Showing papers in "High Performance Polymers in 2006"
TL;DR: In this paper, a series of low-melting phthalonitrile oligomers were obtained using a modified-Ullman ether reaction between a bisphenol and a dihalobenzene to form a hydroxyl-terminated oligomeric intermediate.
Abstract: A series of low-melting phthalonitrile oligomers were prepared in which variable-length multiple aromatic ether linkages interconnect the terminal phthalonitrile units These materials were designed to address the need for a processable resin system with good high-temperature properties The melt-processable oligomers are obtained using a modified-Ullman ether reaction between a bisphenol and a dihalobenzene to form a hydroxyl-terminated oligomeric intermediate that is endcapped by reaction with 4-nitrophthalonitrile Viscosity measurements show that the phthalonitrile oligomers are polymerized at a moderate temperature (200°C) using the typical aromatic diamine curing additives, bis[4-(4-aminophenoxy)phenyl]sulfone and 1,3-bis(3-aminophenoxy)benzene The oligomeric phthalonitrile/diamine mixtures exhibit a low complex melt viscosity (001-01 Pa s) at 200°C Differential scanning calorimetric analysis is used to follow the polymerization as the oligomeric phthalonitrile/diamine mixtures are heated to ele
141 citations
TL;DR: Polybenzoxazine as a novel phenolic type thermoset has been developed to overcome the shortcomings associated with the use of the traditional phenolics as mentioned in this paper, which can be prepared from cyclic benzoxazines.
Abstract: Polybenzoxazine as a novel phenolic type thermoset has been developed to overcome the shortcomings associated with the use of the traditional phenolics. It can be prepared from cyclic benzoxazines ...
113 citations
TL;DR: The film properties of polyimides (PIs) containing para-ester linkages in the main chains, poly(ester imide)s (PEsI) are reported in this paper.
Abstract: The film properties of polyimides (PIs) containing para-ester linkages in the main chains, poly(ester imide)s (PEsI) are reported in this paper. An ester-containing dianhydride monomer (TAHQ) was synthesized from hydroquinone and trimellitic anhydride chloride. PEsIs derived from TAHQ and various diamines with stiff/linear structures, p-phenylenediamine (PDA), trans-1,4-cyclohexanediamine (CHDA), 2,2′-bis(trifluoromethyl)benzidine (TFMB), 4-aminophenyl-4′-aminophenylbenzoate (APAB), and 4,4′-daminobenzanilide (DABA), exhibited extremely low linear coefficient of thermal expansion (CTE) values, for example, CTE = 3.2 ppm K-1 for TAHQ/PDA and 3.3 ppm K-1 for TAHQ/APAB. The results revealed that the para-ester linkages behave as a rod-like segment favorable for thermal imidization-induced in-plane orientation. Copolymerization with flexible 4,4′-oxydianiline made precise CTE matching possible between PEsI/copper substrate and the significant improvement of film toughness at the same time. Wide-angle X-ray di...
74 citations
TL;DR: In this paper, a modified multiwalled carbon nanotubes (MWCNTs), vapor-grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated.
Abstract: In an effort to improve polymer thermal conductivity (TC), UltemTM 1000 was compounded with nano-fillers of carbon allotropes. As-received and modified multiwalled carbon nanotubes (MWCNTs), vapor-grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. Functionalization of MWCNTs was performed to improve the TC compatibility between the resin and MWCNTs. It was postulated that this may provide an improved interface between the MWCNT and the polymer which would result in enhanced TC. The nano-fillers were mixed with UltemTM 1000 inthemeltandinsolution at concentrations ranging from 5 to 40 wt.%. Ribbons were extruded from the blends to form samples where the nano-fillers were aligned to some degree in the extrusion direction. Samples were also fabricated by compression molding resulting in random orientation of the nano-fillers. Thermal properties of the samples were evaluated by differential scanning calorimetry (DSC) and thermal gravimetric analyzer (TGA). Tensile properties of aligne...
61 citations
TL;DR: In this paper, room-temperature vulcanized silicone rubber (RTV-SR)/organic montmorillonite (OMMT) nanocomposites were prepared by a solution intercalation process.
Abstract: Novel room-temperature-vulcanized silicone rubber (RTV-SR)/organic montmorillonite (OMMT) nanocomposites were prepared by a solution intercalation process. Di(2-oxyethyl)-12 alkane- 3 methyl-amine ...
39 citations
TL;DR: In situ anionic polymerization of °-caprolactam in the presence of SiO2 and silanated siO2nanoparticles was promoted as a route for the synthesis of two series of nylon 6/SiO2 nanocomposites.
Abstract: In situ anionic polymerization of °-caprolactam in the presence of SiO2 and silanated SiO2nanoparticles was promoted as a route for the synthesis of two series of nylon 6/SiO2 nanocomposites. The process was performed at 160°C well below the melting temperature of the nylon 6 (Tm ~ 225°C) and initiated/activated with sodium dicaprolactamato-bis(2-methoxyethoxo)aluminate/N,N′[methylene-di(4,4′phenylene)bis-carbamoyl]bis-δ-caprolactam system. The nanocomposites obtained exhibit higher onset decomposition temperatures than neat nylon 6 and a tendency of reduction of the polymer yields, degree of polymerization, water absorption and melting temperatures with silica content increasing. The crystallization temperature, Tc of the nanocomposites reaches a maximum value at 2.0 wt.% of the nanoparticles. The mechanical tests of nanocomposites revealed an increase in flexural modulus as a function of filler percentage and a decrease in notched impact strength by addition of the modified silica (over 4.0 wt.%) and un...
39 citations
TL;DR: In this article, highly soluble addition-type imide oligomers were synthesized from 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 9,9-bis(4-aminophenyl)fluorene (BAFL), 4, 4′-diaminodiphenyl ether (4,4-ODA), and 4-phenylethynylphthalic anhydride(PEPA) to fabricate carbon fiber-reinforced plastics (CFR
Abstract: Novel highly soluble addition-type imide oligomers were synthesized from 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 9,9-bis(4-aminophenyl)fluorene (BAFL), 4,4′-diaminodiphenyl ether (4,4′-ODA), and 4-phenylethynylphthalic anhydride (PEPA) to fabricate carbon fiber-reinforced plastics (CFRP) by routing imide solution prepreg. The imide oligomers were soluble in aprotic polar solvents of more than 35 wt.%. Imide oligomers consisting of less than 50mol% BAFL per total diamine had good processability when using a hot press. The glass transition temperature (Tg)values of the cured resins were higher than 340°C. The Tg values increased when the BAFL component increased. The 5% weight loss temperatures (Td5) were higher than 550°C. The elongations-at-break of the BAFL copolymers were less than that of the polymer without BAFL. An imide solution prepreg was prepared from the imide oligomer solution and carbon fibers. Polyimide/carbon fiber composite without voids was fabricated from the imide solutio...
30 citations
TL;DR: In this paper, the authors used polycondensation of 2-(6-oxido-6H-dibenz >c,e 1,2< oxaphosphorin-6-yl)-1,4-benzenediol with different aromatic dicarboxylic acids using a SOCl2/pyridine condensing agent.
Abstract: Phosphorus-containing polyesters were prepared by polycondensation of 2-(6-oxido-6H-dibenz >c,e 1,2< oxaphosphorin-6-yl)-1,4-benzenediol with different aromatic dicarboxylic acids using a SOCl2/pyridine condensing agent. The polymers were soluble in polar organic solvents such as N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran and chloroform. They showed high thermal stability having a decomposition temperature above 360°C and char yield at 700°C in the range of 19-32%. The glass transition temperature was in the range of 180-194°C. Solutions of the polymers in N,N-dimethylformamide showed fluorescence having maximum emission wavelength around 362 nm. One of the polymers exhibited thermotropic liquid crystalline behavior
30 citations
TL;DR: In this article, a graft copolymer was synthesized via living radical polymerization, and the graft was transformed into proton exchange membranes for direct methanol fuel cell (DMFC) application.
Abstract: Well-defined poly(2,6-dimethyl-4,4′-phenylene oxide)-g-poly(styrenesulfonic acid) (PPO-g-PSSA) graft copolymer was synthesized via living radical polymerization. For the graft copolymer, poly(2,6-dimethylphenylene oxide) (PPO) was brominated first, and the brominated PPO (PPO-Br) was used as a macroinitiator in the atom transfer radical polymerization (ATRP) of styrenesulfonic acid sodium salt. The number of grafts per PPO chain and the molecular weight of the graft were controlled by adjusting the degree of bromination, and conversion in ATRP, respectively. The graft copolymers obtained were transformed into proton exchange membranes for direct methanol fuel cell (DMFC) application. The performance of the membranes was measured in terms of water uptake, proton conductivity, methanol permeability, and thermal stability. The water uptake, ion exchange capacity (IEC), and proton conductivity of the membranes increased with PSSA block content. Very low methanol permeability and good proton conductivity were ...
27 citations
TL;DR: In this paper, a pendent group attachment of an amino group-functionalized zirconium complex to co-polyamic acid precursors was facilitated by a stoichiometric amount of dicyclohexyl carbodiimide.
Abstract: The goal of this research is to increase the metal-organic concentration in Kapton-like polyimides (PIs) to achieve increased atomic oxygen (AO) resistance while retaining desirable film properties Co-polyamic acid (PAA) precursors were prepared using a novel polymer building block, mellitic acid dianhydride (MADA), to provide sites for pendent group attachment Attachment of an amino group-functionalized zirconium complex to the co-PAA precursors was facilitated by a stoichiometric amount of dicyclohexylcarbodiimide The viscous solutions which resulted were characterized by thin layer chromatography (TLC), viscosity, and gel permeation chromatography (GPC), or treated with excess poor solvent to precipitate powder samples, or cast onto glass slides and heated to produce imidized films Powder samples were dissolved in deuterated solvent for proton nuclear magnetic resonance analysis, or characterized by thermogravimetric analysis and differential scanning calorimetry Film samples were characterized by
26 citations
TL;DR: In this article, the alicyclic polyimides were prepared by reacting bicyclo[2.1]heptane-2,3,5,6-tetracarboxylic 2,3-5, 6-dianhydride (BHDA) with aliphatic or aromatic diamines in hexamethylphosphoramide.
Abstract: The alicyclic polyimides were prepared by reacting bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic-2,3-5,6-dianhydride (BHDA) with aliphatic or aromatic diamines in hexamethylphosphoramide. The poly(amic acid)s possessed inherent viscosities (νinh)in the range from 0.13 to 0.38, and they formed free-standing and flexible films after being cast then cured. The fully alicyclic polyimide films exhibited a cutoff around 230 nm, and are transparent even in the near infrared region. The optically estimated e of the fully alicyclic polyimides was about 2.6. All the alicyclic polyimide possessed negligibly small birefringence below 10-4. Semi-aromatic polyimide PI(BHDA + 1,3-BAB) had good thermal stability with no significant weight loss up to 350°C, and the T5 was around 450°C, although the Tg was as low as 197°C. All polyimides exhibited broad dispersive peaks of diffraction around 16° (2τ). The PI(BHDA + BBH) film possessed a tensile modulus of 2.05 GPa and a tensile strength of 52 MPa, and these values can comp...
TL;DR: In this article, a novel chlorinated diamine monomer with keto group, 4,4′-dichloro-3,3′diamino benzophenone (DADCB) was prepared through the nitration of dichloro benzophenones (DNDCB) followed by catalytic reduction with SnCl4 and HCl.
Abstract: A novel chlorinated diamine monomer with keto group, 4,4′-dichloro-3,3′-diamino benzophenone (DADCB) was prepared through the nitration of dichloro benzophenone (DNDCB) followed by catalytic reduction with SnCl4 and HCl. Chlorinated polyimides (IVa-e) were synthesized from the above diamine with various commercially available dianhydrides via one-step and two-step methods. Polyimides IVa-e have inherent viscosity in the range 0.98–1.42 dL g° 1 in the one-step method and 0.70–0.95 dL g° 1 (thermal imidization) and 0.84–1.33 dL g° 1(chemical imidization) in the two-step method. The polyimidesprepared by the one-step method and chemical imidization method exhibited excellent solubility, but those prepared via thermal imidization exhibited limited solubility. Polyimide° lms exhibited tensile strength 95–121MPa, percentage elongation 8–13% and tensile modulus 1.6–2.4 GPa. The T g of the polyimides are in the range 272–297° C and T10 values are in the range 510–542° C in N2 and 460–498° C in air with more than ...
TL;DR: In this paper, some representative thermal, chemical and mechanical properties of commercial type polyimides are presented in this second paper in a series on using water as solvent in polyimide synthesis.
Abstract: Some representative thermal, chemical and mechanical characteristics of ‘commercial type’ polyimides are presented in this second paper in a series on using water as solvent in polyimide synthesis....
TL;DR: In this paper, the molecular structure formed in the gelation process is controlled by varying the equivalence ratio of end-crosslinker to oligomer during the preparation of poly(amide acid) gels.
Abstract: Network formation in the gelation process of end-crosslinked poly(amide acid) gels, which are the precursor of end-crosslinked polyimide gels, was studied by scanning dynamic light scattering. The gelation process is essentially non-reversible due to the formation of covalent bonds. The molecular structure formed in the gelation process is controlled by varying the equivalence ratio of end-crosslinker to oligomer during the preparation. It was found that a couple of relaxation modes are observed in the gelation point even for semi-rigid poly(amide acid) solutions. This is similar to flexible polymer solutions and convenient to characterize the molecular structure in the gelation processes. The fast mode is related to the cooperative diffusion process of the network structure formed by over lapped macromolecules, i.e., gel mode, which determines the averaged mesh-size of the network structure. The slow mode is related to the relaxation time of the formation of the transient network structure, which shows a...
TL;DR: In this paper, high performance bismaleimide (BMI) matrix composites reinforced with graphite fibers were prepared and toughened with a thermoplastic component (PEK-C) by using different toughening methods.
Abstract: High-performance bismaleimide (BMI) matrix composites reinforced with graphite fibers were prepared and toughened with a thermoplastic component (PEK-C) by using different toughening methods. Four experimental options were conducted using the neat BMI matrix, toughened BMI matrix with PEK- C, BMI laminates periodically interleaved with neat PEK-C films (Ex-situ concept 1) and BMI laminates periodically interleaved with BMI/PEK-C blend films (Ex-situ concept 2), respectively. The laminates were tested for compression strength after impact using an impact energy of 2 J mm 1 . The highest impact damage resistance was obtained for the laminates toughened using the Ex-situ concept 2, especially, when PEK-C/BMI two-component films, cast from a mixture of PEK-C : BMI = 60 : 40 were interleaved between the BMI laminate plies. Interleaving the pure thermoplastic film also gave good results (Ex-situ concept 1). There were two peak temperatures evident in the dynamic mechanical thermal analyses of the ex-situ toughened laminates implying that phase separation had occurred. The glass transition temperature of the toughened BMI laminates was slightly reduced due to the lower glass transition temperature of PEK-C. Morphological investigations revealed that a granular structure was present in the interply region presumably due to spinodal decomposition and coarsening. The results of this study are presented herein.
TL;DR: In this paper, a series of brush polyimide (PI) composed of two 4nalkyloxyphenyloxy bristles per repeat unit on a semi-rigid poly(4,4′-methylenyldiphenylene pyromellitimide), Cm-PMDA-MDA PIs, were synthesized and their nanoscale thin films prepared by conventional spin-coating of their soluble poly(amic acid) precursor solutions and subsequent drying and thermal imidization in a nitrogen atmosphere.
Abstract: A series of well-defined brush polyimide (PI) composed of two 4-n-alkyloxyphenyloxy bristles per repeat unit on a semi-rigid poly(4,4′-methylenyldiphenylene pyromellitimide), Cm-PMDA-MDA PIs, were synthesized and their nanoscale thin films prepared by conventional spin-coating of their soluble poly(amic acid) precursor solutions and subsequent drying and thermal imidization in a nitrogen atmosphere. All the PIs were determined to be a positively birefringent polymer. The surface morphology and molecular orientation of each PI in films before and after rubbing were investigated in detail by atomic force microscopy, optical retardation analysis, and linearly polarized infrared spectroscopy. The sequence of the rubbing-induced polymer segmental orientations was further investigated in detail. In addition, the liquid crystal alignment and pretilt ability of the rubbed PI films were examined, and their thermal stability investigated. The present study provides important information on the sequence of the polym...
TL;DR: In this article, the authors present an interesting study on molecular self-assembly and its effect on steric recognition by molecularly imprinted polymers with S-naproxen as the template and acrylamide as the functional monomer.
Abstract: This article presents an interesting study on molecular self-assembly and its effect on steric recognition by molecularly imprinted polymers. With S-naproxen as the template and acrylamide as the functional monomer, the self-assembly appears to play important roles in the selective adsorption, affecting not only the adsorption amount but also the enantioselective recognition. Both of them become evident by the change of monomer–template ratio. An increase in the monomer–template ratio will result in a higher level of adsorption. The best selectivity for steric recognition is, however, shown at an optimal composition (corresponding to the saturation interaction of monomer and template). A higher or lower monomer–template ratio leads to a dramatic decrease in this selectivity. Related information indicates that this may be a result from the matched arrangement between the binding sites and the template, which makes the binding sites capable of selectively recognizing the imprint species.
TL;DR: In this article, the authors investigated the physical and gas transport properties of novel hyperbranched polyimide-silica hybrid membranes with polyamic acid as a precursor and 3-aminopropyltrimethoxy-silane (APTrMOS) as the end groups.
Abstract: Physical and gas transport properties of novel hyperbranched polyimide-silica hybrid membranes were investigated. Hyperbranched polyamic acid as a precursor was prepared by polycondensation of a triamine monomer, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and a dianhydride monomer, 4,4′-oxidiphthalic anhydride (ODPA), and subsequently modified the end groups by 3-aminopropyltrimethoxy-silane (APTrMOS). Hyperbranched polyimide-silica hybrid membranes were prepared using the polyamic acid, water, and tetramethoxysilane (TMOS) by the sol-gel method and thermal imidization. The 5% weight-loss temperature and glass transition temperature of the hybrid membranes determined by TGDTA measurements considerably increased with increasing silica content, indicating effective cross-linking at polymer-silica interface mediated by APTrMOS. CO2, O2, N2, and CH4 permeability coefficients of the hybrid membranes increased with increasing silica content. In addition to the increased permeability, CO2/CH4 selectivity of the ...
TL;DR: In this paper, the effect of temperature and duration of reaction on the extent of sulfonation was investigated, and the structural characterization of these sulfonated polymers was done by FT-IR and 1H-NMR spectroscopy.
Abstract: The sulfonation of commercially available poly (ether imide) (PEI) (Ultem) was carried out using chlorosulfonic acid (16% w/v) in dichloroethane solution. The effect of temperature (0–60 C) and the duration (1–16 h) of reaction on the extent of sulfonation was investigated. Structural characterization of these sulfonated polymers was done by FT-IR and 1H-NMR spectroscopy. The thermal stability of sulfonated PEI in the N2 atmosphere decreased with the increase in extent of sulfonation. A multistep degradation was observed and the lowest char residue at 800 C was obtained in samples having a high extent of sulfonation.
TL;DR: In this paper, four novel sulfonated diamine monomers which are isomers to each other, 4,4′-bis(4-aminophenoxy)biphenyl-3, 3,3′-disulfonic acid (pBAPBDS), 4, 4′-is(3-, 3-, 4-, 4-amino-2-sulfophenoxy), 3,5,8-naphthalenetetetracarboxylic dianhydride (NTDA), 2,2,2′-
Abstract: Four novel sulfonated diamine monomers which are isomers to each other, 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (pBAPBDS), 4,4′-bis(3-aminophenoxy)biphenyl-3,3′-disulfonic acid (mBAPBDS), 2,2′-bis(4-aminophenoxy)biphenyl-5,5″-disulfonic acid (oBAPBDS), and 4,4--bis(4-amino-2-sulfophenoxy)biphenyl (iBAPBDS), were synthesized and the related sulfonated polyimides (SPIs) were prepared from these sulfonated diamines and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA). The resulting SPIs had the same chemical composition and ion exchange capacity (IEC) but quite different solubility behaviors and water stability. Nonlinear sulfonated diamine (m-BAPBDS and oBAPBDS)-based polyimides showed much better solubility in many organic solvents than the linear diamine (pBAPBDS and iBAPBDS)-based ones. It was found that the water stability of the SPI membranes was the total effects of solubility stability and hydrolysis stability. Solubility stability is mainly determined by the IEC level and the conf...
TL;DR: In this article, a mixture of PETI-330 and carbon nanofibers (CNFs) is used to investigate the potential of CNF composites as a high performance structural medium.
Abstract: Multifunctional composites present a route to structural weight reduction. Nanoparticles such as carbon nanofibers (CNF) provide a compromise as a lower cost nanosize reinforcement that yields a desirable combination of properties. Blends of PETI-330 and CNFs were prepared and characterized to investigate the potential of CNF composites as a high performance structural medium. Dry mixing techniques were employed and the effect of CNF loading level on melt viscosity was determined. The resulting powders were characterized for degree of mixing, thermal and rheological properties. Based on the characterization results, samples containing 30 and 40 wt% CNF were scaled up to approx.300 g and used to fabricate moldings 10.2 cm x 15.2 cm x 0.32 cm thick. The moldings were fabricated by injecting the mixtures at 260-280 C into a stainless steel tool followed by curing for 1 h at 371 C. The tool was designed to impart high shear during the process in an attempt to achieve some alignment of CNFs in the flow direction. Moldings were obtained that were subsequently characterized for thermal, mechanical and electrical properties. The degree of dispersion and alignment of CNFs were investigated using high-resolution scanning electron microscopy. The preparation and preliminary characterization of PETI-330/CNF composites are discussed. Keywords: resins, carbon nanofibers, scanning electron microscopy, electrical properties, thermal conductivity,injection
TL;DR: In this article, the direct polycondensation of aromatic diamines and tetracarboxylic acids was studied using imidazolium-type ionic liquids as the reaction medium.
Abstract: The direct polycondensation of aromatic diamines and tetracarboxylic acids was studied using imidazolium-type ionic liquids as the reaction medium. Polyimides with inherent viscosities of 0.05 dL g-1 could be prepared in high yields by this novel polycondensation at 150°C for 12 h without polyamic acids. In this reaction, ionic liquids could catalyze the condensation and cyclodehydration reaction of dicarboxylic acids and amines to directly give imide rings.
TL;DR: In this paper, a phenolic novolac was modified with hydroxyl terminated polybutadiene (HTPB) using resole as compatibilizer, and the fracture behavior was characterized by scanning electron microscopy.
Abstract: Phenolic novolac was modified with hydroxyl terminated polybutadiene (HTPB) using resole as compatibilizer. These systems were characterized by differential scanning calorimetry, and IR analysis. Neat resin castings were prepared with varying percentages of HTPB. The fracture toughness of these systems was assessed by evaluating the critical stress intensity factor (K lt;subgt;Iclt;/subgt;) using single-edge notch, three-point bend specimens. The fracture behavior was characterized by scanning electron microscopy. These studies revealed that the fracture toughness of the phenolic novolac resin was improved by blending it with HTPB due to the formation of a heterogeneous phase with minute particles of elastomer, which arrests the propagation of cracks.
TL;DR: Two functional N-substituted maleimide monomers were copolymerized with N Vinyl-2-pyrrolidone (NVP) at 90°C in the presence of 2,2′-azobisisobutyronitrile as initiator in dimethylformamide as mentioned in this paper.
Abstract: Two functional N-substituted maleimide monomers, namely N-(4-carboxyphenyl)maleimide (CPMI) and N-(4-formylphenoxy-4′-carbonylphenyl) maleimide (FCPMI), were copolymerized with N Vinyl-2-pyrrolidone (NVP) at 90° C in the presence of 2,2′-azobisisobutyronitrile as initiator in dimethylformamide. The monomers reactivity ratios were calculated by extended Kelen–Tudos and Mao–Huglin methods. The average reactivity ratios and Alfrey–Price Q and e Values were found to be r1 = 0.028, r2 = 0.347, Q1 = 0.035, e1 = 1.013 for CPMI/NVP system and r1 = 0.044, r2 = 0.060, Q1 = 0.145, e1 = 1.297 for the FCPMI/NVP system. The distribution of monomer sequences along the copolymer chain was calculated using a statistical method based on the obtained reactivity ratios. The thermal properties of the resulting copolymers were also investigated. These copolymers exhibit fairly high thermal stability with decomposition temperatures above 230° C. The effect of the N-substituents on the radical copolymerization of the above funct...
TL;DR: In this article, a carbon fiber-reinforced PMR-type polyimide composites were prepared from T-300 carbon fibers and polyimides matrix resin derived from 4,4′-methylenediamine (MDA), p-phenylenediamines (p-PDA), diethyl ester of 3,3′,4,4-4, 4′-oxydiphthalic acid (ODPE) and monoethyl esters of cis-5-norbornene-endo- 2,3-dicar
Abstract: Carbon fiber-reinforced PMR-type polyimide composites were prepared from T-300 carbon fibers and polyimide matrix resin derived from 4,4′-methylenediamine (MDA), p-phenylenediamine (p-PDA), diethyl ester of 3,3′,4,4′-oxydiphthalic acid (ODPE) and monoethyl ester of cis-5-norbornene-endo- 2,3-dicarboxylic acid (NE). The rheological properties of the PMR polyimide matrix resin were investigated. Based on this information, an optimized molding cycle was designed for fabricating T-300/PI composites. The composites exhibited high thermal stability and good mechanical properties. The glass transition temperature (Tg) determined by dynamic mechanical analysis and the decomposition temperature at 5% of weight loss (T5) were higher than 360 and 540°C, respectively. The flexural strength and shear strength of the composites were 1560 and 95 MPa, respectively. The composite also exhibited good thermal-oxidative stability and hygrothermal resistance as evaluated under the conditions of isothermal aginginairat320°C an...
TL;DR: In this article, the effect of curing conditions on zinc oxide nanoparticle formation was investigated using transmission electron microscope observation, where the size, distribution and density of zinc oxide particles were strongly dependent on the curing conditions.
Abstract: Zinc oxide nanoparticles were formed by reacting polyamic acid (PAA) with Zn during curing. In this paper, we investigated the effect of curing conditions on the zinc oxide nanoparticle formation. The polyimide (PI) precursors used in this study were biphenyltetracarboxylic dianhydride-p-phenylene diamine (BPDA-PDA) type and oxydiphthalic dianhydride 3-sulful dianhydride (ODPA-3SDA) type PAAs. Zn thin films were deposited on silicon substrates by DC magnetron sputter. PAA was then spin-coated onto Zn thin films and the PAA/metal films were cured at various conditions. The characterization using transmission electron microscope observation was carried out to investigate the size and distribution of zinc oxide particles. Zinc oxide nanoparticles were formed in the PI film regardless of the curing conditions. The size, distribution and density of zinc oxide particles were strongly dependent on the curing conditions..
TL;DR: In this paper, a series of reduced charge clays were prepared by heat treatment of the lithium bentonite at 130 C, 150 C, or 170 C. The level of silicate dispersion in a thermosetting polyimide matrix was dependent upon the temperature of Li-clay heat treatment as well as the organic modification.
Abstract: The naturally occurring sodium and calcium cations found in bentonite clay galleries were exchanged with lithium cations. Following the cation exchange, a series of reduced charge clays were prepared by heat treatment of the lithium bentonite at 130 C, 150 C, or 170 C. Inductively coupled plasma (ICP) analysis showed that heating the lithium clay at elevated temperatures reduced its cation exchange capacity. Ion exchange of heat-treated clays with either a protonated alkyl amine or a protonated aromatic diamine resulted in decreasing amounts of the organic modifier incorporated into the lithium clay. The level of silicate dispersion in a thermosetting polyimide matrix was dependent upon the temperature of Li-clay heat treatment as well as the organic modification. In general, clays treated at 150 C or 170 C, and exchanged with protonated octadcylamine or protonated 2,2'-dimethlybenzidine (DMBZ) showed a higher degree of dispersion than clays treated at 130 C, or exchanged with protonated dodecylamine. Dynamic mechanical analysis showed little change in the storage modulus or T(sub g) of the nanocomposites compared to the base resin. However, long term isothermal aging of the samples showed a significant decrease in the resin oxidative weight loss. Nanocomposite samples aged in air for 1000 hours at 288 C showed of to a decrease in weight loss compared to that of the base resin. This again was dependent on the temperature at which the Li-clay was heated and the choice of organic modification.
TL;DR: In this paper, a liquid crystalline thermoset, D2A1, was synthesized from the reaction between DOMS and aniline, which was characterized with cross-polarized optical microscopy, differential scanning calorimetry, thermogravimetric analysis (TGA) and other techniques.
Abstract: 4,4′-diglycidyloxy-α-methylstilbene (DOMS) and a novel liquid crystalline thermoset, D2A1 which is obtained from the reaction between DOMS and aniline were synthesized. The thermosets have been characterized with cross-polarized optical microscopy, differential scanning calorimetry, thermogravimetric analysis (TGA) and other techniques. D2A1 was smectic at room temperature and turned to nematic at 85°C upon heating, then turned isotropic at 135°C. Activation energies for decomposition (Ed) using TGA were calculated according to the technique of Flynn-Wall to determine Ed as a function of conversion α by a weight loss process.
TL;DR: In this article, several novel sulfonated polyimides (SPIs) derived from KDNTDA were synthesized and their structures were characterized by IR and 1H NMR.
Abstract: 4,4′-Ketone dinaphthalene 1,1′,8,8′-tetracarboxylic dianhydride (KDNTDA) was prepared by a new route including six steps with an overall yield of 19%. The structure was confirmed by IR, 1H NMR and UV spectroscopy. Several novel sulfonated polyimides (SPIs) derived from KDNTDA were synthesized and their structures were characterized by IR and 1H NMR. Their reduced viscosity ranged from 0.8 to 4.5 dL g-1 at 35°C. They had good solubility in common aprotic solvents not only in triethylamine salt form but also in proton form. The co-SPIs showed anisotropic membrane swelling with larger swelling in thickness than in plane, while the homo-polymer displayed isotropic membrane swelling. The thermal stability measurements revealed that sulfonic acid group in KDNTDA-based SPIs were stable up to 300°C. They displayed reasonably high proton conductivity, water stability and mechanical properties.
TL;DR: Aromatic polyimides having phenyl groups at the 2 and 2′ positions of the diphenyl ether moiety were synthesized from bis(4-amino-2-biphenyl) ether and various tetracarboxylic dianhydrides by the conventional two-step procedure using N-methyl-2pyrrolidone (NMP) as a solvent.
Abstract: Aromatic polyimides having phenyl groups at the 2- and 2′-positions of the diphenyl ether moiety were synthesized from bis(4-amino-2-biphenyl) ether and various tetracarboxylic dianhydrides by the conventional two-step procedure using N-methyl-2-pyrrolidone (NMP) as a solvent [Morikawa et al., Polymer Journal37, 759, 2005]. The phenyl groups at the 2,2′-position of the phenyl ether improved the solubility of polyimides without decreasing the thermal and thermo-mechanical properties. In this paper, soluble polyimides were synthesized in a one-step procedure by reacting this diamine with various tetracarboxylic dianhydrides in m-cresol at 190°C, and the properties, especially the thermal properties, thermo-mechanical properties and solubility were compared with those of the polyimides synthesized by the two-step procedure.