Phenylethynylnaphthalic endcapped imide oligomers with reduced cure temperatures

A series of 4-(2-phenylethynyl)-1,8-naphthalic anhydride (PENA) endcapped imide oligomers with different chemical backbones and calculated number average molecular weights (Calc’d M_n) were successfully synthesized and characterized. The PENA-endcapped imide oligomers were mixtures of mono- and double-endcapped imide oligomers with polymerization degree (P_n) of 1-5 and number average molecular weights (M_n) of 2515-3851 g/mol. determined by GPC. Study on effect of chemical structures on the curing behaviors of two model compounds: PENA-m based on PENA and PEPA-m derived from 4-phenylethynylphthalic anhydride (PEPA) revealed that PENA-m showed the cure temperature of 50 °C lower than PEPA-m and the activity energy of thermal curing reaction for PENA-m was also lower than that of PEPA-m. The PENA-endcapped imide oligomers could be melt at temperatures of >250 °C with the minimum melt viscosity of 1.2-230 Pa s at 275-301 °C and the widen melt processing windows, along with 10-40 °C lower cure temperature than the PEPA-endcapped analogue.The PENA-endcapped imide oligomers could be thermally cured at 350 °C/1 h to afford the thermally cured polyimides with good combined thermal and mechanical properties including T_g of 344-397 °C (DMA), T_d of 443-513 °C, tensile strength of as high as 54.7 MPa, flexural strength of as high as 126.1 MPa and modulus of as high as 2.3 GPa, respectively.     

Hyperbranched aromatic poly(ether imide)s: Synthesis,characterization, and modification

The synthesis and characterization of hyperbranched aromatic poly(ether imide)s are described. An AB₂ monomer, which contained a pair of phenolic groups and an aryl fluoro moiety activated toward displacement by the attached imide heterocyclic ring, was prepared. The nucleophilic substitution of the fluoride with the phenolate groups led to the formation of an ether linkage and, subsequently, to the hyperbranched poly(ether imide), which contained terminal phenolic groups. A similar one‐step polymerization involving a monomer that contained silyl‐protected phenols yielded a hyperbranched poly(ether imide) with terminal silylated phenols. The degree of branching of these hyperbranched polymers was approximately 55%, as determined by a combination of model compound studies and ¹H NMR integration experiments. End‐capping reactions of the terminal phenolic groups were readily accomplished with a variety of acid chlorides and acid anhydrides. The nature of the chain‐end groups significantly influenced physical properties, such as the glass‐transition temperature and the solubility of the hyperbranched poly(ether imide)s. As the length of the acyl chain of the terminal ester groups increased, the glass‐transition temperature value for the polymer decreased, and the solubility of the polymer in polar solvents was reduced, becoming more soluble in nonpolar solvents. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2536–2546, 2001     

Soluble and curable prepolymers from polyallyl ester monomers containing aromatic imide groups

Five polyallyl ester monomers that contain aromatic imide groups were synthesized as thermally stable laminating resins. From these monomers soluble and low-melting prepolymers were obtained by radical polymerization in aprotic polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, or N-methyl -2-pyrrolidone. The prepolymers are oligomeric compounds in which DP = 3–6 and have lower melting points than the corresponding monomers. It is assumed that the reaction of solvent molecule participates in the polymerization. Whereas, the bulk and the solution polymerization in n-butyl acetate or n-propyl alcohol yielded insoluble and infusible polymer. The relatively low-melting prepolymers were curable at 150–180°C without the evolution of volatile by-products. Resulting glass-fiber laminates have no glass transition point below 300°C and thermooxidative stability at 330°C.     

Phenylethynyl-terminated imide oligomers and polymers therefrom

Two new phenylethynyl endcapping compounds, 3- and 4-amino-4′-phenylethynylbenzophenone, were synthesized and used to terminate imide oligomers from 3,4′-oxydianiline and 4,4′-oxydiphthalic anhydride at a calculated molecular weight of 9000 g/mol and from 3,4′-oxydianiline (0.85 mol), 1,3-bis (3-aminophenoxy) benzene (0.15 mol), and 3,3′,4,4′-biphenyltetracarboxylic dianhydride at a calculated molecular weight of 5000 g/mol. Glass transition temperatures for the cured oligomers were ～ 249°C for the former and 272°C for the latter. Films cured at 350°C for 1 h were tough and flexible and provided high tensile properties. The uncured oligomers were readily compression molded to provide tough, solve nt-resistant moldings. © 1994 John Wiley & Sons, Inc.     

3‐Phenylethynyl phthalimide end‐capped imide oligomers and the cured polymers

In the past decades, 4‐phenylethynyl phthalic anhydride (4‐PEPA) has been the most important endcapper used for thermoset polyimide. As the isomer of4‐PEPA, 3‐phenylethynyl phthalic anhydride (3‐PEPA) has attracted our interest. In this article, 3‐PEPA was synthesized and a comparative study with 4‐PEPA on curing temperature, curing rate, thermal and mechanical properties of oligomers and cured polymers was presented. The new phenylethynyl endcapped model compound, N‐phenyl‐3‐phenylethynyl phthalimide, was synthesized and characterized. The molecular structure of model compound was determined via single‐crystal X‐ray diffraction and the thermal curing process was investigated by Fourier transform infrared. Differential scanning calorimetry clearly showed that the model compound from 3‐PEPA had about 20 °C higher curing onset and peak temperature than the 4‐PEPA analog. This result was further proved by the dynamic rheological analysis that the temperature of minimum viscosity for oligomers end‐capped with 3‐PEPA was above 20 °C higher than that of the corresponding 4‐PEPA endcapped oligomers with the same calculated number average molecular weight. The cured polymer from 3‐PEPA displayed slightly higher thermal oxidative stability than those from 4‐PEPA by thermogravimetric analysis. The thermal curing kinetics of 3‐PEPA endcapped oligomer (OI‐5) and 4‐PEPA endcapped oligomer (OI‐6) fitted a first‐order rate law quite well and revealed a similar rate acceleration trend. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4227–4235, 2008     

Cyclopolycondensation. XII. Polymerization mechanism of polybenzoxazinones in polyphosphoric acid medium

The polymerization mechanism of polyphosphoric acid (PPA) solution polymerization of an aromatic diaminodicarboxylic acid with aromatic dicarboxylic acid derivatives was studied. By means of NMR methods, the initiation process for the polymerization of polybenzoxazinone in PPA medium was elucidated. The NMR spectra of a series of compounds were taken, and the salt formation of amino groups of monomer with PPA and the equilibrium between the salt and the free amino group were determined. It was established that the polymerization proceeded through the formation of phosphorylated intermediates to give the salt of amino groups of monomer with PPA. In the second step, the amine–PPA salt dissociates into the free amino group and PPA at the polymerization temperature above 140°C. Polymerization proceeds through the attack of “free” amino on phosphorylated carbonyl compounds to form polyamide acid of high molecular weight, and on subsequently being heated in PPA at higher temperatures, it undergoes an intramolecular cyclodehydration along the polymer chain to form polybenzoxazinones.     

A study of the kinetics of the microwave cure of a phenylethynyl‐terminated imide model compound and imide oligomer (PETI‐5)

The kinetic mechanism of the microwave cure of a simple phenylethynyl‐terminated imide model compound, 3,4′‐bis[(4‐phenylethynyl)phthalimido]diphenyl ether (PEPA‐3,4′‐ODA) and a phenylethynyl‐terminated imide oligomer (PETI‐5, M_n 5000 g/mol) was studied. Dielectric properties of the model compound and PETI‐5 were measured in the microwave range from 0.4 GHz to 3 GHz. FTIR was used to follow the cure of the model compound (PEPA‐3,4′‐ODA), while thermal analysis (DSC) was used to follow the cure of the PETI‐5 oligomer. The changes in room temperature IR absorbance of phenylethynyl triple bonds at 2214 cm⁻¹ of PEPA‐3,4′‐ODA as a function of cure time were measured after cure temperatures of 300, 310, 320, and 330 °C. The changes in the glass‐transition temperature, T_g, of PETI‐5 as a function of cure time were measured after cure at 350, 360, 370, and 380 °C, respectively. The T_g 's were determined to calculated the relative extent of cure, x, of the PETI‐5 oligomer according to the DiBenedetto equation. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 27.6 kcal/mol as determined by infrared spectroscopy. For PETI‐5, the reaction followed 1.5th order, yielding an activation energy of 17.1 kcal/mol for the whole cure reaction, as determined by T_g using the DiBenedetto method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2526–2535, 2000     

Synthesis and characterization of polyimides endcapped with phenylethynylphthalic anhydride

The synthesis of high glass transition temperature (T_g > 300°C), amorphous, soluble, poly-imide oligomers of controlled molecular weight endcapped with 4-phenylethynylphthalic anhydride endcapping agent is described. The 4-phenylethynylphthalic anhydride was employed to afford a higher curing temperature (380–420°C) which widens the processing window compared to unsubstituted acetylene-endcapped polyimides. The polyimides were synthesized via solution imidization techniques, using the ester-acid of various dianhydrides and aromatic diamines. A “ one-pot” procedure utilizing NMP as the solvent and o-dichlo-robenzene as the azeotroping agent reproducibly produced fully imidized, but yet soluble wholly aromatic polyimides. Thermally cured samples were prepared with gel contents of up to 98% that displayed good solvent resistance. Glass transition temperatures comparable to high molecular weight linear analogs were produced. These polyimides also show excellent thermal stability as judged by thermogravimetric analysis (TGA). Model phenylethynyl imide compounds were synthesized and used to follow and elucidate the nature of the products formed from the phenylethynyl curing by using high temperature magic-angle ¹³C nuclear magnetic resonance (MAS NMR). Preliminary results indicate that the cure reaction can be followed by MAS NMR. However, the nature of the products being formed during the curing process is difficult to determine by the solid-state MAS NMR alone. Differential scanning calorimetry (DSC) data clearly show that the model system does indeed melt and displays a wide window before the strong cure exotherm is observed. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of new polyimides containing ethynylene linkages

We have synthesized a series of new diamines containing bis(ethynylaniline) linkages by bromine substitution reaction of ethynylaniline with 4,4′-bis(4-bromophthalimido)diphenylether (PODA) or 1,4-bis(4-bromophthalimido)benzene (PPDA). The intermediates were separated at each step, purified and characterized by the spectroscopic techniques. The model compound having imide and triple bond moiety was synthesized in order to elucidate the nature of the products formed from the ethynyl curing by FT-IR spectroscopy. The polymerization reaction of ethynylaniline diamines with various dianhydrides gave fully imidized and soluble aromatic polyimides. The thermally cured polyimide samples displayed good solvent resistance. The thermal crosslinking of triple bond moieties in the main chain was carried out by heating in the temperature range from 150 to 400 °C. The glass transition temperature of polyimide completely disappeared after heat treatment at 400 °C for 5 min. The polyimides derived from diamines containing bis(ethynylaniline) groups were thermally stable after heat treatment.     

Novel method for preparation of poly(benzoxazinone‐imide)

A novel method was developed to prepare poly(benzoxazinone‐imide) by the dealcoholization of poly(amide‐imide), having pendent ethoxycarbonyl groups, which was prepared from poly(amide acid). The poly(amide acid) was prepared from the reaction of pyromellitic dianhydride and 4,4′‐diamino‐6‐ethoxycarbonyl benzanilide. The curing behavior of the poly(amide acid) was monitored by DSC, which indicated the presence of two broad endotherms, one with maximum at 153 °C due to imide‐ring formation and the other with maximum at 359 °C due to benzoxazinone‐ring formation. The poly(amide acid) was thermally treated at 300 °C/1 h to get poly(amide‐imide) with pendent ester groups, then at 350 °C/2 h to convert into poly(benzoxazinone‐imide) by dealcoholization. Viscoelastic measurements of the poly(amide‐imide) showed that the storage modulus dropped at about 280 °C with glass‐transition temperature (T_g ) at about 340 °C. The storage modulus of poly(benzoxazinone‐imide), however, was almost constant up to 400 °C and no T_g was detected below 400 °C. Also, the tensile modulus and tensile strength of the poly(benzoxazinone‐imide) was much higher than that of the poly(amide‐imide). The 5% decomposition of poly(benzoxazinone‐imide) film was at 535 °C, which reflects its excellent thermal stability. Also, poly(benzoxazinone‐imide) showed more hydrolytic stability against alkali in comparison to polyimides. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1647–1655, 2000     

Synthesis of novel liquid crystal compounds with aromatic amide mesogenic cores

The synthesis and properties of a new series of compounds having aromatic amide mesogenic cores are reported. Most of these new compounds are thermotropic mesogens. In consideration of the fact that aromatic amides form crystals of high melting point which is unfavourable for the formation of thermotropic liquid crystals, we make use of lateral substitution to decrease both the packing efficiency and the hydrogen bonding, so that the melting temperature of the aromatic amides is sufficiently depressed. The lateral substituent used in these new compounds is bromine. In order to investigate the influence on properties of the end groups, different alkoxy, alkyl and other groups are used at the two ends of the rod-like molecules. The two ends are either identical or different, with an electron-donating alkoxy as one end and the electron-accepting cyano group as the other. The results indicate that appropriate lateral and terminal substitution is essential for the aromatic amides to form thermotropic liquid crystals. The peculiar mesophase characterized by an X-ray diffraction pattern of a SmC phase, but a texture of a nematic phase is also noted.     

Curing Studies of New Polyimide Model Compounds with Molecular Weights of About 1000 g/MOL

Abstract

Two new polyimide model compounds with molecular weights of ～1000 g/mol have been synthesized. While the amino terminated compound, 4,4′-bis-N-[N′-(4-aminophenoxy-4′-phenyl)-pyromellitimido]diphenylether,O(PO)₂, undergoes a branching or crosslinking side reaction, the corresponding anhydride terminated oligomer N,N′-bis[4(N-(3′,4′-bishydroxycarbonyl)phthal-imido)phenoxy-4′-phenyl]pyromellitimide dianhydride, P(OP)2, loses its anhydride functionality completely upon thermal treatment. In the case of O(PO)₂, the formed C=N species can be detected with Raman spectroscopy rather than FT-IR spectroscopy because of its low molecular absorptivity in the infrared region. The formation of imine bonds caused by the attack of terminal amino groups on the imide carbonyl group is evident by the appearance of peaks at about 1665 cm-¹ in the Raman spectra. The same behavior can be observed in bulky polyimides blended with an increasing amount of O(PO)2 upon curing.     

Benzocyclobutene in polymer synthesis. II. Solid state diels–alder polymerization utilizing an in situ generated diene and an alkyne

A novel class of aromatic imide AB-monomers with benzocyclobutene and an alkyne (primarily phenylethynyl group) as the reactive units have been prepared. The monomers have been utilized in thermally induced Diels–Alder polymerizations. The differential scanning calorimetric study of the AB-monomers provided two observations: (i) primary acetylene began its homopolymerization (202°C max.) before the electrocyclic ring opening of benzocyclobutene (270°C max.); (ii) the phenoxy group connecting between phenylacetylenyl group and the aromatic imide fragment suppressed polymerization in Diels–Alder fashion. Furthermore, thermoxidative stability evaluation on the cured samples (250°C for 8 h and then 350°C for another 8 h under N₂ atmosphere), carried out at 650°F (air) for 200 h, indicated the more rigid phenylethynyl phthalimide system was the most heat-resistant.     

Hydrazine-based polyimides and model compounds

The reaction of hydrazine hydrate with aromatic anhydrides may give either N-amino imides or cyclohydrazides. The conditions that favor the formation of N-aminoimides, in which the imide contains respectively a 5- and 6-membered ring, are discussed. These compounds may be reacted with aromatic anhydrides to give N-N-linked imides. The properties of a number of model compounds and polymers are described, and it is shown that those compounds which have alternating 5- and 6-membered imide rings give the maximum oxidative stability in air at 400°C.     

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 phtlialic 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′EPDA-based thermosets exhibited excellent thermal properties, with glass transition temperatures of up to 455℃, and 5% mass loss temperatures of up to 569℃ in air. The thermosets based on 3,3-BPDA showed superior thermal properties compared to those derived from TriA-X series oligomers.     

In situ EPR spectroscopy of aromatic diyne cyclopolymerization

Electron paramagnetic resonance (EPR) spectroscopy was successfully used for the first time to follow the Bergman cyclization of bis-ortho-diynyl arene (BODA) compounds. Five BODA monomers with different spacer (X) and terminal groups (R) were compared. In situ polymerization via EPR spectroscopy yielded first-order rate expressions. Monomers with spacer -O- or -C(CF(3))(2) and terminal group R = Ph exhibited similar kinetic behavior upon thermal polymerization, whereas monomers with pyridine and thiophene terminal groups gave significantly higher rates of polymerization over phenyl-terminated derivatives. A model compound, 1,2-bis(phenylethynyl)benzene, was used to probe the polymerization mechanism, and radical intermediates were found to be stable indefinitely at room temperature.     

Study of the reaction mechanism of the copper chelate with DGEBA using DSC

The reaction mechanism of metal-containing and complex compound with epoxy oligomer of diglycidyl ether of bisphenol A (DGEBA) was studied using dynamic DSC technique. It is shown that cure reaction of the epoxy oligomers with copper acetate proceeds at two stages: through coordination of cation with the epoxy group, and through ionic polymerization at high temperatures. Mechanism of curing of DGEBA with copper chelate depends on equilibrium process of dissociation of the chelate which, in turn, depends not only on temperature of curing but also on concentration of the hardener. At the dissociation temperature of the hardener, polymerization proceeds according to ionic mechanism. Hardening of the epoxy oligomers due to interaction of epoxy groups with unconnected amine groups predominate at higher temperatures or at higher concentrations of the hardener. At low temperatures and small concentrations of the hardener, polymerization proceeds according to catalytic ionic mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of β-amino carbonyl compounds via a Zn(OTf)2-catalyzed cascade reaction of anilines with aromatic aldehydes and carbonyl compounds

A Zn(OTf)₂-catalyzed cascade reaction of anilines with aromatic aldehydes and carbonyl compounds was described. This one-pot three-component reaction afforded the corresponding β-amino carbonyl compounds, β-amino esters, and β-amino ketones in good to excellent yields. The reaction was also applied for the liquid-phase synthesis of β-amino carbonyl compound library using PEG as a support.     

Thermal analysis of phenylethynyl end-capped fluorinated imide oligomer afr-pepa-4

Thermal analysis of phenylethynyl end-capped imide oligomer AFR-PEPA-4 was performed to characterize cure reaction, thermal stabilities and semicrystalline behavior of AFR-PEPA-4 oligomer and its cured polyimide. Cured AFR-PEPA-4 polyimide showed high T _gs up to 418°C. Both AFR-PEPA-4 oligomer and polyimide exhibit excellent thermal stabilities comparable to PETI-5 polyimides. AFR-PEPA-4 imide oligomer has a T _m of 330°C and exhibits spherulite crystalline morphology in the film. The crystallinity in AFR-PEPA-4 films could not be regenerated under any annealing conditions after the initial melt.     

Synthesis and characterization of phenylethynyl-terminated polyimide oligomers derived from 2,3,3′,4′-diphenyl ether tetracarboxylic acid dianhydride and 3,4′-oxydianiline

With the goal of improving processability of imide oligomers and achieving high toughness of thermosetting polyimides, a series of 4-phenylethynylphthalic anhydride(PEPA)-terminated imide oligomers prepared by the reaction of 2,3,3',4'-diphenyl ether tetracarboxylic acid dianhydride(a-ODPA) and 3,4'-oxydianiline(3,4'-ODA) with different molecular weights(degree of polymerization: n = 1?9) were formed. The resultant oligomers with different molecular weights were characterized for their chemical architecture, cure behavior, thermal properties, solubility in organic solvents and rheological characteristics. Besides, the thermal properties and tensile test of cured polyimide films were also evaluated. The imide oligomer(degree of polymerization: n = 1) has some somewhat crystalline phase, and imide oligomers(degree of polymerization: n = 2?9) showed excellent solubility(40 wt%) in N-methyl-2-pyrrolidone(NMP) and N,Ndimethylacetamide(DMAc) at room temperature. Furthermore, the rheological properties of imide oligomers showed very low melt viscosity and wider processing window. The cured films exhibited good thermal properties with the glass transition temperatures of 282?373 ?C and 5 wt% thermal decomposition temperatures higher than 551 ?C in nitrogen atmosphere. The elongation at break of the prepared films was found to be high(almost 9.3%).