For cationic polymerization

We shall consider these points below. The mechanism for cationic polymerization continues to include initiation, propagation, transfer, and termination steps, and the rate of polymerization and the kinetic chain length are the principal quantities of interest. 

The catalysts for cationic polymerization are either protonic acids or Lewis acids, such as H2SO4 and HCIO4 or BF3, AICI3, and TiCl4 ... 

Methacrylate monomers do not generally polymerize by a cationic mechanism. In fact, methacrylate functionaUty is often utilized as a passive pendent group for cationicaHy polymerizable monomers. Methacrylate monomers also have been used as solvents or cosolvents for cationic polymerizations (90,91). 

The controlled synthesis of polymers, as opposed to their undesired formation, is an area that has not received much academic interest. Most interest to date has been commercial, and focused on a narrow area the use ofchloroaluminate(III) ionic liquids for cationic polymerization reactions. The lack of publications in the area, together with the lack of detailed and useful synthetic information in the patent literature, places hurdles in front of those with limited loiowledge of ionic liquid technology who wish to employ it for polymerization studies. The expanding interest in ionic liquids as solvents for synthesis, most notably for the synthesis of discrete organic molecules, should stimulate interest in their use for polymer science. 

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-... 

Results of these orienting experiments compiled in Table 3 in regard to the effect of temperature, medium polarity, initiator concentration, monomer concentration, and coinitiator concentration are similar to those reported by others36"39 for cationic polymerization of a-methylstyrene. For example, decreasing temperature, the molecular weight increases and increasing medium polarity, the yield increases. 

According to Table 10, the relationships for cationic polymerization are not as simple in comparison to those above. Although it is clearly possible to assert limits for characterizing the polymerizability, all parameters used characterize the evident polymerizable monomers acroleine (R = —CHO) and methyl vinyl keton (R = —COCH3) or the non-polymerizable monomer vinyl acetate (R = —OCOCH3) contrary to experimental results. 

Yagci, Y. and Endo, X N-Benzyl and N-Alkoxy Py ridium Salts as Thermal and Photochemical Initiators for Cationic Polymerization. Vol. 127, pp. 59-86. 

A variety of initiators have been used for cationic polymerization. The most useful type of initiation involves the use of a Lewis acid in combination with small concentrations of water or some other proton source. The two components of the initiating system form a catalyst-cocatalyst complex which donates a proton to monomer... 

The catalysts used for cationic polymerizations are usually Lewis acids that contain a small amount of water. 

The most commonly used catalysts for cationic polymerization are the Lewis acids BFa, A1C18, SnCl4, FeCl3, etc. There are two plausible modes of action for a Lewis acid. One of these, and rather a doubtful one, is the formation of a zwitterion and the growth at the positive end of the zwitterionic chain. 

Another reaction that has been applied to the generation of highly functionalized polymers is cationic polymerization [12-15]. Catalysts for cationic polymerizations are aprotic acids, protic acids, or stable carbocation salts. In these processes, the catalyst generally reacts with a cocatalyst to form an active initiated species. Initiation takes place by protonation of the monomer (Fig. 2A). Monomers that possess cation stabilizing groups, such as electron rich olefins, are preferred as they more readily undergo the desired polymerization process... 

Developments in the Theory of Cationic Polymerization VII. Theoretical Attempts at Improving Initiators for Cationic Polymerization of Alkenes, S.D. Pask and P.H. Plesch. European Polymer Journal, 1982, 18, 839-846. 

The rates of all single-step reactions increase as the temperature increases. This may not be true for multistep reactions such as those involved with multistep polymerizations, here the cationic polymerization. For cationic polymerizations the activation energies are generally of the order > E > E. Remembering that the description of the specific rate constant is... 

The chemical and kinetic relationships for the anionic polymerization of acrylonitrile follow the same three major steps found for cationic polymerizations (1) initiation, (2) propagation, and (3) termination ... 

Quantitative aspects of photopolymerization have been described in Sec. 3-4c. There are some differences between radical and cationic photopolymerizations. The dependence of Rp on light intensify is half-order for radical polymerization, but first-order for cationic polymerization. Radical photopolymerizations stop immediately on cessation of irradiation. Most cationic photopolymerizations, once initiated, continue in the absence of light because most of the reaction systems chosen are living polymerizations (Sec. 5-2g). 

The actual species responsible for cationic polymerizations initiated by ionizing radiation is not established. The most frequently described mechanism postulates reaction between radical-cation and monomer to form separate cationic and radical species subsequently, the cationic species propagates rapidly while the radical species propagates very slowly. The proposed mechanism for isobutylene involves transfer of a hydrogen radical from monomer to the radical-cation to form the r-butyl carbocation and an unreactive allyl-type radical ... 

For cationic polymerization with an acid whose anion Z is nucleophilic, initiation involves the sequence described by Eq. 7-51 plus the formation of XXIX. XXIX propagates by a sequence similar to that described by Eqs. 7-52 and 7-53 except that a growing polymer chain possesses a Z—CO— end group instead of a lactam end group. 

The initiator concentrations required for cationic polymerizations are smaller than those for radical polymerizations frequently 10 to 10" mol of initiator per mol monomer is sufficient to achieve a high rate of reaction. The effect of initiator concentration on the rate and average degree of polymerization depends on the monomer and a variety of other factors and does not follow a consistent pattern. 

Fig. 2 Various types of photoinitiators (1) peroxides, (2) azo compounds based on AIBN, (3) benzoin ethers, (4) triplet photosensitizers, (5) onium salts for cationic polymerization, and (6) controlled free radical polymerization with photoiniferters...

For cationic SIP, limitations when applied to surfaces are also evident. Like anionic polymerization, SIP on particles has been abundantly reported by several groups, most notably on work by Tsubokawa et al. The use of nanoparticles has also been widely reported. The same assumptions were made for cationic polymerization based on the grafting of electrophiles on surfaces and the reactivity of nucleophilic monomers for cationic polymerization. 

Some common initiators for cationic polymerization reactions are protonic acids, Friedel-Crafts catalysts (Lewis acids), compounds capable of generating cations, or ionizing radiation. 

The recent development of several new classes of practical photoinitiators for cationic polymerization has now made it possible to utilize this chemistry in a number of ways to produce highly sensitive photoresists (142-144). The facile synthesis of onium salts (I-III)... 

Polymerization of isobutylene, in contrast, is the most characteristic example of all acid-catalyzed hydrocarbon polymerizations. Despite its hindered double bond, isobutylene is extremely reactive under any acidic conditions, which makes it an ideal monomer for cationic polymerization. While other alkenes usually can polymerize by several different propagation mechanisms (cationic, anionic, free radical, coordination), polyisobutylene can be prepared only via cationic polymerization. Acid-catalyzed polymerization of isobutylene is, therefore, the most thoroughly studied case. Other suitable monomers undergoing cationic polymerization are substituted styrene derivatives and conjugated dienes. Superacid-catalyzed alkane selfcondensation (see Section 5.1.2) and polymerization of strained cycloalkanes are also possible.118... 

Dependence of Rp on the half order of the sensitizer is abnormal for cationic polymerization. Photochemistry of the gold salt seems to be complicated and no investigation has been made on this problem. 

The polymerization kinetics of propylene, 3-methyl-l-butene, and 4-methyl-l-pentene can be described by Eq. (12) and it is felt that this scheme may be generally valid for cationic polymerization of olefins as there is no reason to suspect that a fundamental difference in polymerization mechanism exists in the case of the three monomers cited above as compared with other cationically polymerizable olefins. 

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