Styrene decomposition temperature

The problem with peroxides is that they are thermally unstable and do not survive the polymerization to reach the devolatilizer. Blakemore [23] solved this problem by using cyclic peroxides which have very high decomposition temperatures. Their thermal stability is due to the peroxide bond reforming once broken, because the two oxy radicals cannot escape each other so they recouple. If styrene happens to be in the vicinity of the cyclic peroxide while it is a dioxyradical, the diradical adds across the styrene double bond (Scheme 4.1). 

Pyrolysis gas chromatography can be used to determine the acrylonitrile content of the SAN copolymer [7-9]. It is a method that heats the polymer above the decomposition temperature, then separates and identifies the low molecular weight compounds formed. The primary decomposition products are styrene, acrylonitrile, and propionitrile, and the styrene content of the copolymer is directly proportional to the styrene yield from pyrolysis [8]. 

Figure 18.9. Predicted glass transition temperature (thin line) and half decomposition temperature (thick line) of amorphous random copolymers of styrene and oxytrimethylene, as functions of the composition.

Althought this decomposition mechanism is not yet well-defined (homolytic cleavage, reductive dimerization. hydride formation, or other mechanisms), it is practically meaningful. Styrene polymerization by CpTiMea/FAB carried out in the low-temperature regime (below the decomposition temperature) produces only atactic polystyrene, possibly via a car-bocationic polyaddition. However, at higher polymerization temperatures (above the decomposition temperature), highly syndiotactic polystyrene can be obtained by coordinative 2,1-polyinsertion. ... 

Thermoplastics such as polypropylene, polycarbonate, nylon, and thermo set such as epoxy, as well as thermoplastic elastomers such as butadiene-styrene di block copolymer, have been reinforced with carbon nanofibers for example. Carbon nanofibers with 0.5 wt% loading were dry-mixed with polypropylene powder by mechanical means, and extruded into filaments by using a single screw extruder. Decomposition temperature and tensile modulus and tensile strength have increased because of dispersion of CNF [121] (Fig. 8.19). 

Higher amounts of AN raise this curve to above the decomposition temperature however, at 13% or more AN the SAN copolymers are not miscible with MPC. Polystyrene forms miscible blends with poly-(vinyl methyl ether), PVME, that phase separate at quite low temperatures. Copolymerization of very small amounts of acrylic acid with styrene dramatically elevates the phase separation... 

The TG profiles of vinyl triethoxy silane-methyl methacrylate (VTES-MMA) copolymers in N2 have been reported to be similar to that of PMMA [a.l85]. However, the initial decomposition temperature (IDT) of the copolymers decreased with increasing VTES content in the copolymer. This behaviour was attributed to the decrease in the molecular weight of these copolymers during degradation. A similar tendency for TG was also reported for styrene-siloxane block copolymers synthesised with a living anionic initiator [a.l86]. 

The choice of the proper peroxy initiator largely depends on its decomposition rate at the reaction temperature of the polymerization. BPO is the major initiator for bulk polymerization of polystyrene or acrylic ester polymers, where temperatures from 90°C to 220°C are encountered. Dilau-royl, dicaprylyl, diacecyl, and di- err-butyl peroxides are also used. In the case of suspension polymerization of styrene, where temperatures between 85°C and 120 C are applied, the initiators also range in activity from BPO to di-tm-butyl peroxide. In suspension polymerization of vinyl chloride (reaction temperatures of 45-60°C for the homopolymer), thermally very labile peroxides such as diisopropyl peroxydicarbonate and rm-butyl peroxy-pavilate are used. 

AlkyUithium compounds are primarily used as initiators for polymerizations of styrenes and dienes (52). These initiators are too reactive for alkyl methacrylates and vinylpyridines. / -ButyUithium [109-72-8] is used commercially to initiate anionic homopolymerization and copolymerization of butadiene, isoprene, and styrene with linear and branched stmctures. Because of the high degree of association (hexameric), -butyIUthium-initiated polymerizations are often effected at elevated temperatures (>50° C) to increase the rate of initiation relative to propagation and thus to obtain polymers with narrower molecular weight distributions (53). Hydrocarbon solutions of this initiator are quite stable at room temperature for extended periods of time the rate of decomposition per month is 0.06% at 20°C (39). 

Ethylbenzene Hydroperoxide Process. Figure 4 shows the process flow sheet for production of propylene oxide and styrene via the use of ethylbenzene hydroperoxide (EBHP). Liquid-phase oxidation of ethylbenzene with air or oxygen occurs at 206—275 kPa (30—40 psia) and 140—150°C, and 2—2.5 h are required for a 10—15% conversion to the hydroperoxide. Recycle of an inert gas, such as nitrogen, is used to control reactor temperature. Impurities ia the ethylbenzene, such as water, are controlled to minimize decomposition of the hydroperoxide product and are sometimes added to enhance product formation. Selectivity to by-products include 8—10% acetophenone, 5—7% 1-phenylethanol, and <1% organic acids. EBHP is concentrated to 30—35% by distillation. The overhead ethylbenzene is recycled back to the oxidation reactor (170—172). 

Decomposition to styrene and carbon dioxide has been observed upon heating the acid to temperatures in excess of 150°C. The decarboxylation process can be accelerated with the addition of a bicycHc amine base (9). 

A second crystallization from dichloromethane-pentane is sometimes necessary to achieve material having this melting point. Styrene glycol dimesylate must be stored in a refrigerator, since slow decomposition takes place at room temperature. 

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