Styrene units

FIGURE 1111 Cham propagation in polymerization of styrene The growing polymer chain has a free radical site at the benzylic carbon It adds to a molecule of styrene to extend the chain by one styrene unit The new polymer chain is also a benzylic radical it attacks another molecule of styrene and the process repeats over and over again... 

Structures of styrene, divinylbenzene, and a styrene-divinylbenzene co-polymer modified for use as an ion-exchange resin. The ion-exchange sites, indicated by R, are mostly in the para position and are not necessarily bound to all styrene units. 

The number of styrene units in an average sequence is a little larger than the length of the average hemin sequence. It is not unreasonable to describe the hemin clusters as isolated, on the average, in this molecule. The product rir2 = 11.7 in this system, which also indicates a tendency toward block formation. Use Eq. (7.37) with [Mi]/[M2] = 0.046 and the rj and r2 values to evaluate... 

Styrene is manufactured from ethylbenzene. Ethylbenzene [100-41-4] is produced by alkylation of benzene with ethylene, except for a very small fraction that is recovered from mixed Cg aromatics by superfractionation. Ethylbenzene and styrene units are almost always installed together with matching capacities because nearly all of the ethylbenzene produced commercially is converted to styrene. Alkylation is exothermic and dehydrogenation is endothermic. In a typical ethylbenzene—styrene complex, energy economy is realized by advantageously integrating the energy flows of the two units. A plant intended to produce ethylbenzene exclusively or mostly for the merchant market is also not considered viable because the merchant market is small and sporadic. 

Polystyrene [9003-53-6] (PS), the parent of the styrene plastics family, is a high molecular weight linear polymer which, for commercial uses, consists of - 1000 styrene units. Its chemical formula (1), where n = - 1000, tells htde of its properties. 

Random copolymers of butadiene and styrene have been known for over half a century and such polymers containing about 25% of styrene units are well known... 

In Chapters 3 and 11 reference was made to thermoplastic elastomers of the triblock type. The most well known consist of a block of butadiene units joined at each end to a block of styrene units. At room temperature the styrene blocks congregate into glassy domains which act effectively to link the butadiene segments into a rubbery network. Above the Tg of the polystyrene these domains disappear and the polymer begins to flow like a thermoplastic. Because of the relatively low Tg of the short polystyrene blocks such rubbers have very limited heat resistance. Whilst in principle it may be possible to use end-blocks with a higher Tg an alternative approach is to use a block copolymer in which one of the blocks is capable of crystallisation and with a well above room temperature. Using what may be considered to be an extension of the chemical technology of poly(ethylene terephthalate) this approach has led to the availability of thermoplastic polyester elastomers (Hytrel—Du Pont Amitel—Akzo). 

Insertion of styrene units into the macromolecules of AN polymers causing steric hindrances because of the threedimensional phenyl groups, results in an appreciable decrease of the rate of thioamidation in comparison with PAN. 

At any point in the chain, there is a 75% probability of finding a butadiene unit and a 25% probability of finding a styrene unit. 

In these styrene copolymers with isopropenylferrocene, the low inclusion of styrene units could be attributed to the greater reactivity of isopropenylferrocene, and vinylferrocene has been assumed to have an r value greater than styrene by Aso and Kunitake.30... 

The greatest use of latex paints for indoor applications is based upon vinyl acetate, which constitutes 85% of the total polymer usage, the remainder being acrylates (e.g., n-butyl acrylate). For outdoors or bathroom usage, acrylates are the major components. For various applications, e.g., wood paints, styrene copolymerised with acrylates are used. Flowever, yellowing of the styrene units occurs. 

The formation of inter- and intrapolymer complexes has also been shown to affect the polymerization kinetics. For example, Ferguson and Shah (1968) investigated the influence of intrapolymer complexation on the kinetics of AA in the presence of copolymer matrices composed of either A-vinylpyrrolidone and acrylamide or A--vi nyl pyrrol idone and styrene. The polymerization rate reaches a maximum in the vicinity of AA to VP ratio equal to one for the VP/AAm matrix. This maximum in the polymerization rate is most pronounced in the presence of copolymer with the highest content of VP. When the hydrophilic acrylamide is replaced with the more hydrophobic styrene monomer in the copolymer matrix, the observed maximum in AA polymerization rate occurred at a lower than equimolar ratio of AA to VP. The hydrophilic groups of VP were interacting with the hydrophobic nucleus consisting of the styrene units in the VP/St copolymer, and were thus unable to participate in the formation of the complex unlike in the case of VP/AAm copolymer matrix. 

The oxonium ion resulting from Reaction (Dl) is a derivative of a dioxacyloheptane. A further styrene unit could be incorporated into its near branch by a reaction analogous to route (D2). The product of Reaction (D2) could incorporate a styrene unit into the ring by route (Dl). 

The Y-group (like the linear branches of the oxonium ions in Reactions (Dl) and (D2)) is mobile over all the oxygen atoms in the system. Thus further styrene units can be incorporated by Reaction (E) until all the formal oxygens have been converted into ether oxygens, and an alternating copolymer is obtained. Reactions (Dl) and (D2) could also only give copolymers with not more than 50% of styrene. 

Experiment [20], however, shows that when a great excess of styrene is used, sequences of up to four styrene units can be formed, although the formation of styrene sequences is under all conditions much less probable than the formation of dioxolan sequences. Thus both reaction mechanisms require a reaction step such as (F) whereby sequences of styrene units can be formed ... 

Even further advantages in transparency are obtained with special styrene-butadiene block copolymers consisting predominantly of styrene units (88, 89 ). Such products have been in use for a few years now for transparent packagings and other purposes numerous other applications are feasible. 

Fig. 12. Separation of styrene oligomers by reversed-phase (left) and size-exclusion chromatography (right) (Reprinted with permission from [121]. Copyright 1996 American Chemical Society). Conditions (left) column, molded poly(styrene-co-divinylbenzene) monolith, 50 mm x 8 mm i.d., mobile phase, linear gradient from 60 to 30% water in tetrahydrofuran within 20 min, flow rate 1 ml/min, injection volume 20 pi UV detection, 254 nm (right) series of four 300 mm x 7.5 mm i.d. PL Gel columns (100 A, 500 A, 105 A, and Mixed C), mobile phase tetrahydrofuran, flow rate, 1 ml/min injection volume 100 pi, toluene added as a flow marker, UV detection, 254 nm temperature 25 °C,peak numbers correspond to the number of styrene units in the oligomers...

The reaction rate varies with the change in the solvent composition. The catalysis of pyridine-Cu in DMSO-benzene mixed solvent is summarized in Fig. 4 (a). The rate constant of the catalyst reoxidation (k0) and the overall rate increase although the rate constant of electron-transfer (ke) decreases with the benzene content. Instead of the benzene solvent, the copolymer of vinylpyridine with styrene (PSP) was used as a polymer ligand, as shown in Fig. 4 (b). The overall rate and k0 increase with the styrene content in the PSP ligand, just as the solvent effect of benzene. Only several times amount of styrene unit to Cu ion (as polymer concentration ca. 0.1 wt% of the solvent) affects... 

On this basis it was reasoned that a benzyl group in a ketene acetal should greatly increase the extent of cleavage during polymerization and, therefore, should increase the efficiency of chain transfer. That in fact is what occurred when an equimolar mixture benzyl methyl ketene acetal (XIV) and styrene was heated at 120°C in the presence of di-tert-buty1 peroxide an oligomer with 80% styrene units and capped with a carbomethoxy group was obtained. 

Starting from the commercially available aldehyde (12), styrene (13) was prepared by a straightforward synthetic sequence (Scheme 11.3). Subsequent esterification of the phenol with succinate-derivatized poly(ethylene glycol) monomethyl ether (MeO-PEG) appended the styrene unit to approximately 50% of the free acid groups in (14). The loading in (15) was estimated by 500 MHz NMR spectroscopy to be about 0.1 mmol g . In a final step, the polymer-bound catalyst was ob-... 

Another type of copolymer is a block copolymer. Here a low molecular weight polymer may be extended by reaction with a new monomer. Recall that we talked about living polymers in this Chapter, Section 2.3. If, for example, we polymerized styrene alone first, then added some butadiene and polymerized it further, we would have a number of styrene units bundled together and a number of butadienes also together. 

One approach is the use of copolymers. There are a number of variations to this. In some situations, polymer-copolymer combinations are used where the adage the enemy of my enemy is my friend comes into play. Thus, the random copolymer of styrene and acrylonitrile forms a miscible blend with PMMA. The copolymer is composed of nonpolar styrene units and polar acrylonitrile units that are incompatible with one another. These units will blend with PMMA in order to avoid one another. 

Kraton, the yellow rubber-like material often found on the bottom of running shoes, is a copolymer whose structural information is known. It is formed from a group of styrene units, i.e., a block of polystyrene, attached to a group of butadiene units, or a block of... 

Problems—what is the approximate molecular weight of a single polystyrene chain that has 1000 styrene units in it ... 

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