Imide-aryl ether benzoxazole random copolymers

Novel imide-aryl ether benzoxazole copolymers were prepared and their morphology and mechanical properties investigated. A key feature of these copolymers is the incorporation of a benzoxazole moiety by the use of 2,2′-bis[4-(3-aminophenoxy)phenyl]-6,6′-bibenzoxazole or 2,2′-bis[4-(4-aminophenoxy)-phenyl]-6,6′-bibenzoxazole as co-diamines in polyimide syntheses. The preparation of these diamines involved the nucleophilic aromatic substitution of 2,2′-bis(4-fluorophenyl)-6,6′-bibenzoxazole with either 3- or 4-aminophenol in the presence of K₂CO₃. The diamines were co-reacted with various compositions of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) to synthesize the desired poly(amic acids). Films were cast and cured (350°C) to effect the imide formation, affording films with elongations between 40 and 110% and moduli in the 2000–2750 MPa range. The copolymers exhibited good dimensional (T_g in excess of 300°C) and thermal stability. Wide-angle X-ray diffraction measurements on the copolymers showed that the ordered morphology characteristic of PMDA/ODA polyimide was retained. Improvements in the auto-adhesion were observed, particularly in those copolymers which displayed a T_g.     

Preparation and properties of novel poly(urethane-imide)s

A series of poly(urethane-imide)s were prepared by a novel approach. Polyurethane (PU) prepolymer was prepared by the reaction of polyester polyol and 2,4-tolylenediisocyanate (2,4-TDI), and then end-capped with phenol. The PU prepolymer was blended with poly(amide acid) or oligo(amide acid) prepared from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and oxydianiline (ODA) at room temperature in various weight ratios. The blend films obtained by casting and then drying were not transparent, suggesting that phase separation occurred between the polyimide (PI) and PU components. The films became transparent, however, after thermal treatment at 100°C and then 200°C for 1 h each, irrespective of the ratio of the two components. The poly(urethane-imide) films showed good solvent-resistance. Dynamic mechanical analysis of the films showed that glass transition temperatures (T_g) shifted depending on the ratio of PI and PU components. This shift of T_g, along with the transparency of the films, suggests that the PU and PI components employed here are miscible to some extent and that domains of each phase by microphase separation are small. Tensile measurement of the blend films from poly(amide acid) showed that the films are plastic or elastic, depending on the ratio of the components. Thermal stability of the PU was found to increase by the incorporation of polyimide component.     

Organo-soluble, segmented rigid-rod polyimide films: 2. Properties for microelectronic applications

The essential properties of polyimide films of importance in microelectronic applications are thermal and thermo-oxidative stability, dimensional stability, glass transition behaviour and the relative permittivity (dielectric constant ′). A segmented rigid-rod polyimide was synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) in order to develop new materials for microelectronic applications. The thermal and thermo-oxidative stability were investigated by determining the thermal degradation activation energy in air (210 kJ mol⁻¹) and in nitrogen (303 kJ mol⁻¹). The thermal stability was further studied through thermogravimetry-mass spectroscopy. The coefficient of thermal expansion, which indicates the dimensional stability, was measured via a tension mode of a thermomechanical analyser and doubly extrapolated to zero stresses, and was 6.98 × 10⁻⁶°C⁻¹ for the BPDA-PFMB films. The glass transition temperature, measured thermomechanically, was found to be 287°C. The dielectric constant for the films, measured after ageing at 50% relative humidity for 48 h at 23°C, was between 2.8 and 2.9 in a frequency range from 0.1 kHz to 1 MHz. The temperature and frequency dependence of the dielectric behaviour is also discussed.     

Synthesis and Characteristics of Novel Poly(Imide Siloxane) Segmented Copolymers

New poly(imide siloxane) copolymers for possible use as tough environmentally stable structural matrix resins and structure adhesives have been prepared. Thus, 3,3'-4,4'-benzophenone tertracarboxylic dianhydride was reacted with various Mn aminopropyl-terminated polydimethylsiloxane oligomers and a meta-substituted diamine “chain-extender” such as 3,3'-diaminodiphenyl sulfone or 3,3'-diaminobenzophenone to produce the siloxane-modified poly(amic acid). Thin films were cast from the reaction mixtures and subsequent thermal dehydration produced the poly(imide siloxane) block or segmented copolymers. Upper “cure” temperatures of 300°C were used to insure complete imidization. By varying the amount and molecular weight of the siloxane oligomer, a variety of novel copolymers of controlled composition have been synthesized. Tough, transparent, flexible soluble films were produced by this method. The thermal and bulk properties of films having low to moderate siloxane content closely resemble those of the unmodified polyimide controls. However, toughness and surface behavior can be enhanced.     

New kinds of phenylethynyl-terminated polyimide oligomers with low viscosity and good hydrolytic stability

In continuing studies to develop low melt viscosity phenylethynyl end-capped imide oligomers for aerospace applications, new kinds of all-aromatic phenylethynyl-terminated imide oligomers were prepared by the reaction of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) or biphenylenetetracarboxylic dianhydride (s-BPDA) with 2,5-bis(4-aminophenoxy)-biphenyl (p-TPEQ) and 4-phenylethynylphthalic anhydride (PEPA) or 4-(1-phenylethynyl)1,8-naphthalic anhydride (PENA). The oligomers bearing pendant phenyl groups exhibit much lower melt viscosities at low temperatures, and thus provide wide processing window. The thermal curing process of the oligomers was investigated with DSC. The tensile and thermal properties of the cured films were evaluated. Oligomers derived from PENA cured at lower temperatures and the corresponding cured polymers show better hydrolytic stability than those of PEPA. Results showed that the utilization of diamine monomer (p-TPEQ) can improve the processability and solubility of phenylethynyl-terminated imide oligomers without sacrificing their thermo-oxidative stability.     

Novel organosoluble fluorinated polyimides derived from 1,6-bis(4-amino-2-trifluoromethylphenoxy)naphthalene and aromatic dianhydrides

A novel trifluoromethyl-substituted bis(ether amine) monomer, 1,6-bis(4-amino-2-trifluoromethylphenoxy)naphthalene, was prepared through the nucleophilic substitution reaction of 2-chloro-5-nitrobenzotrifluoride and 1,6-dihydroxynaphthalene in the presence of potassium carbonate in dimethyl sulfoxide, followed by catalytic reduction with hydrazine and Pd/C in ethanol. A series of new fluorinated polyimides were synthesized from the diamine with various commercially available aromatic tetracarboxylic dianhydrides via a conventional two-stage process with the thermal or chemical imidization of the poly(amic acid) precursors. Most of the polyimides obtained from both routes were soluble in many organic solvents such as N-methyl-2-pyrrolidone and N,N-dimethylacetamide. All the polyimides could afford transparent, flexible, and strong films with low moisture absorptions of 0.12–0.52% and low dielectric constants of 2.75–3.13 at 10 kHz. Thin films of these polyimides showed an UV–vis absorption cutoff wavelength at 376–428 nm, and those of polyimides from 4,4′-oxydiphthalic dianhydride (ODPA) and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) were essentially colorless. The polyimides exhibited excellent thermal stability, with decomposition temperatures (at 10% weight loss) above 530 °C in both air and nitrogen atmospheres and glass transition temperatures (T_gs) in the range of 241–298 °C. For a comparative study, some properties of the present fluorinated polyimides were compared with those of structurally related ones prepared from 1,6-bis(4-aminophenoxy)naphthalene and 2,6-bis(4-amino-2-trifluoromethylphenoxy)naphthalene.     

Internal plasticization of polyimides with alkyl 3,5-diaminobenzoate compounds

An investigation was carried out to improve polyimide processability via internal plasticization. This approach entailed the synthesis of a series of diamines in which the length of the alkyl group in alkyl 3,5-diaminobenzoates was varied from one to eighteen carbons. The polyimides obtained from several of these diamines were found to have increased solubility, a lower glass transition temperature and improved processability. Copolyimides were synthesized from 4,4′-oxydianiline, n-octadecyl 3,5-diaminobenzoate and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride. It was found that incorporating only 10% of the plasticizing diamine improved processability sufficiently enough to allow moulding of the neat resin. This was in marked contrast to the parent polymer which was an insoluble and infusible polyimide.     

Copolyimides from 2,3,3′,4′-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride with 4,4′-oxydianiline

A series of copolyimides were prepared via the polyamide acids (polyamic acids) from the reaction of 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) and pyromellitic dianhydride (PMDA) with 4,4′-oxydianiline (4,4′-ODA) at dianhydride molar ratios of 9:1, 7:3, 1:1, 3:7 and 1:9. Homopolymers and a 1:1 polymer blend were also prepared. Films from the 7:3, 1:1 and 3:7 molar ratio polyamide acids reacted for 5-6 h at ambient temperature were brittle, whereas films from the same polyamide acids reacted for 24-48 h at ambient temperature were fingernail creaseable. The difference was apparently due to the initial formation of incompatible block domains that underway randomization upon longer reaction time. The differential scanning calorimetric (DSC) curves of some of the brittle films quenched after heating to 400 °C had two apparent glass transition temperatures (T_gs), indicative of two block domains. The creaseable films quenched after heating to 400 °C had single T_gs. Wide-angle X-ray diffraction showed all films to be amorphous even though the initial DSC curves showed strong endothermic peaks, generally associated with crystalline melts. These strong endotherms near the T_g region were thought to be due to relaxation of regions in the highly stressed films. Films of copolyamide acids from the reaction of 1:1 molar ratios of 3,3′,4,4′-oxydiphthalic anhydride/a-BPDA and 3,3′,4,4′-biphenyltetracarboxylic dianhydride/a-BPDA with 4,4′-ODA reacted for 6 h were fingernail creaseable. The chemistry and the properties of the copolymers are compared with those of the homopolymers.     

Addition polyimide adhesives containing various end groups

Addition polyimide oligomers have been synthesized from 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride and 3,3′-methylenedianiline using a variety of latent crosslinking groups as end-caps. The nominal 1300 molecular weight imide prepolymers were isolated and characterized for solubility in amide, chlorinated and ether solvents, melt-flow and cure properties, glass transition temperature, and thermal stability on heating in an air atmosphere. Adhesive strengths of the polyimides were obtained both at ambient and elevated temperatures before and after aging at 232°C. Properties of the novel addition polyimides were compared to a known nadic end-capped adhesive, LARC-13.     

马来酰亚胺封端的叔丁基侧基聚酰亚胺合成和应用研究

用自制的叔丁基二胺单体1,4-双（4-氨基苯氧基）-2-叔丁基苯（BATB）与三种二酐3,3’,4,4’-二苯醚四酸二酐（ODPA）、3,3’,4,4’-二苯甲酮四酸二酐（BTDA）、2,2’-双[4-（3,4-二羧苯氧基）苯基]丙烷四酸二酐（BPADA）反应,以马来酸酐作为封端剂得到了一系列链中含酰亚胺环的内扩链双马来酰亚胺,齐聚物的相对分子质量控制为4000～10000。将所得的溶解性好的双马来酰亚胺固体粉末溶于极性溶剂后,直接涂覆铜箔形成20μm涂层,干燥,再经程序升温固化,可以得无胶型挠性覆铜板,具有优异的耐热性、尺寸稳定性及低的吸水性。     

High-performance polymer films. III. Preparation and characterization

A series of polyimide and copolyimide films were prepared by film casting, drying, and thermal imidization from the respective precursor poly(amic acid) (PAA) and copoly(amic acid) solutions derived from two dianhydrides, pyromellitic dianhydride (PMDA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), and two diamines, 4,4′-oxydianiline (ODA) and a proprietary aromatic diamine (PD) as monomers. Depending on the solution's inherent viscosity value (molecular weight) and the nature of the polymer chains (derived from rigid or flexible monomers), precursor poly(amic acid) and copoly(amic acid) solution concentrations of 8–12% (w/w) were found to be suitable for the preparation of good quality polyimide/copolyimide films. The recovery of film toughness and creasability from the brittleness at the intermediate temperature of the cure cycle depended not only on the molecular weight of the precursor poly(amic acids)/copoly(amic acids) but also on their chain flexibility. The poly(amic acid) derived from both rigid dianhydride and diamine practically gave rise to a brittle film of polyimide even after curing to 360°C. The resulting polyimide and copolyimide films were compared with Du Pont's Kapton H film. The density of the films was in the range 1.39–1.42 g/cm³. The thickness of most of the films was in the range 20–30 μm. The HPF 3 film, based on PMDA–PD, appeared to be highly colored (reddish brown), and the HPF 2 film, based on BTDA–ODA, had the lightest yellow coloring among the films in this investigation, including Kapton H film. HPF 2, HPF 6, and HPF 8 films were more amorphous than the other films. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 976–988, 2001     

Process optimization of a thermoplastic polyimidesulphone

This study reports the detailed characterization of an experimental thermoplastic polyimidesulphone adhesive based on 3,3′-diaminodiphenylsulphone and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride. Model compounds were also examined. Thermal cyclization of the amide-acid to the imide was studied by a variety of techniques including differential scanning calorimetry, thermogravimetric analysis, mass spectroscopy, in-situ diffuse reflectance — Fourier transform infrared spectroscopy and flow measurement. Characterizations were continued during the processing of adhesive tapes and the fabrication, bonding and testing of lap shear specimens. The results provide fundamental insights into the role of cure chemistry, and the effects of residual solvent and volatiles on processing and performance. These insights and the resulting chemical models should lead to more efficient processing cycles for these and other related thermoplastic adhesive systems.     

Preparation and Properties of Cyano-Containing Polyimide Films Based on 2,6-Bis(4-aminophenoxy)- benzonitrile

Summary A series of cyano-containing polyimides were synthesized from 2,6-bis(4-amino- phenoxy)benzonitrile and some aromatic dianhydride monomers by solution polycondensation. The poly(amic acid) films could be obtained by solution-cast from N-methyl-2-pyrrolidinone solutions and thermally converted into tough polyimide films. Structure and physical properties of thin films of those polyimides were measured by FTIR, TGA, dynamic mechanical analysis and LCR hitester et al. Results showed that the polyimides prepared from 2,6-bis(4-aminophenoxy)- benzonitrile and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride or 4,4’-(hexafluoropropylidene)diphthalic anhydride exhibited more excellent energy-damping characteristic and excellent solubility in NMP, DMF, DMAc, DMSO, THF and CHCl₃, whereas the polyimides from 2,6-bis(4-aminophenoxy)benzonitrile and 3,3’,4,4’-biphenyltetracarboxylic dianhydride or Pyromellitic dianhydride were insoluble in polar and nonpolar organic solvents. All polyimides indicated higher glass transition temperatures, excellent thermal stability and tensile properties. Incorporating a nitrile group into the polyimide backbone would enhance the dielectric constant of the polyimide films.     

A comparison of poly(ether imide)s from diamines with 2-aminophenoxy or 4-aminophenoxy units: Synthesis, characterization and properties

A series of new 3- and 4-ring bis(2-aminophenoxy) aromatic diamines were prepared. These, and corresponding, conventional bis(4-aminophenoxy) diamines were reacted with several aromatic bis(ether anhydride)s to form poly(ether imide)s. The diamines with 4-aminophenoxy groups gave high-molecular-weight polymers that were cast into films with good mechanical properties. In contrast, in almost all cases, diamines with 2-aminophenoxy groups only gave low-molecular-weight powdery products that could not be cast into coherent films. The low-molecular-weight products, prepared from stoichiometrically equal amounts of monomers, were examined by mass spectrometry and shown, in most cases, to consist primarily of cyclic oligomers; traces of linear oligomers were identified in some samples. Apart from a polyimide prepared from pyromellitic dianhydride and 4,4′-bis(2″-aminophenoxy)biphenyl, the only products found to contain significant proportions of linear oligomers were those prepared with a stoichiometric imbalance of monomers. End groups of the various linear oligomers were identified. The 2-aminophenoxy groups predispose the oligomers to cyclize as amic acids, and to remain as cyclics on imidization. In some cases [1+1] cyclic oligomers were observed although the most common species were the [2+2] cyclic dimers.     

Novel initiators for the synthesis of propylene oxide oligomers by anionic ring opening polymerization

A series of potassium alcoholates was obtained from the reaction between KOH and ethylene glycol, resorcinol, 4,4′-bisphenol A, 4,4′-(1,3 phenylenediisopropylidene)-bisphenol, 4,4′-sulfonyldiphenol. These salts were employed to initiate the anionic ring opening polymerization of propylene oxide (PO). The molecular weight distribution of the propylene oxide oligomers prepared by this method and the initiator structure were correlated. These oligomers were characterized through Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) spectroscopies and size exclusion chromatography (SEC). It was found that the molecular weight and polydispersity of the synthesized poly(propylene oxide) (PPO) is highly dependant on the initiator structure and solubility in the reactive medium. The oligomers obtained using di-potassium resorcinolate exhibited a molecular weight distribution more polydisperse than that of PO oligomers synthesized by means of di-potassium ethylene glycolate. In the case of the PO polymerizations started by the potassium salts of 4,4′-bisphenol A, 4,4′-(1,3 phenylenediisopropylidene)-bisphenol and 4,4′-sulfonyldiphenol, the oligomer chains showed very broad molecular weight distributions. In general, lower solubility and augmentation of the polymer polydispersity were observed when the number of aromatic rings in the initiator structure increased. The experimental results were contrasted with those obtained from quantum chemical semiempirical calculations at AM1 level. The peculiar behavior exhibited by the initiators with an aromatic structure could be explained in terms of different reactivities of the initiation sites. The theoretical studies revealed that the ring in the aromatic initiators promotes an unsymmetrical growing when the PPO chains are formed. In contrast, the identical reactivity of both initiation sites in the ethylene glycolate produces a symmetrical growing during the PO polymerization.     

Synthesis and nonvolatile memory characteristics of thermally, dimensionally and chemically stable polyimides

A series of soluble poly(amic acid) precursors were prepared from a new carbzole-containing monomer, 3,3′-bis[9-carbazole(ethyloxy)biphenyl]-4,4′-diamine (HAB-CBZ) by polycondensation with four different aromatic dianhydrides: pyromellitic dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-diphenylethertetracarboxylic dianhydride (ODPA), and 3,3′,4,4′-diphenylsulfonyltetracarboxylic dianhydride (DSDA). From the precursors, nanoscale thin films of polyimides (PIs) were prepared by spin-coating and subsequent thermal imidization. All the PIs exhibited excellent thermal and dimensional stability. In particular, the PIs based on the PMDA and BPDA units revealed excellent chemical resistance to organic solvents, in addition to the high thermal and dimensional stability, which are required for the fabrication of high performance memory devices in three-dimensionally multi-stack structure. Devices fabricated with nanoscale thin PI films exhibited excellent unipolar write-once-read-many-times (WORM) memory behavior with a high ON/OFF current ratio of up to 10¹⁰. The active PI films were found to operate at 2.2-3.3 V, depending on the chemical structures. This study found that the imide rings as local charge trap sites are necessary to enhance the memory performance in addition to carbazole moiety. All the results collectively indicate that the thermally, dimensionally and chemically stable PIs of this study are a promising material for the mass production at low cost of high performance, programmable nonvolatile WORM memory devices that can be operated with low power consumption in unipolar switching mode.     

一类含甲基结构高透明聚酰亚胺的合成与性能研究

以2,6-二氨基甲苯、3,3'',4,4''-联苯四甲酸二酐、3,3'',4,4''-二苯醚四甲酸二酐为原料，间甲酚作为溶剂，经一步法高温共缩聚，制备一系列可溶性共聚型聚酰亚胺(MPI)。利用红外光谱（FTIR）、核磁共振波谱（1H NMR）、差式扫描量热仪（DSC）、热重分析仪（TGA）和紫外-可见光分度计（UV）等测试仪器对MPI进行结构与性能表征。结果表明：红外与核磁的数据说明成功合成了含甲基结构的聚酰亚胺；该系列的含甲基聚酰亚胺在室温下可溶于N-甲基吡咯烷酮（NMP）、N,N-二甲基乙酰胺（DMAc）、二氯甲烷（CH2Cl2）三氯甲烷（CHCl3）、二甲基亚砜（DMSO）等有机溶剂，具有良好的溶解性和成膜性，并随着联苯酐的含量增加溶解性降低；同时该系列MPI制得的薄膜具有良好的光学透过性能，在紫外光波长450 nm时的透过率均在74%以上，截止波长在350 nm左右；该系列MPI的起始分解温度均大于457 ℃，800 ℃氮气氛围中的焦炭产率均大于63%，玻璃化转变温度在260 ℃~285 ℃之间，表现出优异的热学性能。此外，MPI-1~MPI-4薄膜还具有良好的机械性能，其弹性模量在1.7~2.1 GPa，拉伸强度在89.7~120.6 MPa，断裂伸长率在19.7%~28.4%。     

1,4-Bis(2,3-dicarboxyl-phenoxy)benzene dianhydride-based phenylethynyl terminated thermoset oligoimides for resin transfer molding applications

A series of thermoset oligoimides have been prepared by the thermal polycondensation of 1,4-bis(2,3-dicarboxyl-phenoxy)benzene dianhydride with three different aromatic diamines in the presence of 4-phenylethynylphthalic anhydride as an end capping reagent. The aromatic diamines included 4,4′-oxydianiline, 2,2′-bis(trifluoromethyl)benzidine (TFDB) and 2-phenyl-4,4′-diaminodiphenyl ether (p-ODA). Effects of the chemical structures and molecular weights of the oligoimides on their aggregated structures, melt processability as well as the thermal and mechanical properties of the cured films were then systematically investigated. X-ray diffraction results indicated that ODA series oligoimides and TFDB series oligoimides showed crystallinity; however, the asymmetrical p-ODA enables the p-ODA series oligoimides to exhibit amorphous forms. So the p-ODA based oligoimides with molecular weight of 750 g mol⁻¹ showed much lower melt viscosity at a low temperature and the melt viscosity could maintain below 1 Pa s⁻¹ after isothermal aging for 2 h at any temperature in the range of 220–280 °C by rheological measurements. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47967.     

The alkylation of biphenyl over three-dimensional large pore zeolites: The influence of zeolite structure and alkylating agent on the selectivity for 4,4′-dialkylbiphenyl

Catalytic properties of three-dimensional zeolites, Y (FAU), Beta (BEA), and CIT-1 (CON) zeolites were examined in the alkylation, isopropylation, sec-butylation, and tert-butylation, of biphenyl (BP), and compared to those of H-mordenite (MOR). The selectivities for 4,4′-dialkylbiphenyl (4,4′-DABP) varied with the types of zeolite and of alkylating agent. FAU, BEA, and CON gave only low selectivities for 4,4′-diisopropylbiphenyl (4,4′-DIPB) in the isopropylation, and predominant isomers were bulky and thermodynamically unstable 2,x′-DIPB (2,2′-, 2,3′-, and 2,4′-) at lower temperatures, and bulky and thermodynamically stable 3,4′- and 3,3′-DIPB at higher temperatures: this is quite different from catalytic features over MOR, which gave 4,4′-DIPB with high selectivities at moderate temperatures. These results suggest that FAU, BEA, and CON have no shape-selective nature in the isopropylation, and that the reaction is principally controlled kinetically at lower temperatures, and thermodynamically at higher temperatures. The sec-butylation gave similar results to the isopropylation. Although the selectivities for 4,4′-di-sec-butylbiphenyl (4,4′-DSBB) were higher than those in the isopropylation, predominant isomers were 2,x′-DSBB (2,2′-, 2,3′-, and 2,4′-) at lower temperatures, and 3,4′- and 3,3′-DSBB at higher temperatures. The tert-butylation gave 4,4′-di-tert-butylbiphenyl (4,4′-DTBB) in moderate to high selectivities over all zeolites at moderate temperatures: the selectivity for 4,4′-DTBB was higher than 80% over BEA and CON; however, it still remained at 50% over FAU. FAU channels with super cages are too large for selective formation of 4,4′-DTBB.

From these results, it is concluded that the selectivity for 4,4′-DABP in the alkylation over MOR, FAU, BEA, and CON is determined by the exclusion of bulky isomers at their transition states, and that the exclusion is caused by the steric restriction at the transition states of bulky isomers by the zeolite channels.     

Preparation and properties of novel fluorinated polyimides based on 2,2′,6,6′-tetrafluorobenzidine

Fluorinated polyimides were prepared from 2,2′,6,6′-tetrafluorobenzidine and four conventional dianhydride monomers by a solution polycondensation reaction followed by a chemical imidization. Polyimide based on 2,2′,6,6′-tetrafluorobenzidine and hexafluoroisopropylidene bis(3,4-phthalic anhydride) (6FDA) is soluble in organic solvents such as NMP, DMA, DMF, THF, chloroform, and acetone while those based on 2,2′,6,6′-tetrafluorobenzidine and pyromellitic dianhydride (PMDA), benzophenone-3,3′,4,4′-tetracarboxylic acid dianhydride (BTDA), diphenylether-3,3′,4,4′-tetracarboxylic acid dianhydride (ETDA) are not. Polyimide from 2,2′,6,6′-tetrafluorobenzidine and 6FDA possesses high optical transparency at 350–700 nm and has a in-plane refractive index of 1.558 at 632.8 nm. All polyimides exhibit glass transition temperatures above 350°C. They also possess very high thermal stability. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1605–1609, 1998