Chlorostyrene cationic copolymerization

TABLE 6-9 Steric Effects in Cationic Copolymerization of a- and (i-Methylstyrenes (Mx) with p-Chlorostyrene (M2)a b... 

Ionic copolymerizations are more complicated than free-radical ones. Various complicating factors arise from effects of the counterions and from influences of the solvents. These affect the reactivity ratios. In addition, monomer reactivity is affected by the substituents. They influence the electron densities of the double bonds and, in cationic polymerizations, the resonance stabilization of the resultant carbon cations. Yet, the effects of the counterions, the solvents, and even the reaction temperatures can be even greater than that of the substituents in cationic polymerizations. There are only a few studies reported in the literature, where the reactivity ratios were determined for different monomers, using the same temperature, solvent, and counterion. One such study was carried out on cationic copolymerizations of styrene with two substituted styrenes. These were a-methylstyrene, and with chlorostyrene. " The relative reactivity ratios of these substituted styrenes were correlated with Hammett pa values. The effect of the substituents on reactivity of styrene fall in the following order ... 

The effect of solvents on the reactivity ratios in cationic copolymerizations can be seen from copolymerizations of isobutylene withp-chlorostyrene, using aluminum bromide as the initiator. ... 

The effect of solvents on the reactivity ratios in cationic copolymerizations can be seen from copolymerizations of isobutylene with p-chlorostyrene, using aluminum bromide as the initiator [376]. The ri and r2 values in hexane for isobutylene and chlorostyrene copolymerization are both equal to 1.0. In nitrobenzene, however, ri is equal to 14.7 and r2 is equal to 0.15. 

This insensitivity to solvent polarity and temperature may relate to early cationic copolymerization studies carried out by Overberger, Arnold and Taylor and by Marvel and Dunphy. These groups found reactivity ratios for the cationic copolymerization of styrene and a-methylstyrene with chlorostyrene to also be insensitive to solvent and temperature changes. 

It has previously been shown that large changes can occur in the rate of a cationic polymerization by using a different solvent and/or different counterion (Sec. 5-2f). The monomer reactivity ratios are also affected by changes in the solvent or counterion. The effects are often complex and difficult to predict since changes in solvent or counterion often result in alterations in the relative amounts of the different types of propagating centers (free ion, ion pair, covalent), each of which may be differently affected by solvent. As many systems do not show an effect as do show an effect of solvent or counterion on r values [Kennedy and Marechal, 1983]. The dramatic effect that solvents can have on monomer reactivity ratios is illustrated by the data in Table 6-10 for isobutylene-p-chlorostyrene. The aluminum bromide-initiated copolymerization shows r — 1.01, r2 = 1.02 in n-hexane but... 

It was found that a mixture of 4-vinylpyridine with p-chlorostyrene copolymerizes without any initiator in the presence of poly(maleic anhydride) at 50°C in DMF. The fact that poly(maleic anhydride) cannot initiate the polymerization of styrene or phenyl vinyl ether shows that poly(maleic anhydride) does not act as a normal anionic or cationic initiator. The compositions of copolymers obtained with various initial compositions of... 

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