Phenylethynyl-terminated Imide Oligomers Research Articles

Sulphur-containing phenylethynyl terminated polyimide via chemical crosslinking method for excellent thermal properties and antibacterial performance

Thermal stability and antibacterial property of polyimide have emerged as two significant property parameters when used in the aerospace field. In this work, sulphur-containing linkage is introduced into the polyimide by using phenylethynyl terminated imide oligomers (PETI) and sulphur agent. The curing properties of this new type of thermosetting polyimide were studied by Fourier transform infrared (FTIR) and Raman spectra, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA). The sulphur-containing polyimide shows a unique thermoplastic-like glass transition behavior rather than typical thermoset behavior. Its film material shows the tensile strength and modulus of 59.46 MPa and 1767 MPa respectively, which have increased to 187.68% and 155.16% when compared with the control sample cured at 381 °C. And the mechanical retention rates of tensile strength and modulus reach 96.8% and 82.1% respectively after 371 °C/100 h aging. In addition, it shows potential value in the fabrication of carbon fiber reinforced composite and antibacterial materials. Though the curing temperature of PETI oligomer decreases from 381 °C to 300 °C, the prepared PI/CF composite shows excellent mechanical performance, and the interlaminar shear strength, the flexural strength, and the flexural modulus reach 104.53 MPa, 1846.71 MPa and 129.24 GPa, respectively. Also, the novel polyimide shows excellent antibacterial performance, with antibacterial retention rate to negative E. coli and positive S. aureus of 90.4% and 89.1%, respectively.

High temperature phenylethynyl-terminated imide oligomers derived from asymmetric diphenyl ether diamines for resin transfer molding

Resin transfer molding (RTM) require phenylethynyl-terminated imide oligomers (PETIs) to exhibit low melt temperatures and better melt stability. To decrease the melt temperatures of PETIs and improve their resin transfer moldable processability, asymmetric 4,4′-diaminodiphenyl ether substituted by fluorine (F-ODA), trifluoromethyl group (3F-ODA) or phenyl group (p-ODA) were introduced. Asymmetric molecular structure and substituent groups decrease the melt temperatures of PETIs, endowing PETIs with the wider processing temperature windows and low minimum melt viscosity (<1 Pa s). These polyimides show pot lives of 30–60 min at 260–280 °C. Furthermore, the effects of backbone structure on melt fluidity of imide oligomers were discussed by the calculation of viscous activation energy (Ea,η) and analysis of Molecular Dynamics. PETI-3F and PETI-P based on 3F-ODA and p-ODA exhibit low and stable melt viscosities (<1 Pa s) at 250–270 °C and 260–270 °C for 4 h respectively, enabling the successful fabrication of carbon fiber reinforced polyimide composites via RTM process. After cured at 380 °C, the thermosets of PETI-3 and PETI-4 show high Tg of 412 °C and 402 °C and good thermal stability (Td5>550 °C). Cured PETI-3 and PETI-4 also show good mechanical properties (tensile strength >50 MPa). In comparison with p-ODA, 3F-ODA could provide PETIs with superior resin transfer moldable processability and higher heat-resistance and is more suitable to synthesize PETIs for RTM application, because of better balance between polymer segmental mobility and polymer chain packing.

Phenylethynyl-terminated Imide Oligomers Modified by Reactive Diluent for Resin Transfer Molding Application

Phenylethynyl-terminated Imide Oligomers Modified by Reactive Diluent for Resin Transfer Molding Application

Type and Size Selectivity of Single-Walled Carbon Nanotubes by Phenylethynyl Terminated Imide Oligomers

Aromatic polyimides are well-known as high-performance polymer materials which have excellent properties such as high thermal stability, strong mechanical strength, and superior chemical resistance. However, rigid backbones of oligomers and strong chain interactions result in lower processibility. Our molecular modeling suggests that the enhancement of nanotube solubilization is attributed to the formation of self-assembled intermolecular structures associated with the inclusion of curing agents, in conformity with experimental findings. On the other hand, isolation of single-walled carbon nanotubes (SWNTs) with specific chirality and diameter is critical for achieving optimum performances of SWNTs in various application. Our studies reveal that phenylethynyl terminated imide (PETi) oligomer selectively enriches metallic and semiconducting (6, 5) SWNT.

Resin Transfer Moldable Fluorinated Phenylethynyl-Terminated Imide Oligomers with High Tg: Structure-Melt Stability Relationship.

Phenylethynyl-terminated aromatic polyimides meet requirements of resin transfer molding (RTM) and exhibits high glass transition temperature (Tg) were prepared. Moreover, the relationship between the polyimide backbones structure and their melting stability was investigated. The phenylethynyl-terminated polyimides were based on 4,4′-(hexafluorosiopropylidene)-diphthalic anhydride (6FDA) and different diamines of 3,4′-oxydianiline (3,4′-ODA), m-phenylenediamine (m-PDA) and 2,2′-bis(trifluoromethyl)benzidine (TFDB) were prepared. These oligoimides exhibit excellent melting flowability with wide processing temperature window and low minimum melt viscosities (<1 Pa·s). Two of the oligoimides display good melting stability at 280–290 °C, which meet the requirements of resin transfer molding (RTM) process. After thermally cured, all resins show high glass transition temperatures (Tgs, 363–391 °C) and good tensile strength (51–66 MPa). The cure kinetics studied by the differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (13C NMR) characterization and density functional theory (DFT) definitely confirmed that the electron-withdrawing ability of oligoimide backbone can tremendously affect the curing reactivity of terminated phenylethynyl groups. The replacement of 3,4′-ODA units by m-PDA or TFDB units increase the electron-withdrawing ability of the backbone, which increase the curing rate of terminated phenylethynyl groups at processing temperatures, hence results in the worse melting stability.

Effect of Blending Modifications for Phenylethynyl-terminated Polyimides

A reactive diluent (ODA-PEPA) and a flexible phenylethynyl-terminated imide oligomer (PEI-PEPA) were designed and synthesized based on the 2,3,3’,4’-diphenyl ether tetracarboxylic acid dianhydride (a-ODPA), 3,4’-oxydianiline (3,4’-ODA), and 4-phenylethynylphthalic anhydride (PEPA). Solution blended systems with the addition of 5, 10, and 15 wt% ODA-PEPA to PEI-PEPA oligomer and their cured resin systems were prepared. Results showed that ODA-PEPA is semi-crystalline in nature. The Tg values of cured resins were improved from 273 °C to 280 °C by the addition of ODA-PEPA, due to the higher crosslink densities. In addition, rheological properties of blends showed lower melt viscosity and wider processing window, revealing improved melt processabilities for potential application in making advanced composites. The isothermal viscosity in 280 °C of PEI-PEPA containing 15 wt% ODA-PEPA reactive diluent decreased by two thirds, due to the low molecular weight of ODA-PEPA. The cured blends demonstrated high thermal stability and heat resistance. 5 wt% thermal decomposition temperatures (Td5) of the cured blends were above 549 °C and 547 °C in N2 and air atmosphere, respectively. The char yield reported at 800 °C in N2 atmosphere increased from 58.8% to 63.7 % with the addition of ODAPEPA. Meanwhile, the cured polyimides blends possessed good bond strength (> 9.3 MPa).

Highly Soluble Phenylethynyl-terminated Imide Oligomers and Thermosetting Polyimides Based on 2,2′,3,3′-Biphenyltetracarboxylic Dianhydride

The properties of a series of imide oligomers were characterized according to their molecular weights, solubility, and thermal and rheological properties. This series of imide oligomers was synthesized via a two-step method using 2,2′,3,3′-biphenyltetracarboxylic dianhydride(3,3′-BPDA) and aromatic diamines as the monomers, and 4-phenylethynyl phthalic anhydride(PEPA) as the end-capping agent. The imide oligomers based on 3,3′-BPDA showed excellent solubility in low boiling point solvents and low melt viscosity, which were attributed to their unique bent architectures. High-performance thermosetting polyimides were produced from these oligomers via thermal crosslinking of the phenylethynyl groups. The mechanical and thermal properties of the thermosets were studied using tensile testing, dynamic mechanical thermal analysis(DMTA), and thermogravimetric analysis(TGA). The 3,3′-BPDA-based thermosets exhibited excellent thermal properties, with glass transition temperatures of up to 455 °C, and 5% mass loss temperatures of up to 569 °C in air. The thermosets based on 3,3′-BPDA showed superior thermal properties compared to those derived from TriA-X series oligomers.

Heat-resistant sandwich structure with carbon fiber-polyimide composite faces and a carbon foam core

This paper presents the processing and properties of a new heat-resistant sandwich structure, which consist of carbon fiber-polyimide composite face sheets and a carbon foam core. A novel phenylethynyl-terminated imide oligomer (TriA-X) was applied for both matrix resin and film adhesive. Mechanical properties of the sandwich structures were evaluated using flat-wise tension tests, and three-point bending tests. Bending strength of the sandwich panel was almost constant up to 250 °C. The bending rigidity of the sandwich panels showed good agreement with the numerical result by considering the temperature-dependent elastic modulus of CFRP and carbon foam. Thermal insulating properties of the sandwich structures were evaluated using infrared lamp heating tests in a vacuum chamber, resulting in good thermal insulating property. Heat transfer analysis of the sandwich structures was conducted using finite element method. Comparison with heating test results, the validity of the heat transfer analysis model was successfully demonstrated.

Influence of different ratios of a-ODPA/a-BPDA on the properties of phenylethynyl terminated polyimide

A series of phenylethynyl-terminated imide oligomers based on 3,4′-oxydianiline (3,4’-ODA), with different content of 2,3,3′,4′-oxydiphthalic dianhydride (a-ODPA) and 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), have been prepared by chemical imidization process. The effects of different dianhydrides ratios on curing behavior, solubility, melt viscosity of oligomers, glass transition temperature (Tg), coefficient of thermal expansion (CTE), thermal stability, mechanical performance of films, and adhesive properties were evaluated systematically. The prepared oligomers with more content of a-ODPA exhibited sufficient solubility in some solvents, lower melt viscosity and better adhesion. The cured resins with more content of a-BPDA exhibited lower CTE value, higher Tg and thermal stability in N2 and air atmosphere. The Tg value of the cured a-BPDA/3,4’-ODA/PEPA system (Oligo-5) was 338 °C by tan δ. Meanwhile, the obtained polyimide films based on a-ODPA/a-BPDA monomers possessed high tensile strength (> 98.0 MPa) and strain (> 10.3%). These detailed results may provide some help to choice suitable matrix resin for structural adhesive and high-performance resin-based composite materials.

Synthesis and characterization of a carborane-containing monofunctional imide monomer as a modifier for imide oligomer

A novel carborane-containing imide monomer (CB-PEPA) was synthesized and used as a modifier for phenylethynyl-terminated imide oligomer (PI-mPDA) to study the effect on the performance of the oligomers and thermosetting polyimide materials. The curing behavior of the blends of CB-PEPA and PI-mPDA was investigated by differential scanning calorimetry (DSC). It showed that CB-PEPA had a melting point at 183°C. Nonisothermal DSC showed that imide monomer had higher activation energy than that of bifunctional imide oligomer. Rheometer study showed that the monomer CB-PEPA could be used as a reactive diluent for PI-mPDA to reduce the minimum melt viscosity and broaden the process window of imide system. Thermogravimetric analysis showed that the char yield of resin increased with the addition of CB-PEPA. The resin derived from a 25 wt% CB-PEPA loading in PI-mPDA exhibited a high char yield of 81.0% at 800°C in nitrogen. Due to the steric hindrance and rigid group of carborane, the Tg of composites also increased with the addition of CB-PEPA. Composites derived from a 10 wt% CB-PEPA loading in PI-mPDA exhibited the relatively higher flexural strength and interlaminar shear strength.

Development of novel cardo-containing phenylethynyl-terminated polyimide with high thermal properties

A phenylethynyl-terminated reactive diluent [Card-4-phenylethynylphthalic anhydride (PEPA)], which contained fluorenyl cardo structures, was successfully synthesized and used as a modifier for flexible phenylethynyl-terminated imide oligomer (PEI-PEPA). The chemical structure, crosslink characterization, molecular weights, and thermal properties of the products were characterized. The imide systems with addition of 10, 20, 30, and 40 wt% Card-PEPA to PEI-PEPA (PEI-PEPA-Card) and their cured resin systems were prepared. The thermal curing behaviors of imide systems at different heating rates were analyzed by using differential scanning calorimetry. Thermal properties such as glass transition temperature (Tg) and char yield at 800°C of the resultant resin systems were studied by differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The rheological properties were also investigated using a dynamic rheometry. These properties were found to be outstanding compared with pure PEI-PEPA. The uncured imide systems exhibited lower Tg and lower isothermal viscosity with addition of Card-PEPA. Furthermore, the Tg and char yield of the cured resin systems increased with addition of Card-PEPA. The cured resin systems containing 40 wt% Card-PEPA exhibited the highest Tg of 359°C and char yield at 800°C of 66.5%. Copyright © 2016 John Wiley & Sons, Ltd.

2,3,3′,4′-Oxydiphthalic dianhydride-based phenylethynyl-terminated imide oligomers for low-temperature resin transfer molding applications

A series of imide resins were prepared using 2,3,3′,4′-oxydiphthalic dianhydride, 4-phenylethynylphthalic anhydride, and aromatic diamines (1, 3-bis(3-aminophenoxy), 3,4′-oxyaniline, 2,2′-bis (trifluoromethyl) benzidine, and m-phenylenediamine) as starting materials. These imide oligomers were characterized by means of Fourier transform infrared spectroscopy, differential scanning calorimetry, intrinsic viscosity measurements, and rheological measurements. Some of these oligomers exhibited low (&lt;1 Pa·s at 250°C) and stable (&gt;2 h at 250°C) melt viscosity, which was highly desirable for resin transfer molding process. Thermosetting polyimides (PIs) were then produced from these oligomers via thermal cross-linking reaction of phenylethynyl group. The properties of the thermosets were studied using tensile and flexural testing, dynamic mechanical thermal analysis, and thermogravimetric analysis. The cured PIs exhibited a good combination of thermal and mechanical properties, with a tensile strength of 31–76 MPa, flexural strength of 38–142 MPa, glass transition temperatures of 233–358°C, and 5% weight loss temperatures of 540–545°C under nitrogen atmosphere.

Phenylethynyl-terminated imide oligomers derived from thioetherdiphthalic anhydride isomers with decreased melt viscosities

A series of oligomers based on the mixture of thioetherdiphthalic anhydride isomers and 4,4′-oxydianiline with 4-phenylethynylphthalic anhydride as reactive endcapping reagent were prepared. The calculated molecular weights were in the range of 1150–5070 g mol−1 with different degrees of polymerization ( n = 1, 3, 5, 7, and 9). The effect of molecular weight of the aromatic oligomers on their processability and solubility as well as the thermal and mechanical properties of the thermal-cured polyimides (PIs) was systematically investigated. The typical oligomer (Oligo-1) could be melted at temperatures of 289–334°C to yield stable molten fluid with melt viscosity below 1.0 Pa s. The melt viscosity of the oligomers increased with the increasing molecular weight. After thermally curing at 370°C, the thermoset PIs exhibited good thermal properties. The glass transition temperatures of oligomers measured by differential scanning calorimetry were in the range of 286–326°C, and the temperature of 5% weight loss was higher than 524°C. The cured films also showed good mechanical properties with tensile strength above 72 MPa and modulus more than 2.5 GPa.

Non-isothermal curing kinetics, chemorheological behaviour, and IR spectral study of two trifunctional phenylethynyl-terminated imide oligomers compared with the corresponding bifunctional structure

Two trifunctional phenylethynyl-terminated imide oligomers, m-TPEPA and p-TPEPA, were systematically compared with the corresponding bifunctional phenylethynyl-terminated imide oligomer, BPEPA. The non-isothermal curing kinetics, Master Plots method, and rheological behaviour of the three high performance oligomers were systematically studied by dynamic DSC, small amplitude oscillatory shear rheometry, and infrared spectroscopy. The results show that the activation energy ( Ea) depended on the extent of conversion evaluated with three different methods, and the lower Ea values of the trifunctional oligomers, which may lead to different curing reactions, compared with the sustained growth of Ea values of BPEPA. The chemorheological properties of the oligomers were measured and fit numerically with the dual Arrhenius model and gel model. Moreover, the degree of cure (agel ) at the gel time (tgel ) was calculated by the value of glass transform temperature at different curing temperature combined with rheological and isothermal DSC results. According to structural changes during the curing reaction characterised using FTIR spectra, it was inferred that the structures of the cured trifunctional imide resins have cis-configurations, which may change the part of the configuration from cis to trimerisation with the lower activation energies found in the later part of the conversion, while the difunctional imide structure is trans.

Rheological behaviour and cure kinetic studies of a trifunctional phenylethynyl-terminated imide oligomer

A phenylethynyl-terminated imide oligomer (PETI)was prepared from a triamine and 4-phenylethynylphthalic anhydride. The oligomer can be used to prepare high performance resin-based composite material via resin transfer moulding due to its low melt viscosity. The cured resin also exhibited excellent thermal stability with 5% weight loss at temperature above 531°C and higher glass transition temperature Tg (410°C) than PETI series as a result of the introduction of star-branched units. The rheological properties of the oligomer were measured and numerically fit with the dual Arrhenius model. The curing of the resin was also studied by dynamic and isothermal differential scanning calorimetry measurements. Based on the experimental data, both the curing reaction rate and the curing degree were calculated in the dynamic mode and tested under isothermal conditions.

Highly soluble phenylethynyl-terminated imide oligomers based on KAPTON-type backbone structures for carbon fiber-reinforced composites with high heat resistance

Novel addition-type phenylethynyl-containing imide oligomers (degree of polymerization: n=1–10) derived from 1,2,4,5-benzenetetracarboxylic dianhydride or pyromellitic dianhydride (PMDA), 2-phenyl-(4,4′-diaminodiphenyl ether) (p-ODA) and 4-phenylethynylphthalic anhydride (PEPA) were prepared and evaluated as a matrix resin for high heat-resistant carbon fiber-reinforced composites. The uncured imide oligomers showed good solubility (>30 wt%) in N-methyl-2-pyrrolidone and very low melt viscosities. These imide oligomers were successfully converted to crosslinked structures after curing at 370 °C. The glass transition temperature (Tg) and the elongation at break (ɛb) of the cured imide resin were found to be excellent (almost 340 °C and >15%, respectively). The carbon fiber prepreg was prepared from the imide oligomer solution and used to fabricate void-free laminates with high Tg. The thermal and mechanical properties of the laminates were determined at ambient temperature.

Synthesis and characterization of fluorinated polyimide oligomers terminated with a phenylethynyl group

Novel all-aromatic phenylethynyl-terminated imide oligomers were prepared by the reaction of 4,4-oxydiphthalic anhydride (ODPA) or 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 1,4-(4-amino-2-trifluoromethyl-phenoxy)-2-(3′-trifluoro-methylphenyl) benzene and 4-(1-phenylethynyl)1,8-naphthalic anhydride (PENA). The resulting polymers were thermally crosslinked at 370°C. The cured polymers exhibited good solvent resistance and high thermal stability up to 540°C under nitrogen. They also exhibited small light absorption at 1.31 and 1.55μm. The refractive index of the polymers was in the range of 1.5515–1.5976 at 1550nm. The surface relief depth of the phenylethyl terminated imide (PETI) oligomer films before and after curing was less than 1nm over a range of 1μm×1μm.

Synthesis and characterization of soluble phenylethynyl-terminated imide oligomers derived from pyromellitic dianhydride and 2-phenyl-4,4′-diaminodiphenyl ether

Novel addition-type imide oligomer (degree of polymerization: n=1–10) derived from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 2-phenyl-(4,4′-diaminodiphenyl ether) (p-ODA) which has asymmetric and non-planar structure, and 4-phenylethynylphthalic anhydride was synthesized for the matrix resin of high heat resistant carbon fiber-reinforced composites. The uncured imide oligomers (degree of polymerization: n=1–4) showed good solubility (more than 30wt.%) in aprotic solvents such as N-methyl-2-pyrrolidone (NMP). These imide oligomers also showed a very low viscosity. These data were accomplished by preventing the aggregation caused by the pendant phenyl group of p-ODA. The imide oligomers were successfully converted to cross-linked structures after curing at 370°C. The glass transition temperature and elongation at break (εb) of the cured imide resin were found to be very high (almost 360°C and >15%) respectively.

Rheological Behaviors Characterization and Modeling of a Novel Three-Branched Phenylethynyl-Terminated Imide Oligomer

To prepare novel polyimides with enhanced thermal stability and low melt viscosity, a novel three-branched phenylethynyl-terminated imide oligomer was introduced. The oligomer can be used to prepare high performance resin-based composite material via resin transfer molding (RTM) due to its low melt viscosity (&lt;2Pa.s) between 250°C and 320°C. The cured resin exhibits excellent thermal stability and higher glass transition temperature than PETI series as a result of the introduction of star-branched units. In this research, the rheological properties of the oligomer were measured and numerically fit with the dual Arrhenius model to predict the progression of the viscosity during cure. The calculated kinetic activation energies for gelation with two different Arrhenius equations, 120.8kJ/mol and 164kJ/mol, respectively,had some differences. The numerical results were compared with the experimental measurements, and it was found that the model predicts the experimental observations quite well.

Fluorinated phenylethynyl-terminated imide oligomers with reduced melt viscosity and enhanced melt stability

Two novel fluorinated phenyethynyl-contained endcapping agents, 4-(3-trifluoromethyl-1-phenylethynyl)phthalic anhydride (3F-PEPA) and 4-(3,5-bistrifluoromethyl-1-phenylethynyl)phthalic anhydride (6F-PEPA) were synthesized, which were employed to synthesize two fluorinated model compounds, N-phenyl-4(3-trifluoromethyl)-phenylethynylphthalimide (3F-M) and N-phenyl-4(3,5-bitrifluoromethyl)-phenylethynyl phthalimide (6F-M). The thermal cure kinetics of 3F-M and 6F-M were analyzed using DSC and compared to the unfluorinated derivative, N-phenyl-4-phenylethynylphthalimide (PEPA-M). The thermal cure temperatures of 3F-M and 6F-M were 399 and 412 °C, which were 22 and 35 °C higher than that of PEPA-M, respectively. The thermal cure kinetics of 3F-M and 6F-M best fit a first-order rate law, although 3F-M and 6F-M reacted slower than PEPA-M. However, the exothermic enthalpy of 3F-M and 6F-M were only half of PEPA-M. Based on the model compounds study, a series of fluorinated phenylethynyl-terminated imide oligomers (F-PETIs) with different calculated molecular weights (Calc'd Mn) were synthesized by thermal polycondensation of 2,3,3′,4′-biphenyltetracarboxylic acid dianhydride (a-BPDA) and 3,4′-oxydianiline (3,4′-ODA) using 3F-PEPA or 6F-PEPA as the endcapping agent. The substituent effects of the trifluoromethyl (−CF3) groups on the thermal cure behavior and melt processability of F-PETIs were systematically investigated. Experimental results reveal that the melt processability of F-PETI was apparently improved by the reduced resin melt viscosities and the enhanced melt stability due to the incorporation of the −CF3 groups in the imide backbone. All of those F-PETIs exhibit outstanding thermal and mechanical properties.