Oxidation of Monolayers of Partly Converted Dimethoxy-Substituted Poly(p-phenylenevinylene) Precursor Polymers at the Air-Water Interface

We observed that the poly(p-phenylenevinylene) units in Langmuir monolayers of partly converted dimethoxy-substituted poly(p-phenylenevinylene) precursor polymers oxidize at the air-water interface. This reaction even happened in the dark and therefore can not be attributed to a photooxygenation reaction with singlet oxygen. We assume that ground-state triplet oxygen is polarized at the air-water interface and forms a weakly bound complex with the double bond to give a reactive intermediate state, which lowers the activation energy of the oxidation reaction. The air-water interface thus works as a catalyst in this reaction.

Rheological Behavior of Precursor PPV Monolayers

The rheological behavior of different precursor poly(p-phenylene vinylene) (prec-PPV) monolayers at the air-water interface was investigated using an interfacial stress rheometer (ISR). This device nicely reveals a transition of the precursor poly(2,5-dimethoxy-1,4 phenylene vinylene) (prec-DMePPV) monolayer from Newtonian to elastic behavior with increasing surface pressure. The transition is accompanied by an increase in the modulus. This behavior coincides with the coagulation of different 2D condensed domains as revealed by Brewster angle microscopy (BAM). However, partly converted prec-DMePPV monolayers show elastic behavior even at low surface pressures, although a sudden increase of the moduli does occur. This phenomenon is attributed to enhanced hydrophobic interactions between the conjugated moieties in the partly converted polymers. The latter also explains the stretching behavior of the partly converted prec-DMePPV upon transfer in Langmuir-Blodgett-type vertical dipping. The increase of the moduli which is observed is much more gradual in the precursor poly(2,5-dibutoxy-1,4-phenylene vinylene), prec-DBuPPV, a monolayer which is in agreement with the expected expanded state of the latter monolayer.

Pre-M Phase-promoting Factor Associates with Annulate Lamellae in Xenopus Oocytes and Egg Extracts

We have used complementary biochemical and in vivo approaches to study the compartmentalization of M phase-promoting factor (MPF) in prophase Xenopus eggs and oocytes. We first examined the distribution of MPF (Cdc2/CyclinB2) and membranous organelles in high-speed extracts of Xenopus eggs made during mitotic prophase. These extracts were found to lack mitochondria, Golgi membranes, and most endoplasmic reticulum (ER) but to contain the bulk of the pre-MPF pool. This pre-MPF could be pelleted by further centrifugation along with components necessary to activate it. On activation, Cdc2/CyclinB2 moved into the soluble fraction. Electron microscopy and Western blot analysis showed that the pre-MPF pellet contained a specific ER subdomain comprising "annulate lamellae" (AL): stacked ER membranes highly enriched in nuclear pores. Colocalization of pre-MPF with AL was demonstrated by anti-CyclinB2 immunofluorescence in prophase oocytes, in which AL are positioned close to the vegetal surface. Green fluorescent protein-CyclinB2 expressed in oocytes also localized at AL. These data suggest that inactive MPF associates with nuclear envelope components just before activation. This association may explain why nuclei and centrosomes stimulate MPF activation and provide a mechanism for targeting of MPF to some of its key substrates

In-Plane Orientation in Langmuir-Blodgett Multilayers of a Partly Converted Flexible Poly(p-phenylenevinylene) Precursor Polymer

The dimethoxy-substituted precursor poly(p-phenylenevinylene) (prec-DMePPV) was partly converted to dimethoxy-PPV by exposing the precursor solution in chloroform to daylight. The monolayer and transfer behavior of this partly converted precursor (pc-DMePPV) was studied with the Langmuir-Blodgett technique. In contrast to prec-DMePPV, an excellent transfer behavior was found for pc-DMePPV, and it was possible to build up multilayer films. The observed Z-type transfer behavior was peculiar, because the transfer ratio was higher than 1, and after deposition the monolayer expanded. Although the pc-DMePPV is not a rigid-rod-like polymer, an in-plane orientation of the chain in the transfer direction was found in the multilayers. We assume that, due to hydrophobic intra- and intermolecular interactions between the conjugated parts in the chains, the monolayer of pc-DMePPV can be considered as a 2D physical network, and the obtained orientation in the dipping direction is due to the stretching of this network during deposition. After each dip the monolayer relaxes, restoring the free volume again as observed by the expansion of the film. After full conversion to dimethoxy-PPV (DMePPV) by thermal treatment of the multilayer, the dipping-induced in-plane orientation was preserved.

Dipping induced orientation in Langmuir–Blodgett multilayers of a flexible PPV precursor polymer

The Langmuir monolayers of a chloroform soluble dimethoxy substituted precursor poly(p-phenylenevinylene) (PPV) with a methoxy leaving group were studied. During storage in chloroform the precursor polymer is partly converted to PPV. Multilayer films could only be prepared of this partly converted precursor. When a monolayer of this polymer containing 5% PPV units was deposited, an orientation of the polymer chain along the dipping direction was found. Whereas a monolayer containing 14% PPV units showed no orientation in the dipping direction. It is assumed that a monolayer of the precursor containing 5% PPV units can be considered as a 2D flexible network and the obtained orientation in the dipping direction is due to stretching of this network during deposition.

Mixed Monolayers and Multilayers of Poly(Isocyanide)S with Nonlinear Optically-Active Side-Chains

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Second-Harmonic Generation from Floating Monolayers and Langmuir-Blodgett Multilayers of Poly(isocyanide)s

Floating monolayers as well as Langmuir-Blodgett (LB) films of poly(isocyanide)s containing NLO-active side chains appear to be capable of generating second-harmonic light. Spin-coated films and cast films of these polymers do not shown this behavior. These results indicate that the NLO activity of the LB films originates from the orientation of the side chains obtained at the air-water interface. In the case of poly(isocyanide)s with relatively hydrophobic side chains the second-harmonic intensities generated from the LB films are small, probably because the films are of the Y-type. Poly(isocyanide)s with more hydrophilic side chains form LB films which are Z-type. These films show stable second-harmonic generation without the need of poling with high electrical fields at high temperatures.

Langmuir-Blodgett mono- and multilayers of (di)alkoxy-substituted poly(p-phenylenevinylene) precursor polymers. 2. Stability, transfer, and multilayer structure of (di)alkoxy-substituted precursor PPVs

The Langmuir monolayer stability and transfer properties of (di)alkoxy-substituted precursor PPVs were studied. All polymers formed stable monolayers, but the packing of the monomeric units in the monolayer depended strongly on the substituents. The less closely packed monolayers can be transferred with the Langmuir-Blodgett technique, while the closely packed monolayers, with strong pi-pi interaction between the aromatic rings, can only be transferred with the Langmuir-Schaefer technique due to the stiffness of the monolayers. Transmission and grazing incidence reflection FT-IR spectroscopy in combination with IR spectra computer simulations revealed that in many instances the orientation of the precursor at the water interface is largely preserved after transfer of the monolayer. The roughness and the thickness of the multilayers were determined by small-angle X-ray reflection

Langmuir-Blodgett Mono- and Multilayers of (Di)alkoxy-Substituted Poly(p-phenylenevinylene) Precursor Polymers. 1. Langmuir Monolayers of Homo- and Copolymers of (Di)alkoxy-Substituted Precursor PPVs

The Langmuir monolayer behavior of (di)alkoxy-substituted precursor poly(p-phenylenevinylenes) (PPVs) with a methoxy-leaving group was studied. The average orientation of the aromatic ring and the ether groups at the air-water interface was elucidated by external FT-infrared reflection spectroscopy measurements at the air-water interface combined with FT-IR computer simulations. The aromatic rings of the precursors, except those of the dibutoxy-substituted one, take on, directly after spreading, an almost perpendicular orientation to the water subphase. The isotherms of these precursors showed no special transitions, and these polymers can be considered to be in a condensed or 2-D collapsed state with lateral cohesive π-π interactions between the aromatic rings as the most prominent interaction leading to this condensed state. The aromatic rings of the dibutoxy-substituted precursor are lying flat at the water surface at large areas per repeating unit and can be considered to be in the expanded state directly after spreading. The isotherm of this precursor showed two transitions because here the chain conformation is predominantly determined by the butyl chains and not by the main chain.

Mixed mono- and multilayers of poly(isocyanide)s with non-linear optically active side chains

The properties and structure of Langmuir-Blodgett mono- and multilayers of several poly(isocyanide)s with non-linear optically active side-chains were studied. These polymers formed very rigid layers or layers which appeared to be unstable. To circumvent this problem they were mixed with other poly(isocyanide)s or with amylose-butyrate. Transmission electron microscopy studies of the polymeric mixtures revealed that phase separation occurred in all cases and that only poly(isocyanide)s substituted with hydrophilic side chains formed monomolecular layers. Depending on the nature of the polymer which was used for mixing, the dye polymers could be deposited with Y- or Z-type transfer. Second-harmonic intensities generated from these films were small in the case of the Y-type multilayered films and moderately high in the case of the Z-type films.