Cationic polymerization living polymerizations

There are very few reports available on the living cationic polymerization of N-vinylcarbazol, one of the most reactive monomers for cationic polymerization. Living polymerization of N-vinylcarbazol was reported in toluene or CH2CI2 solvent system using only HI [93] and I2 as initiator in CH2CI2 and CH2CI2/CCU 1/1 (v/v)... 

There are very few reports available on the living cationic polymerization of N-vinylcarbazole, one of the most reactive monomer for cationic polymerization. Living polymerization... 

Electrolytic polymerizations were described in the section dealing with cationic polymerizations. Anionic polymerizations can also be initiated in an electric field. When LiAlHj or NaAl(C2H5)4 are used as electrol3Tes in tetrahydrofuran solvent living polymers can be formed from a-methylstyrene [190]. The deep red color of carbanions develops first at the cathode compartments of divided cells. 

Turpentine, Monoterpenes, a-Pinene, p-Pinene, Cationic polymerization. Radical polymerization. Copolymerizations, Living polymerization, Mechanisms, Polymer properties... 

Living radical polymerization Redox initiation Activation energy Cationic polymerization Living cationic polymerizations Gegen ion... 

Since the discovery of living cationic systems, cationic polymerization has progressed to a new stage where the synthesis of designed materials is now possible. The rapid advances in this field will lead to useful new polymeric materials and processes that will greatiy increase the economic impact of cationic initiation. 

Cationic Polymerization. For decades cationic polymerization has been used commercially to polymerize isobutylene and alkyl vinyl ethers, which do not respond to free-radical or anionic addition (see Elastomers, synthetic-BUTYLRUBBEr). More recently, development has led to the point where living cationic chains can be made, with many of the advantages described above for anionic polymerization (27,28). 

The observation in 1949 (4) that isobutyl vinyl ether (IBVE) can be polymerized with stereoregularity ushered in the stereochemical study of polymers, eventually leading to the development of stereoregular polypropylene. In fact, vinyl ethers were key monomers in the early polymer Hterature. Eor example, ethyl vinyl ether (EVE) was first polymerized in the presence of iodine in 1878 and the overall polymerization was systematically studied during the 1920s (5). There has been much academic interest in living cationic polymerization of vinyl ethers and in the unusual compatibiUty of poly(MVE) with polystyrene. 

VEs do not readily enter into copolymerization by simple cationic polymerization techniques instead, they can be mixed randomly or in blocks with the aid of living polymerization methods. This is on account of the differences in reactivity, resulting in significant rate differentials. Consequendy, reactivity ratios must be taken into account if random copolymers, instead of mixtures of homopolymers, are to be obtained by standard cationic polymeriza tion (50,51). Table 5 illustrates this situation for butyl vinyl ether (BVE) copolymerized with other VEs. The rate constants of polymerization (kp) can differ by one or two orders of magnitude, resulting in homopolymerization of each monomer or incorporation of the faster monomer, followed by the slower (assuming no chain transfer). 

Besides being used as initiators and monomers, azo compounds may also be used for terminating a cationic polymerization. Thus, the living cationic polymerization... 

In view of the great structural similarity between the propagating sites in the cationic polymerization of P-PIN and isobutylene and their respective polymers (4), and our considerable experience accumulated with the LC Pzn of isobutylene [1-3], efforts have been made to adapt LC Pzn conditions found to yield living polyisobutylenes for the polymerization of p-PIN. 

Higashimura, T. and Sawamolo, M Living Polymerization and Selective Dimerization Two Extremes of the Polymer Synthesis by Cationic Polymerization. Vol. 62, pp. 49-94. 

Cationic polymerization of ethylene oxide is accompanied by depolymerization and oligomerization. It has been reported that ethylene oxide polymerized cation-ically with the living dication of tetrahydrofuran and a surface active material was obtained290. ... 

It is to be noted that N-vinylcarbazole (NVC) undergoes also living cationic polymerization with hydrogen iodide at —40 °C in toluene or at —78 °C in methylene chloride and that in this case no assistance of iodine as an activator is necessary 10d). NVC forms a more stable carbocation than vinyl ethers, and the living propagation proceeds by insertion between the strongly interacting NVC-cation and the nucleophilic iodide anion. 

Provided that the uncomplexed species is suceptible to destruction, while the complex is protected, the lifetime of living polymer increases at higher monomer concentrations. Cationic polymerization of propylene induced by AlBr3. HBr studied by Fontana and Kidder22) exemplifies perhaps such a system. 

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

Indeed, cumyl carbocations are known to be effective initiators of IB polymerization, while the p-substituted benzyl cation is expected to react effectively with IB (p-methylstyrene and IB form a nearly ideal copolymerization system ). Severe disparity between the reactivities of the vinyl and cumyl ether groups of the inimer would result in either linear polymers or branched polymers with much lower MW than predicted for an in/mcr-mediated living polymerization. Styrene was subsequently blocked from the tert-chloride chain ends of high-MW DIB, activated by excess TiCU (Scheme 7.2). 

Allcock HR, Crane CA, Morrissey CT, Nelson JM, Reeves SD, Honeyman CH, and Manners I. Living cationic polymerization of phosphoranimines as an ambient temperature route to polyphosphazenes with controlled molecular weights. Macromolecules, 1996, 29, 7740-7747. 

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