To improve adhesion between polypyrrole and glass, new pyrrole-substituted organotrialkoxysilanes coupling agents are synthesized and studied. Solubility, hydrolysis, and selfcondensation features in aqueous solutions are investigated by IR, 1 H, and 29 Si NMR spectroscopies. Varying the experimental conditions of pyrrole chemical polymerization on glass fibers surfaces indicates that a preliminary substrate treatment with these coupling agents and the use of a chemical vapor deposition process jointly lead to very thin (around 50 nm) polypyrrole layers with a particularly even and homogeneous aspect and adhering perfectly to glass surfaces. This last point has been plainly demonstrated by pull-out tests on conductive fibers embedded in resin and by tensile pull-off tests on silica plates. An unexpected effect of the use of specific silanes, when compared to commercial coupling agents, is an enhancement of polypyrrole conductivity (typically 150-200 S/cm), which can be related to the high regularity of the deposit.

We present a series of new 6,6‘-distyryl-3,3‘-bipyridine derivatives synthesized via a Knoevenagel condensation reaction and disubstituted with electron donor and acceptor groups. These molecules were characterized by spectroscopic methods (NMR, Raman, UV−vis, photoluminescence). These compounds were all found to exhibit thermotropic liquid crystalline (LC) phases, the structures of which were analyzed by DSC and temperature-dependent X-ray diffraction. The high degree of conjugation and the mesogenic character of these molecules could lead to nonlinear optical (NLO) applications for the “push−pull” compounds. Absorption in the UV range and blue fluorescence are other characteristics of some members of this group. The latter property opens up applications as light-emitting diodes (LEDs).

Chemical as well as structural modifications of highly branched polycyanurates can be achieved by using the reaction of dicyanates with monofunctional phenols.The key products of this reaction are iminocarbonic esters formed by addition of cyanato and phenolic groups. Two mechanisms are discussed for the second reaction step: an addition of two cyanato groups and an iminocarbonic ester (Route A) and a stepwise addition of iminocarbonic esters (Route B).The crucial difference between the two reactions is the number of abstracted phenolic groups per formation of one triazine ring: one for Route A and three for Route B. The effects of these reaction mechanisms on the gelation behavior and network buildup are studied theoretically with the help of cascade theory as well as experimentally by the reaction of dicyanate of bisphenol A with five different monophenols. The results clearly show that only with a model which is based on Route B can both the critical conversions at the gelation threshold and the gel fractions be modeled quantitatively. Furthermore, phenols with low pK, values were found to have an increased tendency of incorporation into the network.

SynopsisThe chromatographic analysis of resol solutions in tetrahydrofuran solvent, by means of a set of columns packed with crosslinked polystyrene gels, has been carried out with adequate resolving power for a clear-cut qualitative or semiquantitative difierentiation between various types of resols to be practicable. The resulting chromatograms, which show the distribution of different constituents by molecular size, could be interpreted by the use of reference substance and by calibrating the system with a number of compounds of known structures. The method has been used to investigate the way in which various reaction parameters (nature of catalysts, proportion of starting material, treatments undergone by the resols) affect the composition of resols. Different commercial products have been thus characterized. It has also afforded an insight into the progress of the polycondensation reaction as a function of time and helped to state the reactivity of different groups and unblocked ring positions. Thus, an hydroxymethyl group appears to be more reactive in the para than in the ortho position. Otherwise the reactivity of unblocked ring positions would be enhanced by an hydroxymethyl group in the ortho rather than para position.