Soluble wholly aromatic polyamides containing unsymmetrical pyridyl ether linkages

Wholly aromatic polyamides were synthesized from the amidation reaction between unsymmetrical diamine containing a pyridyl ether linkage and aromatic dicarboxylic acid chloride. The resulting polyamides containing pyridyl ether linkages showed high thermal stability (T_d5=467 °C) and enhanced solubility in organic solvents compared with the analogous polyamides having phenyl ether linkages. Substitution of just a single atom in a repeating unit was effective to disrupt the strong inter-chain interaction of parent aramid polymers.     

DSC, dielectric and dynamic mechanical behavior of two- and three-component ordered polyurethanes

Liquid crystalline (LC) polyurethanes were made from two diisocyanates (flexible HMDI and stiff TDI) (DIs), mesogenic diol (D) and a polybutadiene-diol (B) with stoichiometric ratios of reactive hydroxy (OH) and isocyanate (NCO) groups ((NCO)_DI/((OH)_D+(OH)_B)=1/1). Two- (B/DIs, D/DIs) and three-component ((D+B)/DIs, D/B=1/1 by weight) polymers were prepared and their dielectric, dynamic mechanical and DSC behavior was investigated. For neat B, the glass transition temperature T_gB (∼−46 °C) was detected. Two-component B/HMDI and B/TDI polymers have exhibited a homogeneous structure with the glass transition temperatures T_gU∼−9 and 2 °C. On the other hand, for D/DI polymers on cooling from the melt and subsequent heating the glass transitions at T_gU∼41 °C (D/HMDI) and 58 °C (D/TDI) together with nematic and smectic mesophases were found. In three-component systems, additional glass transitions at T_gB∼−41 °C (B/D/HMDI) and −31 °C (B/D/TDI) were observed. This means that the polymers exhibit a distinct two-phase structure with soft polybutadiene (B) and hard polyurethane (D/DI) phases. In hard polyurethane phase, the glass transitions at T_gU and LC mesophases similar to those found in two-component D/DI polyurethanes were detected. Dielectric and dynamic mechanical results correlate well with DSC measurements.     

Synthesis of nitrile and benzoyl substituted poly(biphenylene oxide)s via nitro displacement reaction

A series of substituted poly(biphenylene oxide)s (PBPOs) was synthesized via nucleophilic nitro displacement reactions. High molecular weight PBPO's with nitrile groups were effectively synthesized from the polymerization of A-B type monomers with K₂CO₃ as a base in N-methyl-2-pyrrolidinone (NMP) at 140 °C. The polymers are completely amorphous, soluble in polar aprotic solvents, and formed flexible films on solution casting. Para-linked PBPO with nitrile groups showed excellent thermal properties such as high 5% weight loss temperature above 530 °C and T_g at 241 °C which is higher than those of commercially available PPO™ (T_g=210 °C). The pendent nitrile groups of PBPO were easily transformed to carboxylic acid groups by acidic hydrolysis.     

Soluble polyimides from unsymmetrical diamine containing benzimidazole ring and trifluoromethyl pendent group

New unsymmetrical diamine monomer containing both the benzimidazole ring and trifluoromethyl group, 6,4′-diamino-2′-trifluoromethyl-2-phenylbenzimidazole, was prepared from 2-bromo-5-nitrobenzotrifluoride and 4-nitro-1,2-phenylenediamine. The monomer was polymerized with ODPA, BTDA and 6FDA by using one-pot synthetic method to obtain corresponding polyimides. All the prepared polyimides were soluble in aprotic polar solvents. Incorporation of trifluoromethyl groups unsymmetrically in the rigid polyimides improves their solubility without decreasing their physical properties. The polymers showed high glass transition temperature (T_g = 289-352 °C), high thermal stability (T_d10 > 500 °C), and relatively low coefficient of thermal expansion (CTE = 26.1-46.4 ppm/°C) because of their rigid-rod like structure. Also, they showed low refractive indexes (n = 1.46-1.68) and low birefringence (Δ ≈ 0.02) due to the trifluoromethyl pendent groups that interrupt chain packing and increase free volume.     

Microdeformation mechanisms in thin films of amorphous semi-aromatic polyamides

Optical and transmission electron microscopy have been used to investigate the microdeformation mechanisms in thin films of amorphous semi-aromatic polyamides with different chemical structures and chain lengths. In the chosen range of test temperatures (between −120 °C and the principal mechanical relaxation temperature, T_α), three successive microdeformation mechanisms were identified: chain scission crazing (CSC) at the lowest temperatures, shear deformation zones (SDZs) at intermediate temperatures and chain disentanglement crazing (CDC) at the highest temperatures. The critical stress for SDZ formation was identified with the experimental yield stress, whereas the critical stresses for CSC and CDC were derived from model expressions, using experimental data for the molecular mass between entanglements, the monomeric friction coefficient and the plastic flow stress. Variations in the transition temperatures among the different polymers were attributed to differences in the temperature dependence of the yield stress, and hence to variations in chain mobility, which could be accounted for in terms of the chemical structure.     

Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks (T_c1 and T_c2) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature (T_g) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa₃B₅O₁₀. The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa₃B₅O₁₀ and CaB₂O₄.     

Formation of filamentous carbon during methane decomposition over Co-MgO catalysts

The carbon formation during methane decomposition was investigated at 900 °C over the 48 wt% Co-MgO catalysts as a function of the calcination temperature T_c used in their preparation. Examination of the carbonaceous deposits by transmission electron microscopy revealed three kinds of structures: shapeless tangles, shell-like materials, and carbon filaments. In another set of experiments, the structural characteristics of the calcined catalysts were investigated using temperature-programmed reduction (TPR) and X-ray diffraction (XRD). Co₃O₄, Co₂MgO₄, and (Co, Mg)O (solid solution of CoO and MgO) were identified for T_c≤700 °C, Co₃O₄ and (Co, Mg)O for T_c=800 °C and only (Co, Mg)O for T_c=900 °C. It was found that the metal particles originated from the reduction of the solid solution favored the formation of filamentous carbon. A possible explanation is proposed.     

Reversible thickness control of polymer thin films containing photoreactive coumarin derivative units

The reversible control of the thickness of polymer thin films was investigated using (meth)acrylic polymers containing photoreactive coumarin derivative units in the side chain. Coumarin derivative units underwent dimerization and the reverse-dimerization by photoirradiation and were used as a reversible cross-linking point. The homopolymer of 7-methacryloyloxy-4-methylcoumarin (T_g = 194 °C) did not cause changes in film thickness after photoreactions. The homopolymer of 7-(2′-acryloyloxyethoxy)-4-methylcoumarin (AEMC) (T_g = 89 °C) decreased 19% of film thickness by photodimerization and 73% of the decreased thickness was recovered after the reverse-dimerization and the subsequent thermal annealing at 130 °C. The reverse-dimerization of the copolymer of AEMC and n-butyl acrylate (AEMC content = 19 mol%, T_g = 11 °C) resulted in 53% of recovery from the decreased film thickness without annealing. The mobility of polymer main-chain was revealed to be essential factor to change film thickness by photoreactions. Photodimerization of coumarin derivative units in low glass transition temperature (T_g) tended to proceed faster than in high T_g polymers and resulted in larger decrease in film thickness.     

Synthesis and characterization of perfluorocyclobutyl (PFCB) polymers containing pendent phenylphosphine oxide

Three phenylphosphine oxide (PPO) containing trifluorovinyl aryl ether monomers were synthesized and polymerized via thermal cyclodimerization affording perfluorocyclobutyl (PFCB) polymers containing PPO pendent groups. The new polymers exhibited moderate to high glass transition temperatures (T_g=145-217 °C) and good thermal stability in nitrogen (5% weight loss, T_d>402 °C). Copolymerization with traditional PFCB forming monomers such as 4,4′-(trifluorovinyloxy)biphenyl resulted in film forming transparent thermoplastic copolymers with improved solubility and further enhanced thermal stability. Semi-fluorinated PPO containing polymers of this type may find potential application as space environment durable materials.     

Soluble and curable poly(phthalazinone ether amide)s with terminal cyano groups and their crosslinking to heat resistant resin

Soluble and curable aromatic polyamides have great potential use as processable and heat-resistant polymeric materials. In this study, a novel series of soluble aromatic polyamides (CN-PPAs) containing phthalazinone moiety and crosslinkable terminal cyano groups were synthesized by polycondensation of 1,2-dihydro-2-(4-carboxyphenyl)-4-[4-(4-carboxyphenoxyl)phenyl]-phthalazinone (DHPZ-DC) with calculated 4,4′-oxydianiline (ODA), followed by end-capping with 4-cyanobenzoic acid (CBA). Thermal crosslinking of CN-PPAs, catalyzed by zinc chloride, was then performed in the presence of terephthalonitrile (TPH) via heating either their films or powders up to 300-340 °C. The uncured synthesized polymers have good solubility while the cured samples become insoluble in common organic solvents. Spectra and elemental analysis measurements demonstrate cyclization reaction of terminal cyano groups to form s-triazine rings. The presence of TPH and ZnCl₂ is effective in promoting thermal crosslinking and s-triazine forming reaction of the CN-PPAs under normal pressure. The resulting cured samples exhibit no T_g up to 400 °C by DSC and have excellent thermal stability. This kind of cyano-terminated poly(phthalazinone ether amide) may be a good candidate as matrix for high performance polymeric materials.     

Thermally reversible cross-linked polyamides and thermo-responsive gels by means of Diels-Alder reaction

Cross-linked polyamides and polyamide gels were prepared from maleimide-containing polyamides and a tri-functional furan compound and showed thermal reversibility in cross-linking behavior and in gel formation through Diels-Alder (DA) and retro-DA reactions. The rate constant k of the DA cross-linking reaction were 1.25-4.83×10⁻⁵ dm³ mol⁻¹ s⁻¹ in the temperature range of 20-60 °C with an activation energy of 32.1 kJ mol⁻¹. The cross-linking densities, thermal properties, and thermal reversibility of the polyamides/furan polymers were adjustable with the contents of maleimide groups in polyamides.     

Physical aging of thin glassy polymer films monitored by gas permeability

The physical aging at 35 °C of three glassy polymers, polysulfone, a polyimide and poly(2,6-dimethyl-1,4-phenylene oxide), has been tracked by measurement of the permeation of three gases, O₂, N₂, and CH₄, for over 200 days. Several techniques were used to accurately determine the thickness of films (∼400 nm-62 μm) in order to obtain absolute permeability coefficients and to study the effects of film thickness on the rate of physical aging. Each film was heated above the polymer T_g to set the aging clock to time zero; ellipsometry revealed that this procedure leads to isotropic films having initial characteristics independent of film thickness. A substantial pronounced aging response, attributed to a decrease in polymer free volume, was observed at temperatures more than 150 °C below T_g for thin films of each polymer compared to what is observed for the bulk polymers. The films with thicknesses of approximately 400 nm of the three polymers exhibit an oxygen permeability decrease by as much as two-fold or more and about 14-15% increase in O₂/N₂ selectivity at an aging time of 1000 h. The results obtained in this study were compared with prior work on thickness dependent aging. The effects of crystallinity on physical aging were examined briefly.     

Soluble aromatic polyamides bearing asymmetrical diaryl ether groups

A series of novel aromatic polyamides containing asymmetrical diaryl ether structure were synthesized by the phosphorylation polyamidation of 5-(4-aminophenoxy)-1-naphthylamine with various dicarboxylic acids. The polymers were obtained in high yields and moderately high inherent viscosities (0.74-1.36 dl/g). Except for one example, all the polyamides were amorphous and readily soluble in many organic solvents and could afford flexible and tough films via solution casting. The cast films exhibited good mechanical properties with tensile strengths of 90-128 MPa, elongations at break of 9-64%, and initial moduli of 2.08-3.08 GPa. Glass-transition temperatures ranged from 222 to 288 °C by DSC. Thermal stabilities by TGA for the polymer series ranged from 462 to 517 °C in air at the point of 10% weight loss. These polyamides displayed a lower crystallinity and better solubility and film-forming capability than the corresponding analogues derived from symmetrical 1,5-diaminonaphthalene and 1,5-bis(4-aminophenoxy)naphthalene.     

High optical transparency, low dielectric constant and light color of novel organosoluble polyamides with bulky alicyclic pendent group

Novel optically transparent, low dielectric and highly organosoluble alicyclic polyamides derived from bulky alicyclic diamine containing trifluoromethyl group on either side, 1,1-bis[4-(2-trifluoromethyl-4-aminophenoxy)phenyl]-4-tert-butylcyclohexane (BTFAPBC), were prepared. The polyamides were obtained in almost quantitative yields and showed inherent viscosity values between 0.55 and 0.72 dL g⁻¹ in DMAc solution. Most of the polyamides showed excellent solubility in polar solvents such as N-methyl-2-pyrrolidinone (NMP), N,N′-dimethyl acetamide (DMAc), N,N′-dimethyl formamide (DMF), pyridine, cyclohexanone, γ-butyrolactone and chloroform. The cut-off wavelength for polyamides ranged from 350 to 388 nm. Polyamides with alicyclic tert-butylcyclohexyl cardo and trifluoromethyl substituents exhibited low dielectric constants ranging from 3.29 to 3.98 (at 100 Hz) compared with commercially available polyamides [Amodel^®, 4.2-5.7 at 100 Hz]. Polyamides showed glass transition temperatures in the range of 244-266 °C and possessed a coefficient of thermal expansion (CTE) of 60-75 ppm °C⁻¹. Thermogravimetric analysis data showed that the polyamides were stable up to 430 °C and the 10% weight loss temperature was found to be in the range of 437-466 °C in nitrogen atmosphere. The polyamide films had a tensile strength in the range of 66-103 MPa, elongation at break in the range of 5-8%, and tensile modulus in the range of 1.5-2.2 GPa. Due to their properties, the polyamides could be considered as engineering plastic and photoelectric materials.     

Syntheses and properties of aromatic polyamides derived from 4,4′-oxydibenzoic acid and aromatic diamines

A series of aromatic polyamides were synthesized by direct polycondensation of 4,4-oxydibenzoic acid with various aromatic diamines inN-methyl-2-pyrrolidone (NMP) solution containing dissolved calcium chloride, using triphenyl phosphite and pyridine as condensing agents. The resultant polyamides had inherent viscosities of 0.21-1.48 dL/g. Most of the polymers were organo-soluble and could be solution-cast into flexible and strong films. The glass transition temperatures (T_gs) of most polyamides could be determined with the help of differential scanning calorimetry (DSC) traces, which were recorded in the range of 170–275 °C. Thermogravi metric data of these polymers indicated that most of the polyamides showed no significant weight loss before 450 °C in either air or nitrogen atmospheres.     

New sheet molding compound resins from soybean oil. I. Synthesis and characterization

Thermosetting resins were synthesized from soybean oil, which are suited to sheet molding compound (SMC) applications. It was achieved by introducing acid functionality and CC groups onto triglyceride molecules. The acid groups can react with divalent metallic oxides and/or hydroxides to form the sheet, while CC groups undergo free radical polymerization. An acrylated epoxidized soybean oil (AESO), which has an average of 3.4 acrylates per triglyceride, was used as starting material. The hydroxyl groups on AESO reacted with maleic anhydride (MA) to render acid groups on the molecule. The resulting monomer was then copolymerized with 33 wt% styrene to form rigid polymers. Dynamic mechanical analysis showed storage moduli (E′) for these polymers ranging from 1.9 to 2.2 GPa at room temperature, and the glass transition temperatures (T_g) in the range of 100-115 °C. Both the E′ and T_g were increased by increasing the molar ratio of MA to AESO, and the transition from the glassy to the rubbery state was broadened by increasing the amount of MA. The effect of styrene as a comonomer was also examined, and a final formulation for SMC was optimized. The resulting resins exhibited appropriate viscosity during the SMC thickening process.     

The nucleation and crystallization of MgO-B2O3-SiO2 glass

The nucleation and crystallization of MgO-B₂O₃-SiO₂ (MBS) glass were studied by means of a non-isothermal, thermal analysis technique, X-ray diffraction and scanning electron microscopy. The temperature range of the nucleation and the temperature of the maximum nucleation rate for MBS glass were determined from the dependences of the inverse temperature at the DSC peak (1/T_p) and the maximum intensity of the exothermic DSC crystallization peak ((δT)_p) on the nucleation temperature (T_n). For MBS glass the nucleation occurred at 600-750 °C, with the maximum nucleation rate at 700 °C, whereas the nucleation and crystal growth processes overlapped at 700 °C < T ≤ 750 °C. The analyses of the non-isothermal data for the bulk MBS glass using the most common models (Ozawa, Kissinger, modified Kissinger, Ozawa-Chen, etc.) revealed that the crystallization of Mg₂B₂O₅ was three-dimensional bulk with a diffusion-controlled crystal growth rate, that n = m = 1.5 and that the activation energy for the crystallization was 410-440 kJ/mol.     

The phase structure and electric properties of low-temperature sintered (K,Na)NbO3-based piezoceramics modified by CuO

0.25 wt% CuO-doped (Li,K,Na)(Nb,Ta)O₃–AgSbO₃ lead-free piezoceramics with pure perovskite structure were successfully prepared at a sintering temperature below 1000 °C. The sintering temperature of KNN-based piezoceramics was effectively reduced by about 100 °C due to the enhanced densification process induced by the addition of CuO. Besides, the acceptable sintering temperature window was broadened by the addition of CuO. It is found that the CuO-doped samples show slightly higher tetragonal–orthorhombic phase transition point (T_T−O) but a lower Curie point (T_c), compared to undoped ones. The KNN-based piezoceramics became “hard” as CuO was added, supported by an increase of Q_m. Fairly good electrical properties of d₃₃^*=383 pm/V, ε_r=860, Q_m=188 and T_c=215 °C could be obtained in dense CuO-modified KNN-based piezoceramics sintered at 970 °C, demonstrating promising potential in practical applications.     

Thermal, spectroscopy, and morphological studies on polymorphic crystals in poly(heptamethylene terephthalate)

Polymorphism and its influential factors in poly(heptamethylene terephthalate) (PHepT) were probed using differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and wide angle X-ray diffraction (WAXD). PHepT exhibits two crystal types (α and β) upon crystallization at various isothermal melt-crystallization temperatures (T_cs) by quenching from different T_maxs (maximum temperature above T_m for melting the original crystals). Melt-crystallized PHepT with either initial α- or β-crystal by quenching from T_max lower than 110 °C leads to higher fractions of α-crystal, but crystallization from T_max higher than 140 °C leads to higher fractions of β-crystal. In addition to T_max, polymorphism in PHepT is also influenced by crystallization temperature (T_c = 25-75 °C). When PHepT is melt-crystallized from a high T_max = 150 °C (completely isotropic melt), it shows solely β crystal for higher T_c, and solely the α-crystal for T_c < 25 °C; in-between T_c = 25 and 35 °C, mixed fractions of both α- and β-crystals. However, by contrast, when PHepT is melt-crystallized from a lower T_max = 110 °C, it shows α-crystal only at all T_cs, high or low.     

Aromatic polyamides bearing ether and isopropylidene or hexafluoroisopropylidene links in the main chain

Two multiring, flexible dicarboxylic acids, 4,4'-[isopropylidenebis(1,4-phenylene)dioxy] dibenzoic acid (3) and 4,4'-[hexafluoroisopropylidenebis(1,4-phenylene)dioxyldibenzoic acid (3-F), were synthesized through the nucleophilic fluorodisplacement ofp-fluorobenzonitrile by the dipotassium bisphenolates of the corresponding bisphenol precursors followed by alkaline hydrolysis. Two series of aromatic polyamides 5_a–k and 5_a–k-F containing both ether and isopropylidene or hexafluoroisopropylidene linkages between phenylene units were prepared by direct polycondensation of diacids 3 and 3-F, respectively, with various aromatic diamines using triphenyl phosphite and pyridine as condensing agents in aN-methyl-2-pyrrolidone (NMP) solution containing dissolved calcium chloride. The resulting polyamides of 5 and 5-F series have inherent viscosities of 0.92–1.29 dL/g and 0.60–0.92 dL/g, respectively. Most of these polymers are amorphous in nature, are soluble in polar solvents such as NMP,N,N-dimethylacetamide (DMAc), andN,N dimethylformamide (DMF), and can afford tough and flexible films by solution casting. Differential scanning calorimetry shows T_gs ranging from 175 to 239 °C for the 5 series polyamides and ranging from 172 to 267 °C for the 5-F series polymers. Both classes of polyamides show good thermal stability, with the 5-F series polyamides being more stable.