Yoichi Shindo

Structure and properties of AOT reversed micelles as studied by the fluorescence probe technique

Abstract The microviscosity in the water pool of Aerosol OT (AOT) reversed micelles was estimated with the fluorescence yield of a viscosity-sensitive fluorescence probe, auramine O (AuO), and the steady-state fluorescence depolarization of xanthene dyes solubilized in the micellar core. The fluorescence yield measurement of AuO showed that the microviscosity η w at the vicinity of the AOT anionic head groups falls abruptly up to R w ([H 2 O]/[AOT])=10 and then gradually decreases until the upper limit of the water solubilization. The η w −R w curve almost coincides with the curve obtained from the steady-state fluorescence depolarization of RhB. Thus, the availability of the AuO method was confirmed. Fluorescence depolarization of xanthene dyes with different ionic characters evidently demonstrated the heterogeneity of the water pool. The effects of temperature, surfactant concentration, solvent, and counterion on the microviscosity were examined to obtain a more detailed picture of the static structure of AOT reversed micelles. In addition, the fluorescence depolarization of a solubilized dye demonstrated that dynamic fluctuation occurs at the vicinity of the phase separation in the cooling process. Finally, the intermicellar aggregation state was studied by utilizing the excitation energy transfer phenomenon. A suitable combination of donor and acceptor molecules solubilized in the water pool illustrates that AOT reversed micelles are not randomly dispersed in an isolated state in a nonpolar medium, but are clustered through intermicellar coagulation.

Improvement of thermoplasticity for s‐BPDA/PDA by copolymerization and blend with novel asymmetric BPDA‐based polyimides

Asymmetric biphenyl type polyimides (PI) derived from 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) and p-phenylenediamine (PDA) or 4,4′-oxydianiline (ODA) show higher Tgs, and much better thermoplasticity than the corresponding isomeric PIs from symmetric 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA). In addition, a-BPDA-derived PIs are completely amorphous owing to their bent chain structures and highly distorted conformations, whereas the PIs from s-BPDA are semicrystalline. a-BPDA-derived PIs possessing these properties or the a-BPDA monomer were used as a flexible blend component or a comonomer to improve the insufficient thermoplasticity of semirigid s-BPDA/PDA homo polymer. The blends composed of s-BPDA/PDA (80%) with a-BPDA-derived PIs (20%), as well as the s-BPDA/PDA-based copolymer containing 20% a-BPDA, showed a certain extent of thermoplasticity above the Tgs without causing a decrease in Tg. In addition, these blends and copolymer provided comparatively low thermal expansion coefficient (ca. 18 ppm). The improved film properties for the blends are related to good blend miscibility. On the other hand, when s-BPDA/ODA was used as a flexible matrix polymer instead of a-BPDA-derived PIs, the 80/20 blend film annealed at 400°C exhibited no prominent softening at the Tg. This result arises from annealing-induced crystallization of the flexible s-BPDA/ODA component. Thus, these results revealed that a-BPDA-derived PIs are promising candidates as matrix polymers for semirigid s-BPDA/PDA for the present purpose.

Thermo-Processable Polyimides with High Thermo-Oxidative Stability as Derived from Oxydiphthalic Anhydride and Bisphenol a Type Dianhydride

Two series of homopolyimides based on oxydiphthalic anhydride and bisphenol A bisether-4-diphthalic anhydride were synthesized with 12 kinds of aromatic diamines. Several thermo-processable homopolyimides were the focus of further investigation. The structure–property relationships of these homopolyimides were examined as functions of the glass transition temperature (T g), melting point (T m), thermal decomposition temperature (T d), and melt-flowability. The effects of the chemical and higher-order structures on these properties were discussed in this work to obtain an indication for the molecular design of high-performance thermoprocessable polyimides. A series of thermoplastic copolyimides were prepared to achieve higherT g and T d without sacrificing thermo-processability. The copolyimides investigated exhibited a comparable or lower melt viscosity, higher T g and T d, and higher long-term thermo-oxidative stability than those of ULTEM type polyimides. One of them exhibited a low melt viscosity (4700 poise at 400 °C), a high T g (224 °C), and excellent thermo-oxidative stability.

Photocrosslinking of polymers containing cinnamoyl groups: the effects of cinnamoyl contents in copolymers on the reaction in solutions

Abstract The effects of cinnamoyl contents in copolymers of 2-cinnamoyloxyethyl methacrylate with methyl methacrylate on the competitive intra- and intermolecular photocrosslinking were studied in THF solutions irradiated with a high-pressure Hg lamp at 30. The kinetic parameters for intra- and intermolecular crosslinking in degassed and aerated THF solutions were calculated from the initial concentration dependence of the rate of cyclodimer formation of cinnamoyl groups in copolymers by spectrophotometric measurements or from the data of the change in weight-average molecular weight by light-scattering measurements at various concentrations of copolymers. The quantum yields for intramolecular crosslink formation, Φ D intra , increase linearly with increasing CEMA mol% in a copolymer with a slope of 1 × 10 −4 per CEMA mol% in a copolymer. The parameters for intermolecular crosslink formation, K D inter , on the contrary, decrease with the extent of reaction, because the increase of intramolecular crosslinks prevents the interpenetration of polymer coils. The second virial coefficient becomes progressively smaller as the cyclodimerization proceeds; at the onset of gelation it reaches almost zero. The magnitudes of 〈 s 2 〉 1 2 and M w are related to the degree of the competition between intra- and intermolecular crosslinking. The contraction of polymer coils proceeds by predominant intramolecular crosslinking in dilute solution, and the contraction ratio, g = 〈 s 2 〉 cr / 〈 s 2 〉 1 , becomes 0.3–0.02 at the gel point, showing that the volume of the crosslinked polymer coil shrinks to 1 6 – 1 350 of the volume of corresponding linear polymer with the same molecular weight.

Photoisomerization of ethyl cinnamate in dilute solutions

Abstract The quantum yields for the elementary steps of photoisomerization of ethyl cinnamate in dilute solutions (about 10 −5 M) were determined by combining direct irradiation and irradiation sensitized with Michlers ketone at 30 °C. The quantum yields Φ( cis → trans ) and Φ( trans → cis ) for the overall photoisomerization are 0.26 and 0.29 respectively in ethanol and the sum of the these values is much smaller than unity, indicating the existence of direct deactivation of the excited singlet state of each isomer without passing through a twisted singlet state. The fraction Φ im α and Φ im β of each excited singlet state which is directly deactivated into the same isomeric form are 0.47 for 1 C f * and 0.39 for 1 C c * , and the fraction δ( 3 C * → C c ) of twisted triplet state which is deactivated into the cis form is 0.54.

Unique fluorescence behavior of perylenetetracarboxydiimides in polyimide systems

Perylenetetracarboxydiimide (PEDI) molecularly dispersed in polyamic acid (PAA) and polyimide (PI) films has unique fluorescence properties. An originally strong fluorescence of PEDI is efficiently quenched in the PAA films. The systematic variation of the chain structure of the PAA matrices revealed that the aromatic amide groups in the PAA chains function as a quencher. When a PAA derived from 3,4,3′4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA), BPDA/PDA, was used as a matrix polymer, the fluorescence of the dye dispersed in the film increased abruptly as imidization of the matrix proceeds. But annealing at temperatures higher than 320°C in the step-heating process caused a gradual decrease in the fluorescence intensity. The decreased intensity results from the dye–PDA units interactions intensified by the denser molecular packing of the matrix polymer chains. PEDI shows significant dependence of the fluorescence intensity on the chain structure of the PI matrices. In the various PI films containing a fixed diamine component, the dye fluorescence intensity reduces linearly with an increase in the intramolecular charge transfer ability of the PI matrices. From the result, we propose a fluorescence quenching mechanism through multistep electron transfer processes. The BPDA/PDA polyimide matrix leads to a strong PEDI fluorescence whereas the pyromellitic dianhydride (PMDA)-based PI matrices do not. For the blends composed of these PIs, the fluorescence of PEDI bound into the main chains provides a valuable indicator of the miscibility on the molecular level.

Photocrosslinking of polymers containing cinnamoyl groups: The change in polymer coil dimension during the reaction in solution

Abstract Intra- and intermolecular photocrosslinking reactions of poly(2-cinnamoyloxyethyl methacrylate) (PCEMA) and copoly(CEMA/MMA) in dilute solution under u.v. light irradiation at 30°C were studied by u.v. absorption, light scattering, GPC and viscosity measurements. The contraction of polymer coils proceeds due to predominant intramolecular photodimerization in very dilute solution. When the polymer concentration increases, competition between intra- and intermolecular photodimerization is observed, and the volume of polymer coils increases gradually due to the increase in molecular weight caused by the intermolecular reaction overcoming the contraction caused by the intramolecular reaction. The contribution of intramolecular crosslinking is much more important in the presence of oxygen than in its absence, showing that the shorter lifetime of the excited singlet state makes intermolecular photodimerization difficult.

Photocrosslinking of polymers containing cinnamoyl groups: The effect of molecular weight of copolymers on the reaction in solutions

Abstract The rate and the change in polymer coil dimension during the competitive intra- and intermolecular photocrosslinking reactions were studied for copolymers of 2-cinnamoyl-oxyethyl methacrylate with methyl methacrylate having various degrees of polymerization ( N n = 650–5600 ) in tetrahydrofuran solution under u.v. irradiation at 30°. The rate parameter, K D inter , for intermolecular reaction is proportional to N n −0.46 and the quantum yield, Φ D intra , decreases linearly with a slope of 2 × 10 −7 per N n of copolymers. The number of cinnamoyl groups for intramolecular crosslinking increases with increasing the molecular weight. The magnitude of the contraction of polymer coils due to intramolecular crosslinking increases as the molecular weight decreases. The contraction ratio, g = 〈s 2 〉 cr 〈s 2 〉 1 , becomes 0.02–0.05 at the gel point in a dilute solution, showing that the volume of the crosslinked polymer coil shrinks up to 1 350 - 1 100 of the volume of the corresponding linear polymer with the same molecular weight. The gel formed contains many intramolecular cross-links.

Photocrosslinking of polyimide containing benzophenone unit: Intra- and intermolecular reactions in solution

Abstract The photocrosslinking, using a high-pressure Hg lamp at 30°, of a polyimide from 3,3′-diethyl-4,4′-diamino-diphenylmethane with benzophenonetetracarboxylic dianhydride in aerated and degassed solutions was studied by i.r. spectroscopic, viscosity and light-scattering measurements. The quantum yields for intermolecular reactions are φAirinter/[C]0 = 0.68 l mol−1 and φVacinter/[C]0 = 1.8 l mol−1, and the quantum yields for intramolecular reactions, including some side reaction with the solvent, are φAirintra = 0.96 × 10−2 and φVacintra = 1.8 × 10−2 in the presence and absence of oxygen, respectively; they were calculated from the initial concentration dependence on the rate of decrease of benzophenone groups in the polymer. The magnitudes of M w and 〈s 2 〉 1 2 are governed by the competition between intra- and intermolecular crosslinking; the contraction ratio, g = 〈s2〉cr/〈s2〉1, of a polymer coil because of intramolecular crosslinking becomes 0.02 at the onset of gelation in a degassed dilute solution. The polyimide in dichloromethane behaves like a flexible polymer which forms many intramolecular crosslinks during photocrosslinking.

Conditions of organosol formation from metal soaps in higher alcohols and the shape of the dispersed particles

ABSTRACT Seven bivalent metal soaps and six trivalent metal soaps were prepared from the various kinds of fatty acids. Upon heating metal soap suspensions in organic solvents, organosols of metal oxides were formed and they showed the special characteristics in color. The scanning electron microscopic examination of the organosol particles showed the spherical, cubic, or irregular shape of 0.3~3.0 μm size. The shape and size of the particles were affected by the type of netal, the concentration of soaps, heating temperature, and the presence of a reducing agent. No relationship between the particles size of organosol and the carbon number of metal soaps was observed in this study. The stable organosol of monodispersed particles were successfully formed upon heating from Co, Mn and Fe metal soaps in 1-decanol containing a reducing agent.