Methoxystyrene cationic polymerization

TABLE 5-7 Effect of Solvent on Cationic Polymerization of p-Methoxystyrene by Iodine at 30 C... 

This same research group also reported [318] the cationic polymerization of p-methoxystyrene in miniemulsion. DBSA was used as both a protonic initiator and surfactant. A monomer conversion of 100% was achieved in eight hours at 60 °C. Molecular weights were low (approximately 1,000) and solids of up to 40% could be achieved with good colloidal stability. Polymerization takes place at the interface, initiated by the proton, and terminated by water. Molecular weight increased with conversion, suggesting either reversible termination or decreasing termination. 

The ABA-type block copolymers B-86 to B-88 were synthesized via termination of telechelic living poly-(THF) with sodium 2-bromoisopropionate followed by the copper-catalyzed radical polymerizations.387 A similar method has also been utilized for the synthesis of 4-arm star block polymers (arm B-82), where the transformation is done with /3-bromoacyl chloride and the hydroxyl terminal of poly(THF).388 The BAB-type block copolymers where polystyrene is the midsegment were prepared by copper-catalyzed radical polymerization of styrene from bifunctional initiators, followed by the transformation of the halogen terminal into a cationic species with silver perchlorate the resulting cation was for living cationic polymerization of THF.389 A similar transformation with Ph2I+PF6- was carried out for halogen-capped polystyrene and poly(/>methoxystyrene), and the resultant cationic species subsequently initiated cationic polymerization of cyclohexene oxide to produce... 

Problem 8.20 Give plausible explanation for the following facts. Primary and secondary alkyl halides are generally ineffective as initiators of cationic polymerization of monomers such as isobutene and styrene, but t-butyl and cumyl chlorides are effective. On the other hand, triphenylmethyl chloride and cyclo-heptatrienyl (tropylium) chloride are not very efBcient in polymerizing isobutylene and styrene but produces rapid polymerization of p-methoxystyrene, vinyl ethers and N-vinylcarbazole. 

Predict the order of reactivity (and justify your prediction) of the given monomers, (a) Styrene, 2-vinylpyridine, 3-vinylpyridine, and 4-vinyl pyridine in anionic polymerization, (b) Styrene, p-methoxystyrene, p-chlorostyrene, and p-methylstyrene in cationic polymerization. 

Cationic polymerization allows the formation of poly-p-methoxystyrene particles. ... 

Initiations of polymerizations of vinyl and other monomers by metal alkyls generally take place by anionic mechanisms. This is discussed further in this chapter. There are, however, reports in the literature of cationic polymerizations that are initiated by some metal alkyls. These are polymerizations of monomers like vinyl ethers, o- and p-methoxystyrene, and isobutylene " that are initiated by compounds like dialkyl aluminum chloride. 

Living cationic polymerizations have been carried out with a number of monomers, such as isobutylene, styrene, p-methylstyrene, p-methoxystyrene, A/-vinyl caibazole, and others. To achieve living conditions, it is necessary to match the propagating carbon cation with the counterion, the solvent polarity, and the reaction temperature. Some examples are presented in Table 3.2. 

Cationic polymerization can also be performed in direct miniemulsion in the presence of water. p-Methoxystyrene (p-MOS) was polymerized using the inisurf (= initiator - - surfactant) dodecylbenzenesulfonic acid with a monomer [91]. In the presence of ytterbium triflate, inverse systems were formed [92]. Although the rate of polymerization was found to be slower than for direct systems, the molecular weights obtained were shown to be larger. The polymerization was initiated by l-chloro-l-(p-methoxyphenyl)ethane (p-MOS-HCl), and catalyzed by trisdodecyl sulfate ytterbium, which served simultaneously as a surfactant and as a Lewis acid [93]. The Lewis acid surfactant did not play the expected role, however, as the p-MOS-HCl was hydrolyzed. The resulting hydronium protonated the SDS surfactant, which then served as an inisurf in the interfacial cationic polymerization process. 

Five tri-and tetra-substituted electron-poor olefins 1-5 containing 3-anionic leaving groups initiated cationic polymerization of p-methoxystyrene with widely varying rates. Compounds 1 and 2 were highly active organic initiators. 

Cationic polymerization of para-methoxystyrene occurs much more rapidly than cationic polymerization of styrene. Explain this difference in rate. 

Higashimura, T, Mitsuhashi, M. and Sawamoto, M. (1979) Synthesis of p-methoxystyrene-isobutyl vinyl ether block copolymers by living cationic polymerization with iodine. Macromolecules, 12, 178-183. 

Very iuteresting is the leceutly developed cationic polymerization metiiod, catalyzed with diazonium compounds. It runs at room temperature and tire formed polymers exhibit a high molecular weight. An example of such a reaction is the polymerization of 4-methoxystyrene under the influence of 4-nitrobenzenediazonium hexafluorophosphate, in which the poly (4-methoxystyrene) with a molecular weight of more than 100,000 is obtained ... 

No true living cationic vinyl polymers are known at present, although the papers of Skorokhodov on 1,2-dimethoxyethylene 1011 and of Higashimura on the I2-initiated polymerization of vinyl ethers, p-methoxystyrene (Sect. 15.3.1.1.3) and of N-vinyl carbazole 102) approach living features. It is possible, however, to prepare a vinyl polymer with an end-group that is inactive towards its own monomer but is able to convert a heterocyclic monomer into the onium ion, in this way starting the polymerization of a second monomer. The application of this approach for the synthesis of block copolymers is described below. 

The controlled polymerization of p-methoxystyrene was also demonstrated in aqueous media using the /7-methoxystyrene HCl adduct as initiator and Yb(OTf)3 as Lewis acid activator [81]. Very recently, the aqueous living cationic suspension polymerization of styrene and methoxystyrene was reported by Ganachaud using the water adduct of p-methoxystyrene as initiator and B(CgF5)3 as water tolerant Lewis acid activator [82, 83]. 

In (A), the reaction will predominate on the left-hand side. Exceptions appear to be olefins with strong electron-releasing substituents that confer thermodynamic stability to the newly formed cation, -CH2-CHR . This either results from a suitable charge delocalization over the 7r-electron system or from the presence of a heteroatom. Accordingly, only those olefins that possess relatively strong nucleophilic characteristics can be polymerized by stable carbon cations. Such olefins are alkyl vinyl ethers, A -vinyl carbazole, p-methoxystyrene, indene, and vinylnaphthalenes. Styrene and cf-methylstyrene, however, will not polymerize, because they are less reactive. 

The initiator cation formed in this way can, in many cases then add directly on to the monomer to form the monomer cation. Examples of this are the polymerization of p-methoxystyrene or epoxides with trityl hexa-chloroantimonate, the polymerization of tetrahydrofuran with acetyl perchlorate, and the polymerization of vinyl ethers and A -vinyl carbazole with tropylium hexachloroantimonate, for example ... 

Similar results were reported in polymerizations of styrene with CH3COCIO4, CF3SO3H, CF3COOH, CISO3H, FSO3H [109]. Pseudo-cationic mechanism was also claimed in polymerizations of some styrene derivatives, like /7-methyl styrene, /7-methoxystyrene, andp-chlorostyrene with these protonic acids [109]. 

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