Multifunctional spectroscopy

Determination of the acidic sites through IR spectroscopy of adsorbed CO is a valuable tool for the choice of the support when selective or multifunctional processes are to be set up. This technique allowed to identify a particular kind of silica as the support of choice for the selective hydrogenation of citral to citronellal and sepiolite as a Lewis acid support able to promote the one-step transformation of citral into menthol. 

Crosslinked polymer networks formed from multifunctional acrylates are completely insoluble. Consequently, solid-state nuclear magnetic resonance (NMR) spectroscopy becomes an attractive method to determine the degree of crosslinking of such polymers (1-4). Solid-state NMR spectroscopy has been used to study the homopolymerization kinetics of various diacrylates and to distinguish between constrained and unconstrained, or unreacted double bonds in polymers (5,6). Solid-state NMR techniques can also be used to determine the domain sizes of different polymer phases and to determine the presence of microgels within a poly multiacrylate sample (7). The results of solid-state NMR experiments have also been correlated to dynamic mechanical analysis measurements of the glass transition (1,8,9) of various polydiacrylates. 

Under UV-laser irradiation, photosensitive multifunctional acrylate resins become rapidly cross-linked and completely insoluble. The extent of the reaction was followed continuously by both UV and IR spectroscopy in order to evaluate the rate and quantum yield of the laser-induced polymerization of these photoresist systems. Two basic types of lasers emitting in the UV range were employed, either a continuous wave (C.W.) argon-ion laser, or a pulsed nitrogen laser. 

Table 3.11. The chemistry of tribofilm generated by multifunctional additives composed of soft-core and hard-core reverse micelles (RMs) in oil formulation. Evaluation of tribofilm by XANES spectroscopy (Varlot et al., 2001)...

An examination of the photo-induced electron transfer processes between the quinone (268) and multifunctional porphyrins has been carried out. Chloranil has been used as an electron accepting sensitizer in the presence of the silylenols (269) and (270). The reactions can be carried out in both methylene chloride and acetonitrile and result in the conversion of the enols into the corresponding ketones. Other studies on the same systems have shown that the outcome of the irradiation at X > 380 nm can be influenced by solvent polarity and by added salt. ° Time-resolved spectroscopy has been used to study the excited singlet state of /7-chloranil. ... 

Extensive research has been conducted in the field of multi-photon spectroscopy for the past several decades. However, until recently, multi-photon processes did not find widespread applications due to the small multi-photon absorptivity of materials. The contributions from several research groups to develop a new generation of multifunctional organic materials with sufficiently large multi-photon absorption cross-sections have opened up a number of novel applications in photonics and biophotonics. 

In order to improve performance and processing efficiency of radiation curable systems it has been proposed that curing should be monitored using a technique of mechanical spectroscopy SS and in relation to this other workers have found that the molecular weight and structure of the diol component of multifunctional acrylates influenced the mechanical properties of the UV cured films produced 52,193. urea group in the resin tended to enhance the modulus of the cured film whereas a vinyl caprolactam diluent reduced resin viscosity for ease of coating. 

The efficiency of various substituted benzophenones for initiating the photopolymerization of multifunctional monomers in condensed phase was evaluated by IR spectroscopy from conversion versus exposure time kinetic curves. The best results were obtained with diphenoxy- benzophenone (DPB) associated to an hydrogen donor, like methyl- diethanolamine, for a one to one mixture of hexanetfrol-diacrylate (HDDA) and of a polyurethane-diacrylate (Actilane 20 fix)m SNPE). Figure 1 shows some typical polymraization profiles obtained for a 30 im thick film exposed, in the presence of air, to the UV radiation of a medium pressure mercury lamp at a light intensity of 1.5 X lO einsteins l cm-2. 

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