Atactic polystyrene brittleness

At room temperature, atactic polystyrene is well below its glass transition temperature of approximately 100 °C. In this state, it is an amorphous glassy material that is brittle, stiff, and transparent. Due to its relatively low glass transition temperature, low heat capacity, and lack of crystallites we can readily raise its temperature until it softens. In its molten state, it is quite thermally stable so we can mold it into useful items by most of the standard conversion processes. It is particularly well suited to thermoforming due to its high melt viscosity. As it has no significant polarity, it is a good electrical insulator. 

Atactic polystyrene (aPS) is clear, transparent and easily fabricated, and has reasonable mechanical and thermal properties but is slightly brittle and softens near 100 °C. It is readily attacked by a large variety of solvents, including dry-cleaning agents. Its stability to outdoor weathering is poor it turns yellow and... 

Polystyrene is a linear polymer that, in principle, can be produced in isotactic, syndiotactic, and atactic forms. The commercial product or general-purpose polystyrene is atactic and as such amorphous isotactic polystyrene is more brittle and more difficult to process than atactic polystyrene. It is therefore not of commercial interest. 

A material that solidifies from the molten state without crystallization, a supercooled liquid whose shear viscosity is t > 10 Pas, a liquid whose rigidity is great enough to be put to use, or a glassy state of matter. A typical glassy material is hard and brittle (tensile modulus E 70 GPa, tensile strength a 0.5 GPa). Typical polymeric glasses are atactic polystyrene, atactic polymethylmethacrylate, polycarbonate, etc. 

The Raman spectrum of PS shows a couple of distinctive doublets at 1603 and 1584 cm and at 1033 and 1002 cm , both ring-mode vibrations, and both characteristic of a monosubstituted aromatic compound. The Raman band at 622 cm is also indicative of the substituted benzene ring. In addition, there are a few IR absorption peaks due to functional groups such as terminal vinyl group at 907 and 980 cm (refer to 910 and 990 cm peaks of PE) and the irons C=C double bond at 967 cm" resulting from termination reactions. Note also that these bands can also be assigned to trace amounts of butadiene that are sometimes added to polystyrene when it is used for making thin films. This addition adds some flexibility and reduces the brittle nature of the polystyrene film. Atactic polystyrene has bands related to its atactic nature at 1370, 1328, 1306, 1070, and 943 cm and the isotactic form exhibits bands at [62] 1364, 1314, 1297 cm and a doublet at 1075 and 1056 cm (see Fig. 32). As isotactic polystyrene crystallizes, the doublet is seen to shift to 1080 and 1048 cm, and a new band appears at 985 cm The crystallinity may be determined from the intensity of the 985 cm band, and the ratio 566/ 543 is used to evaluate the content of isotactic sequence. For refer-... 

Amorphous polymers of commercial importance include polymers which are glassy or rubbery at room temperature. Many amorphous thermoplastics, such as atactic polystyrene and poly (methyl methacrylate), form brittle glasses when cooled from the melt. The glass transition temperature, Tg or glass-rubber transition, is the temperature above which the polymer is rubbery and can be elongated and below which the polymer behaves as a glass. Thermal analysis of amorphous polymers shows only a glass transition temperature whereas crystalline poly-... 

As polystyrene obtained by free radical polymerisation technique is atactic it is therefore non-crystalline. The isotactic polystyrene is obtained by the use of Ziegler-Natta catalysts and n-butyl lithium. Isotactic polystyrene is having a high crystalline Melting point of 250°C. It is transparent. It is more brittle than the atactic polymer. 

Polystyrene. Polystyrene [9003-53-6] is a thermoplastic prepared by the polymerization of styrene, primarily the suspension or bulk processes. Polystyrene is a linear polymer that is atactic, amorphous, inert to acids and alkalies, but attacked by aromatic solvents and chlorinated hydrocarbons such as dry cleaning fluids. It is dear but yellows and crazes on outdoor exposure when attacked by uv light. It is brittle and does not accept plasticizers, though rubber can be compounded with it to raise the impact strength, ie, high impact polystyrene (HIPS). Its principal use in building products is as a foamed plastic (see Foamed plastics). The foams are used for interior trim, door and window frames, cabinetry, and, in the low density expanded form, for insulation (see Styrene plastics). 

PS polystyrene, oldest synthetic polymer, atactic, amorphous, clear and brittle. 

Polystyrene (PS) in its atactic and syndiotactic forms is a brittle thermoplastic, even in an orientated state [4]. To improve the toughness of aPS, impact modification has been practised for a long time, either by polymerizing the styrene in the presence of a polybutadiene rubber leading to high-impact polystyrene, commonly called HIPS, or by blending the polystyrene with multi-block copolymers, mainly of the styrene-butadiene-styrene (S-B-S) type. 

Polystyrene (PS) as normally prepared is essentially linear and atactic. Isotactic polymers can be made but this is not of commercial interest because of increased brittleness and more difficult processing than the atactic product. The major application of polystyrene is in packaging. Specific additives are incorporated to achieve product characteristics that depend on the end usage. 

Polystyrene produced by free radical polymerization techniques is atactic and therefore non-crystalline. However, isotactic polystyrene has been prepared by the use of Ziegler-Natta catalysts and n-butyllithium. Isotactic polystyrene has a high crystalline melting point of 230°C, which makes it a difficult material to process also it is less transparent and more brittle than the atactic polymer. For these reasons isotactic polystyrene has not achieved commercial importance. 

Polystyrene (PS) is prepared by the polymerization of styrene (CeHs—CH=CH2), also known as vinylbenzene. Commercial PS is mostly of the atactic variety and is therefore amorphous. The polymer, on decomposition, unzips and forms the monomer with some benzene and toluene. Its major defects are poor stability to weather exposure, turning yellow and crazing in sunlight. In spite of these drawbacks and its brittleness it has found wide use as molded containers, Uds, bottles, electronic cabinets. As a foamed plastic it is used in packaging and insulation. The thermal conductivity of the expanded PS foam is about 0.03 Wm K The foam can absorb aromatic hydrocarbons usually found in the exhaust of automobiles and buses, causing the foam to disintegrate after long periods of normal exposure to a polluted environment. 

Polystyrene is an important commercial thermoplastic that has been described by Priddy [121]. Its entanglement molecular weight is aroimd 18,000 and for both structure-rheology studies and commercial applications, molecular weights much higher than this are of primary interest. Nearly all commercial polystyrene is atactic and is thus a transparent glass at temperatures below its Tg, which is 100 °C. New catalyst systems are able to produce isotactic and syndiotactic versions, but these have not found practical applications to date due to their brittleness. 

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