The effect of furan molecular units on the glass transition and thermal degradation temperatures of polyamides

Interfacial polymerization is used to prepare biobased furan polyamides from the carbohydrate‐derived monomer, 2,5‐furan dicarboxylic acid, aromatic diamines, and varying chain length aliphatic diamines. The molecular weights of the furan polyamides variations range 10,000–70,000 g/mol. These biobased polyamides have improved solubility relative to petroleum‐derived polyamides affording enhanced processability options. The glass transition temperatures (T_g) of the biobased furan polyamides are higher than that of aliphatic analogs, but lower than phenyl‐aromatic analogs. The T_g for these furan polyamides are as high as 280 °C. Also, the furan polyamide glass transition temperatures increase with decreasing aliphatic diamine chain length similar to results exemplified in petroleum‐based nylons. Group contribution parameters are determined for furans to enable simple prediction of the glass transition temperature and decomposition temperature of furan polyamides. The molar glass transition function for the furan is calculated to be 27.6 ± 1.5 K kg/mol. Thermal analysis measurements of the biobased furan polyamides have maximum thermal degradation temperatures at 350 °C or higher, similar to that of aliphatic polyamides when scaled with the number average molecular weight. The molar decomposition temperature functions are determined to be 37 K kg/mol for furans bonded to aliphatic units and 42 K kg/mol for furans bonded to phenyl units. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45514.     

Hybrid Sol–Gel Glasses with Glass‐Transition Temperatures Below Room Temperature

Melting gels are hybrid gels that have the ability to soften and flow at around 100°C for some combinations of mono‐ and di‐substituted alkoxysiloxanes, where substitutions are either all aromatic or all aliphatic. In this study, melting gels were prepared using phenyltriethoxysilane (PhTES) and dimethyldiethoxysilane (DMDES), meaning both an aromatic and aliphatic substitution. Differential scanning calorimetry was performed to identify glass‐transition temperatures, and thermal gravimetric analysis coupled with differential thermal analysis (TGA‐DTA) was performed to measure weight loss. The glass‐transition temperatures (T_g) ranged from ?61°C to +5.6°C, which are between the values in the methyl only system, where all T_g values are less than 0°C, and those values in the phenyl only system, where T_g values are greater than 0°C. The T_g decreased with an increase in the DMDES fraction. Below 450°C, the gels lost little weight, but around 600°C there was a drop in weight. This temperature is lower than the temperature for gels prepared with only aromatic substitutions, but higher than that for gels prepared with only aliphatic substitutions. Final heat treatment was carried out at 150°C for the gel with 80%PhTES‐20%DMDES (in mol%), and the consolidation temperature increased with increasing DMDES content to 205°C for the gel with 50%PhTES‐50%DMDES. After this heat treatment, the melting gels no longer soften.     

Synthesis and properties of silicon-containing bismaleimide resins

Two novel bismaleimide (BMI) monomers containing silicon atom in the structure, i.e., bis[4-(4-maleimidophenylcarbonyloxy)phenyl]dimethylsilane (BMI-SiE1) and bis[4-(4-maleimidophenyloxycarbonyl)phenyl]dimethylsilane (BMI-SiE2), were designed, synthesized, and polymerized with and without the use of diamine as comonomers to yield novel silicon-containing BMI resins. Both monomers obtained are readily soluble in organic solvents, such as chloroform and N, N-dimethylformamide. Differential scanning calorimetry and thermogravimetric analysis investigation of these two monomers indicated a high polymerization temperature (T_p > 240°C) and a good thermal and thermo-oxidative stability of cured BMI resins. The onset temperature for 5% weight loss was found to be above 450°C in nitrogen and above 400°C in the air. Polymerization of BMI-SiE1 and BMI-SiE2 with 4,4′-diaminodiphenylether (DPE) yielded a series of polyaspartimides that had good solubility and could be thermally cured at 250°C. TGA investigations of the cured diamine-modified BMI resins showed onset of degradation temperatures (T_ds) in the range of 344–360°C in nitrogen and 332–360°C in the air. Composites based on the cured diamine-modified BMI resins and glass cloth were prepared and characterized for their dynamic mechanical properties. All the composites showed high glass transition temperatures (e.g., >190°C) and high bending modulus in the range of 1000–2700 MPa. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and properties of bismaleimide resins of aromatic sulfone ether diamine

Aromatic sulfone ether diamine, bis[4-(4-aminophenoxy)phenyl]-sulfone (SED), was prepared by the nucleophilic aromatic substitution of 4,4′-dichlorodiphenylsulphone by p-aminophenolate. The reaction was conducted in the presence of excess potassium carbonate as a weak base, toluene as the dehydrating agent and N-methylpyrrolidone as the dipolar aprotic solvent. SED showed good solubility in common organic solvents, such as dioxan, tetrahydrofuran, butanone and acetone. SED was reacted with maleic anhydride to obtain aromatic sulfone ether bismaleimide, bis[4-(4-maleimidophenoxy)phenyl]-sulfone (SEM). The compounds were characterized by FTIR and ¹H NMR analysis. Furthermore, copolymer resins of SED with 4,4′-bismaleimidodiphenyl methane (BMI) and SEM were prepared. After curing, crosslinked resins with better thermal stability resulted. The temperature at maximum rate of weight loss (T_max) and the heat-resistant temperature index (T_i) in air were found to be 426°C, 208°C and 579°C, 221°C for BMI/SED and SEM/SED resins, respectively. Compared with the corresponding 4,4′-diaminodiphenyl methane (DDM) system, BMI/SED and SEM/SED showed a slight decrease in T_max and T_i SED-modified BMI/amine resin based glass cloth laminates for printed circuit boards showed higher mechanical properties than those of the corresponding unmodified system. With SED instead of the original amine component in 3–5% weight fraction, the tensile strength, flexural strength and impact strength of the laminates increased markedly. Meanwhile, the stripping strength and weld resistance were also improved by the addition of SED.     

Structure–stability correlation of copolyimide membranes derived from aliphatic/alicyclic/aromatic diamine and aromatic dianhydrides

New polyamic acids with ‐A‐B‐A‐C‐ type periodic sequence of monomeric units (A derived from a diamine, B from benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride, and C from benzene‐1,2,4,5‐tetracarboxylic dianhydride) are prepared and transformed into polyimide membranes that are examined by various methods in order to investigate the influence of diamine units (aliphatic, alicyclic, or aromatic) on the morphology, thermal stability, and mechanical properties of membranes. Small‐ and wide‐angle X‐ray scattering and Atomic force microscopy show amorphous character of all membranes except for those containing hexane‐1,6‐diamine units. Thermogravimetric analysis reveals a decrease in the initial decomposition temperature from 551/501 °C to 437/395 °C (for N₂/O₂ atmosphere) when going from membranes with aromatic to those with aliphatic diamine units. Dynamic mechanical analysis shows quite high initial storage modulus (2100–3300 MPa) for all membranes at frequencies of 1, 10, and 20 Hz. The properties of prepared copolymeric polyimide are promising for a wide range of their potential technological applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45227.     

Thermal behavior of aliphatic–aromatic poly(ether-amide)s

The thermal properties of a set of experimental aliphatic–aromatic polyamides containing ether linkages were examined as a function of their chemical structure. Variations of the glass transition temperature (T_g) and melting temperature (T_m) could be correlated with the length of the aliphatic spacers and with the orientation of the phenylene rings. Polymers with a high concentration of p-oriented phenylene units showed a higher T_g than those containing mainly m-oriented ones; T_g values ranged from 110 to 155°C. Surprisingly, a negligible dependence of T_gs on the nature of flexible spacers was observed. For all of the polymers, the thermal stability was virtually the same, about 440°C, when tested by dynamic thermogravimetric analysis (TGA). However, quite different levels of thermal stability were found by isothermal TGA analysis for polyamides with different flexible spacers. Moreover, the poly(ether-amide)s described here compare fairly well with wholly aromatic polyamides when measured by dynamic TGA; but isothermal TGA measurements clearly demonstrated that they decompose faster than aromatic polyamides. Treatment of the TGA curves by the method of McCallum provided kinetic data that confirmed a better long-term stability for poly(ether-amide)s with a higher proportion of para-oriented phenylene rings. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:975–981, 1998     

Studies of phosphonate‐containing bismaleimide resins. I. Synthesis and characteristics of model compounds and polyaspartimides

Two phosphonate‐containing bismaleimide (BMI) [(4,4′‐bismaleimidophenyl)phosphonate] monomers with different melting temperatures and similar curing temperatures were synthesized by reacting N‐hydroxyphenylmaleimide with two kinds of dichloride‐terminated phosphonic monomers. The BMI monomers synthesized were identified with ¹H‐, ¹³C‐, and ³¹P‐nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The phosphonate‐containing BMI monomers react with a free‐radical initiator to prepare phosphonate‐containing BMI polymers and also with various aromatic diamines to prepare a series of polyaspartimides as reactive flame retardants. The polymerization degrees of polyaspartimides depend on the alkalinity and nucleophility of diamines as chain extenders. Differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA) were used to study the thermal properties of the phosphonate‐containing BMI resins such as the melting temperature, curing temperature, glass transition temperature (T_g), and thermal resistance. All the phosphonate‐containing BMI resins, except the BMI polymers, have a T_g in the range of 210–256°C and show 5% weight loss temperatures (T_5%) of 329–434 and 310–388°C in air and nitrogen atmospheres, respectively. The higher heat resistance of cured BMI resin relative to the BMI polymer is due to its higher crosslinking density. Since the recrosslinking reactions of BMI polymers and polyaspartimides occur more easily in an oxidation environment, their thermal stabilities in air are higher than are those in nitrogen gas. In addition, the thermal decomposition properties of polyaspartimides depend on the structures and compositions of both the diamine segments and the BMI segments. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1919–1933, 2002     

Preparation,analysis, and isothermal crystallization behavior of poly[1,3‐bis(aminomethyl)cyclohexamethylene oxamide]

Poly[1,3‐bis(aminomethyl)cyclohexaneoxamide] (PBAC2) was synthesized using 1,3‐bis(aminomethyl)cyclohexane (BAC) and dibutyl oxalate (DO) via spray/solid‐state polycondensation (SSP). The structure of the synthesized polyoxamide was confirmed by ¹H‐nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy. The weight average molecular weight (M_w) of the polyoxamides prepared was 1.35 × 10⁵. The polyoxamides showed excellent thermal properties with glass transition temperature (T_g) of 150 °C, melting temperature (T_m) of 318 °C, crystallization temperature(T_c) of 253 °C, and initial degradation temperature (T_d) of 417 °C suggesting higher thermal stability than commercial polyamide 6 (T_d = 378 °C). Kinetic studies of PBAC2 predicted a two‐dimensional crystal growth. X‐ray diffraction powder diffraction suggested that the polymer has high crystallinity. A saturated water absorption of 2.8 wt % was recorded for the new polyoxamide, giving it a competitive edge for applications in civil aviation, reinforced plastics, and electronics industry where precise dimensional stability and high thermal resistance properties are a priority. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46345.     

High glass transition temperature bismaleimide‐triazine resins based on soluble amorphous bismaleimide monomer

A novel bismaleimide (DOPO‐BMI) with unsymmetrical chemical structure and DOPO pendant group has been prepared. The particular molecular structure makes DOPO‐BMI show an intrinsic amorphous state with a T_g about 135°C and excellent solubility in most organic solvents, which is beneficial to the processability of bismaleimide composite materials. A series of bismaleimide‐triazine (BT) resins have been prepared based on DOPO‐BMI and 2,2‐bis(4‐cyanatophenyl)propane at various weight ratios. The prepared BT resins show outstanding solubility in organic solvent and low viscosity about 10–671 mPa s at 180°C. The cured BT resins exhibit high glass transition temperature (T_g) over 316°C. As the weight ratio of DOPO‐BMI increases to 80% (BT80), the T_g can rise to 369°C (tan δ). The cured BT resins also show good thermal stability with the 5% weight loss temperature over 400°C under both nitrogen and air atmosphere. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42882.     

Synthesis of soluble and thermally stable polyamides from diamine containing (quinolin‐8‐yloxy) aniline pendant group

A novel diamine monomer having pendant 4‐(quinolin‐8‐yloxy) aniline group was successfully synthesized via aromatic substitution reaction of 8‐quinolinol with p‐fluoronitrobenzene followed by Pd/C catalyzed hydrazine reduction, amidation reaction between 4‐(quinolin‐8‐yloxy) aniline and 3,5‐dinitrobenzoylcholoride followed by Pd/C catalyzed hydrazine reduction. The diamine monomer was fully characterized by using FTIR, ¹H‐NMR, ¹³C‐NMR, and elemental analysis. The diamine monomer was polymerized with various aromatic and aliphatic dicarboxylic acids to obtain the corresponding polyamides. The polyamides had inherent viscosity in the range of 0.30–0.41 dL/g and exhibited excellent solubility in the polar aprotic solvents such as DMAc, NMP, N,N‐dimethylformamide, Pyridine, and DMSO. The glass transition temperatures (T_g) of the polymers are high (up to 313°C) and the decomposition temperatures (T_i) range between 200 and 370°C, depending on the diacids residue in the polymers backbone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and properties of polytriazoleimide containing anthracene,pyridine and 1, 2, 3‐triazole groups and their nanocomposites with titanium dioxide

A novel anthracene, pyridine and 1, 2, 3‐triazole containing diamine was synthesized by copper catalyst 1, 3‐dipolar cycloaddition of azides and alkynes groups (Click reaction). A series of polytriazoleimide (PTAI) nanocomposites were successfully prepared by condensation polymerization between the synthesized diamine monomer and commercially available pyromellitic dianhydride with different weight percentage of titanium dioxide (TiO₂). The structure of the monomer and polymer were confirmed by the fourier transform infrared and nuclear magnetic resonance spectroscopy. The synthesized PTAI is readily soluble in common polar solvents. The PTAIs naocomposites exhibited high thermal stability, the temperature corresponding to a 5% weight loss in the range of 495°C–555°C, excellent flame retardancy (char yield were found to be in the range of 48.1–66.4) and high glass transition temperature (T_g) at (267°C–294°C). Furthermore incorporation of TiO₂ into the PTAI matrix significantly improve the dielectric constant (2.70–4.75 at 1MHz) and dielectric loss (0.06–0.46 at 1 MHz). POLYM. ENG. SCI., 59:129–138, 2019. © 2018 Society of Plastics Engineers     

Fabrication and characterization of soluble,high thermal,and hydrophobic polyimides based on 4‐(3,5‐dimethoxyphenyl)‐2,6‐bis(4‐aminophenyl)pyridine

A novel aromatic diamine monomer, 4‐(3,5‐dimethoxyphenyl)‐2,6‐bis(4‐aminophenyl)pyridine (DPAP) was successfully synthesized by 4′‐nitroacetophenone and 3,5‐dimethoxybenzaldehyde as raw material. The structure of DPAP was confirmed by Fourier transform infrared, nuclear magnetic resonance, and mass analysis. A series of polyimides (PIs) were obtained by polycondensation with various dianhydrides via the conventional two‐step method. These PIs showed good solubility in organic solvents. They also presented high thermal stability, the glass transition temperatures (T_g) of polymers were in the range of 325–388 °C, and the temperature at 10% weight loss was in the range of 531–572 °C. Furthermore, these polymers also exhibited outstanding hydrophobicity with the contact angles in the range of 89.1°–93.5°. Moreover, the results of wide‐angle X‐ray diffraction (WAXD) confirmed these polymers showed amorphous structure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45827.     

Facile Synthesis of Ferrocene-Based Polyamides and Their Organic Analogues Terpolyamides: Influence of Aliphatic and Aromatic Sequences on Physico-Chemical Characteristics

Efforts have been devoted to synthesize and characterize processable polymers with desired properties. Herein, four different series of aromatic and aliphatic terpolyamides were prepared via solution phase polycondensation of 4,4′-oxydianiline and hexamethylenediamine (HMDA) with various diacids chlorides (isophthalyol dichloride, terepthalyol dichloride, 1, 1′-ferrocene dicarboxylic acid chloride and trans-azobenzene-4, 4′-dicarbonyl chloride). The structural, morphological and physico-chemical nature of as prepared polymers was explored by Fourier-transform infrared spectroscopy, scanning electron microscopy, thermal analysis (TGA and DSC), and wide-angle x-ray diffraction. Moreover, an aliphatic diamine was incorporated in varying concentration as a flexible methylene spacer and the effect of its concentration on the properties of polyamides was also studied. Changes in various physico-chemical properties such as solubility, inherent viscosity, surface morphology and flame retarding behaviour were investigated. Marked difference in morphology and solubility was observed with the change in the ratio of segments in the chain. Inherent viscosities of polymers ranged from 1.8052–1.6274 dl/g indicating reasonably moderate molecular weights. Interestingly, ferrocene based aromatic polymers were more thermally stable (T_g 260 °C, T_i 310 °C, T_h 525 °C, T_f 720 °C, for PF₀), and also found to exhibit best flame retarding behavior (limiting oxygen index value for PF₀is LOI 33.15%).

     

Accelerant‐promoted free radical polymerization of methacrylates by stabilized nitroxide unimolecular initiators: synthesis and characterization

BACKGROUND: This investigation evaluates the effectiveness of initiator adducts for living and controlled polymerization of methacrylates, crosslinking of dimethacrylates and thermal stabilities of the resulting polymers. Adducts of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy with benzoyl peroxide and with azobisisobutyronitrile were prepared and evaluated as stabilized unimolecular initiators for the free radical polymerization of methacrylate monomers using sulfuric acid as catalyst. The monomers used were methyl methacrylate, triethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA). RESULTS: Successful polymerization was achieved at 70 and 130 °C with reaction times ranging from 45 min to 120 h. The dispersity (D) of poly(methyl methacrylate) (PMMA) was 1.09–1.28. The livingness and extent of control over polymerization were confirmed with plots of M_n evolution as a function of monomer conversion and of the first‐order kinetics. The glass transition temperature (T_g) for PMMA was 123–128 °C. The degradation temperature (T_d) for PMMA was 350–410 °C. T_d for poly(TEGMA) was 250–310 °C and for poly(EBPADMA) was 320–390 °C. CONCLUSION: The initiators are suitable for free radical living and controlled polymerization of methacrylates and dimethacrylates under mild thermal and acid‐catalyzed conditions, yielding medium to high molecular weight polymers with low dispersity, high crosslinking and good thermal stability. Copyright © 2008 Society of Chemical Industry     

Synthesis and characterization of novel polyimides derived from 2‐amino‐5‐(4‐aminophenyl)‐thiazole

A new kind of aromatic unsymmetrical diamine monomer containing thiazole ring, 2‐amino‐5‐(4‐aminophenyl)‐thiazole (AAPT), was synthesized. A series of novel polyimides were prepared by polycondensation of AAPT with various aromatic dianhydrides by one‐step polyimidation process. The synthesized polyimides had inherent viscosity values of 0.36–0.69 dL/g and were easily dissolved in highly dipolar solvents. Meanwhile, strong and flexible polyimide films were obtained, which have good thermal and thermo‐oxidative stability with the glass transition temperatures (T_g) of 276.7–346.1°C, the temperature at 5% weight loss of 451–492°C in nitrogen and 422–440°C in air, as well as have outstanding mechanical properties with the tensile strengths of 94–122 MPa, elongations at breakage of 5–18%. These films also had dielectric constants of 3.12–3.38 at 10 MHz. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and electro‐optic properties of novel Y‐type polyimides with highly enhanced thermal stability of second harmonic generation

BACKGROUND: In the development of nonlinear optical (NLO) polymers for electro‐optic device applications, stabilization of electrically induced dipole alignment is one of the important criteria. Polyimides for NLO applications have attracted attention because of their high T_g values and high thermal stability. In this work we designed and synthesized a new type of NLO polyimide, in which the pendant NLO chromophores are parts of the polymer backbone. These mid‐type NLO polymers are expected to have the merits of both main‐chain and side‐chain NLO polymers: stabilization of dipole alignment and good solubility. RESULTS: 3,4‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐4′‐nitrostilbene dianhydride was prepared and reacted with the corresponding aromatic diamine to yield unprecedented Y‐type polyimides containing 3,4‐dioxynitrostilbenyl groups as NLO chromophores, which constituted parts of the polymer backbones. The resulting polyimides are soluble in polar solvents such as dimethylformamide and dimethylsulfoxide. These polymers showed a thermal stability up to 320 °C in thermogravimetric thermograms with T_g values obtained from differential scanning calorimetry thermograms in the range 143–164 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064 nm^?1 fundamental wavelength were around 9.45 × 10^?18 C. CONCLUSION: The dipole alignment exhibited exceptionally high thermal stability even at 30 °C higher than T_g. There was no SHG decay below 180–190 °C because of the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. Copyright © 2007 Society of Chemical Industry     

Network polyester films from glycerol and dicarboxylic acids

This paper presents information on the preparation of the network polyester films from glycerol (Y_g) and aromatic dicarboxylic acids of phthalic anhydride (P), dimethyl isophthalate (I) and dimethyl terephthalate (T), as well as aliphatic dicarboxylic acids of adipic, sebacic, 1, 10-decanedicarboxylic and 1, 12-dodecanedicarboxylic acids, and their properties. Y_g and dicarboxylic acid were polycondensed immediately before the gelation started. The prepolymers obtained were cast from DMF solution and successively post-polymerized at various temperatures and times to form networks. The resultant films were transparent, flexible and insoluble in organic solvents. Heat distortion temperature (T_h) measured by a penetration mode of thermomechanical analysis increased with increasing post-polymerization temperature and time, and then leveled out. T_h values corresponded well to the glass transition temperature (T_g) measured by differential thermal analysis (DTA). T_h was 152°C, 162°C and 197°C for Y_gP, Y_gI and Y_g T post-polymerized at 270°C for 6 h, respectively. T_h values of network films made from aliphatic dicarboxylic acids could not be observed until complete probe penetration occurs, as a result of thermal decomposition because the T_g is lower than room temperature. The degree of reaction estimated from the IR absorbance of hydroxyl and methylene groups was in the range of 60–80%. Two diffraction peaks appeared in the wide-angle X-ray scattering pattern, suggesting some ordered structure owing to the regular networks. Density decreased with increasing post-polymerization time and temperature, in the order Y_gP > Y_gI > Y_gT. Network films made from aliphatic dicarboxylic acids had much lower tensile strength and Young's modulus, and greater elongation, than those made from dicarboxylic acids, as a result of the T_g being below room temperature.     

Effects of the o‐aromatic ring in the molecular chain on the properties of polyester polyols

A series of liquid polyester polyols from adipic acid (AA), phthalic anhydride (PA), ethylene glycol, propanediol‐1,2, and trihydroxymethylpropane, varying in the molar ratio of PA to AA, were prepared. The effects of the o‐aromatic ring in the molecular chain, which came from PA, on the viscosity, glass‐transition temperature, and thermal degradation temperature of the polyester polyols were studied with viscometry, differential scanning calorimetry, and thermogravimetry. The intrinsic viscosity and glass‐transition temperature increased with the concentration of the o‐aromatic ring increasing. The temperature of the maximum thermal degradation rate for aliphatic polyester polyols was 434.20°C. Two steps of thermal degradation were found when there were o‐aromatic rings in the molecular chain. One thermal degradation temperature was 358.36–360.48°C, and the other was 412.85–427.18°C. Polyester polyols with o‐aromatic rings had higher stability at lower temperatures (<240.00°C). However, aliphatic polyester polyols had higher stability at higher temperatures (300.00–480.00°C). The activation energy and order of degradation were calculated from thermogravimetric curves. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1617–1624, 2002     

Soluble polyimides with propeller shape triphenyl core for membrane based gas separation

This article reports the synthesis and characterization of a series of new aromatic polyimides (PIs) having bulky tert butyl group containing propeller shaped triphenylamine unit in its structure. The PIs were prepared by the reaction of 4,4′‐diamino‐4″‐(2,4,6‐tri‐tert‐butylphenoxy) triphenylamine with different commercially available aromatic dianhydrides through the formation of corresponding poly(amic acid)s and subsequent thermal cycloimidization. The PIs showed high glass transition temperature (T_g up to 270 °C) and thermal stability (T_d10 up to 475 °C). The PI membranes showed good mechanical properties with tensile strength up to 70 MPa, excellent separation performance [P(CO₂) = 100.8, P(O₂) = 40.4 barrer], and good permselectivity [P(CO₂)/P(CH₄) = 50.9, P(O₂)/P(N₂) = 7.6]. The membranes exhibited extremely high solubility selectivity for the CO₂/CH₄ gas pair due to the strong affinity between CO₂ and nitrogen atoms of tertiary amine in triphenylamine. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46658.     

Superstructure and mechanical properties of poly(ethylene terephthalate) fibers zone‐drawn under critical necking tension

The superstructure and mechanical properties of poly(ethylene terephthalate) fibers zone‐drawn under a critical necking tension (σ_c) were studied. σ_c was defined as the minimum tension needed to generate a neck at a given drawing temperature (T_d) and was measured over a temperature range of 70–120°C. The σ_c value increased rapidly with decreasing T_d in the temperature range below 85°C, but the temperature dependence of σ_c was small above 85°C. The neck profile relied on T_d, becoming more shapely with decreasing T_d. A neck with a gradual decrease in diameter was observed in the fibers drawn at 100°C and above. The draw ratio increased significantly with increasing T_d above 90°C, but birefringence decreased. Density decreased gradually with increasing T_d, and fiber drawn at 120°C had a density of 1.347 g/cc. Wide‐angle X‐ray diffraction photographs of the fibers drawn at 100°C and below showed reflections due to crystallites, but a photograph of the fiber obtained at 120°C showed a ring‐like amorphous halo. The storage modulus (E′) at 25°C increased progressively with decreasing T_d, and the fiber drawn at 70°C had the maximum E′ value among the fibers drawn at a series of T_d's. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 179–185, 2002