P. Hodge

Chain extension and crosslinking of telechelic oligomers—I. Michael additions of bisamines to bismaleimides and bis(acetylene ketone)s

Some commercial amine-ended oligo(oxypropylene)s and oligo(oxyethylene-b-oxypropylene)s, and an amine-ended oligo(dimethylsiloxane), have been chain extended via Michael additions with some simple bismaleimides and bis(acetylene ketone)s. The polymers so-formed have molar masses of up to ca 20,000, corresponding to degrees of polymerization of the starting oligomers of up to ca 15. The polymers are either linear (and therefore soluble) or crosslinked, depending upon the starting materials and the precise conditions of preparation. Also, block copolymers can be prepared by chain extending mixtures of bisamine-ended oligomers, or by reacting an amine-ended oligomer with one having terminal maleimide groups.

LANGMUIR–BLODGETT FILMS OF SIMPLE ESTERIFIED PORPHYRINS

Abstract Protoporphyrin IX dimethyl ester, cobalt mesoporphyrin IX dimethyl ester, and tetra(4-carbomethoxyphenyl)porphyrin form condensed Langmuir films which can be transferred at 20–30 mN m −1 to quartz or aluminized substrates by an unusual Z deposition process. Some preliminary electrical measurements for Al/porphyrin/Au in a conventional sandwich cell arrangement and for Au/porphyrin/Au on quartz in a surface cell arrangement are reported. The capacitance and dark d.c. conductance of monolayers and multilayers on aluminium suggest that films of uniform quality and high dielectric constant have been produced. Protoporphyrin IX dimethyl ester is highly photoconductive in both cell arrangements, with a conductivity anisotropy of 10 4 −10 5 . Its action spectrum corresponds closely to the absorption spectrum of the solid film. The behaviour is compared and contrasted with that of chlorophyll-a and of the cobalt complexes of chlorophyll-a and the mesoporphyrin and is discussed in terms of the film structure which allows close packing of the porphyrin rings.

X-ray analysis of some porphyrin and polymer Langmuir-Blodgett films

Derivatives of mesoporphyrin IX dimethylester, poly(octadec-1-ene-maleic anhydride) and poly(styrene-maleic anhydride) have been prepared as Langmuir-Blodgett (LB) films. Examining their layer structure using X-ray diffraction analysis has led to several interesting and important conclusions about their packing arrangement.

Langmuir-Blodgett films from preformed polymers: derivatives of octadec-1-ene-maleic anhydride copolymers

Abstract We show here that good quality Langmuir-Blodgett films of octadec-1-ene- maleic anhydride copolymer derivatives can be deposited onto a number of substrates. The effects on the isotherm, deposition and packing of a number of derivatives are studied and these copolymers compared with a number of possible alternative amphiphilic polymer systems.

Electrical conductivity in Langmuir-Blodgett films of porphyrins: in-plane and through-the-film studies

Abstract We have prepared Langmuir-Blodgett (LB) multilayers of several metal complexes of mesoporphyrin IX dimethyl ester and investigated their dark conductivity normal to the film plane (on aluminized glass substrates with a gold top electrode) and parallel to the film plane (on quartz substrates with two interdigitating gold top electrodes). The silver(II) complex is amongst the most conductive of LB film materials yet measured in the film plane (resistivity, 4 × 10 4 Ω m) and the conductance is anisotropic. The dependence of the current on film thickness, voltage, temperature and frequency has been extensively investigated in both directions and reveals that these multilayers have some unusual conductivity properties which are quite different from those normally reported for conventional insulating multilayers. Conduction through the film is barrier limited with some evidence that the barrier is in the first few monolayers of the film. Conduction along the film is bulk limited but does not scale with thickness, the thinnest films ( n ⩽ 5 layers) being anomalously resistive. The conduction in both directions is thermally activated, with the same activation energy (0.43–0.48 eV). The results are discussed in terms of two possible models: one model involves structural defects in the films and the other model assumes that a depletion layer occurs in the film near an interface as in a conventional semiconductor.

Phase transfer catalysed polymer-supported Wittig reactions

Abstract Arylsubstituted olefins can be prepared in high yield using phase transfer catalysed polymer-supported Wittig reactions.

Electron-beam resists from Langmuir-Blodgett films of poly(styrene/maleic anhydride) derivatives

Abstract A range of styrene/maleic anhydride polymer derivatives and some related polymers have been synthesized and their performance as electron-beam resists assessed, initially as spin-coated films and then as Langmuir-Blodgett (LB) films on silicon. The effects of molecular structure, molecular weight and packing have been investigated in designing materials for optimum sensitivity and resolution. The most promising materials contain vinyl or ethynyl crosslinking groups and are negative resists, resolution ≈ 0.25 μm and gel dose in the range 1–40 μC cm −2 . Exposed and developed LB films only 50 layers (≈ 50 nm) thick have good plasma etch resistance, allowing the processing of tri-level resist structures (polyimide/Al/LB film) with little loss of resolution. This indicates that LB films based on poly(styrene/maleic anhydride) have the potential for the fabrication of submicrometre electronic devices.

Optical and structural characterization of Langmuir-Blodgett multilayers of non-polymeric and polymeric hemicyanines

Abstract Non-polymeric and polymeric amphiphilic hemicyanine dyes have been synthesized and extensively characterized as Langmuir films by their isotherm properties, and as Langmuir-Blodgett films by their deposition behaviour, optical absorption spectra and X-ray diffraction. Multilayers of non-polymeric dyes showed optical evidence for both non-aggregated ( λ max = 492 nm and aggregated ( λ max ≈ 420 nm) chromophores. Halide salts in the subphase, and particularli KI, had a marked effect on the isotherms and iodide ions were incorporated into the multilayers where they favoured a non-aggregated structure, presumably by a spacing effect. In alternating multilayers, aggregate formation was avoided by using the cadmium salts of fatty acids, or a polymer, as the optically inactive material. By contrast, multilayers of a polymeric hemicyanine were always free from chromophore-chromophore interactions however deposited ( λ max = 463 nm) and were clear and homeotropic. X-ray diffraction showed good evidence for a superlattice in multilayers of non-polymeric hemicyanine alternating with cadmium arachidate. These findings will be useful in selecting systems for future non-linear optics applications.

Chain extension and crosslinking of telechelic oligomers—II. Michael additions of bisthiols to bismaleimides, bismaleates and bis(acetylene ketone)s to give linear and crosslinked polymers

Thiol-terminated oligosulfides undergo crosslinking under mild conditions with bismaleimides in the presence of catalytic amounts of triethylamine in polar solvents. The mechanism of crosslinking is thought to be the formation of the thiolate anion which adds to the olefinic group on the maleimide to give a carbanion species which then undergoes further addition reactions. To illustrate this possibility, an ABA block copolymer consisting of oligosulfide (B) and maleimide (A) blocks was prepared by reaction between the oligosulfide and a maleimide in the presence of triethylamine. Reaction between dithiothreitol and a bismaleimide under similar conditions does not result in a crosslinked product and this is attributed to the interaction of hydroxyl groups with any carbanion species formed. Crosslinking was observed in the reaction between an oligosulfide and hexane bismaleate although much more slowly than for bismaleimide. Reactions between dithiothreitol and a bis(acetylene ketone), and an oligosulfide and a bis(acetylene ketone), both resulted in linear polymers of moderate molar mass.

Lightguiding in Langmuir-Blodgett films of preformed polymers

Abstract Preformed polymers, made from derivatives of vinyl-maleic anhydride co-polymers, have been used to produce thick (300–400 layers; 0.5–0.6 μm) Langmuir-Blodgett multilayers. The thermal stability of the films is shown to depend on the relative positions of the side-groups. Those materials which deposited well for large numbers of layers and possessed thermal stability were investigated for evidence of optical waveguiding using light at a wavelength of 633 nm. An attenuation of approximately 10 dB cm -1 was observed in films having a thickness of about 0.5 μm after suitable precautions were taken to exclude dust and bacteria.