Search

A new class of polymer materials has been developed that can convert light energy directly into mechanical work, and show a variety of three-dimensional movements simply from exposure to light. These polymer materials can be fabricated into any shape and size using photolithographic methods and it is expected they will be developed for various applications. In this paper recent progress of this interesting class of polymer material is reviewed.

Electroluminescent (EL) behavior has been evaluated in a cell that contained molecular dispersion of 1,4-bis( N , N -diphenylaminophenyl-1,3,4-oxadiazolyl)benzene (OXD) in various liquid crystals (LC); 4-hexyloxy-4′-cyanobiphenyl, 4-octyloxy-4′-cyanobiphenyl (8OCB) as low molecular-weight LCs and poly(8-(4-cyano-4′-biphenyl)-1-octanoylacrylate), poly(11-(4-cyano-4′-biphenyl)-1-undecanoylacrylate) as polymer LCs. Among the guest/host mixtures examined, the OXD/8OCB mixture showed the most stable LC phase even at the fraction of OXD up to 30 wt.%. EL emission was observed above the temperature where the OXD/8OCB mixture showed an LC phase. Furthermore, an EL device was fabricated that consisted of interdigital electrodes coated onto a glass substrate. It was found that the EL emission from the device was highly polarized.

1,3-Butadiene polymerization was conducted at 0 °C with cobalt dichloride (CoCl2) activated by different cocatalysts: MAO (methylaluminoxane), dried-MAO (substantially free of trimethylaluminum), MMAO (triisobutylaluminum-modified methylaluminoxane), dried-MMAO (substantially free of trialkylaluminum) and TMA (trimethylaluminum). MAO and MMAO were effective cocatalysts for 1,3-butadiene polymerization. CoCl2 activated with MAO showed slowly-initiated living polymerization which has been reported previously, whereas, that with MMAO showed deactivation. Neither dried-MAO nor dried-MMAO, TMA activated the catalyst, whereas dried-MAO-TMA (mixtures of dried-MAO and TMA) and dried-MMAO-TMA (mixtures of dried-MMAO and TMA) allowed the polymerization. These results indicated that trialkylaluminums were necessary with MAOs for generating the active species. Dried-MAO-TMA caused frequent chain transfer reactions, whereas dried-MMAO-TMA showed the living like polymerization not only with slow initiation but with slow propagation also, suggesting that the nature of the active species was strongly dependent on the structure of alkylaluminums and MAOs. The microstructure of the resulting polymers analyzed by 1 H and 13 C NMR was cis-1,4 (98–97%); the percentage slightly decreased in the following order: MAO>dried-MAO>MMAO>dried-MMAO, accompanied by the increase of trans-1,4 and 1,2-inserted units.

The recent highlights in the photoinduced modulation of the liquid-crystalline (LC) alignment and their applications to photonics are reviewed. The molecular alignment of LCs can be controlled by either the photochemical process or the photophysical process and we can change the birefringence as well as refractive index of the material by the modulation of the LC alignment. The photoresponsive LCs show very quick response to stimulus light: the response time is ∼200 ns. Furthermore, the extremely large refractive index modulation (Δ n =∼10 −1 ) can be also induced. The photoresponsive LCs, therefore, are potential materials for holographic recording and other photonic device.

Propene polymerization was carried out by Cp ∗ Ti(CH 2 Ph) 3 , [ t -BuNSiMe 2 (C 5 Me 4 )]TiMe 2 and [ t -BuNSiMe 2 Flu]TiMe 2 combined with dried or SiO 2 -supported methylaluminoxane (MAO). The dried MAO system generally showed higher activity and gave higher molecular weight polypropenes than the SiO 2 -supported MAO system. The decrease in the activity by changing the cocatalyst from dried MAO to SiO 2 -supported MAO was, however, more significant in the cases of [ t -BuNSiMe 2 (C 5 Me 4 )]TiMe 2 and [ t -BuNSiMe 2 Flu]TiMe 2 . The molecular weight distribution of the produced polymers indicated that uniform active species were formed from Cp ∗ Ti(CH 2 Ph) 3 regardless of the cocatalyst employed while the active species derived from [ t -BuNSiMe 2 (C 5 Me 4 )]TiMe 2 and [ t -BuNSiMe 2 Flu]TiMe 2 combined with SiO 2 -supported MAO were inhomogeneous. The microstructure of the produced polymers were independent of the cocatalyst used, and [ t -BuNSiMe 2 Flu]TiMe 2 catalysts produced syndiotactic polypropenes with less regioirregular structure. The Cp ∗ Ti(CH 2 Ph) 3 /SiO 2 -supported MAO system showed a steady polymerization rate with frequent chain transfer at 0 °C while the [ t -BuNSiMe 2 (C 5 Me 4 )]TiMe 2 /SiO 2 -supported MAO system produced the polypropenes with long chain lifetime accompanied by slow deactivation at 0 °C.

Propene polymerization was conducted by [η3:η1-tert-butyl(dimethylfluorenylsilyl)amido]dimethyltitanium combined with B(C6F5)3 or methylaluminoxane (MAO) as a cocatalyst in the presence or absence of various trialkylaluminums: Me3Al, Et3Al, iBu3Al (triisobutylaluminum) and Oct3Al (trioctylaluminum). In the case of living polymerization with B(C6F5)3 at −50°C, addition of Oct3Al and Et3Al increased the propagation rate. Et3Al also acted as a chain transfer reagent and selectively gave Al-terminated polymers, while Oct3Al induced chain transfer reaction only in high concentration. Little polymer was obtained in the presence of Me3Al or iBu3Al. When MAO was used as a cocatalyst, polymerization did not proceed at −50°C. The MAO system, however, showed high activity at 40°C and selectively gave low molecular weight polymers terminated with Al–C bonds. Contrary to the low temperature polymerization with B(C6F5)3 at −50°C, the polymer yield was enhanced by the addition of Me3Al and iBu3Al, while the molecular weight was reduced by Me3Al and enlarged by iBu3Al. On the other hand, Et3Al and Oct3Al significantly decreased both the polymer yield and the molecular weight under these conditions. It was found that additive effects of trialkylaluminums were strongly dependent on polymerization temperature as well as on the structure of the alkyl group.

The unique features of the phosphonium salts as functional materials are reviewed, with emphasis being placed on the comparison between the phosphonium salts and the commonly available quaternary ammonium salts, which have the same structure, differing only in the positively-charged heteroatom. The antimicrobial activity of onium salts with different long-chain segments is described with special reference to structure–activity relationships. The unexpected relationship between the antibacterial activity and the aggregation behavior in aqueous solution (i.e. lyotropic liquid-crystalline properties) was revealed through systematic studies on the antibacterial activity of the phosphonium salts as a novel class of cationic biocides. Furthermore, it is shown that the phosphonium salts can act as thermotropic liquid crystals in spite of the fact that they are amphiphiles without a rigid core.

Ethylene polymerization was conducted with bis(cyclopentadienyl)zirconium dichloride (1) and rac-dimethylsilylenebis(indenyl)zirconium dichloride (2) combined with trialkylaluminum (AlR3; R=methyl (Me), ethyl (Et), isobutyl (iBu))/triphenylcarbenium tetrakis(pentafluorophenyl)borate (Ph3CB(C6F5)4) or tris(pentafluorophenyl)borane (B(C6F5)3) to study the effect of cocatalysts on polymerization rate (Rp). When AlMe3 was used, no activity or very low activity was observed with both zirconocenes regardless of the borane compounds used. The replacement of AlMe3 to AlEt3 or AliBu3 with 1–AlR3/Ph3CB(C6F5)4 caused polymerization and induction time was observed to reach the maximum Rp. Especially in the case of using AlEt3, it took about 30 min to show the activity. When B(C6F5)3 was used, AlEt3 was not effective but AliBu3 gave the highest activity among all the combinations of AlR3 and the borane compounds. In the case of polymerization with 2 using Ph3CB(C6F5)4, high activity was observed with both AlEt3 and AliBu3 without any induction period. When B(C6F5)3 was used instead of Ph3CB(C6F5)4, very low activity was observed with AlEt3. On the other hand, high activity was observed with AliBu3, and the maximum Rp was found at the beginning of the polymerization. The effect of AlR3 on the formation of active species was discussed based on these results.

2-Methoxyalkanoic acids were found to undergo consecutive decarbonylative α,α-diarylation in P 2 O 5 -MsOH instead of Friedel-Crafts type arylation on the carbonyl carbon. The influence of the substituents of the arenes and the carboxylic acids in this reaction was elucidated based on the reaction yields. The reaction behavior was found to be primarily governed by the electron-withdrawing/releasing property of the α-substituents on the carboxylic acids as well as the positive species-accepting ability of the arenes. The steric hindrance was shown to participate in determining the reaction feasibility as a secondary factor.

Optical switching and image storage have been examined by means of liquid crystals (LCs), nematic LCs and ferroelectric LCs. Photochromic molecules were incorporated either by dispersion into host LCs or covalently attached to polymer main chains. These photochromic moieties act as a photoresponsive switch which induces phase transition and change in orientation of LCs, resulting in optical switching and image storage.

Octadecylesters of L -1-naphthylalanine and L -1-pyrenylalanine were synthesized. Both compounds form stable condensed monolayers at the air-water interface and can be transferred onto solid plates by the vertical dipping and horizontal lifting methods to give the alternating Y-type and non-alternating X-type films respectively. The orientation and packing of the aromatic rings depend upon the deposition methods and the surface pressures, as indicated by UV, circular dichroism and fluorescence spectra. Poly-amino acids containing the π-electron systems as a side group could be obtained in the LB films. For the Y-type films, the oligomer was obtained in the first step at 25°C, and then the poly-amino acid with a random coil was produced by increasing the temperature to 40°C, as suggested by the amide I bands at 1690 and 1650 cm −1 . The conversion in the X-type film was very low compared with that in the Y--type film. It is considered that the interlayer reaction propagates by “sewing up” the amino and the ester groups facing each other at the adjacent layers in the Y-type films.

Sol-gel glass thin films were prepared from tetraethyl orthosilicate in the presence of 4-methoxy-4′-(2-hydroxyethoxy)azobenzene (MHAB), 4-methoxy-4′-(N-(3-triethoxysilylpropyl)carbamoylmethoxy)azobenzene (MTAB) and 4,4′-bis(N-(3-triethoxysilylpropyl)carbamoylmethoxy)azobenzene (DTAB). The optical absorption spectra of the three azobenzenes entrapped in the films were investigated. The trans-cis photoisomerization and the thermal reversion of the azobenzene moiety were studied in the glass films and compared with those in solutions as well as in polymethyl methacrylate (PMMA) thin films. Triethoxysilyl groups linked with the azobenzene moiety had no effect on isomerization reactions. The cis fraction of the three azobenzenes in a photostationary state in PMMA was quite similar to that in solution whereas the photoisomerization was strongly suppressed in sol-gel films due to the rigidity of the matrix. The introduction of one triethoxysilyl group has a slight effect on both photoisomerization and thermal reversion in sol-gel films. Photoisomerization of DTAB with two silylating units was depressed in a sol-sol film because both sides of the azobenzene moiety were fixed to the sol-gel glass matrix.

Interaction of a polymeric in-chain quaternary ammonium salt with phospholipid bilayer membranes was studied by time-resolved fluorescence spectroscopy with the aid of a picosecond time-rcorrelated single photon counting system (instrument response function, 70 ps FWHM). Particular attention was paid to a phenomenon of polycation-induced fluidization of the membranes, which was well evaluated by time-resolved fluorescence anisotropy measurements. The fluorescence anisotropy, r ( t ), of 1,6-diphenyl-1,3,5-hexatriene (DPH) embedded in the membranes was analyzed based on the wobbling-in-cone model. Strong interaction was observed between the polycation and a negatively charged phosphatidic acid membrane as demonstrated by a large decrease of residual polarization value on adding the polycation to the acidic phospholipid dispersion. This means that the cone angle of the wobbling-in-cone motion of the DPH molecule increases by the addition of the polycaton, indicative of the polycation-induced fluidization of the acidic membrane. On the other hand, r ( t ) of DPH embedded in a zwitterionic phosphatidylcholine membrane was not affected significantly by the addition of the polycation, which is presumably due to non-binding of the polycation to the zwitterionic membrane. Our results clearly indicate that the polycationic disinfectant interacts strongly with negatively charged membranes, inducing fluidization of the membranes.

It is of great importance in propene polymerization to control molecular weight and molecular weight distribution as well as isotacticity. Propene polymerization was carried out with an isospecific MgCl2/TiCl4-Cp2TiMe2 catalyst in the presence of various kinds of external Lewis bases. It was found that the molecular weight distribution of the isotactic polymer could be controlled while retaining high activity, high isospecificity and high molecular weight only by changing the kind and/or amount of the Lewis bases. © 1997 Elsevier Science Ltd.

In order to improve the electro-optic properties of polymer stabilized ferroelectric liquid crystal display(PS-FLCD) cells, new functional monomer was synthesized. The PS-FLCD cells were fabricated by UV irradiation with varying monomer doping concentrations. The electro-optic properties were with examined with respect to cell morphology of cell and response time.

Interaction of poly(hexamethylene biguanide hydrochloride) (PHMB), which is a polymeric biocide bearing biguanide groups in its main chain, with phospholipid bilayers was studied by the fluorescence depolarization method. A strong interaction of PHMB with negatively charged bilayers composed of phosphatidylglycerol(PG) alone or of PG and phosphatidylcholine (PC) was observed, whereas neutral PC bilayers were not affected. On adding PHMB, the fluorescence polarization of diphenylhexatriene embedded in the negatively charged bilayers was reduced to a great extent, especially in the gel phase. This was interpreted in terms of PHMB-induced expansion and fluidization of the bilayer, which enables the probe molecule to undergo less-hindered torsional motion. Similarity between PHMB and polymyxin B in the structure, the mode of action against bacteria and the interaction with lipid membranes is discussed.

Differential scanning calorimetry (DSC) and fluorescence polarization methods have been used to study the interactions between phospholipid membranes and a polymeric biocide, poly(hexamethylene biguanide hydrochloride) (PHMB). It was found that PHMB had very little effect on neutral lipids such as phosphatidylcholine (PC) and phosphatidylethanolamine (PE), whereas it greatly reduced the phase transition temperature of phosphatidylglycerol (PG), an acidic lipid found in bacteria. Although the corresponding monomeric biocide had a similar effect on the PG bilayer, the behaviour towards mixed lipid bilayers of PC and PG has been shown to be completely different for the polymeric and monomeric biocides: viz. the former can induce isothermal phase separation into a PHMB-PG complex domain and a PC-enriched domain, whilst the latter cannot. This may account for the great difference in bactericidal activity between them. It is suggested that PHMB interacts primarily with negatively charged species in the membranes, inducing aggregation of acidic lipids in the vicinity of the adsorption site, where higher fluidity and higher permeability are expected. The results have shown that two factors might be crucial in the cidal activity of such types of cationic disinfectants as biguanides: phase separation and interaction with the hydrocarbon interior of the membranes. Polymeric biocides could be particularly effective by virtue of their ability to combine hydrophobic character and multiple charges within a single molecule.