Poly polystyrene system compatibility

Mutually compatible polymers are relatively rare [84,85], A typical phase diagram of two incompatible polymers and a common solvent is that determined by Kern for the polystyrene - poly(p - chlorostyrene) - benzene system shown in the Fig. 1.11 [86],... 

On the other hand, some mechanically compatible blends as well as some dispersed two-phase systems have made respectable inroads into the commercial scene. Many of these are blends of low-impact resins with high-impact elastomeric polymers examples are polystyrene/rubber, poly (styrene-co-acrylonitrile) /rubber, poly (methyl methacrylate) /rubber, poly (ethylene propylene)/propylene rubber, and bis-A polycarbonate/ ABS as well as blends of polyvinyl chloride with ABS or PMMA or chlorinated polyethylene. 

Addition of AN to a level of 40% (NBR-40) destroys the phase boundaries entirely, resulting in the microheterogeneous system shown in Figure 3.10. The phase domains ( 100 A) shown in Figure 3.10 are clearly smaller than the polymer molecules themselves, yet the material is not totally compatible. Only a few cases are known in which the phase division in blends is so fine such cases include the IPN s discussed in Chapter 8 and the poly(2,6-dimethyl phenylene oxide)/polystyrene blend described in Section 9.7.1. 

Blends of poly(methacrylic acid) or polystyrene with epoxidised linseed oil are prepared in solution by mechanical mixing in dimethyl sulphoxide (DMSO) or tetrahydrofuran (THF) to improve the performance of the individual components. However, blends of poly(methylacrylic acid) are not able to produce compatible systems, although different compositions (15-55 wt%) of polystyrene blends will form miscible blends. The results show an improvement in properties, including biodegradation of the miscible blends, and the systems are comparable with low density polyethylene. 

As the concentration of a normally compatible resin is increased in a rubber-resin blend, a level is reached where two phases appear. Natural rubber blended with a poly (vinyl cyclohexane) resin and styrene-butadiene rubber blended with a polystyrene resin, systems which were compatible at the 50% resin level, appear to have two phases at the 75% resin level. 

Brekner, M,( Cantow, H.J., and Schneider, H,A, (1985) Interactions in compatible polymer systems - 1. Viscoelasticity and ass transition of polystyrene-poly(vinylmethylether) blends, Pdlym. BuU., 14 (1), 17-24. 

Two of the major practical uses of miscible polymer blends or alloys are to obtain a compromise in properties between two polymers, such as in the system polystyrene-poly(2,6-dimethyl-l,4-phenylene oxide), (Noryl), and in polymeric plasticizers, especially for PVC. In a recent discussion of the effect of compatibility on polymer mixtures it was pointed out that properties such as the moduli of a... 

The miscibility of some polymer blends is of considerable technological importance although, fundamentally, the reasons for the miscibility are not completely understood. Polystyrene (PS) and poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) is one such system. 2D correlation studies have been made on a blend of 80% of the former and 20% of the latter by Palmer et al. [31]. The results suggest a different dynamic behaviour for the PS and PPO portions of the blend, depsite their compatibility, with the PS chains responding to the perturbing force faster than those of PPO. Some asynchronous cross peaks develop between the constituents, indicating the possible existence of submolecular level microheterogeneity. 

Although knowledge of the interfacial tension in polymer/polymer systems can provide important information on the interfacial stmcture between polymers and, thus, can help the understanding of polymer compatibility and adhesion, reliable measurements of surface and interfacial tension were not reported until 1965 for surface tension [135,138] and 1969 for interfacial tension [127,154] because of the experimental difficulties involved due to the high polymer viscosities. Chappelar [145] obtained some preliminary values of the interfacial tension between molten polymer pairs using a thread breakup technique. The systems examined included nylon with polystyrene, nylon with polyethylene (PE), and poly(ethylene tere-phthalate) with PE the values are probably only qualitatively significant [174]. 

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