Search

A Z type sexiphenyltetracarboxylic dianhydride, 3,3′′′′′,4,4′′′′′-1,1′:2′,1′′:4′′,1′′′:4′′′,1′′′′:2′′′′,1′′′′′-sexiphenyltetracarboxylic dianhydride (1), was synthesized in seven steps from diethyl 4-bromophthalate. Aromatic polyimides (PI1x) were synthesized from 1 and various aromatic diamines (x) by both a conventional two-step procedure and a one-step procedure, and the properties were compared with those of the polyimides (PI2x) previously prepared from rigid 3,3′′′′′, 4,4′′′′′-p-sexiphenyltetracarboxylic dianhydride (2), the isomer of 1. The values of glass transition (Tg) temperatures are much higher (270–345 °C) than those of the corresponding PI2x, and the decrease in the storage modulus at Tg is larger than that of the corresponding PI2x.

Ni(0)-catalyzed coupling polymerizations of 3,6-di(4-chlorophenyl)-3,6-dihydrophthalic acid diethyl ester 1 were accompanied by isomerization of the 1,4-cyclohexadiene moiety into a 3,5-cyclohexadiene group, yielding a conjugated polymer. The structure of this conjugated polymer was the same as that of the conjugated polymer from 3,6-di(4-chlorophenyl)-1,2-dihydrophthalic acid diethyl ester 2. The number-average degree of polymerization was only ∼7 due to the low solubility of the conjugated polymer. The conjugated polymer exhibited a λ max at 430 nm in the absorption spectrum, and could be applied as a photo-sensitizer of a solar cell. The incident monochromatic photon (450 nm)-to-current conversion efficiencies of photocurrent from an indium-titanium oxide (ITO)/TiO2 electrode modified with the conjugated polymer was 6.1% in the I3−-3I− electrolyte wet system. The conjugated polymer exhibited a glass transition temperature of 210 °C and was converted by thermal treatment at 300 °C to poly(p-phenylene) (PPP) with the elimination of ethoxycarbonyl groups. Ni(0)-catalyzed coupling polymerizations of 3,6-di(4-chlorophenyl)-3,6-dihydrophthalic acid diethyl ester 1 were accompanied by isomerization of the 1,4-cyclohexadiene moiety into a 3,5-cyclohexadiene group, yielding a conjugated polymer. The structure of this conjugated polymer was the same as that of the conjugated polymer from 3,6-di(4-chlorophenyl)-1,2-dihydrophthalic acid diethyl ester 2. The conjugated polymer exhibited a λ max at 430 nm in the absorption spectrum, and could be applied as a photo-sensitizer of a solar cell. The incident monochromatic photon (450 nm)-to-current conversion efficiencies of photocurrent from an ITO/TiO2 electrode modified with the conjugated polymer was 6.1% in the I3--3I- electrolyte wet system.

Hyperbranched poly(ether ether ketone)s with hydroxyl terminal groups are prepared by a one-step polycondensation of 3,5-dihydroxy-4′-(4-fluorobenzoyl)diphenylether (AB2-type monomer) through an aromatic nucleophilic substitution reaction. With the help of model compounds, 1H-NMR studies reveal that the degree of branching of the poly(ether ether ketone)s is about 52%. The possibility of entanglement among the hyperbranched polymer molecules is suggested from comparison of their glass transition temperatures with the corresponding dendrimers and the optimized structure of the hyperbranched polymers. The terminal hydroxyl groups were readily functionalized, yielding hyperbranched polymers with a variety of different functional chain ends. The nature of the chain end is shown to dramatically affect the properties of the hyperbranched polymers. Hyperbranched poly(ether ether ketone)s with hydroxyl terminal groups were prepared by a one-step synthesis of an AB2-type monomer 3,5-dihydroxy-4′-(4-fluorobenzoyl)diphenylether through an aromatic nucleophilic substitution reaction. The degree of branching determined by 1H-NMR analysis was about 52%. The reduced viscosities of the hyperbranched polymers were higher than those of the corresponding dendrimers, the glass transition temperatures of the hyperbranched polymers were higher than those of the dendrimers and the existence of entanglement among the hyperbranched polymer molecules was suggested.

A new phenylated diamine, bis(4-amino-2-biphenyl)ether, was synthesized in five steps starting from 3-chloro-4-fluoronitrobenzene. New aromatic polyimides having phenyl groups at the 2- and 2′-positions of the diphenyl ether moiety were prepared from this diamine and various tetracarboxylic dianhydrides by the conventional two-step procedure that included ring-opening polymerization in NMP and subsequent thermal cyclic dehydration. The polyimides were characterized by differential scanning calorimetry (DSC), thermogravimetry, and dynamic mechanical analysis (DMA). Typical polyimides showed excellent thermal stability, and had glass transition temperature (Tg) above 250 °C. As for the series of polyimides prepared from tetracarboxylic anhydrides having linear phenylene moiety, the introduction of phenyl group at the 2- and 2′-positions of phenyl ether improved thermal and thermo-mechanical properties as well as the solubility of polymers.

A new rigid tetracarboxylic dianhydride, 3,3''''',4,4'''''-p-sexiphenyltetracarboxylic dianhydride, was synthesized in seven steps starting from diethyl 4-bromophthalate. New aromatic polyimides containing a p-sexiphenyl unit were synthesized from this tetracarboxylic dianhydride and various aromatic diamines by the conventional two-step procedure of ring-opening polyaddition in a polar amide-type solvent and subsequent thermal cyclic dehydration. These polyimides had inherent viscosities of 1.20—1.69 dL g-1, and were insoluble in organic solvents. The polyimides were characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), wide-angle X-Ray diffraction measurements, and dynamic mechanical analysis (DMA). Typical polyimides were noncrystalline and showed excellent thermal stability, and had glass transition temperatures (Tg) at about 250°C. Decrease in the modulus at the glass transition temperature was less than corresponding polyimides having no p-sexiphenyl unit due to the presence of the rigid p-sexiphenyl unit.

New highly branched poly[(ether)-(ether ether ketone)] dendrimers were synthesized by the convergent approach using two building blocks, 3, 5-dihydroxybenzyl alcohol, 1, and 3, 5-dihydroxy-4′-(4-fluorobenzoyl)diphenylether, 2, alternatively. The reaction of p-fluorobenzonitrile and 1 gave 3, 5-di(4-cyanophenoxy)benzylalcohol (the first generation dendron, G1-OH). After G1-OH was converted to 3, 5-di(4-cyanophenoxy)benzylbromide (G1-Br), the resultant benzylic bromide functionality was allowed to react with 2 to yield the second-generation dendron (G2-F). The third-generation dendron (G3-OH) was obtained by the reaction of G2-F and 1, and the fourth-generation dendron (G4-F) was obtained by reaction of G3-Br derived from G3-OH, with 2. Finally, dendrimers, Den-(G2)3 and Den-(G4)3 were synthesized by reaction of G2-F and G4-F with trifunctional core, respectively. Analysis was made of these structurally unambiguous dendrons and dendrimers by gel permeation chromatography (GPC) and matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectroscopy. 1H and 13C NMR spectra were consistent with the structures of these dendrons and dendrimers.

New highly branched poly(ether ether ketone) dendrimers were synthesized by the divergent approach through aromatic nucleophilic substitution reactions. 3,5-Dimethoxy-4'-(4-fluorobenzoyl)diphenylether, 1, and 1,3,5-tris[p-(3,5-dihydroxyphenoxy)phenyl]benzene, G0-OH, were used as a building block and starting core, respectively. The reaction of 1 with G0-OH gave the first-generation dendrimer (G1-OMe), which possessed 12 methoxy groups on the periphery. After the methoxy groups were converted to hydroxy groups by treatment with pyridine hydrochloride, the resultant phenol functionality (Gl-OH) was allowed to react with 1 to yield the second-generation dendrimer (G2-OMe) which possessed 24 methoxy groups. By repeating these procedures G3-OMe dendrimer and G3-OH dendrimer possessing 48 methoxy and hydroxy groups, respectively, on the periphery were obtained. 1 H and 13 C NMR spectra were consistent with the structures of these dendrimers. Molecular weights and molecular weight distribution determined by gel permeation chromatography indicated that the dendrimers possessed remarkably narrow molecular weight distribution. Analysis was made of these structurally unambiguous dendrimers by matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectroscopy. The characteristics of these dendrimers, Gn-OMe and Gn-OH, such as solubility and thermal properties were compared.

A new highly phenylated diamine, 1,4-bis(4-aminophenyl)-2,3-diphenylnaphthalene, was synthesized in two steps starting from 2,5-bis(4-nitrophenyl)-3,4-diphenylcyclopentadienone. New aromatic polyamides containing tetraphenylnaphthalene unit were prepared by low temperature solution polycondensation of this diamine with various aromatic dicarboxylic acid chlorides. These polyamides had inherent viscosities of 0.45—0.82 dlg−1. Polyamides with m-phenylene moiety and flexible connecting group were soluble in various organic solvents such as N,N-dimethylacetamide and N-methyl-2-pyrrolidone, but those with rigid symmetric structures were soluble in only hot N,N-dimethylacetamide and N-methyl-2-pyrrolidone. The glass transition temperature of the polyamides ranged from 268 to 366°C, and the 10% weight loss temperatures were above 500°C in air.

Poly(vinylpyrrolidone)-silica hybrid films were readily prepared by the sol-gel process. The obtained films containing less than 8 wt% silica had well dispersed silica particles. However, the NMR and IR results showed that the hydrolysis and condensation of tetraethoxysilane were incomplete.

Functional groups, such as dimethylamino and hydroxy groups, were introduced to the periphery position of the third generation starburst polysiloxane (G3) prepared by the divergent method. Phenylsilane unit of the second generation polymer (G2-Ph) was converted to the diethylaminosilane unit (G2-DEA) via the corresponding bromosilane (G2-Br) generated by the reaction of the phenylsilane with bromine. Next, G2-DEA was reacted with the building block possessing one silanol and two dimethylamino, or one silanol and two benzyloxy unit, yielding the starburst polysiloxanes possessing 24 dimethylamino groups (G3-DMA) or benzyloxy groups (G3-Bz) at the periphery position. The latter polymer was converted to G3-OH which had 24 hydroxy groups. The IR, 1H NMR, and GPC measurements supported a successful introduction of these functional groups. The solubility of the starburst polysiloxanes was remarkably affected by the functional groups.

A new class of polyimide-silica hybrid films were successfully prepared by the sol-gel reaction starting from tetraethoxysilane (TEOS) in the solution of polyamic acid in N,N-dimethylacetamide. The hybrid films were obtained by the hydrolysis-polycondensation of TEOS in the polyamic acid solution, followed by heating at 270°C. Fairly flexible films were obtained up to 70 wt% of silica content. The films containing the silica less than 8 wt% were yellow and transparent, whereas the films with higher silica content were yellow and opaque. The density of the silica in the hybrid films was estimated to be 1.65 gcm−3. The 29Si nuclear magnetic resonance spectrum indicated that the silica in the films consisted of non-hydroxy, monohydroxy, and dihydroxy siloxane structures. Silica particles with diameter of around 5 μm were observed in the hybrid films by scanning electron microscopy. The density, decomposition temperature, and modulus of the hybrid films increased with increasing the silica content, whereas the tensile strength and elongation at break of the films decreased in this order. The glass transition temperature of the hybrid films showed the minimum at 8 wt% of silica content. The linear thermal expansion coefficient of the silica in the hybrid films was estimated to be 1.3×10−5 K−1.

Polyimide Langmuir-Blodgett (LB) film containing tetraphenylporphyrin (TPP) unit was newly prepared on the surface of tin dioxide electrode by “Precursor method” (Electrode I), and the generation of photocurrent was measured by the wet system. The photocurrent spectrum obtained was very similar in shape to the absorption spectrum of the LB film. The quantum efficiency of the electrode modified by one layer of the polyimide LB film was 0.178, and the values decreased with increasing the number of layers. The long term stability of the photocurrent of Electrode I was compared with that of the electrode possessing the monomeric TPP LB film prepared from a 1:1 mixture of monoamino-TPP and stearic acid (Electrode II). These two electrodes were stable under the irradiation of monochromatic light of 430 nm, while in the case of the direct irradiation of the xenon lamp, Electrode I kept the same level of the initial photocurrent for a long time, but Electrode II decreased to 50% within one hour. The absorption spectra indicated that both LB films did not come off from the surface of the electrodes during the photocurrent measurements. The decrease of the photocurrent of Electrode II was explained by the hydrophobicity of the surface of the LB film possessing the long alkyl chain and by the diffusing effect of the reducing agent in the electrolyte solution.

Preparation and Monolayer Thickness of Langmuir–Blodgett Films of Polyimides Having Various Chemical Structures