Polystyrene stability

Figure 9. Impact polystyrene. Impact retention as a function of 45° south direct Florida exposure for impact polystyrene stabilized with 0.50% of various light stabilizers) Izod impact measurement.

Figure 10. Impact polystyrene (12% Aliphatic flame retardant, 4% antimony oxide). Color (Hunter L-b) as a function of Carbon Arc Fadeometer exposure for flame retardant impact polystyrene stabilized with 0.50% of...

Some results obtained by Doroszkowski and Lamboume for the distance dependence of the steric repulsion for polystyrene stabilizing moieties in toluene are shown in Fig. 13.1. Also shown are the predictions of the theory of Hesselink et al. (1971) including the individual osmotic and elastic components. These were obtained by a numerical Derjaguin-like integration procedure that transformed flat plate potentials into potentials for spheres. It... 

Fig. I3.I. The distance dependence of the steric interaction free energy for polystyrene stabilized latex particles in toluene 1, experimental results 2, theoretical mixing term 3, theoretical elastic term 4, total theoretical terms (after Doroszkowski and Lamboume, 1973).

Doroszkowski and Lamboume (1971) also performed similar experiments on poly(methyl methacrylate) particles stabilized by poly(12-hydroxystearic acid) of low molecular weight (1600). These were spread at the -heptane/water interface. The results for this system are less amenable to comparison with theory than those described above for polystyrene stabilized latices because of the lower molecular weight of the stabilizing chains and their highly-branched character. 

Ohtaka et al. [69] have introduced a linear polystyrene stabilized PdO nanoparticles (PS-PdO NPs) as an eco-friendly heterogeneous catalyst which was found to be highly efficient for Sonogashira reaction in H2O. The Sono-gashira cross-coupling between o-halo phenol and terminal alkyne produced benzofuran in the presence of PS-PdO NPs in presence of EtsN in water at 80°C for 20h (Scheme 48). 

The thermal decomposition of Pd(OAc)2 in the presence of linear polystyrene in aqueous medium afforded the linear PS-PdO NPs. The mixture of Pd(OAc)2 and linear polystyrene was added to 1.5mol/L aqueous K2CO3 and the reaction mixture was stirred for Ih at 90 °C. The polystyrene stabilized PdO nanoparticles were separated out from the solution after which the color became black. It has been speculated that the degree of immobilization of palladium is dependent on the molecular weight of polystyrene. The formation of PdO NPs was indicated by spec-trochemical data analysis like XRD, TEM (Scheme 49). 

Carbanions stabilized by phosphorus and acyl substituents have also been frequently used in sophisticated cyclization reactions under mild reaction conditions. Perhaps the most spectacular case is the formation of an ylide from the >S-lactam given below using polymeric Hflnig base (diisopropylaminomethylated polystyrene) for removal of protons. The phosphorus ylide in hot toluene then underwent an intramolecular Wlttig reaction with an acetyl-thio group to yield the extremely acid-sensitive penicillin analogue (a penem I. Ernest, 1979). 

Polystyrene is rigid with excellent dimensional stability, has good chemical resistance to aqueous solutions, and is an extremely clear material. 

Physical Stabilization Process. Cellulai polystyrene [9003-53-6] the outstanding example poly(vinyl chloride) [9002-86-2] copolymers of styrene and acrylonitrile (SAN copolymers [9003-54-7]) and polyethylene [9002-88-4] can be manufactured by this process. 

Physical Stabilization Process. CeUular polystyrene, ceUulose acetate, polyolefins, and poly(vinyl chloride) can be manufactured by this... 

Cross-linked macromolecular gels have been prepared by Eriedel-Crafts cross-linking of polystyrene with a dihaloaromatic compound, or Eriedel-Crafts cross-linking of styrene—chloroalkyl styrene copolymers. These polymers in their sulfonated form have found use as thermal stabilizers, especially for use in drilling fluids (193). Cross-linking polymers with good heat resistance were also prepared by Eriedel-Crafts reaction of diacid haUdes with haloaryl ethers (194). 

Nickel dialkyldithiocarbamates stabili2e vulcani2ates of epichlorhydrinethylene oxide against heat aging (178). Nickel dibutyldithiocarbamate [56377-13-0] is used as an oxidation inhibitor in synthetic elastomers. Nickel chelates of substituted acetylacetonates are flame retardants for epoxy resins (179). Nickel dicycloalkyldithiophosphinates have been proposed as flame-retardant additives for polystyrene (180—182) (see Flame retardants Heat stabilizers). 

Noryl. Noryl engineering thermoplastics are polymer blends formed by melt-blending DMPPO and HIPS or other polymers such as nylon with proprietary stabilizers, flame retardants, impact modifiers, and other additives (69). Because the mbber characteristics that are required for optimum performance in DMPPO—polystyrene blends are not the same as for polystyrene alone, most of the HIPS that is used in DMPPO blends is designed specifically for this use (70). Noryl is produced as sheet and for vacuum forming, but by far the greatest use is in pellets for injection mol ding. 

Specialty Polystyrenes. These include ionomers and PS of specified tacticity, as well as stabilized PS. 

Because of this interaction, PVP has found appHcation in surfactant formulations, where it functions as a steric stabilizer for example to generate uniform particle-size polystyrene emulsions (110—112). In a variety of formulations, a surfactant s abiHty to emulsify is augmented by PVP s abiHty to stabilize coUoids stericaHy and to control rheology. 

When used alone at low temperatures, diaLkyl thiodipropionates are rather weak antioxidants. However, synergistic mixtures with hindered phenols are highly effective at elevated temperatures and are used extensively to stabilize polyolefins, ABS, impact polystyrene (IPS), and other plastics. 

The Q-e Scheme. The magnitude of and T2 can frequentiy be correlated with stmctural effects, such as polar and resonance factors. For example, in the free-radical polymerization of vinyl acetate with styrene, both styrene and vinyl acetate radicals preferentially add styrene because of the formation of the resonance stabilized polystyrene radical. 

PL can be used as a sensitive probe of oxidative photodegradation in polymers. After exposure to UV irradiation, materials such as polystyrene, polyethylene, polypropylene, and PTFE exhibit PL emission characteristic of oxidation products in these hosts. The effectiveness of stabilizer additives can be monitored by their effect on PL efficiency. 

A high-impact polystyrene (polystyrene SBR blend) may have seven times the impact strength of ordinary polystyrene, but about half the tensile strength, a lower hardness and a softening point some 15°C lower. Because of the rubber content there may be a reduction in light and heat stability and stabilisers are normally incorporated. 

In the 1990s this approach became more common in order to ensure sufficient compressive strength with the trend to lower bulk densities. Furthermore the proportion of SAN to polyol has been increased to about 40%. This may lead to serious stability problems and care must be taken to control the size and distribution of the particles and prevent agglomeration. Polymer polyols using polystyrene as the polymer component have recently become available (Postech-Shell) and are claimed to exhibit good stability, low viscosity and less discolouration as well as providing price advantages. 

---