Cationic polymerization Induced

Styrene Free radical polymerization similar to the above. Also susceptible to rapid cationic polymerization induced by AlCb at —80°C and to anionic polymerization using alkali metals or their hydrides —CH2—CH— (ieHs T = 100 Amorphous, even when stretched. Hard. Soluble in aromatic hydrocarbons, higher ketones, and esters... 

Free radical polymerization is slow and yields only very low polymers. Vigorous cationic polymerization induced by BFs-ether complex at temperatures down to —... 

Not susceptible to free radical or anionic polymerization, but cationic polymerization induced by BFs, AICI3, etc., is extremely rapid even at — 100°C... 

New Views on Cationic Polymerizations Induced by Ionizing Radiations (1993)... 

The equilibrium between ions and ion pairs is not maintained in all polymerizing systems. For example, the cationic polymerization induced by ionizing radiation produces the positive and negative ions, the latter initiating a free carbonium ion propagation which is terminated by their collision with negative ions. Such a collision destroys the free ions, and hence their stationary, but not the equilibrium, concentration is determined by their rate of formation and destruction. 

Cationic polymerizations induced by thermally and photochemically latent N-benzyl and IV-alkoxy pyridinium salts, respectively, are reviewed. IV-Benzyl pyridinium salts with a wide range of substituents of phenyl, benzylic carbon and pyridine moiety act as thermally latent catalysts to initiate the cationic polymerization of various monomers. Their initiation activities were evaluated with the emphasis on the structure-activity relationship. The mechanisms of photoinitiation by direct and indirect sensitization of IV-alkoxy pyridinium salts are presented. The indirect action can be based on electron transfer reactions between pyridinium salt and (a) photochemically generated free radicals, (b) photoexcited sensitizer, and (c) electron rich compounds in the photoexcited charge transfer complexes. IV-Alkoxy pyridinium salts also participate in ascorbate assisted redox reactions to generate reactive species capable of initiating cationic polymerization. The application of pyridinium salts to the synthesis of block copolymers of monomers polymerizable with different mechanisms are described. 

When the hardening reaction involves cationic polymerization induced by a Lewis acid, however, the functionality of each epoxy group is 2 and that of structure 1-20 is 4. The general hardening reaction is illustrated in Eq. (1-10) for initiation by BF3, which is normally used in this context as a complex with ethylamine, for easier handling. 

The radlatlon-lnduced cationic polymerization of vinyl and unsaturated monomers In the liquid state has been studied for over 25 years, and the essential features of this type of polymerization appear to be well established (1, ). In contrast to cationic polymerization by catalysts where the propagating species Is usually described as a solvated Ion pair, the distinctive characteristic of cationic polymerization Induced by high energy radiation Is that propagation occurs by free Ions with very large rate constants, the range of kp values for observable polymerization being from 10 ... 

The third curing reaction of importance to the aerospace industry is epoxide homopolymerization. The most prevalent is cationic polymerization induced by Lewis acids and may be illustrated as follows ( ... 

Prof. Szwarc also contributed to the understanding of mechanisms of cationic polymerizations. In addition to the previously mentioned study of the cationic polymerization of styrene initiated by trifluoroacetic acid, he developed novel methods of initiation of cationic polymerization, e.g., the initiation of cationic polymerization by transfer of Cl " and N02 ions, and initiation by electron-transfer. In cooperation with deSorgo and David Pepper, he carried out the first stop-flow study of cationic polymerization that demonstrated the formation of the positive polystyryl cation and allowed its spectrum to be recorded. This work was published in J.C.S. Chem. Comm. 419, (1973). He was the first to point out that cationic polymerization induced by ionizing radiation is propagated by free cations [Makromol. Chem. 35a. 123 (I960)]. 

Roudet, J., Gandini, A., Cationic Polymerization Induced by Arydiazonium Salts, Makromol. Chem. Rapid Commun. 1989,10,277. 

The major portion of the article will be devoted to a discussion of the synthesis and mechanistic aspects of photoinitiation by individual photoinitiator systems. Cationic polymerizations induced by these photoinitiators are dark, i.e., non-photo-chemical, processes which are governed by the same parameters which must be taken into account in polymerizations which occur in the presence of conventional initiators such as Lewis and Bronsted acids. Accordingly, cationic polymerizations induced by halogen and sulfur based onium salt photoinitiators will be discussed only from the context in which they are influenced by factors which have their origin in the photoinitiator. Since the photochemistry of diaryliodonium and triarylsulfonium salts is similar, these two types of photoinitiators will be discussed together. The photolysis of dialkylphenacylsulfonium and dialkyl-4-hydroxyphenylsulfonium salts proceeds by a different mechanism, and they will be discussed separately. 

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