Hydrogels based on N-isopropylacrylamide and methacrylic acid: thermal stability and glass transition behaviour

Summary The thermal stability and glass transition behaviour of crosslinked poly(N-isopropylacrylamide) [P(N-iPAAm)], poly(methacrylic acid) [P(MAA)], their random copolymers and sequential interpenetrating polymer networks (IPNs) have been investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). P(MAA) shows a two-step process of degradation. P(N-iPAAm) shows an unique process of degradation at higher temperature. Copolymers having higher content in N-iPAAm units have a lower thermal stability than their component homopolymers and show an unique degradation process at high temperature. On the contrary, enriched MAA copolymers show better stability but they exhibit two degradation steps at the main degradation region. Sequential IPN samples exhibit a better stability than their component homopolymers and copolymers. The high temperature backbone degradation occurs in only one step, which indicates the formation of a true interpenetrating network. The T _g of the same series of materials has been also measured. A T _g vs composition plot of P(N-iPAAm-co-MAA) copolymers presents a S-shaped curve indicating that structural units interact among them through strong specific interactions. For interpenetrating polymer networks, it seems that only one T _g occurs indicating a good compatibility and interpenetration. Received: 1 December 2001 /Revised version: 12 February 2002/ Accepted: 12 February 2002     

基于一种含吡啶的氟化二胺的聚酰亚胺合成与性能

对苯二酚依次与2-氯-5-硝基三氟甲苯和2-氯-5-硝基吡啶进行亲核取代反应，还原后制备了一种含吡啶杂环的氟化二胺单体6-{4-[4-氨基-2-(三氟甲基)苯氧基]苯氧基}吡啶-3-胺，并采用两步法将其与二酐聚合，得到4种芳香族聚酰亚胺（PI）。对所得PI的溶解性、耐热稳定性、光学性能、力学性能进行了测试。结果表明，基于4,4’-氧双邻苯二甲酸酐和六氟二酐的PI在常见有机溶剂中均具有良好的溶解性。N2氛围下，这些PI的5%和10%热失重温度分别在548.8～594.2和566.3～609.7℃之间，玻璃化转变温度在226～290℃之间，具有良好的耐热稳定性。这些PI薄膜有较好的光学透明度和力学性能，截止波长在382～438 nm范围内，500 nm处的透过率在52%～78%范围内，拉伸强度为98.3～110.5 MPa，杨氏模量为1.86～2.14 GPa，断裂伸长率为9%～23%。     

Poly(urethane-imide-imide), a new generation of thermoplastic polyurethane elastomers with enhanced thermal stability

A new generation of polyurethane thermoplastic elastomers were synthesized via the reaction of NCO-terminated polyurethane with 2,2′-pyromellitdiimidodisuccinic anhydride chain extender. The starting materials and polymers were characterized by conventional methods and physical, mechanical and thermal properties were studied. In comparison to typical polyurethanes, these polymers exhibited improved thermal stability as well as good processability and flexibility.     

Effect of side chain structure of polyimides on a pretilt angle of liquid crystal cells

A series of poly(amic acid)s had been synthesized from cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) and 4,4′-diaminodiphenyl methane (DDM) and functional diamines with various side chain structures. The functional diamines, like 3,5-diamino benzoic acid hexadecane-1-yl ester which had long alkyl or rigid alicyclic side chains with different flexibility had been synthesized. Pretilt angles of liquid crystal cell fabricated with the poly(amic acid)s were measured and investigated factors affecting on the pretilt angles. The pretilt angles of the liquid crystal on the polyimide (5a) with rigid side group was 0.6°, on the other hand, the pretilt angle on the polyimide (5b) and (5c) with flexible side chains were very high above 89.6°. Furthermore, the pretilt angle of liquid crystal on the polyimide (5c) film having rigid cylindrical structure with 6-methylheptyl at the chain end was still high above 86.0° even after the rubbing process.     

In situ poling and imidization of amorphous piezoelectric polyimides

An amorphous piezoelectric polyimide containing polar functional groups has been developed using a combination of experimental and molecular modeling for potential use in high temperature applications. This amorphous polyimide, (β-CN)APB/ODPA, has exhibited good thermal stability and piezoelectric response at temperatures up to 150 °C. Density functional calculations predicted that a partially cured amic acid (open imide ring) possesses a dipole moment four times larger than the fully imidized closed ring. In situ poling and imidization of the partially cured (β-CN)APB/ODPA was studied in an attempt to maximize the degree of dipolar orientation and the resultant piezoelectric response. A positive corona poling was used to minimize localized arcing during poling and to allow use of higher poling fields without dielectric breakdown. The dielectric relaxation strength, remanent polarization, and piezoelectric response were evaluated as a function of the poling profile. The partially cured, corona poled polymers exhibited higher dielectric relaxation strength (Δε), remanent polarization (P_r) and piezoelectric strain coefficient (d₃₃) than the fully cured, conventionally poled ones.     

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。     

过渡金属氧化物对苯并恶嗪热稳定性影响研究

将过渡金属氧化物TiO2、MnO2、CuO、Cu2O、ZnO、ZrO2以及Y2O3、CeO2、Sm2O3、Gd2O3分别添加到苯酚/4,4'-二苯甲烷二胺型苯并恶嗪(BB)中间体中,制备了过渡金属氧化物/BB固化物,通过FTIR、TGA和DMA分析研究了过渡金属氧化物对苯并恶嗪热稳定性的影响。结果表明,这些氧化物的添加不改变BB固化物的化学结构;除ZnO外,其他氧化物均使BB的热稳定性和800℃残炭率降低,这是由于过渡金属氧化物与BB中N原子间配位作用的形成削弱了C—N键,使其更易断裂。     

Adhesion of polyimides to ceramics: Effects of aminopropyltriethoxysilane and temperature and humidity exposure on adhesion

The effects of both y-aminopropyltriethoxysilane (APS) and elevated temperature and humidity (T&H) exposure on the adhesion of pyromellitic dianhydride-oxydianiline polyimide to SiO₂, Al₂O₃, and MgO were studied using XPS, SEM, and peel test. Adhesion and T&H stability of PMDA-ODA on SiO₂ is significantly improved when APS is used at the interface, while no significant improvement is observed for Al₂O₃ or MgO. XPS analysis of the surfaces showed no retention of APS on Al₂O₃ or MgO, while SiO₂ did retain APS, as is expected. The APS retention is affected by surface treatment of the oxide prior to APS application.     

Syntheses of novel soluble carborane polyimides with ultrahigh thermal stability

Novel carborane polyimides were synthesized and studied. Aromatic meta‐carborane diamines of different structures were initially prepared. Polymerization of these new diamines with the commercially available 4,4′‐oxydiphthalic dianhydride led to meta‐carborane polyimides with various structures and thermal properties. The amorphous polymers obtained are of moderate molecular weight and show good solubility in organic solvents. Thermal analyses of these polyimides reveal that they have moderate to ultrahigh thermal stability depending on their specific structures, with 5% decomposition temperatures ranging from 382 to 786 °C in nitrogen. Different thermal properties of these polyimides are observed when the analyses are performed in dry air, with 5% decomposition temperatures shifting to temperatures ranging from 388 to 1128 °C. Due to the ever‐present requirement of higher performance polymers in fields like aerospace and defense, the methods developed here could be an impetus for the development of these industries. © 2015 Society of Chemical Industry     

Effect of thermal history on mechanical properties of polyetheretherketone below the glass transition temperature

Tensile properties of polyethertherketone (PEEK) have been studied at 125, 25, and ?100°C for thin films prepared with different thermal histories. Initial morphology was controlled by rate of cooling from the melt. Amorphous films resulted from quenching the melt, while semicrystalline films were obtained by cooling the melt at different rates, or by crystallization of the rubbery amorphous state. The films were characterized using density, X-ray scattering, differential scanning calorimetry, and infrared spectroscopy. Scanning electron microscopy was used to examine fracture surfaces. Degree of crystallinity and rate of cooling from the melt affected the tensile properties at all test temperatures. For films with nearly the same degree of crystallinity, those which were more slowly cooled from the melt fractured at the lowest strain. The amorphous films were most tough, drawing to 233% at ?100°C and to over 500% at 125°C. Films crystallized from the rubbery amorphous state had stress–strain behavior intermediate between that of the amorphous and melt-crystallized films at all test temperatures. Density measurements on the drawn material indicate that void formation occurs simultaneously with the formation of fibrillar crystals. Necking resulted in density increases for amorphous films, and density decreases for the semicrystalline films.     

Effect of thermal history during drying and curing process on the chain orientation of rod-shaped polyimide

Chain orientation in polyimide (PI) film is influenced by the thermal history during drying and curing process. The amount of residual solvent and the degree of imidization, among other factors, play a major role in determining the chain orientation during the process. In the present study, poly(amic acid), the precursor of PI, coated on the glass substrate was imidized to PI through different drying and curing protocols. On the way of complete imidization, the residual solvent concentration and the degree of imidization were characterized using confocal Raman spectroscopy. The poly(amic acid) began to imidize quickly while retaining more solvent in the film as the initial drying temperature increased. The degree of in-plane chain orientation in fully imidized PI film made by different process protocols was compared using polarized Raman spectroscopy. The fully imidized PI showed the lowest degree of in-plane chain orientation when it was processed by the protocol with the highest drying temperature. The difference in the degree of in-plane chain orientation among different PI films significantly influenced the in-plane thermal expansion coefficient, while no significant change in crystallinity or glass transition temperature was observed.     

Organosoluble semi-alicyclic polyimides derived from 3,4-dicarboxy-1,2,3,4-tetrahydro-6-tert-butyl-1-naphthalene succinic dianhydride and aromatic diamines: Synthesis,characterization and thermal degradation investigation

Semi-alicyclic polyimides (PI-1–PI-4) have been prepared from a newly-developed alicyclic dianhydride, 3,4-dicarboxy-1,2,3,4-tetrahydro-6-tert-butyl-1-naphthalene succinic dianhydride (TTDA) and various aromatic diamines. The asymmetrical alicyclic tetralin structure in TTDA endowed the derived PI resins good solubility in various organic solvents. They were soluble not only in polar aprotic solvents but also in solvents with low boiling points including dichloromethane and tetrahydrofuran. Flexible and tough PI films were successfully cast from their N-methyl-2-pyrrolidone (NMP) solution except PI-1 derived from TTDA and 4,4′-oxydianiline (ODA). The PI films exhibited good optical transparency in the ultraviolet and visible light region with optical transmittances around 80% at a wavelength of 400 nm. The PI films showed good thermal stability up to 400 °C in nitrogen, after that they thermally decomposed rapidly. The thermal degradation behaviors of the PIs were investigated by means of thermogravimetric analysis-mass spectrometry (TG-MS), thermogravimetric analysis-Fourier transform infrared spectrometry (TG-FTIR) and the real time FTIR spectra (RT-FTIR) analysis techniques. The results revealed that the decomposition of PI-1 (as a representative) took place mainly in the range of 450–550 °C. The major degradative fragments at 500 °C were clearly identified as the tert-butyl-substituted tetralin moiety and its dealkylation products. Therefore, it can be deduced that for the TTDA-PIs, the single bond bridge attached the maleic anhydride and tetralin anhydride units in TTDA moiety might break first during the heating; thus producing the tetralin fragments.     

Synthesis and thermal polymerization of new polyimides with pendant phthalonitrile units

New polyimides with pendant phthalonitrile units were synthesized via the conventional two-step polymerization approach. The chemical structure of the PIs was confirmed by IR and ¹H NMR spectra. The thermogravimetric analysis and differential scanning calorimetry revealed that the thermal properties of the new PIs along with their solvent-resistance can be promoted after thermal treatment at 300 °C. This promotion can be attributed to the nitrile cure reaction of the phthalonitrile units indicated by the decrease in nitrile absorptions at around 2231 cm⁻¹ of the IR spectra.     

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.     

Addition polyimides. IV. Effect of structure on thermal characteristics

Chain extension reaction of bis(m-maleimido phenyl) methyl phosphine oxide (BP) with 4,4′-diaminodiphenylmethane (BP–M), 4,4′-diaminodiphenyl ether (BP–E), 3,3′- and 4,4′-diaminodiphenyl sulfone (BP–DDS_m and (BP-DDS_m respectively), tris (m-aminophenyl) phosphine oxide (BP–TAP), and 9,9-bis(p-aminophenyl) fluorene (BP–BAF) was carried out by refluxing 1:0.3 molar solution of BP:diamine. The melting temperature and exothermic peak associated with curing of BP decreased by such chain extension. The thermogravimetric analysis indicated more than 60% residual weight at 800°C in nitrogen atmosphere in BP–DDS_m, BP–DDS_p, and BP–TAP resins. These resins can be processed at low temperature and can be used for fabrication of composites with improved properties.     

Effect of thermal history on water sorption,elastic properties and the glass transition of epoxy resins

The DGEBA/TETA (diglycidyl ether of bisphenol-A/triethylene tetramine) system was examined in postcuring conditions at 100°C for 3 and 6 days. Sorption kinetics and equilibria at different temperatures and mechanical tests have been performed on the two sets of samples. Thermal treatment of the epoxy resin containing sorbed water affects its subsequent water sorption characteristics, elastic modulus and glass transition temperature. Attention has also been given to the effects on solubility on thermal history in the presence of water. It was observed that the saturation values in such systems are determined once the higher temperature of the thermal cycle is defined. The differences in solubility of samples with different hygrothermal history are explained in terms of microcavities that can be formed by effect of crazing in the plasticized system exposed to high temperatures.     

Macro and meso porous polymeric materials from miscible polysulfone/polyimide blends by chemical decomposition of polyimides

Novel macro and meso porous polysulfone materials were prepared from miscible blends of polysulfones with a phenylindane containing polyimide by selective chemical decomposition of the polyimide phase using a dilute hydrazine or tetraammonium hydroxide solution in methanol. It was found that the pore size of the material is affected by the backbone structure of the polysulfone selected. The compatibility between the polysulfones and the polyimide is influenced by the polysulfone structure. This in turn affects the pore size and the pore size distribution of the final porous material. Polyether sulfone was found to form most compatible blends that in turn leads to a porous material with the smallest pore size, a meso porous material. The meso porous polyether sulfones are transparent films, with uniform pore sizes in the range of 30 nm, while bisphenol A polysulfone based porous materials are opaque with pore sizes in the range of 200 nm.     

Synthesis of thermal stability and wear resistance of glass ceramics

Translated from Steklo i Keramika, No. 5, pp. 12–13, May, 1990.     

Synthesis and characterization of polyimides with low dielectric constants from aromatic dianhydrides and aromatic diamine containing phenylene ether unit

New aromatic polyimides (PIs) having the lowest dielectric constant in nonfluorinated PIs have been developed from aromatic dianhydrides and an aromatic diamine containing phenylene ether units. The diamine monomer was prepared from 4-bromophenyl ether in five steps. Polycondensations were performed in 1-methyl-2-pyrrolidinone at room temperature for 18 h, giving poly(amic acid)s (PAAs) with inherent viscosities up to 0.53 dl/g. PAAs were converted to corresponding poly(imide)s (PIs) by thermal treatment at 300 °C. New PIs showed good thermal stability (5% weight loss around 450 °C) and the low dielectric constant (2.74).