High-impact polystyrene thermal properties

Polymers derived from polystyrene but having alkyl or aryl groups substituted at the benzene ring were synthesized in an effort to improve some of polystyrene properties such as the impact resistance and obtain qualities similar to those achieved using copolymers with 1,3-butadiene (high impact polystyrene or HIPS). The polymers included In this class are poly(3-methylstyrene), poly(4-methylstyrene) CAS 24936-41-2, poly(4-phenylstyrene) CAS 25232-08-0 [115], as well as poly(2-vinylnaphthalene) CAS 28406-56-6. Some of the reports regarding thermal decomposition of these polymers are summarized in Table 6.2.10. 

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. 

The only effects on the thermal properties seen from the incorporation of a fire retardant additive occurs in the case of high-impact polystyrene (HIPS) where, as shown in Table 8.4, the incorporation of a fire retardant leads to a decease in expansion coefficient and, in the case of the polyesters, where the incorporation of a fire retardant produces a small improvement in heat distortion temperature. 

Saytex CP-2000 is widely used for printed wiring boards laminates made from FR4 epoxies. It is reacted into the epoxy, so that there is no potential for leaching out of the resin. The FR meets the German Dioxin Rule. It is environmentally acceptable, thermally stable at high temperatures and does not disrupt resin properties when soldered. It can be used as an additive in ABS and also as a raw material in brominated epoxy oligomers in ABS and high impact polystyrene (HIPS). 

Interesting research on the dynamic mechanical and thermal properties of fire-retardant high-impact polystyrene (HIPS) is published by Chang and co-workers [19]. HIPS may be produced by the free-radical chain polymerisation of styrene in the presence of an unsaturated elastomer. The authors showed that the melting point of the additive in relation to the processing temperature of the thermoplastics and the compatibility of the additive with the polymer phases are the two important variables governing the interaction of additive with polymer matrix. 

Nanocomposites of syndiotactic polystyrene (sPS) employing MMT-hexadecyltributylphosphonium [40, 41] and high-impact polystyrene (H1PS)/MMT-hexadecyltriphenylphosphonium [42] were prepared by melt-blending and in situ coordination-insertion polymerization. Partially exfoliated or intercalated materials were obtained in all cases, and a decrease of crystallinity of sPS was observed. However, the presence of clay did not have a strong influence on the sPS thermal transitions. Thermal decomposition of the material was slowed and mechanieal properties were improved in the presence of low organoclay content. Intercalated HIPS nanocomposites were obtained, with improved thermal and flame retardant properties compared to pure HIPS (Figure 3.8). 

Mural and co-workers [57] also optimised the mechanical properties of an rPP and recycled high impact polystyrene (rHIPS) blend at a composition of 70/30 wt%. Consequently, this composition was mixed with a styrene-ethylene-butylene-styrene (SEES) block copolymer triblock copolymer and Cloisite 20A OMMT. Using X-ray diffraction, the samples containing 3 wt% of nanoclay were found to lack the characteristic nanoclay peak, which indicated the mixed intercalated and exfoliated clay layers where the intercalated layers were further pushed toward the interphase [76]. The incorporation of a compatibiliser and nanoclay also improved the thermal stability of the PP/HIPS blend. SEES and nanoclay performed as an interfacial compatibiliser, which led to the reduction in particle size of rHIPS and the promotion of interfacial adhesion. 

The most important commercial polymer is a blend of poly[oxy-(2,6-dimethyl-phenylene)] with high-impact polystyrene (HIPS). The corresponding material exhibits variable characteristics, depending on the PS content. It is a widely used technical polymer in mechanical engineering. Indeed, it exhibits a good impact resistance at very low temperatures in addition to its good thermal and mechanical properties. Its marked electrical insulating character even in wet atmospheres finds applications in electric and electronic industries. 

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