Thermal degradation kinetics of polyimide containing 2,6-benzobisoxazole units

A novel polyimide (PI) based on 2,6-bis(p-aminophenyl)-benzo[1,2-d;5,4-d′]bisoxazole has been synthesized via a conventional two-stage procedure with bis(ether anhydrides) (HQDPA). The intermediate poly(amic acid) had inherent viscosities of 1.70 dl/g and could be thermally converted into light yellow polyimide film. The resulted polyimide showed excellent thermal stability, and the glass transition temperatures (T_g) were above 283 °C, the 5% weight loss temperature of the polymer was at 572 °C in N₂. The thermal degradation of the polyimide was studied by thermogravimetric analysis (TGA) in order to determine the actual reaction mechanisms of the decomposition process. The activation energy of the solid-state process was determined using Flynn-Wall-Ozawa method, which does not require knowledge of the reaction mechanism, which resulted to be 361.36 kJ/mol. The activation energy of different mechanism models and pre-exponential factor (A) were determined by Coats-Redfern method. Compared with the value obtained from the Ozawa method, the actual reaction mechanism obeyed nucleation and growth model, Avrami-Erofeev function (A₃) with integral form g(X) = [−ln(1−X)]³.     

Synthesis, characterization, and thermal properties of new silarylene-siloxane-acetylene polymers

New silarylene-siloxane-acetylene polymers have been synthesized by coupling reactions employing 1,3-bis(p-ethynylphenyl)-1,1,3,3-tetraphenyldisiloxane (3) as the key monomer. Their thermal properties have been evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). All of the new polymers showed good thermal stability, with their temperatures at 5% weight loss (T_d5) being higher than 540 °C under nitrogen and higher than 460 °C in air. Their char yields at 1000 °C under N₂ were above 80%. Broad exothermic peaks, attributable to reaction of the acetylenic units, were observed by DSC analysis in the temperature range 270-450 °C.     

Synthesis of novel Y-type polyurethane containing azomethine moiety, as non-linear optical chromophore and their properties

3,4-Di-(2′-hydroxyethoxy)-4′-nitrobenzylidene II was prepared by condensation reaction of 3,4-dihydroxy-4′-nitrobenzylidene I with 1-chloro-2-ethanol. Monomer II was reacted with p-phenylene diisocyanate to yield polyurethane containing the non-linear optical chromophore 3,4-di-(2′-hydroxyethoxy)-4′-nitrobenzylidene. Polymer III shows thermal stability up to 300 °C in TGA thermogram. T_g value of the polymer obtained from DSC thermogram was 110 °C. The resulting polyurethane III was soluble in common organic solvents such as acetone, DMF and DMSO. The values of electro optic coefficient d₃₃ and d₃₁ of the poled polymer film were 3.15 × 10 ⁻⁷ and 1.5 × 10 ⁻⁷ esu, respectively.     

Synthesis and properties of a poly(diphenylacetylene) containing carbazolyl groups

1-(p-N-Carbazolylphenyl)-2-phenylacetylene (p-CzDPA) was polymerized by TaCl₅–co-catalyst systems (cocatalysts: n-Bu₁Sn, Et₃SiH, and 9BBN) to produce acetone-insoluble polymers in about 60-70% yields. Poly(p-CzDPA) was a yellowish-orange solid, most part of which was soluble in toluene, chloroform, etc., and its weight-average molecular weights were around 4×10⁵. This polymer formed a tough film by solution casting, and was thermally very stable (the onset temperature of weight loss in TGA in air 470°C). The oxygen per-meability coefficient of the polymer at 25°C was lower than two barrers. The present polymer showed photoconductivity and redox activity. © 1995 John Wiley & Sons, Inc.     

Molecular design, synthesis and electro-optic properties of novel Y-type polyurethanes with high thermal stability of second harmonic generation

2,4-Di-2^′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3^′-dimethoxy-4,4^′-biphenylenediisocyanate to yield unprecedented novel Y-type polyurethanes (4-5) containing 2,4-dioxybenzylidenemalononitrile group as a nonlinear optical (NLO) chromophore, which constitutes a part of the polymer backbone. The resulting polyurethanes 4-5 were soluble in common organic solvents such as acetone and DMF. Polymers 4-5 showed a thermal stability up to 260 °C from thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) giving T_g values around 143-156 °C. The approximate lengths of aligned NLO-chromophores estimated from AFM images of poled polymer films were about 10 nm. The SHG coefficients (d₃₃) of poled polymer films were around 7.4 × 10⁻⁹ esu. These Poled polymers exhibited a greater thermal stability of dipole alignment even at 10 °C higher than T_g, and no SHG decay was observed below 155 °C due to the partial main chain character of the polymer structure and extensive hydrogen bonds between urethane linkage, which is acceptable for NLO device applications.     

Structure and thermal degradation of poly(vinyl chloride) synthesized by various polymerization catalyst

Relationship between the structure and the thermal stability of poly(vinyl chloride) synthesized by various polymerization catalysts was investigated. The Cp∗Ti(OPh)/MAO catalyst, n-butyllithium (n-BuLi), the Cu(0)/TREN/CHBr₃/DMSO catalyst, benzoyl peroxide/N,N-dimethylaniline (BPO/DMA), 2,2’-azobis(2.4-dimethylvaleronitrile) (V-65) was used as the polymerization catalyst. The temperature of 5% weight loss was in the following order; Cp∗Ti(OPh)₃/MAO (280 °C) > n-BuLi (264 °C) > V-65 (249 °C) > Cu(0)/TREN/CHBr₃/DMSO (215 °C) > BPO/DMA (209 °C), and the rate of weight loss was the reverse order of T_−5% in the isothermal degradation of the polymer from 160 °C to 220 °C. The T_−5% value of the polymer obtained from the polymerization with Cp∗Ti(OPh)₃/MAO catalyst increased with an increase of the molecular weight of PVC, in contrast to that PVC obtained with the radical initiator did not depend on the molecular weight of the polymer. The T_−5% value of PVC macromonomer was 285 °C, while the temperature of non-functionalized PVC was 262 °C, respectively. It is clear that the PVC macromonomer had a good thermal stability regardless of low-molecular weight.     

Preparation and properties of high performance bismaleimide resins based on 1,3,4-oxadiazole-containing monomers

In research towards high performance polymeric materials, two novel series of bismaleimide (BMI) resins based on 1,3,4-oxadiazole-containing monomers have been designed and prepared by the copolymeriziation reaction of 5-tert-butyl-1,3-bis[5-(4-maleimidophenyl)-1,3,4-oxadiazole-2-yl]benzene (Buoxd) or 4,4′-bis[5-(4-maleimidophenyl)-1,3,4-oxadiazole-2-yl]diphenyldimethylsilane (Sioxd) and 4,4′-bismaleimidodiphenylmethane (BMDM) in different feed ratios. The structures, thermal and dynamic mechanical properties of all the resulting BMI resins were carefully characterized by a combination of methods such as IR, DSC, TGA and DMA. Investigation of the copolymerization process has shown that with an increase of the weight ratio of Buoxd or Sioxd, melting transition temperature (T_m) of BMI monomer mixtures decreased and the exothermic polymerization temperature (T_p) increased. For all BMI monomer mixtures, a rapid polymerization process was observed in the early stage, as shown by the IR investigations. No glass transition was observed for the resulting BMI resins in the temperature range from 50 °C to 350 °C, indicating the formation of highly cross-linking networks. The initial thermal decomposition temperatures (T_d) of the BMI resins were in the range of 477-493 °C in nitrogen and 442-463 °C in the air. Dynamic mechanical analysis (DMA) of the composites made of the BMI resins and glass cloth showed high bending modulus not only at room temperature (E′, 1.9-5.3 GPa) but also at high temperature, e.g., 400 °C (E′, 1.7-4.4 GPa).     

Copper/iron-catalyzed Ullmann coupling of diiodo- and dibromoarenes and diphenols for the synthesis of aryl ether macrocycles

Diiodoarenes (or dibromoarenes) reacted with diphenols, catalyzed by CuI/Fe(acac)₃ in the presence of K₂CO₃ in anhydrous DMSO at 110 °C for 7 days under nitrogen atmosphere, to afford macrocyclic aryl ethers effectively. To expand this methodology, a cyclic hepta(p-phenylene oxide) and cyclic deca(p-phenylene oxide) were synthesized in one pot. Some macrocyclic aryl ethers showed strong fluorescence in acetone at 25 °C.     

Photocrosslinkable polymers based on 4-[5-(4-hydroxyphenyl)-3-oxopenta-1,4-dienyl]phenyl-2-methacrylate: photocrosslinking studies and reactivity ratios with vinylcyclohexane

1,5-Bis(4-hydroxyphenyl)penta-1,4,dien-3-one (HPD) was synthesized using p-hydroxybenzaldehyde and acetone in the presence of hydrogen chloride gas. Acrylated derivative of HPD 4-[5-(4-hydroxyphenyl)-3-oxopenta-1,4-dienyl]phenyl-2-methacrylate (HPPMA) was synthesized by reacting HPD and methacryloyl chloride in the presence of triethylamine at 0-5 °C. Homo- and co-polymer (with vinylcyclohexane (VC)) of HPPMA was carried out in methyl ethyl ketone using benzoyl peroxide (BPO) under nitrogen atmosphere at 70 ± 1 °C. All the monomer and polymers were characterized by IR and NMR techniques. Monomer reactivity ratios were calculated using Fineman-Ross (FR), Kelen-Tudos (KT) and extended Kelen-Tudos (ex-KT) methods. Photocrosslinking nature of the polymer samples were carried out in solution phase using tetrahydrofuran (THF) solvent under high frequency UV light. Rate of photocrosslinking of the polymer samples were measured for poly(HPPMA) and for poly(VC-co-HPPMA). Thermal stability of the polymer samples was recorded using thermogravimetric analysis (TGA) method. Molecular weights (M_w and M_n) of the polymer samples were determined using gel permeation chromatographic (GPC) technique.     

Synthesis, characterization, and OLED application of oligo(p-phenylene ethynylene)s with polyhedral oligomeric silsesquioxanes (POSS) as pendant groups

Two new classes of mono- and oligo(p-phenylene ethynylene)s grafted with polyhedral oligomeric silsesquioxanes (POSS) were synthesized via ‘click’ chemistry and palladium-catalyzed Sonogashira cross-coupling. These materials with cubic silsesquioxanes are very robust with excellent thermal stability in air (T_5%loss>330 °C) and exhibited T_g>80 °C. All the compounds showed high photoluminescence with a range of blue emission and quantum yield up to 80% in the solution. Extended π conjugation molecules of oligo-pPEs POSS maintain relatively high PL quantum efficiencies in the solid state, compared to mono-pPEs POSS. A preliminary report is made of some of the materials as multilayer OLED components with active dopants PVK and PBD.     

Lyotropic liquid crystalline poly(aryl ether ketone) copolymer containing phthalazinone moiety and biphenyl mesogen

A novel lyotropic liquid crystalline material poly(aryl ether ketone) copolymer containing phthalazinone moiety and biphenyl mesogen named P-8515 was developed by a mild solution polycondensation method. The molecular weight (M_n) was 53,000 and the value of molecular weight distribution index (MDI) was 2.49 detected by GPC. The critical concentration (C^∗) of P-8515 was 36 wt% and P-8515 exhibited characteristic nematic lyotropic liquid crystalline phases in NMP solution at different concentrations and the phase morphology changed to a typical threaded texture when shear forces were induced from PLM observations. The T_g value was 238 °C and the value for 5% weight loss temperature was 515 °C in nitrogen from DSC and TGA determinations, respectively.     

Synthesis and characterization of side-chain liquid crystalline polymer containing dichroic dye monomer

A series of side-chain liquid crystalline polysiloxanes containing 1-(p-toluidino)-4-anthraquinone undecylenate (TAU) (dye-monomer) and 4-allyloxybenzoyl-4^′-(p-propyl-benzoyl)-p-benzenediol bisate (ABB) (liquid crystalline monomer) side groups were synthesized by copolymeraztion. The molecular structures of the monomers and polymers were confirmed by FT-IR spectroscopy. The optical characterization of the monomer ABB and polymers was made by using polarizing optical microscopy (POM) technique, and their thermal behaviour was investigated by thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC). The conjugate action of the dye (1-(p-toluidino)-4-hydroxyl anthraquinone) and the monomer was analyzed by fluorophotometry. Polymers and monomer ABB revealed nematic phase. And DSC results demonstrated that the glass transition temperatures (T_g) of the polymers increased with the increase in dye-monomer. TGA result showed that the temperatures at which 5% mass loss occurred () for all the polymers were above 270 °C.     

Single-center vs. multi-center post-metallocene catalysts for propylene polymerization

The structural characteristics of polypropylene samples prepared with two post-metallocene catalysts based on complexes bis-{M-(3,5-di-tert-butyl-salicylidene)-4-[bis-(5-methyl-2-furyl)methyl]aniline}titanium dichloride and [(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra(pentafluorophenyl)-1,3-dioxalan-4,4-dimethanol)titanium dichloride are investigated by GPC, ¹³C NMR, IR, DSC, and XRD methods. A combination of the first complex and MAO forms a single-center catalyst which polymerizes propylene to a nearly perfectly atactic polymer. A combination of the second complex and MAO forms a multi-center catalyst system producing polymer mixtures with broad molecular weight distributions containing five to six Flory components with different average molecular weights. Relative contents of the Flory components strongly depend on the type of solvent in the polymerization reactions. Some of the active centers produce high molecular weight, highly isotactic crystalline material with the melting point over 154 °C. The nature of steric errors in these polymer fractions (determined by ¹³C NMR) can be explained by a variant of stereocontrol similar to that exerted by metallocene catalysts of the C₁ symmetry.     

Structural design of imidazolium and its application in PP/montmorillonite nanocomposites

Four kinds of imidazolium surfactants with high thermal stability were designed and synthesized accordingly. The structures of these surfactants were characterized by ¹H NMR spectra. The TGA results indicated that the thermal stabilities of these surfactants with saturated alkyl groups were relatively high and the initial decomposition temperatures at 5% weight loss (T_0.05) were higher than 250 °C. Imidazolium(O) modified montmorillonite (MMT) was prepared by cation exchange. TGA results showed that the OMMT showed obviously higher thermal stability than the surfactants themselves and the T_0.05 values of OMMT were higher than 330 °C. The dihexadecane imidazolium (DHI) with two long tails has the ability to enlarge the interlayer spacing to a bigger degree compared with other imidazolium surfactants with only one long tail. Polypropylene(PP)/OMMT nanocomposites were prepared by solution blending and the effects of these surfactants with different structures on the silicate layer dispersion in PP matrix were measured.     

Facile synthesis and properties of a new generation of soluble and thermally stable polyimides

A new diamine, 1,4-phenylene bis((E)-1-(4-chloro-3-aminobenzylidene) thiourea) (PCABT), containing phenylthiourea and azomethine groups was prepared from the reduction of dinitro compound, 1,4-phenylene bis((E)-1-(4-chloro-3-nitrobenzylidene)thiourea), PCNBT. The structures of resulting monomers were characterized by elemental analysis, FTIR, ¹H and ¹³C NMR techniques. Afterwards, this diamine was reacted with various aromatic dianhydrides (ODPA, BTDA and 6FDA) in glacial acetic acid to afford poly(phenylthiourea azomethine imide)s (PPTAIs) with η_inh of 1.59-1.66 dL/g, depending on the dianhydride used. The ensuing PPTAIs exhibited ample solubility in organic solvents (DMAc, DMF, DMSO and NMP) and were obtained in quantitative yields. Also, all polyimides were amorphous according to wide-angle X-ray determination. GPC measurements of polymers revealed M_w around 69,000-72,000. Moreover, thermogravimetric analyses indicated that PPTAIs were fairly stable up to 550 °C, and 10% weight loss temperatures were recorded in the range of 563-578 °C (N₂ atmosphere). Ultimately, these polyimides own high glass transition temperatures about 281-285 °C.     

Ionic conductivity of conjugated water-soluble rigid-rod polymers

Poly[(1,7-dihydrobenzo[1,2-d:4,5-d′] diimidazole-2,6-diyl)-2-(2-sulfo)-p-phenylene], a conjugated rigid-rod polymer, was derivatized with pendants of propane-sulfonated ionomers. The derivatized rigid-rod polymer was soluble in aprotic solvents as well as in water for isotropic solutions that were processed into isotropic films. Direct-current electrical conductivity σ of the films was measured using the four-probe technique. Room-temperature σ as high as 2.9 × 10^?4S/cm was achieved on pristine isotropic films without using dopants. When the rigid-rod polymer concentration exceeded 25 wt %, the isotropic solution could be transformed into a liquid-crystalline solution that allowed deformations to be applied to produce anisotropic films. Significant increase in σ was obtained in a sheared film along both the parallel direction (∥) and the transverse direction (⊥) with a σ_∥/σ_⊥ = 5. Additionally, enhanced σ was realized in films heat-treated at about 100°C, in the derivatized polymer with higher molecular weight from dialysis, and in substituting the sulfonated ion Na⁺ by H⁺ in the pendants of the polymers. Constant-voltage measurements were applied to the polymers to monitor the σ stability for ascertaining the nature of the conductivity. No electronic contribution in σ was detected. Instead, a monotonically decreasing σ was consistently observed indicative of ionic conductivity. © 1993 John Wiley & Sons, Inc.     

Photoelectrochemical effect with poly(p-phenylene sulfide) films

Poly(p-phenylene sulfide) films coated on conducting SnO₂ and Pt surfaces were found to attain p-type semiconducting properties on electrochemical cycling. Upon illumination of these films with visible light (λ < 500 nm) a photoelectrochemical effect was observed. The performance of a photoelectrochemical cell employing this polymer film coated electrode is discussed.     

Highly phosphonated polypentafluorostyrene: Characterization and blends with polybenzimidazole

In this study we present results of the conductivity and resistance to thermooxidative and condensation reactions of a highly phosphonated poly(pentafluorostyrene) (PWN2010) and of its blends with poly(benzimidazole)s (PBI). This polymer, which combines both: (i) a high degree of phosphonation (above 90%) and (ii) a relatively high acidity (pK_a (–PO₃H₂ ↔ –PO₃H⁻) ∼ 0.5) due to the fluorine neighbors, is designed for low humidity operating fuel cell. This was confirmed by the conductivity measurements for PWN2010 reaching σ = 5 × 10⁻⁴ S cm⁻¹ at 150 °C in dry N₂ and σ = 1 × 10⁻³ S cm⁻¹ at 150 °C (λ = 0.75). Furthermore, this polymer showed only 48% of anhydride formation when annealing it at T = 250 °C for 5 h and only 2% weight loss during a 96 h Fenton test. These properties combined with the ability of the PWN2010 to form homogeneous blends with polybenzimidazoles resulting in stable and flexible polymer films, makes PWN2010 a very promising candidate as a polymer electrolyte for intermediate- and high-temperature fuel cell applications.     

Regularly alternating poly(amideimide)s containing pendent pentadecyl chains: Synthesis and characterization

Two new aromatic diamines containing preformed amide linkages, viz., N,N′-(4-pentadecyl-1,3-phenylene)bis(4-aminobenzamide) I and N,N′-(4-pentadecyl-1,3-phenylene)bis(3-aminobenzamide) II, were synthesized by reaction of 4-pentadecylbenzene-1,3-diamine with 4-nitrobenzoylchloride and 3-nitrobenzoylchloride, followed by reduction of the respective dinitro derivatives. A series of new poly(amideimide)s was synthesized by polycondensation of I and II with four commercially available aromatic dianhydrides, viz., pyromellitic dianhydride (PMDA), 4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA), and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA) in N,N-dimethylacetamide (DMAc) employing conventional two step method via poly(amic acid) intermediate followed by thermal imidization. Reference poly(amideimide)s were synthesized by polycondensation of N,N′-(1,3-phenylene)bis(4-aminobenzamide) and N,N′-(1,3-phenylene)bis(3-aminobenzamide) with the same aromatic dianhydrides. Inherent viscosities of poly(amideimide)s containing pendent pentadecyl chains were in the range 0.37-1.23 dL/g in N,N-dimethylacetamide at 30 ± 0.1 °C indicating the formation of medium to high molecular weight polymers. The poly(amideimide)s containing pendent pentadecyl chains were found to be soluble in N,N-dimethylacetamide, N,N-dimethylformamide, 1-methyl-2-pyrrolidinone and pyridine and could be cast into transparent, flexible and tough films from their N,N-dimethylacetamide solution. Wide angle X-ray diffraction patterns exhibited broad halo indicating that the polymers were essentially amorphous in nature. X-ray diffractograms also displayed sharp reflection in the small angle region (2θ ≈ 3°) for poly(amideimide)s containing pentadecyl chains indicating the formation of layered structure arising from packing of flexible pentadecyl chains. The glass transition temperatures observed for reference poly(amideimide)s were in the range 331-275 °C and those for poly(amideimide)s containing pendent pentadecyl chains were in the range 185-286 °C indicating a large drop in T_g owing to the “internal plasticization” effect of pentadecyl chains. The temperature at 10% weight loss (T₁₀), determined by TGA in nitrogen atmosphere, were in the range 460-480 °C indicating their good thermal stability.     

Preparation and properties of aromatic poly(amide-imide)s derived from N-[3,5-bis(3,4-dicarboxybenzamido)phenyl]phthalimide dianhydride

An imide ring-containing diamide-dianhydride, N-[3,5-bis(3,4-dicarboxybenzamido)phenyl]phthalimide dianhydride (1) was prepared by the reaction of trimellitic anhydride chloride with N-(3,5-diaminophenyl)phthalimide in a medium consisting of methylene chloride and pyridine. A series of new alternating aromatic poly(amide-imide)s having inherent viscosities of 0.26-0.37 dl/g was synthesized using a two-step poly(amic-acid) precursor method. A reference monomer, 1,3-bis(3,4-dicarboxybenzamido)benzene dianhydride (2) without the phthalimido pendant group attached to the polymer main chain was prepared in order to study the structure-property relationship. In this case, the structure effects on some properties of the resulting poly(amide-imide)s including crystallinity, solubility, thermal stability, and film flexibility could be easily clarified. A diamide-triimide (3) as a model compound was also synthesized by the reaction of new dianhydride 1 with aniline to compare the characterization data as well as to optimize the polymerization conditions. The resulting polymers were fully characterized by FT-IR, UV-visible and ¹H NMR spectroscopy. Most of the polymers showed an amorphous nature and were readily soluble in a variety of organic solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), and pyridine. The glass-transition temperatures of these polymers were recorded between 301 and 371 °C. All polymers showed no significant weight loss below 500 °C in nitrogen, and the decomposition temperatures at 10 wt.% loss range from 506 to 543 °C. The films of the resulting poly(amide-imide)s could be cast from their NMP solutions, and the transparency and flexibility of them were investigated.