Styrene cationic polymerization

In cationic polymerization the active species is the ion which is formed by the addition of a proton from the initiator system to a monomer. For vinyl monomers the type of substituents which promote this type of polymerization are those which are electron supplying, like alkyl, 1,1-dialkyl, aryl, and alkoxy. Isobutylene and a-methyl styrene are examples of monomers which have been polymerized via cationic intermediates. 

Coumarone—indene or coal-tar resins, as the name denotes, are by-products of the coal carbonization process (coking). Although named after two particular components of these resins, coumarone (1) and indene (2), these resins are actually produced by the cationic polymerization of predominantly aromatic feedstreams. These feedstreams are typically composed of compounds such as indene, styrene, and their alkylated analogues. In actuaUty, there is very tittle coumarone in this type of feedstock. The fractions used for resin synthesis typically boil in the range of 150—250°C and are characterized by gas chromatography. 

Anionic polymerization is better for vinyl monomers with electron withdrawing groups that stabilize the intermediates. Typical monomers best polymerized by anionic initiators include acrylonitrile, styrene, and butadiene. As with cationic polymerization, a counter ion is present with the propagating chain. The propagation and the termination steps are similar to cationic polymerization. 

Influence of Structure on the Cationic Polymerization of Substituted Styrenes... 

Substituted styrenes are often used for investigating influences of structure, solvent and initiators on the cationic polymerization 1,2). Under constant outer conditions,... 

When one compares the brutto polymerization rate constants, a measure of the reactivity of monomers during cationic homopolymerizations is obtained. It was found for p-substituted styrenes that lg kBr increased parallel to the reactivity, which the monomers show versus a constant acceptor 93). The reactivity graduation of the cationic chain ends is apparently overcomed by the structural influence on the monomers during the entire process of the cationic polymerization. The quantitative treatment of the substituent influences with the assistance of the LFE principle leads to the following Hammett-type equations for the brutto polymerization rate constants ... 

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... 

To further demonstrate the stability and unreactivity of the isopropenylferrocene carbenium ion, a stable derivative of this ion was prepared and evaluated as an initiator for the cationic polymerization of styrene. The derivative prepared for this purpose was the tetrafluoroborate salt of the isopropenylferrocene carbenium ion. Even at 20°C a 26% yield (Mjj = 11,315, = 18,815) of... 

Figure 2.8 Examples of monomers that can undergo cationic polymerization a) isobutylene, b) vtnyf methyl ether,and c) styrene...

Applying these methodologies monomers such as isobutylene, vinyl ethers, styrene and styrenic derivatives, oxazolines, N-vinyl carbazole, etc. can be efficiently polymerized leading to well-defined structures. Compared to anionic polymerization cationic polymerization requires less demanding experimental conditions and can be applied at room temperature or higher in many cases, and a wide variety of monomers with pendant functional groups can be used. Despite the recent developments in cationic polymerization the method cannot be used with the same success for the synthesis of well-defined complex copolymeric architectures. 

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... 

Since the determination of absolute rate constants is one of the most urgent problems in cationic polymerization, and the styrene-perchloric acid system seemed to be so clean and simple, Gandini and Plesch set out first to check Pepper and Reilly s results by determining spectroscopically the concentration of carbonium ions during polymerization, and they intended then to extend the method to other monomers. However, their findings were not as expected. A comparison of spectroscopic and conductivity measurements with rate measurements in an adiabatic calorimeter showed [4] that in methylene dichloride solution ... 

The cationic polymerization of arylenes differs in some respects from that of alkenes. The most notable features are that the degree of polymerization is generally lower and that the proportion of unsaturated end groups is always small [21, 22] and often very variable [10]. In the system styrene-TiCl4-CCl3COOH-toluene low polymers are formed which have tolyl end groups [11]. It is not possible to decide at present whether the transfer reaction involved in this is (VIII) or (IX) ... 

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