Photocrosslinking of Silicones. Part XV. Cationic Photocrosslinking of α, ω, 4-Terminated Disiloxanes

Abstract

The photoinduced cationic crosslinking of α, ω-terminated disiloxanes (epoxy, vinyl ether, propenyl ether) has been investigated by means of Real-Time IR spectroscopy. A lipophilic iodonium salt and three lipophilic sulfonium salts were used as photoinitiator. The crosslinking rate is influenced by the type of α, ω-terminated disiloxane used and differed by a factor of more than 100 from the aliphatic epoxy to the vinyl ether derivatives. Moreover, the sulfonium salts were found to have a lower initiation efficiency than the lipophilic iodonium salt in the various systems studied. These results are in good agreement with the quantum yield of proton formation in a hexamethyldisiloxane/dimethoxyethane mixture. The final degree of conversion is larger with the ene derivatives than with the epoxy derivatives. The application of a kinetic method allows us to estimate the rate constant of the termination step (k_t and for the propenyl derivative the rate constant of the propagation step kp. The termination step can be described by means of a first order reaction. k_t was found to depend on the light intensity and the type of initiators used, whereas k_p is independent of the initiator used.     

Arylsulfimide Polymers. IV. Prototype Transamidations–A Comparison of the Reactions of Benzamides,Benzimides, Sulfonamides,Sulfonimides, and Saccharins

Transamidation reactions of nonpolymerizing systems involving benzamides, phthalimides, arylsulfonamides, benzenedisulfonamides and -disulfonim-ides, and saccharins are described. The study includes reactions of both N-substituted and unsubstituted amides and imides with anilines and aniline hydrochlorides. An evaluation of the results of these reactions, aimed at establishing the optimum conditions for transamidations in polymerizing systems, is also presented.     

A review of: “Instrumental HPTLC,by W. Bertsch,S. Hara,R. E. Kaiser,and A. Zlatkis,editors, H. Verlag,Heidelberg, West Germany, 1980, 390 pp., cloth bound.”

Abstract

To understand the retention mechanisms involved in reversed-phase micelle chromatography, two models were examined to study the temperature and micelle concentration contribution to the retention process. the first model described the temperature contribution, using the van's Hoff equation, for each of the three equilibria: micelle-to-extra-micelle-mobile-phase, extra-micellar-mobile-phase-to-stationary phase and micelle-to-stationary phase. the second model described the temperature contribution on k' irrespective of the various equilibria involved. It was found that the enthalpy of retention obtained with the second model decreased with increasing micelle concentration. This contradicted a primary assumption in the first model that the equilibrium constants were independent of micelle concentration. No relationship was found between the enthalpy of retention evaluated with either model and the polarity of the partitioned solute molecules. A correlation was found between the entropy of retention and the polarity of these molecules. Fluorescence studies indicated that the micelle solvated molecules were probably located in the core of the micelles which contained other mobile phase components such as 1-propanol and water.     

Radiation-Induced,Solid-State Polymerization of Derivatives of Methacrylic Acid. XI. Aspects of the Polymerization of Methacrylic Acid by γ-Irradiation

Aspects of the radiation-induced polymerization of methacrylic acid in the crystalline state have been investigated and utilized to evaluate the mechanism of polymerization. In particular, results for post-irradiation polymerization at 0°C after radiation doses of 0.1 to 2.0 Mrad support the concepts of Lando and Semen that chain initiation essentially all commences at the same time, that chain propagation continues without termination, and that termination of nonpropagating radicals proceeds simultaneously.