Halogenated polystyrenes

A number of halogenated polystyrenes are used in practice, either for specific applications as thermoplastics or in copolymers. Among the halogenated polystyrenes, the most common are the poly(chlorostyrenes). Poly(4-chlorostyrene) can be obtained in isotactic form (CAS 24991-47-7) or in syndiotactic form (CAS 62319-29-3) and is represented by the formula [-CH2CH(p-C6H4CI)-]n. Other poly(chlorostyrenes) include poly(2-chlorostyrene) with CAS 26125-41-7, and poly(3-chlorostyrene) with CAS 26100-04-9, CAS 116002-24-5 (isotactic), and CAS 107830-48-8 (syndiotactic). 

A different chlorinated polystyrene is indicated in literature [1] as poly(chlorostyrene), CAS 9022-52-0. Halogenated polystyrenes also include poly(p-chloro-a-methylstyrene), poly[p-(2,4-dichlorobenzyl)-styrene], etc. Thermal degradation, not necessarily by flash pyrolysis, has been studied and reported for a number of halogenated polystyrenes [2, 3], and poly(a-methylstyrenes). Some of these reports are summarized in Table 6.4.1 [1]. 

Polymers with saturated carbon chain backbone 

The radical formed in the reaction will generate the monomer by p-scissions  

The p-scission is favored compared to other scissions by the strong effect of p-chlorobenzene group. Other reactions likely to occur during the pyrolysis are due to hydrogen transfer reactions followed again by p-scissions as shown in the following schemes  

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Polymers with saturated carbon chain backbone include polyolefins, polystyrenes, halogenated polyolefins, halogenated polystyrenes, polyvinyls substituted with various groups such as -OH, -OR, -0(0)C-R, -C(0)0-R, -C(0)-R, -C5H4N, etc. In this class also are included polyacrylates, polymethacrylates, polymers with ketone groups in the backbone, as well as other polymers with saturated carbon chain backbone. The polymers with a saturated carbon chain backbone form the most important and common class of polymers. 

Table 6.4.1. Summary of reports regarding the thermal decomposition of various halogenated polystyrenes.

Polystyrene can be made into a veiy-low-density foam which has found use in electrical, sound, and heat-insulation applications. The inflammability is a definite setback for such applications, and experiments are under way to use halogenated polystyrene for such purposes or to incoiporate ifiert and fire-resistant or fire-retarding ingredients. Polystyrene foam can also be produced from expandable beads which contain an expansion... 

Scheme 6.11 Mechanism of radiation-induced cross-linking of halogenated polystyrene derivative.

A nickel complex fixed to polystyrene by means of Ni-C through oxidative addition of halogenated polystyrene to Ni(0)-tetra(triphenylphos-phine) [261]. The catalyst was synthesized to an approximate degree of polymerization of 1100 in toluene solution at room temperature in the presence of nitrogen. It was found that the obtained complex was highly active during C2H4-dimerization reactions conducted in the presence of catalyst-toluene suspensions as well as in the gas-solid phase. It was shown that the solvent affects catalyst selectivity. Selectivity was lower in the gas-solid system, and considerable quantities of hexenes and octenes were formed. 

Phosphorus, the most important ligand element, can be introduced via many routes. For example, (1) halogenated polystyrene is reacted with butyllithium followed by reaction with ClPPh2 (Evans et al., 1974) and (2) the resin is treated with PPh2Li (Nonaka et al., 1974) to produce the same functionalized polymer. The supports thus produced have been used to immobilize carbonyls such as Ni(CO)4 (Nonaka et al., 1974), (PPh3)3RhH(CO) (Pittman and Felis, 1974), and Rh6(CO)ig (Collman et al., 1972). 

Chemical Modification of Halogenated Polystyrenes Using Rieke Calcium or Rieke Copper... 

The reaction of halogenated polystyrene with tetrakisftriphenylphos-phine) nickel gives a supported complex. This system, when associated with boron trifluoride etherate, is a catalyst for the dimerization of ethylene. Indeed, at 0°C and atmospheric pressure of ethylene, a suspension in toluene of the polymer-nickel complex, to which has been added BFj-EtjO (BFj/Ni = 20/1 mole), absorbs ethylene selectively, giving butene 1231). 

More detailed studies on the influence of the repartition of the nickel on the polystyrene have been performed [232j. It has been found that the initial rate of dimerization of ethylene is almost independent of the nickel concentration in the polystyryl complex, as long as the same total amount of nickel is utilized in the reaction. This may be understood if the nickel sites are all equivalent, and equally accessible, either to BF3 or to ethylene there is no additional interaction between BF3 and the halogenated polystyrene. 

One of more often observed transformations is reduction or oxidation of transition metals. Metal oxidation on reaction with a polymer will be discussed first. One of the typical processes is oxidative addition of metal(O) to a macroligand. For example, tezrato(triphenylphosphine)metal(0), M(PPh3)4 (M = Pt, Pd, Ni), is oxidized by halogenated polystyrene (PS) to a bivalent state as die functional groups on the polymer become metal ligands (scheme 6). ... 

It is interesting to note that the conversion of electronic to vibrational energy results in scission of the more stable pendant C—H bond rather than the main chain C—C bond. The observed results are consistent with this process because of the glassy nature of the polymer at room temperature. Almost certainly the main-chain bonds break and make . This proposal is supported by the observation that p-halogenated polystyrenes yield the halogen hydride, hydrogen and a cross-linked polymer on photolysis. 

Table 17. Inorganic Synergists—Halogen System for Polystyrene and ABS...

In polymers such as polystyrene that do not readily undergo charring, phosphoms-based flame retardants tend to be less effective, and such polymers are often flame retarded by antimony—halogen combinations (see Styrene). However, even in such noncharring polymers, phosphoms additives exhibit some activity that suggests at least one other mode of action. Phosphoms compounds may produce a barrier layer of polyphosphoric acid on the burning polymer (4,5). Phosphoms-based flame retardants are more effective in styrenic polymers blended with a char-forming polymer such as polyphenylene oxide or polycarbonate. 

Flame Retardants. Flame retardants are added to nylon to eliminate burning drips and to obtain short self-extinguishing times. Halogenated organics, together with catalysts such as antimony trioxide, are commonly used to give free-radical suppression in the vapor phase, thus inhibiting the combustion process. Some common additives are decabromodiphenyl oxide, brominated polystyrene, and chlorinated... 

DMPPO—polystyrene blends, because of the inherent flame resistance of the DMPPO component (oxygen index ca 29.5), can be made flame retardant without the use of halogenated additives that tend to lower impact strength and melt stabiUty in other polymers. Approximately one-half of total Noryl sales volume is in flame-retarded grades, ie, VO or VI in a 1.6-mm section (UL-94). 

Deposition Precursors. Diamond has been deposited from a large variety of precursors which include, besides methane, aliphatic and aromatic hydrocarbons, alcohols, ketones, and solid polymers such as polyethylene, polypropylene, and polystyrene, and halogens. 

The combination of radiation-sensitive and radiation-resistant groups is interesting. Halogen substitution of the phenyl group in polystyrene results in high radiation sensitivity with inter-molecular crosslinking. 

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