Thermal stability, poly -polystyrene

Of all the hydrocarbon-based PEMs, this group most likely has the largest variety of different systems. This is probably due to the wealth of prior knowledge of the nonsulfonated analogues that have been developed over the last several decades as well as the general expectation of higher thermal stability, better mechanical properties, and increased oxidative stability over polystyrene-based systems. Within the context of this section, polyarylenes are systems in which an aryl or heteroaryl ring is part of the main chain of the polymer. This section will, therefore, include polymers such as sulfonated poly (ether ether ketone) and sulfonated poly(imides) but will not include systems such as sulfonated polystyrene, which will be covered in Section 3.3.I.3. 

Blends of polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) can be mixed in the melt as both polymers have reasonable thermal stability. There has however been much discussion as to whether the blends are truly one phase. Some techniques suggest homogeneity while others suggest a heterogeneous structure. On balance it appears that the two polymers are in fact thermodynamically miscible in all proportions but completely efficient mixing is difficult to achieve... 

Almost all metal-catalyzed living polymerizations give polymers capped with halogens that are stable after the usual workup. These terminal halogens would be undesirable, because they may lower the polymer s thermal stability. Dehalogenation by tribu-tyltin hydride (EC-15) is of importance in this respect and effectively works for the bromide terminals in polystyrene, PMMA, and poly(MA) in the presence of copper catalysts.277... 

Multiblock copolymers based on poly(a-methylstyrene) also show significantly better oxidative thermal stability than the block copolymers based on polystyrene. Thus, polystyrene-polydimethyldisiloxane multiblock copolymers lose half of their tensile strength after 80 hours with considerable yellowing at 150°C in air, but corresponding materials based on poly( -methylstyrene) show no discoloration or loss in tensile properties under the same conditions. 

As we said earlier, the introduction of aromatic units into the main chain results in polymers with better thermal stability than their aliphatic analogs. One such polymer is poly(phenylene oxide), PPO, which has many attractive properties, including high-impact strength, resistance to attack by mineral and organic acids, and low water absorption. It is used, usually blended with high-impact polystyrene (HIPS), to ease processability in the manufacture of machined parts and business machine enclosures. 

A number of the important thermoplastics are shovra in Table 1.4, together with a few examples of their more important uses, determined by the outstanding properties of each. Thus, polypropylene, poly(phenylene oxide), and TPX have good thermal stability and can be used for items requiring sterilization. The optical qualities of polystyrene and poly(methyl methacrylate) are used in situations where... 

Composite conductive fibers based on poly(3,4-ethylene-diox)d hiophene]-polystyrene sulfonic acid (PEDOT-PSS) solution blended with polyacrylonitrile (PAN] were obtained via wet spinning. The influence of draw ratio on the morphology, structure, thermal degradation, electrical conductivity, and mechanical properties of the resulting fibers was investigated. The results revealed that the PEDOT-PSS/PAN composite conductive fibers crystallization, electrical conductivity and mechanical properties were improved with the increase of draw ratio. The thermal stability of the fibers was almost independent of draw ratio, and only decreased slightty with draw ratio. Besides, when the draw ratio was 6, the conductivity of the PEDOT-PSS/PAN fibers was 5.0 S cm, ten times the conductivity when the draw ratio was 2 (Fig 5.10]. ... 

A strict comparison of thermal stability can only be made when the samples are evaluated imder identical conditions. Figure 19 shows an example of the stability determination of poly(vinyl chloride) (PVC) and polystyrene (PS) and a... 

In a further smdy, it was investigated if sulfonated low-cost ionomers can also be used as acidic cross-linkers for PBI polymers in order to reduce membrane costs. For this purpose, sulfonated polystyrene (S4a, Fig. 4.5) and poly (a-methylstyrene sulfonic acid), (S4b, Fig. 4.5) have been blended with commercial PBIOO (B4, Fuma-Tech) to 70 wt% PBIOO/30 wt% sulfonated polystyrene blend membranes. The membranes were characterized in terms of chemical stability by the immersion in Fenton s Reagent, thermal stability in terms of TGA-FTIR coupling and in terms of proton conductivity after PA doping [58]. Poly(-a-methylstyrene sulfonic acid) was chosen for comparison with sulfonated polystyrene since it is known that the main radical attack target of polystyrene is the tertiary C-H bond [59] which is not present in poly(a-methylstyrene), leading to verified better radical stabilities of poly(-a-methylstyrene), compared to poly(styrene) [60]. In Table 4.4, the results of thermal and FT stability of the blend membranes B3/S4a and B3/ S4b are listed. 

It should be noted extra-coordination processes are also important in controlling the properties of metallopolymers. Thus mechanical parameters and performance of many metal-containing polymers are determined by the ability of the metals to form ionic or coordination crosslinks (i.e., additional interchain interaction), and to exhibit cohesion and adhesion properties. Formally, unit variability in these cases is determined by the presence of metals in the chain with different coordination numbers. The incorporation of cluster-containing Os3-monomers into a polystyrene or poly(acrylonitrile) chain results in a mutual thermal stabilization of both the polymers and the clusters incorporated into the chains. These effects are observed only in cases where the cluster monomers are chemically bound to the polymeric chain. The influence of the chain may be manifested as the transfer of energy from the rotation-vibration degrees of freedom of the cluster to the translational degrees of freedom of the polymer chain segments at elevated temperatures. 

Thermal stability measurements have been carried out on numerous other polymers including polyethylene ethylene vinyl-alcohol copolymer [12], polyaniline [13], ) 3 s-stilbene-N-substituted maleimides [14], cellulose [15-20], polystyrene [14, 16], ethylene-styrene copolymers [21,22], ST-DVB-based ion exchangers [23], vinyl chloride-acrylonitrile copolymers [24], polyethylene terephthalate [25], polyesters such as polyisopropylene carboxylate [26], polyglycollate [27-29], Nylon 6 [30], polypyromellitimides, poly-N-a-naphthylmaleimides [26,31], polybenzo-bis(amino-imino pyrolenes) [32], polyvinyl chloride [33-35], acrylamide-acrylate copolymers and polyacrylic anhydride [36-38], polyamides [39], amine-based polybenzo-oxazines [40], polyester hydrazides [41], poly-a-methyl styrene tricarbonyl chromimn [42], polytetrahydrofuran [43], polyhexylisocyanate [44], polyurethanes [45], ethylene-... 

Noryl, for example, is composed of polystyrene, an inexpensive polymer, and poly(phenylene oxide) or PPO, a relatively expensive polyether. For the most, the properties of Noryl are additive. For example, Noryl has poorer thermal stability than the polyether alone, but is easier to process. Its single glass transition temperature increases with increasing polyether content. In terms of tensile strength, however,... 

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