Styrene forms

The free styrene monomer is restrained within the gel and further reaction with fumarate groups is determined by the spacial arrangement the styrene polymerizes in homopolymer blocks as it intercepts fumarate reaction sites. As individual micelles expand and deplete available fumarate sites in the short polymer chains, the remaining styrene forms homopolymer blocks that terminate at the boundaries between overlapping micelles (Fig. 4). 

It has been discovered that styrene forms a linear alternating copolymer with carbon monoxide using palladium II—phenanthroline complexes. The polymers are syndiotactic and have a crystalline melting point - 280° C (59). Shell Oil Company is commercializing carbon monoxide a-olefin plastics based on this technology (60). 

Fig. 7. Comparison of the thermal stabihty, ie, formation of monomer and loss of of FRPS and APS upon heating for 2.5 h at 285°C in glass tubes sealed at 0.67 or 13.3 kPa. A is FRPS residual styrene formed B, FRPS loss C, APS loss and D, APS residual styrene formed. To convert kPa to...

It does not matter that there is no known catalyst that can accomplish the reaction in Equation (7.21) directly. Heats of reaction, including heats of formation, depend on conditions before and after the reaction but not on the specific reaction path. Thus, one might imagine a very complicated chemistry that starts at standard conditions, goes through an arbitrary trajectory of temperature and pressure, returns to standard conditions, and has Equation (7.21) as its overall effect. A77. =-1-147,360 J/mol of styrene formed is the net heat effect associated with this overall reaction. 

The separation of benzene from a mixture with toluene, for example, requires only a simple single unit as shown in Figure 11.1, and virtually pure products may be obtained. A more complex arrangement is shown in Figure 11.2 where the columns for the purification of crude styrene formed by the dehydrogenation of ethyl benzene are shown. It may be seen that, in this case, several columns are required and that it is necessary to recycle some of the streams to the reactor. 

Photolysis of methyl-phenyl-diazomethane in cis-butene gives mainly styrene formed by hydride shift and the isomeric cycloaddition products 60—62 139) ... 

As seen from Scheme 7.2, the epoxy-ring cleavage and nickel oxidation proceed simultaneously. The nickel-oxygen bond is formed. This results in the formation of the carbon-nickel biradical in which Ph-CH fragment can rotate freely. The cleavage of the (NiO)-C bond leads to the formation of a mixture of styrenes. At early reaction stages (30 min), cis and trans olefins are formed in 50 50 ratio. After a prolonged contact (30 h), when all possible transformations should be completed, the trans isomer becomes the main product and cis trans ratio becomes 5 95. Such enrichment of the mixture with the trans isomer follows from the formation of the di-P-(trimethylsilyl)styrene anion-radical and its isomerization. The styrene formed interacts with an excess of the nickel complex. 

Upon irradiation, 1,4 polybutadienes and poly(butadiene-styrene) form free radicals relatively readily, and their concentration has been found to increase linearly proportional to dose up to approximately 100 Mrad (1,000 kGy). ... 

One interesting aspect of the polymerization of styrene is its possible pseudoca-tionic propagation. It was observed, for example, that in the presence of HC104 styrene forms only oligomers and no real cationic species could be found.160 161 This led to the suggestion that the initiating species is a perchlorate ester stabilized by monomer molecules ... 

From the n-butylchloride glass containing a small amount of styrene, the observed signal is composed of the spectrum due to n-butyl radicals (see Fig. 5) and a new spectrum, due to the added styrene, with the width of 23 G. The latter is thought to be due to the cation radicals of styrene formed through positive charge transfer from the matrix. This assignment is supported by the comparison between the observed spectral shape and the theoretically expected one. 

A cyclization has also been reported in which the carbon-carbon double bond of styrene forms part of a heterocyclic system in this, 2,3-diphenylfuran (322) is converted by irradiation in benzene into phenanthra[9,10-6]furan (323).349... 

Essentially the same substituents as listed above may be present in the alkene being substituted, with the possible exception of chloro, alkoxy and acetoxy groups on vinyl or allyl carbons. These groups, especially chloro, may be lost or partially lost with palladium when the final elimination step occurs. For example, vinyl acetate, iodobenzene and triethylamine with a palladium acetate-triphenylphosphine catalyst at 100 C form mainly (E)-stilbene, presumably via phenylation of styrene formed in the first arylation step (equation 21 ).6 ... 

Krupp Uhde Styrene Pyrolysis gasoline MORPHYLANE process uses extractive distillation to separate styrene form xylenes and ethylbenzene NA NA... 

In the absence of catalyst, it occurs around 700 to 800< with once-through com er-sions of 20 to 30 per cent and overall yields not exceeding 50 to 60 molar per cent This low performance can be ascribed to the side reactions, especially hydrodealkylation to benzene and toluene, miscellaneous craddngs with the foimadon of coke or water gas, and the alkylation of the styrene formed to methylstyrene and the conversion of the by-products obtained. 

OSHA PEL TWA 1 mg(Fe)/m3 ACGIH TLV TWA 1 mg(Fe)/m3 DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Poison by ingestion and intravenous routes. Experimental reproductive effects. Corrosive. Probably an eye, skin, and mucous membrane irritant. Mutation data reported. Reacts with water to produce toxic and corrosive fumes. Catalyzes potentially explosive polymerization of ethylene oxide, chlorine + monomers (e.g., styrene). Forms shock-sensitive explosive mixtures with some metals (e.g., potassium, sodium). Violent reaction with allyl chloride. When heated to decomposition it emits highly toxic fumes of HCl. 

A significant liquid phase is observed during the flash pyrolysis of polystyrene with styrene as the main component [8]. Except for one experiment by Kaminsky [11] the yield in styrene formed during the flash pyrolysis of PS (between 520 and 710°C) is near 75%. The major other products are aromatic compounds (oligomeric styrenes) [11]. 

The ratio kp/A( will appear frequently in the equations we develop for radical polymerization. The polymerizability of a monomer in a free radical reaction is related to k /rather than to kp alone. From Eq. (6-30) or (6-29), it can be seen that a given amount of initiator will produce more polymer from a monomer with a higher kp/k J ratio. Thus, at 60°C, the kp values for acrylonitrile and styrene are approximately 2000 and 100 liter/mol sec, respectively. The former monomer does not polymerize 20 times as fast as styrene under the same conditions at 60, however, because the respective k, values are780x 10 liter/mol sec. and70x 10 liter/mol sec. ThenArp/A , for acrylonitrile is 0.07 liter / /mol / sec /, which is just six times that of styrene. Styrene forms the less reactive radical in this case... 

Problem 30.5 Explain why radical polymerization of styrene forms branched chains with 4 carbons as in A, but none with 3° carbons as in B. 

Several copolymers are commercially important and used in a wide range of consumer products. For example, the copolymer of vinyl chloride and vinylidene chloride forms Saran, the film used in the well-known plastic food wrap. Copolymerization of 1,3-butadiene and styrene forms styrene-butadiene rubber (SBR), the polymer used almost exclusively in automobile tires. 

The composition of a copolymer produced by simultaneous polymerization of two monomers is usually different from the composition of the comonomer feed from which it is produced. This shows that different monomers have different tendencies to undergo copolymerization. These tendencies often have little or no resemblance to their behavior in homopolymerization. Some monomers are more reactive in copolymerization than indicated by their rates of homopolymerization, and some monomers are less reactive. Thus, vinyl acetate polymerizes about twenty times as fast as styrene in a free-radical reaction, but the product in free-radical polymerization of a mixture of vinyl acetate and styrene is found to be almost pure polystyrene with practically no content of vinyl acetate. By contrast, maleic anhydride, which has very little or no tendency to undergo homopolymerization with radical initiation, undergoes facile copolymerization with styrene forming one-to-one copolymers. 

Cyclic block copolymers of PS and PB were also prepared by a similar method [282].sec-BuLi and l,3-bis(l-phenylethenyl)benzene (DDPE) in a molar ratio 2 1 was the difunctional initiator used for the polymerization of B in the presence of sec-BuOLi. Subsequent addition of styrene forms the living triblock copolymer (+)Li( )PS-fc-PB-fc-PS Lb+). Reaction with the linking agent (DDPE or (CH3)2SiCl2) produced the cyclic block copolymers. 

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