Styrene polymerization, inhibition

Other miscellaneous compounds that have been used as inhibitors are sulfur and certain sulfur compounds (qv), picryUiydrazyl derivatives, carbon black, and a number of soluble transition-metal salts (151). Both inhibition and acceleration have been reported for styrene polymerized in the presence of oxygen. The complexity of this system has been clearly demonstrated (152). The key reaction is the alternating copolymerization of styrene with oxygen to produce a polyperoxide, which at above 100°C decomposes to initiating alkoxy radicals. Therefore, depending on the temperature, oxygen can inhibit or accelerate the rate of polymerization. 

Another appHcation for this type catalyst is ia the purification of styrene. Trace amounts (200—300 ppmw) of phenylacetylene can inhibit styrene polymerization and caimot easily be removed from styrene produced by dehydrogenation of ethylbenzene using the high activity catalysts introduced in the 1980s. Treatment of styrene with hydrogen over an inhibited supported palladium catalyst in a small post reactor lowers phenylacetylene concentrations to a tolerable level of <50 ppmw without significant loss of styrene. 

I. Kende and M. Azori Kinetics of inhibition of styrene polymerization by nitro compounds. IUPAC Symposium on Macromolecular Chemistry, Moscow 1960, Section II 31. 

Lignin Styrene Ozonization avoids inhibiting effect of lignin on styrene polymerization [196]... 

Figure 5(e) Electron micrographs of inhibited styrene polymerized in a middle phase microemulsion containing SDS and 2-pentanol (xlOOO). Reproduced with permission from Ref. 24, Figure 1. Copyright 1988 John Wiley Sons.

Figure 5(g) Electron micrograph of inhibited styrene polymerized in a... 

Styrene is capable of forming moderately stable Co-C bonds.370 The formation and decomposition of adducts between the CCT catalysts and the propagating radicals results in reversible inhibition .123-271 In this case, an induction period is observed at the beginning of polymerization. This induction period is characterized by the steady growth of the rate of polymerization similar to the classic kinetics of a polymerization inhibited by a weak inhibitor. Depending upon conditions, the time required to reach steady-state polymerization kinetics (eq 42) may require tens of minutes. 

The role of sulphur-containing compounds in photopolymerization appears to have attracted some interest. Bis(j -methylpyridazinyl)-3,3 -disulphide has been found to initiate the photopolymerization of styrene but inhibits the thermal polymerization. The role of thiyl radicals (PhS-) in photoinitiated polymerization of vinyl monomers by aromatic thio-compounds has been postulated by several workers. In one study, flash photolysis was used to identify the nature of the radical. Sulphur-containing monomers such as 4-methyl-2-(vinylthio)thiazole and thiocyclanes have been photopolymerized and copolymerized with other vinyl monomers. Luca et al. have devised a mathematical model for the photopolymerization of 2,3-dimethylbutadiene and thiourea. 

It is interesting to mention that the presence of the pigments can significantly change the polymerization kinetics. Retardation of the reaction rate of styrene polymerized on the surface of azo-pigment particles can be attributed, e.g., to the interaction of radical species with nitrobenzene fragments. In the case of quinacridone pigments, a remarkable inhibition period was observed. 

Thus, additives act in various ways. Benzoquinone produces a profound inhibition period in the thermal polymerization of styrene (Figure 20-5). Finally, styrene polymerizes at the same rate as for purely thermal polymerization. Obviously, all free radicals formed react instantaneously with the benzoquinone to produce inactive free radicals. It cannot be distinguished here without further experiments whether the benzoquinone forms a free radical by transfer or is incorporated into the reacting free radical ... 

On the other hand, nitrobenzene does not produce an inhibition period when added to a thermal styrene polymerization. The polymerization proceeds significantly slower, however nitrobenzene is a retarding agent. The... 

This reaction is an endothermic one and toluene and benzene are formed as byproducts. In a typical styrene production unit, two reactors (for which per-pass conversion is 65%) or three reactors (for which per-pass conversion is 70—75%) exist in series and the selectivity to styrene is 93—97%. TaU distUlation towers and high return/reflux ratios are needed for separating styrene from ethylbenzene because the boiling point of styrene (145 °C) differs httle from that of ethylbenzene (136 °C). Styrene polymerization at the distillation temperature is also another important issue. To reduce this problem, special additives, which have high inhibition against polymerization, are added. 

A further important class of retarders, generally less effective than quinones, are the aromatic nitro compounds. They show very different effectiveness toward the retardation of different monomer types the polymerization of vinyl acetate is inhibited, the styrene polymerization is retarded, but there is nearly no influence on the poljunerization rate of acrylates and methacrylates. The effectiveness, however, increases with the number of nitro groups per molecule. 

Besides the cocatalyst, there are some other additives that are capable of influencing the performance of catalyst systems during styrene polymerization. The addition of a proper amount of triisobutylalu-minum (TIBA) to various titanium complex/MAO systems increases the catalyst activity, whereas the addition of TMA or triethylaluminum (TEA) inhibits polymerization. A relatively high molar ratio of TIBA/MAO will cause a reduction in activity and a sharp decrease in the molecular weights of sPS. When a haloalkylaluminum such as AlEt2Cl is used with the CpTiCb/MAO system, only atactic polystyrene is produced by a noncoordination polymerization process, that is, a cationic... 

Here the different steps of the preparation of the nanocomposites are briefly summarized. First, PPO (a low molar mass polymer powder supplied by Sabic-IP, the Netherlands] was end-capped by acetylation in order to avoid inhibition of the styrene polymerization by phenolic OH groups. It was subsequently mixed with styrene and hexadecane. Then the mixture was added to an aqueous solution of 4-dodecylbenzenesulfonic acid (SDBS). This mixture of SDBS/ hexadecane was chosen as a stabilization system since it is suitable to achieve and guarantee efficient stabilization of polymer particles of sizes smaller than 1 ymP The emulsification process was split up into two steps, namely, a first pre-emulsification step performed by ultra-high shear stirring, followed by ultrasonication in order to obtain submicron particles. Finally, the polymerization was initiated and carried out at 80°C under inert atmosphere (final monomer conversion of 90 %]. The latex obtained had a solid content of 23.6 wt% and contained 10 wt% of PPO dissolved in PS and had a particle size of 100 nm. At the end of the polymerization, the PS molar mass was about... 

Aromatic nitro compounds act as inhibitors and show greater tendency toward more reactive and electron-rich radicals. Nitro compounds have very little effect on methyl acrylate and methyl methacrylate [5,10,11] but inhibit vinyl acetate and retard styrene polymerization. The effectiveness increases with the number of nitro groups in the ring [1 13]. The mechanism of radical termination involves attack on both the aromatic ring and the nitro group. The reactions are represented as follows ... 

Copolymers with acrylonitrile, butadiene, isoprene, acrylates, piperjiene, styrene, and polyethylene have been studied. The high cost of sorbic acid as a monomer has prevented large-scale uses. The abiUty of sorbic acid to polymerize, particularly on metallic surfaces, has been used to explain its corrosion inhibition for steel, iron, and nickel (14). 

Styrene 32 (Vinyl benzene) C6H5CH CH2 490 1.1-6.1 0.9 3.6 145 Colourless/oily yellow liquid Penetrating odour Polymerizes slowly in air or light, accelerated by heat or catalysts Ignition/explosion possible Usually inhibited Store <21 °C... 

The presence of stable free radicals in the resin was further suggested by the strong inhibiting effect of traces of this product on the thermal polymerization of styrene. 

Inhibition of olefin polymerization occurred when its basicity was not sufficient to produce an appreciable displacement of initiator from the aldehyde-acid complex isoprene, cyclopentadiene and styrene were in this category. 

Trauzl Test. 21,.4% of TNT when pure (Ref 26) for mixts see below Uses. It does not gelatinize NC (Ref 15). It improves the octane rating of diesel fuels (Ref 26). It decreases the polymerization rate of methyl methacrylate (Ref 24), and styrene (Ref 23), but. does not inhibit the reaction. A review of its use as an oxidizer in rocket propints is given in Ref 33. TeNMe gives yellow to orange colors with olefins and aromatic compds. This is used as a diagnostic test for the presence of these groups in org analysis (Refs 6, 9, 16, 17 29)... 

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