Polystyrene monomer yield

Figure 12.29 shows that using styrene as the monomer yields polystyrene. Transparent plastic cups are made of polystyrene, as are thousands of other household items. Blowing gas into liquid polystyrene generates Styrofoam, widely used for coffee cups, packing material, and insulation. 

Random chain cleavage followed by chain unzipping is characterized by high monomer yields and a slow decrease in the molecular weight of the polymer, for example, exhibited by PMMA, poly(a-methyl styrene), polystyrene polytetrafluoroethylene. 

The optimum pyrolysis temperature is 395°C to give a recovery ratio of 0.97 (i.e. 1000 kg polystyrene will yield 970 L liquid monomer) and 5 to 10% char residue. Fuel made from polystyrene feedstock will be high in aromatic character and have an energy content of 50 MJ/kg and a pour point of —67°C. However the flash point is only 26°C and the cetane rating only 12.6. The fuel needs to be blended with polyolefin-derived diesel or regular diesel in order to upgrade the flash point and cetane rating to within specification. 

The styrene/methyl methacrylate pair contains monomers with different relative reactivity levels in Table 9-1. Polystyryl anion will initiate the polymerization of methyl methacrylate, but the anion of the latter monomer is not sufficiently nucleophilic to cross-initiate the polymerization of styrene. Thus the anionic polymerization of a mixture of the two monomers yields polyfmethyl methacrylate) while addition of methyl methacrylate to living polystyrene produces a block copolymer of the two monomers. 

The authors have further observed that when a deuterium atom is attached to the same carbon atom as a hydrogen, the C-H bond is broken 2.3 times as readily as a C-H bond in the structure -CH2-, and the C-D bond is broken 1.6 times as readily as a C-D bond in the structure -CD2-. Table 1 shows that the monomer yield in thermal degradation of polystyrene and poly(/8-deuterostyrene) at 350 °C in vacuum is the same (42%). Monomer yield from poly(/8-deuterostyrene) should have been much less than that from polystyrene if the abstraction of hydrogen from -CDH- is easier than from-CH2-. 

Polystyrene pyrolysis yielded an oil with a high content of styrene monomer (Fig.4). The reaction conditions were optimized to maximize the yield of styrene. A maximum of l6% (by weight) was obtained. The oil is suitable for reuse in the styrene manufacturing process. 

The most important condition which should be tested experimentally is that of overlap of emission bands. It has been shown that excimer overlap with monomer emission is significant for polystyrene (5) thus any determination of relative excimer/monomer yields must make allowance for this factor. This correction is large when the area of excimer peak is much greater than that of the monomer, a situation which prevails for solutions of polystyrene. Examination of emission spectra of naphthalene containing polymers indicates that when excimer is formed the emission overlaps to a... 

The reactivity of the initiating radicals toward the backbones can vary and this can also vary the efficiency of grafting. Benzoyl peroxide-initiated polymerizations of methyl methacrylate monomer, for instance, in the presence of polystyrene [284] yield appreciable quantities of graft copolymers. Very little graft copolymers, however, form when di-t-butyl peroxide initiates the same reactions. Azobisisobutyronitrile also fails to yield appreciable quantities of graft copolymers. This is due to very inefficient chain transferring to the polymer backbones by t-butoxy and isobutyronitrile radicals. 

In contrast to polystyrene, poly(a-methyl styrene) yields in vacuum pyrolyses at temperatures between 200 and 500°C 95-100% monomer. By comparison, polystyrene only yields about 40.6% [457]. The difference can be attributed to the fact that hydrogen transfer is completely blocked from the sites of chain scission by the methyl groups in the a-positions [457]. As a result, the terminal free-radicals unzip into monomers and dimers. 

Polystyrenes that are substituted on the benzene ring, like poly(vinyl toluene), behave similarly to polystyrene when pyrolyzed [457]. Also, poly(wt-methylstyrene) at 350°C yields 44.4% monomer as compared to polystyrene that yields 40.6% monomer at these conditions. The rate, however, for polystyrene at this temperature is 0.24 mol.%/min, while for poly(w-methylstyrene) it is 0.9 [457]. 

Polystyrene (PS) yields benzene (I = 600) as the major photolysis product with apparently smaller amounts of toluene, ethylbenzene, and styrene formed. Quantitation of the last three materials is complicated by variable amounts of residual monomer in the samples available and a small amount of thermal decomposition occurring in the injection port. 

A possibility to synthesize block copolymers by conventional radical polymerization is given by the application of polymeric initiators [162], Partial decomposition of the polymeric initiators in the presence of styrene yields block copolymers containing polystyrene and part of the polymeric initiator, still containing some initiator functions. These functions can be decomposed in a following step in the presence of an additional monomer yielding block copolymers [157,159-161]. 

C, and styrene production was also more by 11 wt% in the case of waste expanded polystyrene. Oil yield increased from 24 to 98 wt% with increase in reaction temperature from 350 to 480 °C, while styrene selectivity, which was about 76 wt% up to 450 °C, decreased sharply to 49 wt% at 480 °C. This decrease in styrene selectivity takes place with increase in styrene dimer formation from 4 to 10 wt% and production of other chemicals. Also the production of toluene, ethylbenzene and methylstyrene decreased with the same rise in pyrolysis temperature. Thermal degradation of PS was reported to have started with random initiation to form polymer radicals, the main products being styrene and its corresponding dimers and trimers. These results were comparable with studies reported elsewhere on oil yield of 99 wt% with 60 wt% styrene monomer and 25 wt% for other aromatics. Another work has reported on recovery of 58 wt% styrene from thermal degradation of PS at 350 °C after a time of 60 min [a.379]. Furthermore, oil yields of 82 wt% with 70 wt% styrene selectivity and 77 wt% styrene recovery at 580 °C have been reported [a.380]. 

This reaction is most commonly observed with vinyl monomers, yielding polyethylene, polystyrene, polyacrylates, etc... 

Chloromethylated polystyrene - - Styrene monomer Polymer characterisation, monomer yield decreased with increasing chlorine content of polymer [49]... 

Polymerization processes yielding polymers, whose mers are constitutionally identical to the reacting monomers are now classified as addition polymerizations. Thus styrene can be converted, by addition polymerization, to polystyrene ... 

Furthermore, photochemically induced homolytical bond cleavage can also be applied when the prepolymer itself does not contain suitable chromophoric groups [113-115]. Upon thermolysis of ACPA in the presence of styrene, a carboxyl-terminated polystyrene is formed. This styrene-based prepolymer was reacted with lead tetraacetate and irradiated with UV light yielding free radicals capable of initiating the polymerization of a second monomer (Scheme 33) [113]. 

Ethylene is not unique in its ability to form a polymer. Many substituted ethyl-enes, called vinyl monomers, also undergo polymerization to yield polymers with substituent groups regularly spaced on alternating carbon atoms along the chain. Propylene, for example, yields polypropylene, and styrene yields polystyrene. 

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