Cationic-initiated chain polymerization

Isobutylene Cationic-initiated chain polymerization Lubricating oils, sealants... 

Synthetic polymers can be classified as either chain-growth polymen or step-growth polymers. Chain-growth polymers are prepared by chain-reaction polymerization of vinyl monomers in the presence of a radical, an anion, or a cation initiator. Radical polymerization is sometimes used, but alkenes such as 2-methylpropene that have electron-donating substituents on the double bond polymerize easily by a cationic route through carbocation intermediates. Similarly, monomers such as methyl -cyanoacrylate that have electron-withdrawing substituents on the double bond polymerize by an anionic, conjugate addition pathway. 

The radiolysis of olefinic monomers results in the formation of cations, anions, and free radicals as described above. It is then possible for these species to initiate chain polymerizations. Whether a polymerization is initiated by the radicals, cations, or anions depends on the monomer and reaction conditions. Most radiation polymerizations are radical polymerizations, especially at higher temperatures where ionic species are not stable and dissociate to yield radicals. Radiolytic initiation can also be achieved using initiators, like those used in thermally initiated and photoinitiated polymerizations, which undergo decomposition on irradiation. 

For addition polymers four types of polymerization processes are known fi"ee-radical-initiated chain polymerization, anionic polymerization, cationic polymerization, and coordination polymerization (with Ziegler-Natta catalysts). By far the most extensively used process is the free-radical-initiated chain polymerization. However, the more recent development of stereo regular polymers using certain... 

In the presence of cationic initiators, the polymerization of cycloolefins proceeds via a carbocationic pathway in which the initiation, propagation, chain transfer, and termination steps involve the well-documented processes related to carbocation chemistry [1] ... 

With respect to the initiation of cationic chain polymerizations, the reaction of chlorine-terminated azo compounds with various silver salts has been thoroughly studied. ACPC, a compound often used in condensation type reactions discussed previously, was reacted with Ag X , X, being BF4 [10,61] or SbFa [11,62]. This reaction resulted in two oxocarbenium cations, being very suitable initiating sites for cationic polymerization. Thus, poly(tetrahydrofuran) with Mn between 3 x 10 and 4 x lO containing exactly one central azo group per molecule was synthesized [62a]. Furthermore, N-... 

It has been suggested that the amine radical cation (46) is not directly involved in initiating chains and that most polymerization is initiated by benzoyloxy radicals.179 However, Sato et a ." employed spin trapping (3.5.2.1) to demonstrate that the anilinomethyl radical (45) was formed from the radical cation (46) by loss of a proton and proposed that the radical 45 also initiates polymerization. Overall efficiencies for initiation by amine-peroxide redox... 

A similar proton transfer from a growing chain end unit to give an olefinic linkage was observed in the cationic polymerization of 2-tert-butyl-7-oxabicycto[2.2.1 ]-heptane, although the proton liberated did not initiate the polymerization and hence this process was actually a termination34 . 

Monomers, such as ethylene, propylene, isobutylene, and isoprene, containing the carbon-carbon double bond undergo chain polymerization. Polymerization is initiated by radical, anionic or cationic catalysts (initiators) depending on the monomer. Polymerization involves addition of the initiating species R, whether a radical, cation, or anion, to the double bond followed by its propagation by subsequent additions of monomer... 

The bifunctional initiator 4-hydroxy-bulyl-2-bromoisobulyralc, HBBIB, promoted the ATRP of styrene as well as the cationic ring opening polymerization of THF [134], In the presence of Cu/CuBr2/PMDETA styrene was polymerized through the bromoisobutyrate function of HBBIB, to give PS chains end-functionalized with hydroxyl groups, PS-OH. The in situ... 

Before the discovery of the pseudo-cationic reactions, one could say simply that the function of the co-catalyst is to provide cations which can initiate the polymerization [28b]. Although this is still valid for the true cationic polymerizations, it is more difficult to define the function of the co-catalyst in the pseudo-cationic reactions. Very tentatively one can suggest that the co-catalyst is the essential link in the formation of an ester which is the chain-carrier, as in the pseudo-cationic polymerizations catalysed by conventional acids in other words, the co-catalyst and catalyst combine to form an acid, but this, instead of protonating the monomer, forms an ester with it, which is then the propagating species. 

Traditional polymerizations usually involve AB-type monomers based on substituted ethylenes, strained small ring compounds using chain reactions that may be initiated by free radical, anionic or cationic initiators [20]. Alternatively, AB-type monomers may be used in polycondensation reactions. 

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