility in many organic solvents such as N,N‐dimethyl acetamide, N,N′‐dimethyl formamide, N‐methyl pyrrolidone (NMP), dimethyl sulfoxide, and pyridine. These PIs exhibited glass transition temperatures (T_g) between 250 and 325° C. Their initial decomposition temperatures (T_i) ranged between 270 and 450°C, and 10% weight loss temperature (T₁₀) up to 500°C with 68% char yield at 600°C under nitrogen atmosphere. Transparent and hard polymer films were obtained via casting from their NMP solutions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of highly soluble and transparent polyimides

A novel aromatic diamine, 3,3′‐diisopropyl‐4,4′‐diaminophenyl‐4″‐methyltoluene with a 4‐methylphenyl pendant group and isopropyl side groups, was designed and synthesized in this study. Then it was polymerized with various aromatic dianhydrides including pyromellitic dianhydride, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, 4,4′‐oxydiphthalic anhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride via a one‐pot high temperature polycondensation procedure to produce a series of aromatic polyimides. These polyimides exhibited excellent solubility even in common organic solvents, such as chloroform and tetrahydrofuran. The flexible and tough films can be conveniently obtained by solution casting. The films were nearly colorless and exhibited high optical transparency, with the UV cutoff wavelength in the range 302–365 nm and the wavelength of 80% transparency in the range 385–461 nm. Moreover, they showed low dielectric constants (2.73–3.23 at 1 MHz) and low moisture absorption (0.13%–0.46%). Furthermore, they also possessed good thermal and thermo‐oxidative stability with 10% weight loss temperatures (T_10%) in the range 489–507 °C in a nitrogen atmosphere. The glass transition temperatures of all polyimides are in the range 262–308 °C. Copyright © 2012 Society of Chemical Industry     

Resistive switching characteristics of polyimides derived from 2,2′‐aryl substituents tetracarboxylic dianhydrides

2,2′‐Position aryl‐substituted tetracarboxylic dianhydrides including 2,2′‐bis(biphenyl)‐4,4′,5,5′‐biphenyl tetracarboxylic dianhydride and 2,2′‐bis[4‐(naphthalen‐1‐yl)phenyl)]‐4,4′,5,5′‐biphenyl tetracarboxylic dianhydride were synthesized. A new series of aromatic polyimides (PIs) were synthesized via a two‐step procedure from 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride and the newly synthesized tetracarboxylic dianhydrides monomers reacting with 2,2′‐bis[4′‐(3″,4″,5″‐trifluorophenyl)phenyl]‐4,4′‐biphenyl diamine. The resulting polymers exhibited excellent organosolubility and thermal properties associated with T_g at 264 °C and high initial thermal decomposition temperatures (T_5%) exceeding 500 °C in argon. Moreover, the fabricated sandwich structured memory devices of Al/PI‐a/ITO was determined to present a flash‐type memory behaviour, while Al/PI‐b/ITO and Al/PI‐c/ITO exhibited write‐once read‐many‐times memory capability with different threshold voltages. In addition, Al/polymer/ITO devices showed high stability under a constant stress or continuous read pulse voltage of ? 1.0 V. Copyright © 2011 Society of Chemical Industry     

Synthesis,characterization, thermal and optical properties of soluble polyimides derived from an unsymmetrical diamine

A new unsymmetrical diamine monomer, 2,4‐diaminophenyl [4′‐(2′′,6′′‐diphenyl‐4′′‐pyridyl)phenyl]ether, was successfully synthesized by nucleophilic substitution of 1‐chloro‐2,4‐dinitrobenzene with 4‐(2′,6′‐diphenyl‐4′‐pyridyl) phenol. The diamine monomer was characterized by FTIR, ¹H and ¹³C NMR, and elemental analysis techniques and used for the preparation of novel polyimides (PIs) by reaction with commercially available tetracarboxylic dianhydrides such as pyromellitic dianhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride, and bicyclo[2.2.2]‐oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride. These PIs with inherent viscosities ranged from 0.43 to 0.48 dL/g were readily soluble in many organic solvents and afforded tough and flexible films by solution casting. These polymers exhibited T_gs between 237 and 294°C, and 10% weight loss temperatures in excess of 500°C with up to 56% char yield at 600°C in air. Their maximum fluorescence emission in dilute (0.2 g/dL) NMP solution appeared at 450 nm. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of aromatic carboxylic dianhydrides on thermomechanical properties of polybenzoxazine‐dianhydride copolymers

Enhanced thermomechanical properties of bisphenol‐A based polybenzoxazine (PBA‐a) copolymers obtained by reacting bisphenol‐A‐aniline‐type benzoxazine (BA‐a) resin with three different aromatic carboxylic dianhydrides, i.e., pyromellitic dianhydride (PMDA), 3,3′,4,4′ biphenyltetracarboxylic dianhydride (s‐BPDA), or 3,3′,4,4′ benzophenonetetracarboxylic dianhydride (BTDA) were reported. Glass transition temperature (T_g), of the copolymers was found to be in the order of PBA‐a:PMDA>PBA‐a:s‐BPDA>PBA‐a:‐BTDA. The difference in the T_g of the copolymers is related to the rigidity of the dianhydride components. Furthermore, the T_g of PBA‐a:BTDA, PBA‐a:s‐BPDA, and PBA‐a:BTDA films was observed to be significantly higher than that of the neat PBA‐a owing to the enhanced crosslink density by the dianhydride addition. This greater crosslink density results from additional ester linkage formation between the hydroxyl group of PBA‐a and the anhydride group of dianhydrides formed by thermal curing. Moreover, the copolymers exhibit enhanced thermal stability with thermal degradation temperature (T_d) ranging from 410°C to 426°C under nitrogen atmosphere. The char yield at 800°C of the copolymers was found to be remarkably greater than that of the neat PBA‐a with a value up to 60% vs. that of about 38% of the PBA‐a. Toughness of the copolymer films was greatly improved compared to that of the neat PBA‐a. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Synthesis and characterization of novel borosiloxane‐containing aromatic copolyimides with excellent thermal stability and low coefficient of thermal expansion

The properties of borosiloxane‐containing copolyimides with borosiloxane in the main chain and in the side chain were studied. Two series of borosiloxane‐containing copolyimides were synthesized by the reaction of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA ) and 2,3′,3,4′‐biphenyltetracarboxylic dianhydride (a‐BPDA ) with p ‐phenylenediamine (PDA ), 4,4′‐oxydialinine (4,4′‐ODA ) and different borosiloxane diamine monomers (BSiAs ). The synthesized borosiloxane‐containing copolyimides exhibited better solubility than borosiloxane‐free copolyimides and showed high glass transition temperatures (320–360 °C), excellent thermal stability (570–620 °C for T ₁₀), great elongation at break (10% ? 14%) and a low coefficient of thermal expansion (14–24 ppm °C^?1). More specifically, the copolyimides containing BSiA‐2 formed nano‐scale protrusions and the copolyimides containing BSiA‐1 formed micro‐scale protrusions. The contact angles of the copolyimides increased from 72° for neat copolyimide to 96° for 5% of borosiloxane in the main chain of the copolymer up to 107° for 10% of borosiloxane in the side chain of the copolymer. © 2017 Society of Chemical Industry     

Novel phenylethynyl‐endcapped polyimide oligomers: Synthesis and characterization

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     

Preparation and electro‐optic properties of novel Y‐type polyimides with highly enhanced thermal stability of second harmonic generation

BACKGROUND: In the development of nonlinear optical (NLO) polymers for electro‐optic device applications, stabilization of electrically induced dipole alignment is one of the important criteria. Polyimides for NLO applications have attracted attention because of their high T_g values and high thermal stability. In this work we designed and synthesized a new type of NLO polyimide, in which the pendant NLO chromophores are parts of the polymer backbone. These mid‐type NLO polymers are expected to have the merits of both main‐chain and side‐chain NLO polymers: stabilization of dipole alignment and good solubility. RESULTS: 3,4‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐4′‐nitrostilbene dianhydride was prepared and reacted with the corresponding aromatic diamine to yield unprecedented Y‐type polyimides containing 3,4‐dioxynitrostilbenyl groups as NLO chromophores, which constituted parts of the polymer backbones. The resulting polyimides are soluble in polar solvents such as dimethylformamide and dimethylsulfoxide. These polymers showed a thermal stability up to 320 °C in thermogravimetric thermograms with T_g values obtained from differential scanning calorimetry thermograms in the range 143–164 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064 nm^?1 fundamental wavelength were around 9.45 × 10^?18 C. CONCLUSION: The dipole alignment exhibited exceptionally high thermal stability even at 30 °C higher than T_g. There was no SHG decay below 180–190 °C because of the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. Copyright © 2007 Society of Chemical Industry     

Synthesis and characterization of organosoluble and transparent polyimides derived from trans‐1,2‐bis(3,4‐dicarboxyphenoxy)cyclohexane dianhydride

A novel dianhydride, trans‐1,2‐bis(3,4‐dicarboxyphenoxy)cyclohexane dianhydride (1,2‐CHDPA), was prepared through aromatic nucleophilic substitution reaction of 4‐nitrophthalonitrile with trans‐cyclohexane‐1,2‐diol followed by hydrolysis and dehydration. A series of polyimides (PIs) were synthesized from one‐step polycondensation of 1,2‐CHDPA with several aromatic diamines, such as 2,2′‐bis(trifluoromethyl)biphenyl‐4,4′‐diamine (TFDB), bis(4‐amino‐2‐trifluoromethylphenyl)ether (TFODA), 4,4′‐diaminodiphenyl ether (ODA), 1,4‐bis(4‐aminophenoxy)benzene (TPEQ), 4,4′‐(1,3‐phenylenedioxy)dianiline (TPER), 2,2′‐bis[4‐(3‐aminodiphenoxy)phenyl]sulfone (m‐BAPS), and 2,2′‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]sulfone (6F‐BAPS). The glass transition temperatures (T_gs) of the polymers were higher than 198°C, and the 5% weight loss temperatures (T_d5%s) were in the range of 424–445°C in nitrogen and 415–430°C in air, respectively. All the PIs were endowed with high solubility in common organic solvents and could be cast into tough and flexible films, which exhibited good mechanical properties with tensile strengths of 76–105 MPa, elongations at break of 4.7–7.6%, and tensile moduli of 1.9–2.6 GPa. In particular, the PI films showed excellent optical transparency in the visible region with the cut‐off wavelengths of 369–375 nm owing to the introduction of trans‐1,2‐cyclohexane moiety into the main chain. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42317.     

High glass transition temperature bismaleimide‐triazine resins based on soluble amorphous bismaleimide monomer

A novel bismaleimide (DOPO‐BMI) with unsymmetrical chemical structure and DOPO pendant group has been prepared. The particular molecular structure makes DOPO‐BMI show an intrinsic amorphous state with a T_g about 135°C and excellent solubility in most organic solvents, which is beneficial to the processability of bismaleimide composite materials. A series of bismaleimide‐triazine (BT) resins have been prepared based on DOPO‐BMI and 2,2‐bis(4‐cyanatophenyl)propane at various weight ratios. The prepared BT resins show outstanding solubility in organic solvent and low viscosity about 10–671 mPa s at 180°C. The cured BT resins exhibit high glass transition temperature (T_g) over 316°C. As the weight ratio of DOPO‐BMI increases to 80% (BT80), the T_g can rise to 369°C (tan δ). The cured BT resins also show good thermal stability with the 5% weight loss temperature over 400°C under both nitrogen and air atmosphere. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42882.     

Synthesis and characterization of benzimidazole‐based low CTE block copolyimides

A series of block and random copolyimide films were synthesized from various molar ratios of two diamines, rigid 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (APBI) and flexible 4,4′‐oxydianiline (ODA) by polycondensation with dianhydride 3,3′,4,4′‐biphenyltetracarboxylic dianhydride. The contents of APBI ranged from 10 to 60 mol % in copolyimides. The copolyimide films obtained by thermal imidization of poly(amic acid) solutions, were characterized by TMA, DMA, TGA, DSC, wide‐angle X‐ray diffraction, FTIR, tensile testing, water uptake (WU), and dielectric constant measurements. Rigid heterocyclic diamine APBI with interchain hydrogen bonding capability, led to low coefficient of thermal expansion (CTE), high T_g, high thermal stability and better mechanical properties. Increasing the APBI mol % caused a gradual decrease in the CTE and increase in T_g, thermal stability and tensile strength properties of the copolyimides films. Moreover, significantly enhanced thermal and mechanical properties of the block copolyimides were also found as compared to random copolyimides. The block copolyimide with APBI content of 60 mol %, achieved excellent properties, that is, a low CTE (4.7 ppm/K), a high T_g at 377°C, 5% weight loss at 562°C and a tensile strength at 198 MPa. This can be interpreted because of comparatively higher degree of molecular orientation in block copolyimides. These copolyimides also exhibited better dielectric constant and WU. This combination of properties makes them attractive candidates for base film materials in future microelectronics. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Structure and properties for conterminously linked polymer of copoly(amic acid) with triallyl isocyanurate and bismaleimide

The copoly(amic acid)s were prepared from two various diamines 2,2′‐bis (4‐aminophenoxy phenyl) hexafluoropropane or 2,2′‐bis (4‐aminophenoxy phenyl) propane and amine‐terminated oligosiloxane, respectively, with aromatic tetracarboxylic dianhydride (3,3′,4,4′‐benzophenone tetracarboxylic dianhydride). The resulted copoly(amic acid) with various mole ratio of triallyl isocyanurate (TAIC)/4,4′‐bismaleimidophenylmethane (BMI) were subsequently thermally imidized to the corresponding copolyimides. These polymers were characterized using viscometer, differential scanning calorimetry, thermogravimetric analyses, dynamic mechanical analysis (DMA), dielectric analyzer, and scanning electron microscope. The dielectric constant (D_K) and dissipation factor (D_f) of copolyimides with TAIC/BMI were much lower than that of copolyimides without TAIC/BMI. Furthermore, the formation of copolyimides also would enhance their thermal stability and solubility. DMA of copolymers showed only a glass transition temperature (T_g), indicating a random structure and an amorphous state. The morphology of copolyimides revealed no phase separation. This indicates that the homogeneous state has been achieved in this coreaction system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of high‐temperature resistance polyimide foams

A new high‐temperature resistance polyimide foam was synthesized from 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (α‐BPDA) and p‐phenylenediamine (p‐PDA). The structures and foaming process of polyimide precursor powders were characterized by wide‐angle X‐ray diffractometer (WXRD) and the self‐made visualization device, respectively. The imidization degree, thermal mechanical properties and thermal stability of the polyimide foams with different post‐treatment temperatures were also measured by fourier transform infrared spectrometer spectrum (FTIR), dynamic thermal mechanical anaylsis (DMTA), and thermogravimetric analysis (TGA). Results showed that the inflation onset temperatures of polyimide precursor powders ranged from 122 to 135°C with varying the heating rate. And the increase in the imidization degree, glass transition temperatures (T_g) and temperatures for 5 wt% mass loss of high‐temperature resistance polyimide foams can be achieved with increasing post‐treatment temperature. It was quite surprising to find that T_g of high‐temperature resistance polyimide foam post‐treated at 420°C was up to above 450°C, and the char yield at 800°C was more than 60%. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Synthesis and characterization of polyetherimides containing multiple ether linkages and pendent pentadecyl chains

4‐(4‐(4‐(4‐Aminophenoxy)‐2‐pentadecylphenoxy)phenoxy)aniline (APPPA) was synthesized starting from cashew nut shell liquid‐derived bisphenol, i.e. 4‐(4‐hydroxyphenoxy)‐3‐pentadecylphenol, by nucleophilic substitution reaction with 4‐chloronitrobenzene followed by reduction of the formed 4‐(4‐nitrophenoxy)‐1‐(4‐(4‐nitrophenoxy)phenoxy)‐2‐pentadecylbenzene. Three new polyetherimides containing multiple ether linkages and pendent pentadecyl chains were synthesized by one‐step high‐temperature solution polycondensation of APPPA in m‐cresol with three aromatic dianhydrides, i.e. 3,3′,4,4′‐oxydiphthalic anhydride, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride. Inherent viscosities and number‐average molecular weights of the polyetherimides were in the ranges 0.66–0.70 dL g^?1 and 17 100–29 700 g mol^?1 (gel permeation chromatography, polystyrene standards), respectively, indicating the formation of reasonably high molecular weight polymers. The polyetherimides were soluble in organic solvents such as chloroform, dichloromethane, tetrahydrofuran, pyridine, m‐cresol, N,N‐dimethylformamide, N,N‐dimethylacetamide, N‐methylpyrrolidone and dimethylsulfoxide, and could be cast into transparent, flexible and tough films from their solutions in chloroform. The polyetherimides exhibited glass transition temperatures (T_g) in the range 113–131 °C. The lowering of T_g could be attributed to the combined influence of flexibilizing ether linkages and pentadecyl chains which act as ‘packing‐disruptive’ groups. The temperature at 10% weight loss (T₁₀), determined from thermogravimetric analysis in nitrogen atmosphere, was in the range 460–470 °C demonstrating good thermal stability. The virtues of solubility and large gap between T_g and T₁₀ mean that the polyetherimides containing pendent pentadecyl chains have possibilities for both solution as well as melt processability. © 2015 Society of Chemical Industry     

Synthesis and properties of fluorinated bis‐benzocyclobutene‐terminated arylene ether monomers

Four novel bis‐benzocyclobutene‐endcapped arylene ether monomers, 1,1′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1‐phenyl‐2,2,2‐trifluoroethane (BOPP3FE), 1,1′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1‐(3′,5′‐ditrifluoromethyl)phenyl‐2,2,2‐trifluoroethane(BOPP9FE), 2,2′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1,1,1,3,3,3‐hexfluoropropane (BOP6FP), and 2,2′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐propane (BOPP) were prepared and characterized. All the four monomers showed similar curing behaviors under N₂ (Differential scanning calorimetry: extrapolated onset and peak temperatures at 225–229°C and 261–263°C) and demonstrated low and steady melt viscosities between 110 and 200°C, indicating their good processability. After cure, the resulting BCB resins exhibited high T_g (232–282°C) and excellent thermal stability (T_5% > 433°C). The resins also showed good mechanical properties with the flexural strengths of 68–88 MPa and the flexural modulus of 2.52–3.15 GPa. Moreover, the resins also exhibited low dielectric constants (2.58–2.88), low dissipation factors (2.7 to 8.4 × 10?4) and low water absorptions in boiling water for 24 h (0.29–0.59%). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Organosoluble polyimides derived from asymmetric 2‐substituted‐and 2,2′,6‐trisubstituted‐4,4′‐oxydianilines

We report a new method for the preparation of asymmetric diamines using 4,4′‐oxydianiline (4,4′‐ODA) as the starting material. By controlling the equivalents of bromination agent, N‐bromosuccinimide, we were able to attach bromide and phenyl substituents at the 2‐ or 2,2′,6‐positions of 4,4′‐ODA. Thus, four new asymmetric aromatic diamines, 2‐bromo‐4,4′‐oxydianiline (6), 2,2′,6‐tribromo‐4,4′‐oxydianiline (7), 2‐phenyl‐4,4′‐oxydianiline (8) and 2,2′,6‐triphenyl‐4,4′‐oxydianiline (9), were synthesized by this method. Their structural asymmetry was confirmed using ¹H NMR spectroscopy. Asymmetric polyimides (PI10–PI13) were prepared from these diamines and three different dianhydrides (pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride) in refluxing m‐cresol. The formed polyimides, except PI10a derived from 6 and PMDA, were all soluble in m‐cresol without premature precipitation during polymerization. These polyimides with inherent viscosity of 0.41–0.96 dL g^?1, measured at a concentration of 0.5 g dL^?1 in N‐methyl‐2‐pyrrolidone at 30 °C, can form tough and flexible films. Because of the structural asymmetry, they also exhibited enhanced solubility in organic solvents. Especially, polyimides PI11a and PI13a derived from 7 and 9 with rigid PMDA were soluble in various organic solvents at room temperature. The structural asymmetry of the prepared polyimides was also evidenced from ¹H NMR spectroscopy. In the ¹H NMR spectrum of PI11a, the protons of pyromellitic moiety appeared in an area ratio of 1:2:1 at three different chemical shifts, which were assigned to head‐to‐head, head‐to‐tail and tail‐to‐tail configurations, respectively. These polyimides also exhibited good thermal stability. Their glass transition temperatures ranged from 297 to 344 °C measured using thermal mechanical analysis. © 2013 Society of Chemical Industry     

Preparation and properties of polyimide/silica hybrid composites based on polymer‐modified colloidal silica

A new type of polyimide/silica (PI/SiO₂) hybrid composite films was prepared by blending polymer‐modified colloidal silica with the semiflexible polyimide. Polyimide was solution‐imidized at higher temperature than the glass transition temperature (T_g) using 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐diaminodiphenyl ether (ODA). The morphological observation on the prepared hybrid films by scanning electron microscopy (SEM) pointed to the existence of miscible organic–inorganic phase, which resulted in improved mechanical properties compared with pure PI. The incorporation of the silica structures in the PI matrix also increased both T_g and thermal stability of the resulting films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2053–2061, 2006     

Syntheses and properties of polyimides derived from diamines containing 2,5‐disubstituted pyridine group

A series of novel homo‐ and copolyimides containing pyridine units were prepared from the heteroaromatic diamines, 2,5‐bis (4‐aminophenyl) pyridine and 2‐(4‐aminophenyl)‐5‐aminopyridine, with pyromelltic dianhydride (PMDA), and 3,3′, 4,4′‐biphenyl tertracarboxylic dianhydride (BPDA) via a conventional two‐step thermal imidizaton method. The poly(amic acid) precursors have inherent viscosities of 1.60–9.64 dL/g (c = 0.5 g/dL in DMAC, 30°C) and all of them can be cast and thermally converted into flexible and tough polyimide films. All of the polyimides show excellent thermal stability and mechanical properties. The polyimides have 10% weight loss temperature in the range of 548–598°C in air. The glass transition temperatures of the PMDA‐based samples are in the range of 395–438°C, while the BPDA‐based polyimides show two glass transition temperatures (T_g1 and T_g2), ranging from 268 to 353°C and from 395 to 418°C, respectively. The flexible films possess tensile modulus in the range of 3.42–6.39 GPa, strength in the range of 112–363 MPa and an elongation at break in the range of 1.2–69%. The strong reflection peaks in the wide‐angle X‐ray diffraction patterns indicate that the polyimides have a high packing density and crystallinity. The polymer films are insoluble in common organic solvents exhibiting high chemical resistance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1844–1851, 2006