The new generation clear coats introduced in the automotive industry have improved scratch and mar resistance. It is believed that those properties are related to the introduction of new binder technologies leading to higher film cross-link densities. This was relatively easy to accomplish in the automotive industry because baking temperatures are well above the glass-transition temperature (T-g) of the final clear coat film. In car repair coatings, the cross-linking takes place under conditions where the intermediate and/or final film T-g values are above the curing temperature. Such formulations result in vitrification during the drying process, a transition during which chemical cure and solvent release are slowed down substantially. The chemical cure can be improved through more reactive and/or higher functional binders, but this shifts the gel point to shorter times in the drying cycle which may lead to more solvent entrapment, resulting in low film hardnesses and paint defects. This paper describes the overall properties of 2K refinish clear coats based on linear versus branched, random and graft acrylic polyols. The authors will try to correlate overall properties with theoretical predictions and practical results.

Polymers (meth) acrylic copolymers having an OH value from 40 to 260 mg KOH / g and an average molecular mass (Mn) from 1500 to 20,000 g / mol and comprise the following components: A) polymerized monomers of at least olefinically unsaturated epoxy-functional monomer; B) at least one compound having a carboxyl group and at least one hydroxyl group and epoxy functional group reacts with the polymerized olefinic unsaturated monomers; C) at least one olefinically unsaturated monomer further polymerized is different from component A); and D) optionally at least one lactone-reactive polymer.

Catalytic chain transfer polymerisation based on cobalt II or III chelates is a free radical technique which allows the synthesis of functional oligomers with a terminal α-substituted acrylate group. This paper will review the applications of such oligomers in the design of low molecular weight, graft and block copolymer emulsions and dispersions for waterborne, two-component polyurethane paints. Such emulsions and dispersions have a composition and molecular weight control and offer unique properties when compared with binders prepared via conventional techniques.

By successive deposition of monolayers of the hexaalkoxytriphenylene derivative Te(OH)2, organized multilayers with a thickness between 18 and 360 Å can be obtained. Photoexcitation of the Langmuir-Blodgett films, deposited on interdigitating electrodes with a spacing of 100 μm, by a laser pulse of 4 ns full width at half maximum at a wavelength of 320 nm and with an energy between 5 and 200 μJ, induces transient photocurrents. At large applied fields or upon increasing the energy of the laser pulse and at reduced pressure, besides a transient current pulse of which the features are determined by the bandwidth of the experimental setup, a second current pulse grows in and shows a maximum at 1.5 μs after excitation. At low fields, charge generation occurs mainly in the bulk of the sample. In this field range, most charge carriers disappear by trapping or recombination before they can reach the opposite electrode, making it difficult to get information about the transit time. In the high field range, the charge carriers are still due to light absorbed by the Te(OH)2 layers. In this field range, the pressure of air or nitrogen strongly influences the features of the second maximum. The observation of the second maximum above a critical voltage and under optimal pressure conditions, suggests that corona discharging is also an important process. According to this model, the second maximum is related with the transit time of the charge carriers which migrate perpendicular to the substrate.

Using X-ray reflectivity, we have investigated the vertical ordering of multilayers of an asymmetrically substituted triphenylene derivative. A value of 1.37 nm is found for the thickness of an individual monolayer. Detailed fits for the reflectivity data have been performed. The corresponding electron density profiles suggest that very smooth, regular Y-type films are formed. The absence of clear Bragg peaks in the X-ray reflection curve and the small electron density fluctuations in the multilayer can be explained by an interdigitating packing of edge-on oriented disks in adjacent layers.

Langmuir-Blodgett (LB) films of an amphiphilic long-chain derivative of anthracene, of which the molecular packing shows a strong resemblance with the ab-plane of anthracene crystals, were investigated with respect to their photoconductive properties. Efficient photoinduced charge carrier generation and in-plane charge transport have been observed in LB-films of (2A7), using a gap configuration. The wavelength and intensity dependence of the quantum yield of the photocurrent in absence of a photosensitizer suggest an intrinsic bulkcharge generation mechanism. The intensity dependence of the photocurrent suggests a combination of nongeminate and alien recombination of charge carriers. The increase of the quantum yield in the presence of air is an indication that, upon photoexcitation, mobile holes are formed. By covering the multilayer assembly with a rhodamine containing monolayer, a significant increase of the quantum yield is obtained upon excitation of both the anthracene chromophore and the dye. In the case of dye excitation, the values and the field dependence of the photocurrents due to the photosensitized injection of holes from the layer of excited dye molecules into the 2A7 multilayer resemble those obtained for anthracene crystals covered by adsorbed dyes.

The electroluminescent properties of 5′-[4-[bis(4-ethylphenyl)amino]phenyl] -N,N,N′,N′-tetrakis(4-ethylphenyl) -[1,1′:3′,1″-terphenyl]-4,4″-diamine (pEFTP) were investigated in a vapor deposited layer and dispersed in a polymer matrix. Blue–violet electroluminescence was observed, after applying voltages beyond 12 V for the single layer devices and 22 V for the double layer devices. The electroluminescence (EL) spectrum shows two maxima, of which one corresponds to that of the photoluminescence spectrum. Either direct radiative recombination of the hole and the electron residing at two neighboring molecules or phosphorescence is causing this red shifted electroluminescence maximum. Transient electroluminescence measurements allow us to estimate the mobilities of the charge carriers in the different transport layers. The occurrence of an EL overshoot after switching off a voltage pulse, confirms the importance of detrapping and interfacial phenomena in the radiative recombination in pEFTP.

The photophysical properties of hexa (dodecyl) hexa peri benzyl coronene (HBC12), which displays a hexagonal columnar mesophase in a broad temperature domain, have been studied in solution by steady state and time-resolved spectroscopy. These results have been compared with hexa (tertiary butyl) hexa peri benzyl coronene (HBC4) which does not show any liquid crystalline properties. The broadening of the stationary state absorption and fluorescence spectra of HBC12, upon increasing the concentration, suggests the formation of aggregates, which is in line with the multi exponential fluorescence decay of HBC12, observed with time resolved fluorescence experiments. Comparison with the non aggregating HBC4 allowed to attribute the longest decay time to the monomer species. The relative contribution of the short decay times in HBC12 increases as a function of the concentration and the emission wavelength, which suggests that these decays are the result of an ensemble of aggregated species.

Combining stationary and time resolved fluorescence spectroscopy with laser-induced opto-acoustic spectroscopy allowed to investigate the influence of molecular structure and solvent polarity on the rate of the radiative and radiationless decay processes of exciplexes of omega-phenyl-alpha-N,N-dimethylaminoalkanes. By making intersystem crossing to the locally excited state less exergonic increasing the solvent polarity decreased the rate constant for intersystem crossing. The apparent decrease of the fluorescence rate constant in highly polar solvents was attributed to the direct formation of a solvent separated ion-pair. The formation of solvent separated ion-pairs can also explain why, contradicting the predictions of Marcus theory, the rate constant for internal conversion decreases sometimes in highly polar solvents. The solvent dependence of the fluorescence spectra of dialkylamino and diarylamino substituted triphenylbenzene derivatives indicates that in those completely symmetric molecules the emission occurs from a highly polar excited state. The exponential fluorescence decays suggest that equilibration between the different excited species occurs within the time resolution of the experimental set-up. The comparison of compounds with meta- and para-substitution and the comparison of dialkylamino and diarylamino derivatives suggests that either a conjugated intramolecular charge transfer state or a TICT state, in which the amino or the amino moiety rotates out of the plane of the triphenylbenzene moiety, are formed. Comparing the room temperature emission spectra with those at 77 K in isopentane glass allowed to obtain information on the geometry of the species emitting in less polar solvents.

The fluorescence maximum of amino-substituted 1,3,5-triphenylbenzenes dispersed in polystyrene and polycarbonate is shifted to longer wavelengths compared to isooctane, and this shift is larger in polycarbonate than in polystyrene. The shift is attributed to a partial relaxation of the matrix around the dispersed molecules during the excited-state lifetime. The nonexponential fluorescence decays obtained at different emission wavelengths can be analyzed globally assuming a Gaussian distribution of decay rates with a standard deviation that does not depend upon the emission wavelength. This Gaussian distribution of decay rates is attributed to a distribution of sites with different interaction with the polymer matrix. The sites giving the largest excited-state stabilization are characterized by the slowest average decay rate.