Styrene polymerization solvent effects

Photoinitiation of polymerization of MMA and styrene by Mn(facac)3 was also investigated, and it was shown that the mechanism of photoinitiation is different [33] from that of Mn(acac)3 and is subject to the marked solvent effect, being less efficient in benzene than in ethyl acetate solutions. The mechanism shown in Schemes (15) and (16) illustrate the photodecomposition scheme of Mn(facac)3 in monomer-ethyl acetate and monomer-benzene solutions, respectively. (C = manganese chelate complex.)... 

It should be mentioned that the predicted curve at highest benzene level in Figure 13 agrees with classical kinetics (no diffusion-control). It is not clear therefore why measured data at even higher benzene concentrations do not agree with classical kinetics. There may be some subtle chemical interactions at these high solvent levels. Duerksen(lT) fomd similar effects with styrene polymerization in benzene and had to correct kp for solvent. 

Masuda, S., M. Tanaka, and T. Ota. 1984. Solvent effects on the co-polymerization of 5-hexene-2,4-dione and styrene. Chem. Lett. 1327-1330. 

Styrene polymerization initiated by trifluoroacetic acid can be used as a standard in demonstrating the effects of solvent and concentration. Polymerization is favored in more polar solvents and at high acid concentration [101]. Only the 1 1 adduct is formed when acid is slowly added to styrene [100]. However, fast polymerization occurs when styrene is added to the concentrated acid [Eq. (24)]. 

The relevance of thymine/2,6-diaminotriazine interactions has been exploited by a variety of authors to effect a reversible, yet stable association of catalysts, nanoparticles and other fimctional molecules onto polymeric molecules. Thus, Shen et al. [94,95] reported on the formation of catalyst-supported structures for ATRP-polymerization via hydrogenbonding systems (Fig. 19). The relevant Cu(I)-catalyst was affixed onto a poly(styrene) gel either via the thymine/2,6-diaminopyridine or the maleimide/2,6-diaminopyridine couple. The catalyst was able to mediate a living polymerization reaction of MMA in both cases, obviously acting in its dissociated form. The catalyst could be reused, retaining about half of its catalytic activity for further use. A strong solvent effect was observed, explainable by the dissociation of the catalyst from the support upon addition of strongly polar solvents. 

The active site in chain-growth polymerizations can be an ion instead of a free-radical. Ionic reactions are much more sensitive than free-radical processes to the effects of solvent, temperature, and adventitious impurities. Successful ionic polymerizations must be carried out much more carefully than normal free-radical syntheses. Consequently, a given polymeric structure will ordinarily not be produced by ionic initiation if a satisfactory product can be made by less expensive free-radical processes. Styrene polymerization can be initiated with free radicals or appropriate anions or cations. Commercial atactic styrene polymers are, however, all almost free-radical products. Particular anionic processes are used to make research-grade polystyrenes with exceptionally narrow molecular weight distributions and the syndiotactic polymer is produced by metallocene catalysis. Cationic polymerization of styrene is not a commercial process. 

This relationship is in agreement with the known dependence of rate on the square root of initiator concentration, and the rate acceleration tvithin the particles due to hindrance of termination due to the gel effect The effect of a on rate has been noted for styrene polymerizations in mixed solvents. Polymerization proceeds faster in the polar water/ethanol system than in either the less polar etiianol [28] or meihotgrethanol/etiianol blends [46] owing to the greater partitioning of the ncm-polar styrene into the particle. 

Shim, S.E. Oh, S. Chang, Y.H. Jin, M.J. Choe, S. Solvent effect on TEMPO-mediated living free radical dispersion polymerization of styrene. Polymer 2004, 45 (14), 4731-4739. 

The mechanism proposed by Kennedy requires that allylic or tertiary chlorines be attached to the first polymer chain. Chlorobutyl rubber, PVC, and other chlorine-containing polymers usually have 1-2% of mers with chlorines in the required reactive positions. The halogen-containing polymer is dissolved in an inert but polar solvent in the presence of an organoaluminum catalyst and a cationically polymerizable monomer, such as styrene, and polymerization is effected, usually at about — 50 C. The major point is that the second component chains can be initiated only at an active chlorine site on the first polymer. 

Solvents affect free-radical polymerization reactions in a number of different ways. Solvent can influence any of the elementary steps in the chain reaction process either chemically or physically. Some of these solvent effects are substantial, for instance, the influence of solvents on the gel effect and on the polymerization of acidic or basic monomers. In the specific case of copolymerization then solvents can influence transfer and propagation reactions via a number of different mechanisms. For some systems, such as styrene-acrylonitrile or styrene-maleic anhydride, the selection of an appropriate copolymerization model is still a matter of contention and it is likely that complicated copolymerization models, incorporating a number of different phenomena, are required to explain all experimental data. In any case, it does not appear that a single solvent effects model is capable of explaining the effect of solvents in all copolymerization systems, and model discrimination should thus be performed on a case-by-case basis. 

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