Soluble aromatic polyimides with high glass transition temperature from benzidine containing tert-butyl groups

A series of soluble polyimides with high glass transition temperature (T _g ) were prepared from four commercial aromatic dianhydrides (i.e., BPDA, OPDA, 6FDA and BPADA) with a rigid aromatic diamine containing tert-butyl groups (3,3′-di-tert-butylbenzidine) (1). The number-average molecular weights of them were in the range from 4.21?×?10⁴ to 1.25?×?10⁵ with the polydispersity indexes between 2.34 and 3.04 by means of gel permeation chromatography relative to a polystyrene standard. They were able to form transparent, flexible and tough films by polymer solution casting. The transmittance of them was higher than 90 % in a wavelength range of 400–700 nm by UV–vis measurement. The XRD results demonstrated that they were amorphous glassy polymers. Except for polyimide 1-BPADA, the T _g s of the rest were higher than 330 °C, and especially the T _g of polyimide 1-BPDA reached up to 375 °C. They did not show appreciable decomposition up to 500 °C under a nitrogen atmosphere, in other words, the 5 % weight losses of them were in the range from 508 to 523 °C. Most of them exhibited high tensile strength and modulus with a low elongation at break at room temperature. They are potential candidates for high performance materials.     

Preparation and characterization of inherently heat‐sealable polyimides with high glass transition temperatures

A series of inherently heat‐sealable copolyimides (CPIs) with high glass transition temperatures were synthesized from 2,3,3′,4′‐oxydiphthalic anhydride (aODPA) and bicomponent diamines, 4,4′‐oxydianiline (ODA) and para‐phenylenediamine (PDA). The PI chain rigidity was manipulated by the regulation of the diamine ratio, and its effects on the heat sealability and thermal resistance of the derived CPI films were investigated in detail. The results show that these films are in possession of both good heat sealability and thermal resistance due to the synergetic effect of the asymmetry of aODPA and the rigidity of PDA. It is also found that there exists one critical PDA content that distinguishes the heat‐sealing behaviors of the CPI films, and the relevant mechanism was established. Especially for CPI‐5, the heat‐sealing strength is up to 350 N m^?1 simultaneously with a relatively high T_g of 310°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43058.     

Flexible all‐aromatic polyesterimide films with high glass transition temperatures

A series all‐aromatic poly(esterimide)s with different molar ratios of N‐(3′‐hydroxyphenyl)‐trimellitimide (IM) and 4‐hydroxybenzoic acid (HBA) (IM/HBA = 0.3/0.7 and 0.7/0.3) was prepared with the aim to design flexible high T_g films. Melt‐pressed films, either from high molecular weight polymer or cured phenylethynyl precursor oligomers, exhibit T_gs in the range of 200 °C to 242 °C and are brittle. After a thermal stretching procedure, the films became remarkably flexible and very easy to handle. In addition, the thermally stretched 3‐IM/7‐HBA and 7‐IM/3‐HBA films show tensile strengths of 108 MPa and 169 MPa, respectively. Thermal treatment increased the T_g of 3‐IM/7‐HBA from 205 °C to 248 °C, whereas the T_g of 7‐IM/3‐HBA increased from 230 °C to 260 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 133, 44774.     

Investigation of glass transition temperatures of Turkish asphaltenes

Asphaltenes are a major concern in production operations, due to their role in conversion of vacuum residues by processes such as coking, catalytic cracking and hydroconversion. Six Turkish asphaltenes were characterized by elemental content, proton NMR, carbon NMR, GPC, DSC. Differential scanning calorimetry (DSC) provides parameters for comparing the glass transition temperatures, endothermic behavior of asphaltene and a hypothetical melting temperature of the asphaltenes which is within the range of the pyrolysis temperature of asphaltenes. The glass transition temperatures points (T_g) of asphaltenes were determined using DSC. Hypothetical melting point temperature (T_m) of the asphaltenes was also calculated. Among all the asphaltenes tested, Bati Raman showed much higher glass transition temperatures than the others.     

Nanoindentation creep and glass transition temperatures in polymers

The nanoindentation creep behaviour of several different polymers has been investigated. The extent of creep ε is represented by the Chudoba and Richter equation: ε = ε_eln(ε_rt + 1), where t is the loading time and ε_e and ε_r are material constants. Creep was determined in this way for a variety of polymers at T_exper = 301.7 K. Some of the materials studied were far above, some far below and some near their glass transition temperatures T_g. The creep rate ε_r was plotted as a function of y = (T_g ? T_exper); a single curve was obtained in spite of a large variety of chemical structures of the polymers. The ε_r = ε_r(y) diagram can be divided into three regions according to the chain mobility. At large negative y values, the creep rate is high due to the liquid‐like behaviour. At large positive y values in the glassy region, the creep rate is higher than that in the negative y‐value region; the creep mechanism is assigned to material brittleness and crack propagation. In the middle y range there is a minimum of ε_r. These results can be related to glassy and liquid structures represented by Voronoi polyhedra and Delaunay simplices. The latter form clusters; in the glassy material there is a percolative Delaunay cluster of nearly tetrahedral high‐density configurations. The creep mechanism here is related to crack propagation in brittle solids. In the liquid state there is a different percolative Delaunay cluster formed by low‐density configurations, which, as expected, favour high creep rates. Copyright © 2007 Society of Chemical Industry     

杂环型聚酰亚胺的合成与性能比较

利用含有醚、酮及砜基官能团的二胺、二酐单体通过二步法合成了几种不同结构的聚酰亚胺。并应用FT-IR、TGA、DSC、X-Ray等测试方法,对所得聚酰亚胺树脂的性能进行测试与比较。结果表明,不同官能团对聚酰亚胺的性能影响极为不同,醚酮类聚酰亚胺能够在保持其热性能的前提下在一定程度上改善其溶解性,而含砜基聚酰亚胺则能极大地改善溶解性。应当根据具体应用对聚酰亚胺的种类进行选择。     

Derivation of accurate glass transition temperatures by differential scanning calorimetry

Glass transition temperatures, T_g, cannot be directly determined from differential scanning calorimetry (d.s.c.) curves because of kinetic effects which are especially serious for well annealed samples. Using an anionic polystyrene as an example it is shown how d.s.c. data can be transformed to enthalpy curves which give T_g with an accuracy of ±1K. As the rate of cooling through the glassy region is lowered T_g is found to decrease by 2.2 K per decade decrease in cooling rate. Quantitative data are given for the specific heat increment at T_g.     

Preparation and fabrication of aromatic polyimides

Aromatic polyimides were prepared from pyromellitic dianhydride and a number of aromatic diamines. The effect of certain variables on the polymerization to, and the degradation of, the intermediate polypyromellitamic acids was studied, and a previously unrecorded reaction intermediate was isolated and identified. From these studies the conditions necessary to obtain high molecular weights were defined. Techniques were developed for the fabrication of satisfactory films and moldings.     

Characteristics of Bi-based glass powders with various glass transition temperatures prepared by spray pyrolysis

Spherical shape, submicron, and non-aggregated bismuth-based glass powders were prepared. Glass powders with low glass transition temperature melted the silver powders at firing temperatures of as low as 400 °C. After firing at 400 °C, the specific resistances of the silver conducting films obtained from glass powders with glass transition temperatures of 498 and 373 °C were 21.6 and 5.8 μΩ cm, respectively. After firing at 450 and 500 °C, the specific resistances of the silver conducting films obtained from glass powders with glass transition temperature of 425 °C were the lowest, i.e., 3.0 and 3.1 μΩ cm, respectively.     

Morphology control of various aromatic polyimides by using phase separation during polymerization

Morphology control of various aromatic polyimides representative as poly(4,4′-oxydiphenylene pyromelliteimide) was examined by using the phase separation during solution polymerization. Polymerizations of aromatic dianhydrides and aromatic diamines to the polyimides were carried out in poor solvents at 240-330 °C for 6 h with no stirring. Polymerization concentrations were from 0.25% to 3.0%. The polyimides were obtained as yellow precipitates. Two categorized morphologies were created, which were particles and crystals exhibiting lath-like and plate-like habits. These morphologies of polyimides could be selectively controlled by the polymerization conditions. The higher concentrations, less miscible solvents and lower temperatures were preferable to yield the particles via liquid-liquid phase separation. On the contrary, the lower concentration, miscible solvents and higher temperature were desirable to yield the crystals. The polyimide precipitates showed high crystallinity and possessed excellent thermal stability at which the 10 wt% loss temperatures in N₂ were in the range of 590-694 °C.     

Influence of cohesive forces on the glass transition temperatures of polymers

The relationship between cohesive energy (c.e.) or cohesive energy density (c.e.d.) and the glass transition tenperature (T_g) of polymers has been re-examined on the basis of literature data. For polymers with T_g above 25°C., there is no correlation between published or calculated values of c.e. or c.e.d. and T_g. However, for the rest of the polymers there is a linear relationship between c.e.d. and T_g, and a broad relationship between c.e. and T_g. These results imply that c.e.d. is the regulating, though not the only, factor in determining T_g's up to values of approximately 25°C.     

Synthesis of novel heterocyclic polyimides containing trimellitimide acid moieties

4‐Nitrobezoyl chloride (2) was reacted with isoeugenol in chloroform in the presence of triethyl amine and ester (4) was obtained in high yield. Ester (4) was reacted with SnCl₂·2H₂O to give amine‐ester (5), and subsequently was reacted with trimellitic anhydride (6) and novel isoeugenol ester‐imide derivative (7), as a new monomer was obtained in quantitative yield. Compound (7) was characterized by high‐field ¹H–NMR, IR, and elemental analysis and then was used for the preparation of model compound (9) and polymerization reactions. 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione (PhTD) (8) was allowed to react with compound (7). The reaction is very fast and gives only one double adduct (9) via Diels–Alder and ene pathways in excellent yield. The polymerization reactions of novel monomer (7) with bistriazolinediones [bis(p‐3,5‐dioxo‐1,2,4‐triazolin‐4‐ylphenyl)methane (10) and 1,6‐bis(3,5‐dioxo‐1,2,4‐triazolin‐4‐yl)hexane (11)] were carried out in N,N‐dimethylacetamide (DMAc) at room temperature. The reactions are exothermic, fast, and gave novel heterocyclic polyimides (12) and (13) via repetitive Diels–Alder‐ene polyaddition reactions. Some structural characterization and physical properties of these novel heterocyclic polyimides are reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1716–1725, 2001     

Synthesis and characterization of some aromatic polyimides

The diamine 2‐methyl‐1,3‐bis(4‐aminophenyloxy)benzene was prepared via a nucleophilic substitution reaction and was characterized with Fourier transform infrared, elemental analysis, and ¹H‐ and ¹³C‐NMR spectroscopy. The prepared diamine was also characterized with single‐crystal analysis. The geometric parameters of C₁₉H₁₈N₂O₂ were in the usual ranges. The dihedral angles between the central phenyl ring and the two terminal aromatic rings were 88.9 and 91.6°. The crystal structure was stabilized by N? H···N hydrogen bonds. The diamine was then polymerized with 3,3′,4,4′‐benzophenone tetracarboxylic acid dianhydride, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, 3,4,9,10‐perylenetetracarboxylic acid dianhydride, and pyromellitic dianhydride by either a one‐step solution polymerization reaction or a two‐step procedure. These polymers had inherent viscosities ranging from 0.61 to 0.85 dL/gm. Some of the polymers were soluble in most common organic solvents even at room temperature, and some were soluble on heating. The degradation temperatures of the resultant polymers fell in the range of 260–500°C in nitrogen (with only 10% weight loss). The specific heat capacity at 200°C ranged from 1.0 to 2.21 J g^?1 K^?1. The temperatures at which the maximum degradation of the polymer occurred ranged from 510 to 610°C. The glass‐transition temperatures of the polyimides ranged from 182 to 191°C. The activation energy and enthalpy of the polyimides ranged from 44.44 to 73.91 kJ/mol and from 42.58 to 72.08 kJ/mol K, respectively. The moisture absorption was found in the range of 0.23–0.71%. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Gas permeation properties of hexafluoro aromatic polyimides

Two hexafluoro-substituted aromatic polyimides, 6FDA-p-PDA and 6FDA-4,4′-ODA, were synthesized. The influence of some synthetic conditions on physical properties and gas permeabilities of the 6FDA polyimide membranes were studied. Gas permeabilities and permselectivities of six different gases for the homogeneous films have been determined at 15–35°C and at pressures up to 10 atm. 6FDA polyimide composite membranes with asymmetric structure were prepared by the solution-casting method. The membranes showed exceptionally high permeation fluxes and permselectivities. No capability deterioration of asymmetric membrane was observed during 19 days operation with pure gases. © 1993 John Wiley & Sons, Inc.     

Thermal expansion behavior of various aromatic polyimides

The thermal expansion behavior for various aromatic polymides was investigated. Usally polymers, including polyimides, have high thermal expansion coefficients (3–6 × 10^?5 K^?1), compared with metals and ceramics. However, there are some polyimides which have very low thermal expansion coefficients below 1 × 10^?5 K^?1. This property was observed for the polymides obtained from pyromellitic dianhydride or 3,3′ 4,4′-biphenyltetracarboxylic dianhydride and aromatic diamines which were constituted of only benzene rings fused at para positions. It was proposed that their low thermal expansion coefficient related to the linearity in their polymer molecular skeltons.     

Plasticizer compatibility testing: Dynamic mechanical analysis and glass transition temperatures

Plasticizer compatibility with the polymer, which implies that plasticizer and polymer will remain closely associated as the finished polymer product is used, is critically important in determining whether a flexible poly(vinyl chloride) (PVC) product will have an acceptably long service life. However, with traditional test methods, it is often difficult to distinguish degrees of compatibility among relatively compatible ingredients (ingredients that do not dissociate themselves from the polymer in a very short time or under very mild storage conditions). Dynamic mechanical analysis is a commonly used technique for measuring glass transition temperatures, which can be a useful property in comparing additives' compatibilities. Unlike many polymers, flexible PVC shows two glass transition temperatures, one for the polymer segments that show syndiotactic (but noncrystalline) stereochemistry, and one for the polymer segments that show atactic stereochemistry. The glass transition temperature for the atactic segments of flexible PVC provides some information about the plasticizer's compatibility. When the dynamic mechanical analysis temperature sweep for a plasticized PVC compound detects a particularly low glass transition for the atactic polymer segments, this can be an indication that the plasticizer is relatively incompatible with the PVC. J. VINYL ADDIT. TECHNOL., 21:7–11, 2015. © 2014 Society of Plastics Engineers     

High glass transition and thermal stability of new pyridine-containing polyimides: Effect of protonation on fluorescence

A new diamine monomer containing heterocyclic pyridine and triphenylamine groups, 4-(4,4′-diaminotriphenylamine)-2,6-bis(4-methylphenyl)pyridine (4), was synthesized by Chichibabin and nucleophilic fluoro-displacement reactions. The diamine was used to prepare a series of novel polyimides via polycondensation with various aromatic tetracarboxylic dianhydrides in N-methyl-2-pyrrolidinone. The polyimide 4a derived from the diamine 4 with 4,4′-hexafluoroisopropylidenediphthalic anhydride and having high T_g (313 °C), mechanical, and thermal properties was soluble in various organic solvents, such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, N,N-dimethylformamide, pyridine, chloroform, tetrahydrofuran, at room temperature. The polyimide (4a) could be cast into a self-standing film from DMAc solution and was thermally converted into tough and flexible film. The film had high tensile modulus of 2.2 GPa and exhibited excellent thermal stability in both nitrogen and air (T_d¹⁰ > 550 °C). The pristine polymer exhibited the UV-vis absorption bands in the region 240-400 nm and protonated polymer exhibited absorption in the region 390-500 nm. The protonated polymer possessed strong orange fluorescence (around 600 nm) in THF solution after protonation with acids as excited at 438 nm. The fluorescent intensity was influenced by the acid concentrations and the chemical structure of conjugated bases. The fluorescent intensity at 600 nm increased as acid concentration from a lower to a moderate concentration and decreased at higher concentrations.     

New main chain nonlinear optical polymers with high glass transition temperatures

Summary Various 4-methoxy-4-carbomethoxy--amino--cyanostilbenes were prepared as mixtures of E and Z isomers, and polymerized via condensation polymerization using dibutyltin diacetate as catalyst. The resulting low molecular weight homopolymers showed higher glass transition temperatures (168–183°C) than previously reported main chain nonlinear optical (NLO) homopolymers. A high molecular weight (M_n30, 200) copolymer possessed an even higher glass transition temperature of 187°C. The hyperpolarizability of the polymers and a model compound were found by EFISH measurements to be in the range of 61 to 79x10^-48 esu.     

The kinetics of the α relaxation in an amorphous polymer at temperatures close to the glass transition

The kinetics of the α relaxation of a crosslinked copolymer of acrylonitrile and butadiene (T_g = ?7°C) were studied in the temperature range (T_g + 17°C) down to (T_g ? 8°C). The techniques used were shear creep analysed by time-temperature (t-T) superposition and thermal sampling (TS) with correction procedures proposed by McCrum. In this range the kinetics do not follow the compensation rule, as had been proposed in the pioneering TS experiments by Zielinski, Swiderski and Kryszewski and by Lacabanne et al.. The McCrum correction removes a discrepancy between the pioneering TS experiments and the conclusions of classical t-T superposition experiments. The methods of TS and t-T superposition are compared. At low temperatures, below (T_g + 3°C), the TS method is superior: t-T superposition is unreliable due to lack of normalization and to the physical ageing perturbation. At temperatures from (T_g + 3°C) to (T_g + 11°C) t-T superposition is highly reliable since normalization is not required and there is no ageing. At temperatures above (T_g + 11°C) the precision of t-T superposition depends on the validity of the normalization procedure. It has yet to be determined whether or not the compensation rule applies at temperatures below (T_g ? 8°C): the method most likely to settle this important question is TS, mechanical or dielectric variant, with McCrum correction for the distribution of relaxation times.