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For the past half-century, a number of polyesters have been used for application in textile and film manufacturing. Currently, the polyester R&D effort directed toward advanced materials involves further progress in the synthesis given by a wide range of potential monomer combinations, new blending technology, and the use of advanced functional additives. As one such effort, we developed a facile modulation method to afford unique photophysical properties to an aliphatic polyester film. For this purpose, a free-standing film based on a network aliphatic polyester consisting of malonate moiety was successfully prepared. The UV−vis, IR, and photoluminescence studies revealed that the prepolymer underwent a Knoevenagel-type self-condensation in situ in the solid film via thermally reactive processing, leading to formation of certain conjugating structures in the polymer chain:  The film showed an apparent change from colorless to pale yellow by thermal treatment at 240 °C and then emitted a very intense greenish-blue light when excited at wavelengths longer than 325 nm. The characteristic IR absorption peak at 1654 cm^-1, due to the carbon−carbon double bond, appeared and gradually increased with increasing the heating time, whereas the absorptions due to the methylene and carbonyl groups slowly decreased. The thermally treated film was completely homogeneous at the micrometer level without such defects as decomposition and aggregation. The film showed excellent mechanical properties, relatively high density, and thermal stability. In addition, the prepolymer had excellent processability, due to the high adhesiveness, to afford pinholes and thin-line films with several micrometer features.

The present paper reports a new type of polymer-based chemosensor made of stiff fluoroalkylated polysilane, poly(3,3,3-trifluoropropylmethylsilane) (1), which showed a remarkable sensitivity for explosive nitroaromatic compounds (NACs), such as 2,4,6-trinitrophenol (picric acid), 1,3,5-trinitrobenzene (TNB), 2,4-dinitrotoluene (DNT), and m-dinitrobenzene (DNB), by a decrease in the photoluminescence (PL) intensity in the near-UV region with parts per million concentration of NACs in tetrahydrofuran (THF) solution and in the solid film in water. The PL intensity was completely reversible repeatedly after the removal of NACs from the thin film by rinsing with methanol (or water). A linear Stern−Volmer relationship was observed in all of the cases with high quenching constants. The PL quenching efficiency of 1 (Mn = 3.12 × 10⁴, PDI = 3.6, K = 4.15 × 10⁴ M^-1) for picric acid is 198 times better than that of nonfluoroalkylpolysilane, poly(n-propylmethylsilane) (2) (Mn = 2.93 × 10⁴, PDI = 2.1, K = 2.09 × 10² M^-1). The weak noncovalent interaction between Si atoms of σ-conjugated polysilane and N and/or O atoms of electron-deficient NACs may be responsible for electron transfer from the excited state of the polysilane to the electron-deficient NACs, resulting in the PL quenching of 1 in solution and in the thin film by NACs.

Novel helical poly(methyl-3,3,3-trifluoropropylsilane) (1) has been synthesized via Wurtz coupling by taking advantage of noncovalent Si···F−C intramolecular interactions. Such weak Si···F−C interactions make the conformation of the polysilane unique and controllable by proper choice of solvent and molecular weight. We have studied the conformation of polysilane by means of UV absorption, photoluminescence, NMR spectra, and viscosity measurements. Polysilane displayed a 73 helical rodlike conformation in noncoordinating solvents (e.g., toluene and decane) but a globule-like conformation in coordinating solvents (with N, O, or F as donor) at room temperature. The coordinating nature of solvents played an important role for solvatochromic transition rather than the solvent polarity, as such interactions are competitive in the presence of solvents with donor atoms. On the other hand, an analogous nonfluorinated polysilane, poly(n-propylmethylsilane) (2), revealed a disordered conformation in coordinating as well as in noncoordinating solvents. The unusual molecular weight dependent UV spectra of 1 showed an isosbestic point, suggesting the equilibrium between globule- and rodlike conformations at room temperature, which was further evident from the viscosity measurements. The proposed weak intramolecular interaction in 1 was supported by the ²⁹Si NMR and ¹⁹F NMR in noncoordinating and coordinating solvents. The IR spectrum of cast film from a toluene solution of 1 showed an improper blue shift of 12 cm^-1 in C−F stretching frequency compared to the IR spectrum cast from THF, suggesting very weak Si···F−C interaction in analogy with blue-shifted hydrogen bonds.

A new SiH-containing chiral polyacetylene, poly[p-[{(S)-2-methylbutyl}methylsilyl]-phenylacetylene] (1), with a moderate molecular weight (Mw 4.4 × 10⁴; Mw/Mn 2.4) was obtained with [RhCl(nbd)]2−NEt3 catalyst. IR and ¹H NMR studies revealed that the SiH group in 1 remains intact, with no side reactions such as hydrosilylation and hydrolysis. Furthermore, 1 readily turned into a transparent gel film with Si−O−Si linkages simply by standing in air at room temperature. The polymer 1 exhibited a quite large optical rotation ([α]D = 600°, c = 0.12 g/dL in toluene at 25 °C), corresponding to large molar ellipticities ([θ]ext = −5.1 × 10³ deg·cm²·dmol^-1 at 326 nm and 4.7 × 10³ deg·cm²·dmol^-1 at 371 nm). The CD intensity of the gel film scarcely changed in the range from 25 to 85 °C, presumably due to Si−O−Si cross-linking. Moreover, organic−inorganic composite materials were easily obtained by stirring inorganic particles such as titania and silica gel in the polymer solution. The prepared composites were characterized by AFM, EDX, and SEM.

Three types of poly[dialkylsilylenephenyleneethynylenephenylene]s (dialkyl:  2 for n-dodecylmethyl; 5a for di-n-hexyl; 5b for di-n-hexyl-co-dimethyl) were newly prepared by the AB- and AA−BB-type coupling reactions. These polymers afforded moderate molecular weights (Mw) in the range 7.6 × 10³−27 × 10³. As the amount of tetra-n-butylammonium fluoride (TBAF) increases in a THF solution of 2, two π−π* absorption bands at 298 and 317 nm due to the phenyleneethynylenephenylene moiety significantly decreased. Simultaneously, a new intense absorption band at 390 nm characteristic of intramolecular charge transfer (ICT) appeared in place of the original ICT absorption band at 342 nm. Also, the intensity of fluorescence band around 393 nm (excited at 342 nm) significantly decreased upon the addition of TBAF. The changes in UV−vis absorption and fluorescence spectra of the polymers were readily seen by naked eye. As for 2, a novel three-step titration curve of UV absorbance (or apparent GPC retention time) as a function of fluoride concentration was found. It was thus assumed that 2 underwent anion charge-driven coil-to-globule conformational transitions in the presence of TBAF. In addition, the complex forming abilities of the polymers with fluoride ion were greatly dependent on the nature of alkyl groups attached to the silicon atom of the polymers.

A new AB2-type monomer, m-bis[dimethylsilyl]phenylacetylene (2), was obtained by lithiation of m-dibromophenylacetylene followed by reaction with chlorodimethylsilane. Rh-catalyzed hydrosilylation and subsequent aerial oxidation of 2 provided a transparent gel film based on hyperbranched poly[(dimethylsilylene)(m-phenylene)(trans-vinylene)] (1) with siloxane linkages. The SEM and EDX analyses of the gel film revealed that the siloxane linkages were uniformly formed in the polymer matrix without any defects such as phase separation and decomposition. The gel film displayed a weak, but clear absorption in a wide range of wavelengths longer than 300 nm, due to the charge-transfer phenomenon. When excited at the charge-transfer absorption wavelength, the gel film emitted quite intense blue light that could be seen by the naked eye. The gel film showed excellent resistance against various organic solvents.

A novel aliphatic polyester containing a malonate group in the main chain was prepared by one-pot reaction of malonyl dichloride with ethylene glycol in the presence of triethylamine. The NMR, IR, and UV−vis studies revealed that the polymer partially underwent intra- and intermolecular Knoevenagel type self-condensation in solution and solid states, respectively, leading to formation of a certain conjugated structure in the polymer chain. The polymer exhibited a very weak, but clear, absorption around 363 nm as well as an absorption at 322 nm due to carbonyl n−π* transition. Furthermore, the polymer exhibited blue/greenish-blue photoluminescence due to ESIPT when excited at wavelengths longer than 350 nm. This polymer is the first example of a colored and photoluminescent aliphatic polyester.

To achieve fast ion transport in poly(ethylene oxide) (PEO)-based polymer electrolytes, we aimed to increase the ionic conductivity by using supercritical carbon dioxide (scCO2) as a processing solvent. In the crystalline PEO−LiCF3SO3 complex system, a large difference was observed in the conductivities of the original and scCO2-treated samples. In particular, PEO7-LiCF3SO3 (oxyethylene unit:Li = 7:1) increased in conductivity approximately 100-fold at 40 °C with scCO2 processing to a value of 1.8 × 10^-5 S/cm. Differential scanning calorimetry measurement showed that the processing reduces the glass transition temperature (Tg), the melting point of the PEO crystalline phase (Tm1), and the heat of fusion of the crystalline complex part (ΔH2). Raman scattering analysis clearly confirmed the decrease in the triple ion fraction and the increase in the ion pair fraction in scCO2-treated samples. Furthermore, subsequent time dependence of the ionic conductivity shows that scCO2 processing maintains the conductivity more than 10-fold higher for at least one month. As a mechanism, we believe that the CO2 molecules permeated into the sample play a crucial role in the dissociation of ions to increase the conductivity, according to the Lewis acid−base interaction.

The local dynamics of 10 substituted polyacetylenes in the glassy state have been investigated using a quasielastic neutron scattering technique in a time range of picoseconds to several tens of picoseconds to see a relationship between the local mobility and the gas permeability of these polymers. Even in the glassy state, these polymers show quasielastic scattering components, suggesting that certain stochastic motions occur in the glassy state. The dynamic scattering laws S(Q,ω) of the quasielastic components were well fitted to the sum of two Lorentzians, i.e., the narrow (slow) and broad (fast) components. It was found that both the relaxation rate Γn and the fraction An of the narrow (slow) component show positive correlations with oxygen permeability coefficient (PO2), suggesting that the local mobility of the matrix polymers plays an important role in gas permeability. We then defined local flux F, which is the product of Γn and An, as a measure of the local mobility to find that F is proportional to the diffusion coefficient of O2 gas (DO2), i.e., F ∝ DO2. To explain and discuss this relation, we have proposed a random gate model, where mobile side groups in the matrix polymer act as a gate for gas diffusion.

Novel poly(dimethylsilyleneethynylenephenylene) [5] and poly(dimethyl (or diphenyl) silylenephenyleneethynylenephenylene)s [6's] without diyne defects were synthesized by using the Pd/Cu-catalyzed AB-type coupling reaction. 6's showed small but clear π-to-σ charge-transfer absorption bands at longer wavelengths (>340 nm) than those of π−π* absorption bands (<320 nm), whereas the charge-transfer absorption band was not found in 5. When 6's were excited at the π−π* absorption wavelengths, two type of emission were observed:  One is the vibronically structured emission with a maximum around 325 nm due to the locally excited π* state, and the other is the intramolecular charge-transfer emission having a broad and structureless band (emission λmax ca. 370 nm) with a large Stokes shift. On the other hand, when excited at the charge-transfer absorption wavelengths, 6's exhibited only the intramolecular charge-transfer emission with a maximum above 390 nm. This suggests that the indigo blue light emission of 6's is due to the charge-transfer phenomenon and not to the locally excited π* state. The charge-transfer character of 6's was clearly verified by the shift of emission in polar solvents.

The influence of microscale fillers on ethylene–propylene rubbers (EPR) was examined with respect to their vibrational damping capacity and viscoelastic properties. The vibrational damping and dynamic mechanical properties of reinforced EPR were studied in systematic and comparative ways that reinforced the evidence of a direct relation between the vibrational damping loss factor and its mechanical damping loss factor. In this study, the sensitivity of the vibrational damping loss factor of reinforced EPR was quantified with respect to the variation in thickness, filler type, and filler content. Dynamic mechanical relaxation behaviors were also analyzed. The viscoelastic properties in terms of the storage modulus, loss modulus, mechanical damping loss factor, and frequency dependence of molecular relaxation showed interesting results with the filler types and compositions that had good correspondence with the vibrational damping behaviors. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3058–3066, 2001