Benzophenone‐(phenylthio)acetic acid phosphonium salts as initiators of free‐radical photopolymerization of vinyl monomers: Mechanistic studies

The mechanism of the benzophenone‐sensitized photooxidation of phosphonium salts of (phenylthio)acetic acid was studied as a means for understanding how these salts function as coinitiators in the free‐radical photopolymerization of vinyl monomers. Both steady‐state and nanosecond flash photolytic methods were used to determine, in a quantitative manner, the mechanism of primary and secondary photoreactions for three quaternary phosphonium salts containing butyl and/or phenyl groups, i.e., P⁺(C₄H₉)₄, P⁺(C₄H₉)(C₆H₅)₃, and P⁺(C₆H₅)₄. It was found that the initial polymerization rates were the same for all three phoshonium salts of (phenylthio)acetic acid and were equal to those found previously for tetralkyl ammonium salts. The polymerization rates were more than twice the rates found for direct initiation by benzophenone and by the benzophenone‐(phenylthio)acetic acid initiating system. These results correlate well with the large quantum yields of ^?CH₂SC₆H₅ radicals (the main initiating radicals) found in the complementary photochemical investigation. It was found that a detailed knowledge of the photochemical reactions in the photoinitiating systems was critical to understand the kinetics of polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8013–8022, 2008     

Molecular and crystal structure of bis-quinolizidine immonium salts: I. Δ1(6)-dehydro-17-oxosparteinium perchlorate

Journal of Chemical Crystallography - Δ1(6)-Dehydro-17-oxosparteinium perchlorate, [C15H23N2O]+·C10 4 − , is monoclinic:P21,a=8.620(1),b=14.406(2),c=6.825(1) Å,...     

Polymer Inclusion Compounds by Polymerization of Monomers in β-Cyclodextrin Matrix in DMF Solution

The investigations of the synthesis of polyrotaxanes by the radical polymerization of monomers (vinylidene chloride, methyl acrylate, styrene, and methacrylonitrile) in DMF in the presence of β-cyclodextrin have been carried out. The possibility of formation β-cyclodextrin inclusion compounds with some vinyl monomers or some other organic substances in DMF solution has been established. We assume that the inclusion in presence of the solvent is related to the unusual phenomenon of β-cyclodextrin crystallization in hot DMF solutions. The polymerization of vinyl monomers in DMF solution at increased temperatures in the presence of β-cyclodextrin leads to compounds containing a great amount of cyclic compounds (up to 80%). Similar results have been obtained for monomers introduced as previously prepared adducts with β-cyclodextrin. Stable compounds of polymer and β-cyclodextrin have been obtained in the case of vinylidene chloride. The lack of carbohydrate moieties in the product obtained by polymerization of vinylidene chloride in the presence of linear dextrin suggest the inclusion character of the linkage between polymer and β-cyclodextrin molecules. The structure of a topological compound of polyrotaxane type is most feasible after dehydrochlorination.     

Aromatic Amines in Organic Synthesis. Part II. p-Aminocinnamaldehydes

Ten derivatives of p-aminocinnamic aldehydes were prepared from the reaction of either aromatic amines with dimethylaminoacrolein or benzaldehydes with acetaldehyde. Their chemical structure and purity were verified by ¹H NMR, ¹³C NMR and IR spectroscopic methods. We found that the synthesis applying dimethylaminoacrolein as the reagent gets better yields than the one based on the reaction with acetaldehyde. The yields of the cinnamic aldehydes varied according to the type of the amino group and the number and position of the substituents. The basic spectroscopic properties of the p-aminocinnamic aldehydes are also described since the compounds may be a precursor for the synthesis of dyes for diverse applications, e.g., in medicine and optoelectronics.     

Formation of cation–radical anion pairs derived from carboxybenzophenone–tetrabutylammonium salts. Pulse radiolysis studies

Pulse radiolysis of acetonitrile solutions of tetra-n-butyl ammonium salts of 2- and 4-carboxybenzophenones [BP-COO⁻···N⁺(C₄H₉)₄] were performed in order to generate directly the reduced forms of the benzophenone moieties within pre-formed ion pairs. In earlier studies on photochemical electron transfer reactions, ion pairs containing a tetraalkyl ammonium cation and a benzophenone radical anion were formed in an electron transfer to the triplet BP from a quencher consisting of a tetraalkyl ammonium salt of (phenylthio)acetic acid. In the current work, the [BP^•−COO⁻···N⁺(C₄H₉)₄] ion pairs were formed by direct reduction of the salts without the complication of a third moiety, i.e., the (phenylthio)acetic anion. The spectra and kinetic parameters of the radiolytically-reduced salts were compared to the behavior of reduced forms of the 2- and 4-COOH substituted benzophenones. The results from the pulse radiolysis and photochemistry were compared and explained in terms of the different structures of the ion pairs.     

The influence of external uniaxial stretching on the electromigration and diffusion of hydrogen in iron

Electromigration and diffusion of hydrogen in iron, depending on unit elongation, were investigated. The resistivity method was applied in the investigations. It was found that the obtained experimental results cannot be described by means of a single flux of hydrogen, which diffuses in the electric field. In order to explain the obtained results, we assumed the existence of the following two fluxes of hydrogen in the stretched metal: migration, according to the interstitial mechanism, and migration according to the interstitial-defective mechanism. The dependence of effective valences and diffusion coefficients for both mechanisms were determined.     

EPR study of selected gadolinium β-diketonates

Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 5, pp. 165–169, September–October, 1995.     

Styrylpyridinium borate salts as dye photoinitiators of free‐radical polymerization

Styrylpyridinium borate salts photoinitiate free‐radical polymerization. The rate of photopolymerization depends on the ΔG^o of electron transfer between a borate anion and a styrypyridinium cation. This latter value was estimated for a series of styrylpyridinium borate salts, and the relationship between the rate of polymerization and the free energy of activation gives the dependence predicted by the classical theory of electron transfer. This relation was independently observed for the two series of styrylpyridinium borate salts tested—one for the photoredox pair with an iodine atom and the second without. Styrylpyridinium borate salts were stable at ambient temperature in the formulations prepared for the photopolymerization experiments. Photopolymerization initiated by the photoredox pairs tested proceeded by the conventional mechanism in which bimolecular termination occurs by a reaction between two macroradicals. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1433–1440, 2002