Polymerizability of Monomers

Thus monomers like isobutylene (VI), 3-methylbutene-l (VII), styrene (VIII), and vinyl ethers (K) all undergo cationic polymerization. 

Some of these vinyl monomers can delocalize the positive charge, and this also facilitates reactions with cations, e.g., in the polymerization of vinyl ethers  

The alkoxyl substituent thus allows a delocalization of the positive charge over two atoms—the carbon and the oxygen, and this leads to stabilization of the carboniura ion. (If the substituent were not present, e.g., in ethylene, the positive charge would be localized on the single a-carbon atom.) Similar delocalization effects occur with phenyl, vinyl, and alkyl substituents, e.g., for styrene polymerization  

The electron-withdrawing substituents may also stabilize the anion formed by delocalization of the charge, e.g., for acrylonitrile polymerization  

The stabilization of the propagating carbanion occurs by delocalization of the negative charge over the a-carbon and the nitrogen of the nitrile group. 

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The polymerizability of monomers having a 1,5-pentanedioxy central group were lower than monomers containing a diphenyl sulfone group. This was due to a difference in the reactivity and concentration of the cation-radical propagating species in the polymerization [214]. 

Random hydrocarbon copolymers can also be produced by this new equilibrium polymerization method. Copolymers containing octenylene and butenylene linkages in a statistical array based on feed ratio result from the cocondensation of the two respective monomers or by the reaction of diene with unsaturated polymer. More controlled polymer stmctures have also been prepared by the slow addition of a diene solution to an unsaturated polymer containing active catalyst. Substituent effects were shown to dictate the polymerizability of monomers and in some cases selective polymerization of speciflc aUcenes in the monomer resulted in what appears as perfectly alternating copolymers. ... 

Suitability of monomers for cationic polymerization was discussed in the section on polymerizability of monomers and compared in Table 8.1. In short, olefinic monomers with electron-releasing substituents on the a-carbon, that is monomers that behave as a nucleophile (electron donor), can undergo cationic polymerization and the possibility of resonance stabilization of the carbocationic species increases the reactivity of the monomer. The most active vinyl monomers are thus those with electron-releasing substituents or conjugated double bonds in which the positive charge can be delocalized (see Problems 8.17 and 8.18). 

It has already been observed in the polymerization of substituted E-caprolactams 1 1, that the substitution of hydrogen atoms decreases the polymerizability of monomers. The same phenomena were observed in the polymerization of 4,4-dimethyl-, cis-4,5-dimethyl and trans-4,5-dimethyl-Diox 15. ... 

Thermodynamic polymerizability of monomers may be described and compared in various ways. AabG at a given temperature is one of the possible approaches. However, the ceiling temperaorre of monomers in hulk (Tc(hulk)) appears as a useful candidate since this is the upper limit at which the polymer of a given monomer is thermodynamically stable. 

The kinetic polymerizability of monomers belonging to the same class of compounds and studied at similar conditions could be compared using thermodynamic activation parameters. Actually, these parameters are determined from the dependence of the rate constants of elementary reactions (In fep) on 1/T in several instances comparison of fep could be sufficient. Comparison of and A S is more subtle since it provides information on the genuine source of differences in kp and therefore on kinetic polymerizabilities. A good example of such a comparison for CROP of oxetane, 3-methyloxetane, and 3,3-dimethyloxetane is given in a classical work by Saegusa and Kobayashi. ... 

Another unsymmetrical polydiacetylene with the carbazolyl group as one of the substituents was prepared by Dellepiane et al. [386,387]. Since the polymerizability of monomers with two aromatic groups is usually low, the authors expected increased reactivity from l-(A -carbazolyl)penta-5-acetoxy-l,3-diyn (58). However only oligomers were obtained. 

Table 1 Polymerizability of Monomers by Different Polymerization Mechanisms...

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