Styrenes dimerization

When styrene is refluxed with aqueous sulfuric acid two styrene dimers are formed as the major products One of these styrene dimers is 1 3 diphenyl 1 butene the other is 1 methyl 3 phenyhndan Suggest a reasonable mechanism for the formation of each of these compounds... 

Commercial polystyrenes are normally rather pure polymers. The amount of styrene, ethylbenzene, styrene dimers and trimers, and other hydrocarbons is minimized by effective devolatilization or by the use of chemical initiators (33). Polystyrenes with low overall volatiles content have relatively high heat-deformation temperatures. The very low content of monomer and other solvents, eg, ethylbenzene, in PS is desirable in the packaging of food. The negligible level of extraction of organic materials from PS is of cmcial importance in this appHcation. 

Figure 12.3 Clrromatogr-ams of an ignition-resistant high-impact polystyrene sample (a) Microcolumn SEC fi ace (b) capillary GC trace of peak x . Peak identification is as follows 1, ionol 2, benzophenone 3, styrene dimer 4, palmitic acid 5, stearic acid 6, styrene trimers 7, styrene trimer 8, styrene oligomer 9, Irganox 1076 and Irganox 168 10, styrene oligomer 11, nonabromodiphenyl oxide and 12, decabromodiphenyl oxide. Reprinted with permission from Ref. (12).

The dynamic RIS model, which was proposed before to investigate the dynamics of local conformational transitions in polymers, is elaborated to formulate the increase in the number of excimer-forming sites through rotational sampling. Application of the model to the meso and racemic diads in PS confirms the fact that conformational mobility of the chain plays a major role in intramolecular exclmer formation. Comparison with experiments demonstrates that the decay of the monomer fluorescence in styrene dimers is predominantly governed by the process of conformational transitions. 

Styrenes dimerize and cyclodimerize depending on the catalyst, the reaction conditions, and the substrate. a-Methylstyrene gives cyclic dimer 9 in 93% yield (tert-BuOK, 160°C), whereas linear dimers (isomeric 2,5-dipehylhexenes) are formed in 83% yield at higher temperature (225°C).35 In contrast, a very low yield (11%) of cyclic dimer 10 was attained in the reaction of styrene ... 

Although indan formation is significant in styrene polymerizations, j3-proton elimination is much faster than intramolecular alkylation [292]. Unsaturated styrene and a-methylstyrene dimers are prepared quantitatively under high dilution at elevated temperatures without cyclization to indan derivatives [293]. In this case, the carbocations must be quenched before intramolecular cyclization becomes significant at high conversion. However, indan formation competes with depropagation at temperatures above 50° C, which is much too high for unsaturated styrene dimers (D =) to homopolymerize. As outlined in Eq. (95), the unsaturated dimers form indans (Din) in the presence of acid. 

Styrenes, Dimerization and cyclidimerization of styrene and of a- and j5-methylstyrene have been accomplished in the presence of bases. The type of product depends greatly on the styrene and on the specific catalyst used. 

Wiped film evaporators are more effective at removal of components with lower diffusion constants such as styrene dimer and trimer. 

Figure 3.8 Residual styrene dimer as a function of devolatilizer vacuum. Reprinted with permission from B. J. Meister and A. E. Platt. Ind. Eng. Chem. Res., 28. 1662 (1989). Copyright 1989 American Chemical Society...

Analysis and Levels of Styrene Dimers and Trimers in Polystyrene Food Containers... 

In Japan, the production of polystyrene (PS) is fairly high for example, 115 00001 were produced in 1999, involving one of the four major general-purpose type resins. It has been reported that some kinds of styrene oligomers, which are by-products of polymerization, remained in PS products [1]. In the Wingspread statement announced by Colborn et al. in 1996, it was reported that certain synthetic chemicals have endocrine-disrupting effects on humans or animals. Most of these chemicals are pesticides, but styrene dimers (SDs) and trimers (STs) are listed in this statement along with plasticizers and antioxidants [2]. 

STYRENE DIMERS AND TRIMERS IN POLYSTYRENE FOOD CONTAINERS 729... 

Table 31.2 Contents of styrene, butylated hydroxytoluene (BHT) and styrene, dimer and trimers [8]. Reproduced by permission of the Food Hygiene Society of Japan... 

Table 31.4 Contents of styrene dimers and trimers in material of containers [6]°...

Table 31.5 Migration of styrene dimers and trimers from polystyrene products [A a h... 

Figure 31.6 Effects of styrene monomer (SM) (A), styrene dimers (SD-01, SD-08, SD-09) and styrene trimers (ST-01, ST-02, ST-03) (B) on proliferation of MCF-7 cells [10]. The cells were treated with test compounds for 6 days., p < 0.05, 0.01 (vs control). Each value represents the mean SD (rt = 3 wells)...

PS products contain certain kinds of styrene dimers (SDs), such as 2,4-diphenyl-1-butene and cis- and rraws-l, 2-diphenylcyclobutane, and styrene trimers (STs), such as 2,4,6-triphenyl-1-hexene and l-phenyl-4-(l -phenylethyl)tetralin. The contents of these substances differ with each product. It has also been found that SDs and STs migrate into fatty solvents, such as n-heptane or vegetable oil, but the migration into aqueous solvents is very slight. SDs tend to be affected by the heating time of containers involving solvents, and STs tend to be affected by the length of contact time with containers. 

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