Benzoxazines with tolyl, p-hydroxyphenyl or p-carboxyphenyl linkage and the structure-property relationship of resulting thermosets

Three benzoxazines (7-9) with a tolyl, p-hydroxyphenyl or p-carboxyphenyl structure, respectively, were successfully synthesized by a three-pot or two-pot procedure. In the three-pot approach, the first step is the condensation of 2-hydroxybenzaldehyde with p-toluidine, 4-aminophenol and 4-aminobenzoic acid, respectively, forming intermediates (1-3) with an imine linkage. The second step is the addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) on the imine linkage, resulting in intermediates (4-6) with a secondary amine linkage. The last step is the ring closure condensation of (4-6), leading to benzoxazines (7-9). In the simplified two-pot approach, the first two steps-the condensation and imine reduction were carried out in one reactor, so the yield of (4-6) was increased. The structures of monomers (1-9) were characterized and confirmed by 1D and 2D NMR spectra. The synthesized benzoxazines were thermally self-cured or copolymerized with a commercial benzoxazine, bis(3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazin-6-yl)methane (F-a). IR analysis was utilized to monitor the ring-opening reaction of (7-9) and to propose the structures of P(7-9). The microstructure and the structure-property relationship of the resulting homopolymers and copolymers are studied.     

Synthesis and characterization of alternating poly(amide urethane)s from ε-caprolactone, diamines and diphenyl carbonate

The synthesis of alternating poly(amide urethane)s 5a-d was performed in three steps using ε-caprolactone, diamines, and diphenyl carbonate as starting materials. The microstructure and nature of the end groups of the poly(amide urethane)s were determined by means of ¹H NMR spectroscopy, which reveals an alternating sequence of amide and urethane linkages in a linear chain with hydroxy and phenyl urethane end groups. The molecular weight and polydispersity of the polymers obtained (, ) were determined by means of gel permeation chromatography. The thermal properties determined by means of DSC show that the poly(amide urethane)s 5a-d are semicrystalline materials having one or two endothermic transitions similar to the poly(amide urethane)s 10a-d prepared from ε-caprolactam, amino alcohols, and diphenyl carbonate. Thermogravimetric analysis of poly(amide urethane)s 5a-b shows a single step decomposition, while poly(amide urethane)s 10a-c decompose in two steps indicating that different degradation mechanisms are operating.     

Mechanistic study of electrochemical oxidation of catechols in the presence of 4-hydroxy-1-methyl-2(1H)-quinolone: Application to the electrochemical synthesis

Electrochemical oxidation of catechols (1a-1c) has been studied in the presence of 4-hydroxy-1-methyl-2(1H)-quinolone (3) as a nucleophile in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the quinones derived from catechols (1a-1c) participate in Michael addition reactions with 3 to form the corresponding benzofuran (or isochromeno[4,3-c]quinoline) derivatives (6a-6c). The electrochemical synthesis of (6a-6c) has been successfully performed in an undivided cell in good yield and purity. The oxidation mechanism was deduced from voltammetric data and by coulometry at controlled-potential. The products have been characterized after purification by IR, ¹H NMR, ¹³C NMR and MS.     

Electrochemical study of stable N-alkoxyarylaminyl radicals

The electrochemical study of N-tert-butoxy-2,4-diphenyl-6-tert-butylphenylaminyl (1a), N-tert-butoxy-2,4-bis(4-chlorophenyl)-6-tert-butylphenylaminyl (1b), N-[2-(methoxycarbonyl)-2-propyl]-2,4-diphenyl-6-tert-butylphenylaminyl (2), and N-tert-butoxy-2,4,6-tris(4-chlorophenyl)phenylaminyl radicals (3) was performed by cyclic voltammetry using acetonitrile as the solvent and Bu₄NPF₆ as the supporting electrolyte. On cathodic scan (100 mV/s), all the radicals gave chemically reversible cyclic voltammograms, and the were determined to be −1.405 V (1a), −1.310 V (2a), −1.282 V (2b), and −1.195 V (3) (versus Fc⁺/Fc), respectively. On anodic scan (100 mV/s), on the other hand, 1a, 1b and 2 showed chemically reversible cyclic voltammograms, but 3 exhibited a partially reversible couple even on a scan rate of 500 mV/s, indicating that the cation species of 3 was less stable. The determined for 1a, 1b, 2 and 3 were 0.220, 0.280, 0.318 and 0.294 V (versus Fc⁺/Fc), respectively. The electrochemical data were compared with those of thioaminyl radicals, the corresponding sulfur analogues of 1-3.     

Synthesis and gas permeation properties of various Si-containing poly(diarylacetylene)s and their desilylated membranes

Diarylacetylene monomers having trimethylsilyl groups and other substituents (substituted biphenyl, 1a and 1b; trimethylsilylmethylphenyl, 1c-e) were synthesized and polymerized with TaCl₅-n-Bu₄Sn catalyst to produce the corresponding poly(diarylacetylene)s (2a-d). Polymers 2a-c had high molecular weights and were soluble in common organic solvents. Free-standing membranes of 2a-c as well as previously reported 2f-h were prepared by the solution-casting method. Desilylation of these Si-containing polymer membranes was carried out with trifluoroacetic acid to afford 3a, 3b, and 3f-h. Upon desilylation, biphenyl-containing membranes became less permeable (3a, b), whereas fluorene-containing membranes became more permeable (3f-h). In particular, 3h exhibited extremely high gas permeability (PO₂ = 9800 barrers), which is about the same as that of poly(1-trimethylsilyl-1-propyne). Desilylated membranes 3a and 3f-h showed different gas permeability from that of polymers 2i-k which have the identical chemical structures and obtained directly by the polymerization of the corresponding monomers.     

A new facile electrochemical method for the synthesis of 4-(pyridine-2-ylthio)benzene-l,2-diols

Electrochemical oxidation of catechols (1a-1c) has been studied in the presence of 2-mercaptopyridine (3) as a nucleophile in water solution using cyclic voltammetry and controlled-potential coulometry. The results revealed that the quinones derived from catechols (1a-1c) participate in Michael addition reaction with 2-mercaptopyridine (3) and converted to the corresponding (pyridine-2-ylthio)benzene-l,2-diol derivatives (4a-4c), via an EC mechanistic pathway. The electrochemical synthesis of compounds 4a-4c has been successfully performed at a carbon rod electrode and in an undivided cell with good yields and high purity.     

Synthesis of 1,9-bis[glycidyloxypropyl]penta(1′H,1′H,2′H,2′H-perfluoroalkylmethylsiloxane)s and copolymerization with piperazine

A series of 1,9-bis[glycidyloxypropyl]pentasiloxanes (IV-VI) were prepared by the platinum catalyzed hydrosilylation of 1,9-dihydridodecamethylpentasiloxane (I), 1,9-dihydrido-3,5,7-tris(3′,3′,3′-trifluoropropyl)heptamethylpentasiloxane (II), and 1,9-dihydrido-3,5,7-tris(1′H,1′H,2′H,2′H-perfluorooctyl)heptamethylpentasiloxane (III) with allyl glycidyl ether. Subsequently, IV-VI were copolymerized with piperazine to form high molecular weight copoly(carbosiloxane)s (VII-IX). The structures of the 1,9-bis[glycidyloxypropyl]penta-siloxanes (IV-VI) and copoly(carbosiloxane)s (VII-IX) were determined by ¹H, ¹³C, ²⁹Si, and ¹⁹F NMR as well as IR spectroscopy. The molecular weight distributions (M_w/M_n) of VII-IX have been characterized by gel permeation chromatography and their thermal properties measured by differential scanning calorimetry and thermal gravimetric analysis.     

Colorless and high organosoluble polyimides from 2,5-bis(3,4-dicarboxyphenoxy)-t-butylbenzene dianhydride and aromatic bis(ether amine)s bearing pendent trifluoromethyl groups

A series of polyimides III_a-h characterized by colorlessness, high transparency, high solubility, and good mechanical property, was synthesized from the aromatic dianhydride, 2,5-bis(3,4-dicarboxyphenoxy)-t-butylbenzene dianhydride (I), and various aromatic diamines (II_a-h) with pendent trifluoromethyl group via polyaddition, chemical imidization, and direct cast films. The III series showed more colorless than the polyimides (V and VI series) of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) contained, the VI series was synthesized from the II with 6FDA. These films III had cut-off wavelengths between 371 and 376 nm, as well as b* value (a yellowness index) ranging from 3.0 to 4.7. In fact, it is so far the most colorless aromatic polyimide in our systematical researches. The III series had inherent viscosity ranging from 0.72 to 1.33 dL/g and showed excellent solubility in a variety of organic solvents. They were soluble in a concentration of 5-10% in the amide polar solvent, ether solvent, and chlorinated solvent. These films showed strength tensile of 97-123 MPa, dielectric constants of 2.78-3.28 (1 MHz), and moisture absorptions of 0.11-0.36 wt%. The glass transition temperature of the III series was recorded at 214-259 °C, the 10% weight loss temperature was over 468 °C, and the residue was more than 47% at 800 °C in nitrogen.     

Synthesis and properties of ornithine- and lysine-based poly(N-propargylamides). Responsiveness of the helical structure to acids

Ornithine- and lysine-based novel N-propargylamides, N-α-tert-butoxycarbonyl-N-δ-fluorenylmethoxycarbonyl-l-ornithine-N′-propargylamide (1), N-α-tert-butoxycarbonyl-N-?-fluorenylmethoxycarbonyl-l-lysine-N′-propargylamide (2), N-α-fluorenylmethoxycarbonyl-N-δ-tert-butoxycarbonyl-l-ornithine-N′-propargylamide (3), and N-α-fluorenylmethoxycarbonyl-N-?-tert-butoxycarbonyl-l-lysine-N′-propargylamide (4) were synthesized and polymerized with a rhodium catalyst. Polymers with moderate molecular weights were obtained in good yields. Poly(1)-poly(4) showed strong Cotton effects in THF, whose sign and wavelength depended on the substituents. They were satisfactorily converted into the corresponding polymers [poly(1a)-poly(4a)] with free amino groups. Poly(1a) and poly(2a) also formed a helix, while poly(3a) and poly(4a) did not. Poly(1a) and poly(2a) decreased the CD intensity by the addition of m- and o-phthalic acids.     

Performance improvement of polybenzoxazine by alloying with polyimide: effect of preparation method on the properties

Polymer alloys of polyimide and polybenzoxazine were prepared from the combination of a bifunctional benzoxazine monomer, 6,6′-(1-methylethylidene)bis(3,4-dihydro-3-2H-1,3-benzoxazine) (B-a) and a soluble polyimide (PI) or its precursor, poly(amide acid) (PAA), that was synthesized from oxydianiline (ODA) and bisphenol A di(phthalic anhydride) ether (BPADA). It was observed from DSC that the onset temperature for the curing exotherm of B-a in the blend with PAA was remarkably lowered compared with that of pristine B-a, while the curing temperature of B-a in the blend with PI was almost the same as that of pristine B-a. The cast films of PI/B-a or PAA/B-a were thermally treated at 150, 200 and 240 °C for 2 h each, affording deep wine, transparent films. The PI component in the polymer alloy films from PI/B-a dissolved thoroughly. On the other hand, the polymer alloy films from PAA/B-a were not soluble at all in NMP. The polymer alloy films from both PI/B-a and PAA/B-a showed only one glass transition temperature (T_g) from their viscoelastic analyses. The T_g values remarkably increased as the content of PI increased. The thermal stabilities of both films from PI/B-a and PAA/B-a increased as the PI component increased in the similar manner.     

Effects of internal linkage groups of fluorinated diamine on the optical and dielectric properties of polyimide thin films

To investigate the difference of the trifluoromethyl (CF₃) group and ether group affecting the optical property of fluorinated polyimides (PIs), we prepared 4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl ether (4) with three ether groups and 2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane (5) with four CF₃ groups with 2-chloro-5-nitrobenzotrifluoride and 4,4′-dihydroxydiphenyl ether or 2,2-bis(4-hydroxyphenol)hexafluoropropane. Two series of organosoluble and light-colored PIs (4a-4c, 5a-5c) were synthesized from 4 and 5 with various aromatic dianhydrides: 3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA) (a), 4,4-oxydiphthalic anhydride (ODPA) (b), and 4,4-hexafluoroisopropylidenediphthalic anhydride (6FDA) (c), prepared through a typical two-step polymerization method. These PIs were soluble in amide polar solvents and even in less polar solvents. The glass-transition temperatures (T_g) of 4a-5c were 221-249 °C and the 10% weight-loss temperatures were above 530 °C. Their films had cutoff wavelengths between 339 and 399 nm and yellowness index ranges from 1.95 to 42.60. The dielectric constants estimated from the average refractive indices are 2.59-2.93 (1 MHz). In a comparison of the PI series based on 4, 5, and 4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (6), we found that the CF₃ group and ether group on the diamine had almost same effect in lowering the color, but the ether group had better thermal stability. The color intensity of the three PI series was lowered in the following order: 6 > 4 > 5. The PI 5c, synthesized from diamine 5 and dianhydride c, had six CF₃ groups in a repeated segment and ether group at the same time, so it exhibited the lightest color among the three series.     

Organo-soluble phosphinated polyimides from asymmetric diamines

Two new asymmetric diamines (1-2) were prepared via a facile, one-pot procedure. Based on diamine (1-2), a series of asymmetric polyimides (3-4) were prepared in NMP/xylene by high-temperature solution polymerization. The resulting polyimides are readily soluble in some organic solvents, and can be solution casted into flexible and creasable films. An intramolecular charge complex mechanism was proposed to the structure-optical transparency relationship. Polyimides 3-4 display high-Tg (319-401 °C), high moduli (2.40-7.20 GPa), moderate coefficient of thermal expansion (38-53 ppm/°C), and excellent flame retardancy. These results show that the introduction of the asymmetric structure is an effective way to improve organo-solubility while maintaining thermal properties. Because of these properties, polyimides 3-4 can be considered as excellent high-Tg and flame-retardant materials for microelectronic applications.     

Synthesis and electrochromic properties of aromatic polyimides bearing pendent triphenylamine units

A series of aromatic polyimides with pendent triphenylamine group were synthesized from equimolar mixtures of 4,4′-oxydianiline (ODA) and 4-(3,5-diaminobenzamido)triphenylamine (4), 4-(3,5-diaminobenzamido)-4′,4″-di-tert-butyltriphenylamine (t-Bu-4) or 4-(3,5-diaminobenzamido)-4′,4″-dimethoxytriphenylamine (MeO-4) with two aromatic tetracarboxylic dianhydrides (DSDA or 6FDA) via a conventional two-step procedure that included a ring-opening polyaddition to give poly(amic acid)s, followed by chemical imidization. These polyimides exhibited good solubility in polar organic solvents and could be solution-cast into flexible and strong films. They showed excellent thermal stability, with T_g values in the range of 284–309 °C. The polyimides derived from diamines t-Bu-4 and MeO-4 exhibited reversible electrochemical oxidation, accompanied by strong color changes with high contrast ratio and electrochromic stability. For the polyimides derived from diamine 4, the coupling reaction between the triphenylamine radical cations occurred during the oxidative process forming a tetraphenylbenzidine structure, which resulted in an additional oxidation state and color change together with enhanced near-IR absorption at fully oxidized state.     

Metallocene-catalyzed synthesis of polyethylenes with side-chain triarylamines: Effects of catalyst structure and triarylamine functionality

The copolymerization of ethylene with 8-triarylamine (TAA) substituted 1-octene monomers (TAA = triphenylamine (M1), N,N-diphenyl-m-tolylamine (M2), N,N-diphenyl-1-naphthylamine (M3)) using various types of group 4 single-site catalytic systems (Cp₂ZrCl₂ (C1), rac-EBIZrCl₂ (C2), rac-SBIZrCl₂ (C3), i-PrCpFluZrCl₂ (C4), Me₂Si(η⁵-C₅Me₄)(η¹-N-^tBu)TiCl₂ (C5)) was investigated to prepare functionalized polyethylene with side-chain TAA groups. The metallocene/methylaluminoxane (MAO) catalytic systems (C1-C4) efficiently lead to the production of high-molecular-weight poly(ethylene-co-M1). While the C4/MAO catalytic system shows the highest comonomer response, the C5/MAO system exhibits the poor compatibility with the M1 comonomer. Copolymerization results of ethylene with M1-M3 using C4/MAO indicate that M1-M3 are well tolerated by both the cationic active species of C4 and MAO cocatalyst, giving rise to the copolymers with high levels of activity and molecular weight. Inspection of the aliphatic region of the ¹³C NMR spectra of the copolymers (P1-P3) having ca. 11 mol% of M1-M3, respectively, reveals the presence of isolated comonomer units with prevailing [EEMEE] monomer sequences in the polymer chain. UV-vis absorption and PL spectra exhibit an apparent low-energy band broadening for P1 and P2 indicative of intrachain aggregate formation. Whereas P2 and P3 undergo completely reversible one-electron oxidation process, P1 shows relatively poor oxidational stability.     

Highly optically transparent/low color polyimide films prepared from hydroquinone- or resorcinol-based bis(ether anhydride) and trifluoromethyl-containing bis(ether amine)s

Two series of novel polyimides (5a-g and 6a-g) containing flexible ether linkages and pendent trifluoromethyl (CF₃) groups were synthesized from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (3a) and 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride (3b) with various CF₃-substituted aromatic bis(ether amine)s (4a-g) via ring-opening polyaddition to poly(amic acid)s, followed by thermal or chemical imidization. These polyimides were readily soluble in a variety of organic solvents and could be solution-cast into flexible and tough films. The cast films exhibited high optical transparency and almost no color, with a UV-vis absorption edge of 368-382 nm and a very low b^∗ value (a yellowness index) of 6.2-15.5. They had good thermal stability with glass-transition temperatures of 186-288 °C, and most of them did not show significant decomposition before 500 °C. Moreover, these polyimide films also possessed low dielectric constants of 2.79-3.49 (at 1 MHz) and low water uptakes (<0.65 wt%).     

Two-dimensional spin-exchange solid-state NMR study of the crystal structure of cellulose II

A two-dimensional (2D) ¹³C-¹³C spin-exchange NMR experiment was applied to the uniformly ¹³C-enriched cellulose II in order to obtain interatomic distance information in the cellulose II crystal. A radio frequency-driven recoupling (RFDR) rotor-synchronized π pulse sequence was incorporated during the mixing time of the 2D experiment. The 2D spin-exchange NMR recorded with a short mixing time (0.80-2.58 ms) provided the correlations between a pair of strongly coupled ¹³C spins such as neighbor carbon nuclei. This spectrum enabled us to assign all ¹³C resonance lines of two kinds of anhydroglucose residues A and B in the structure of cellulose II. On the basis of the ¹³C resonance assignment of residues A and B, the interatomic distances from each C1 to the other carbon nuclei were compared by measuring the 2D spectra recorded with longer mixing times (5.12-20.48 ms). As a result, it was revealed that the respective residues A and B are composed of independent chains (-A-A- and -B-B- repeating units) and that there are no -A-B- repeating units in the chain. This experimental technique is expected to be applicable to conformation analysis of polysaccharides as well as the other cellulose polymorphs.     

Mechanistic study of the oxidation of catechol in the presence of secondary amines by digital simulation of cyclic voltammograms

Electrochemical oxidation of catechol (1) has been studied in the presence of morpholine (2a), dimethylamine (2b) and diethylamine (2c) as nucleophile in aqueous solution, using cyclic voltammetry and controlled-potential coulometry. The results indicate that the participation of catechol (1) in Michael reaction with 2 to form the corresponding aminoquinone derivatives (5a-5c). Based on ECE mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results.     

Polybinaphthyls incorporating chiral 2,2′-binaphthyl and isoquinoline moieties by Sonogashira reaction

Polymers P-1, P-2, P-3, P-4 and P-5 were synthesized by the polymerization of 5,8-bis(ethynyl)isoquinoline (M-1) with (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-2), (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-2), (R)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((R)-M-3), (S)-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl ((S)-M-3), and rac-6,6′-dibromo-2,2′-bisbutoxy-1,1′-binaphthyl (M-4) under Sonogashira reaction, respectively. Both monomers and polymers were analyzed by NMR, MS, FT-IR, UV-vis spectroscopy, DSC-TGA, fluorescence spectroscopy, GPC and circular dichroism (CD) spectroscopy. CD spectra of polymers P-1 and P-2, P-3 and P-4 are almost identical except that they gave opposite signals at each wavelength. The long wavelength CD effect of P-1 and P-2 can be regarded as the more extended conjugated structure in the repeating unit and the helical backbone in the polymer chain. All five polymers have strong blue-green fluorescence due to the efficient energy migration from the extended π-electronic structure of the repeating unit of the polymers to the chiral binaphthyl core and are expected to provide understanding of structure-property relationships of the chiral conjugated polymers.     

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.