Atactic polystyrene properties

The properties of styrenic block copolymers are dependent on many factors besides the polymerization process. The styrene end block is typically atactic. Atactic polystyrene has a molecular weight between entanglements (Me) of about 18,000 g/mol. The typical end block molecular weight of styrenic block copolymers is less than Mg. Thus the softening point of these polymers is less than that of pure polystyrene. In fact many of the raw materials in hot melts are in the oligomeric region, where properties still depend on molecular weight (see Fig. 1). 

We analyzed the embedded particles with differential scanning calorimetry to identify the property of polystyrene. As shown in Fig, 1, fhe embedded particles show a small peak around 100 °C, which is typical in atactic polystyrene [7]. It is desirable that embedding polymer has a similar melting tempeiature as the final polymer (polyethylene) because a big difference in the melting temperatures between the two polymers may cause a gel problem and poor mechanical properties. 

This section deals with atactic polystyrene homopolymer, and high-impact polystyrene. The properties of SMA are included in Table 4.36 and are not otherwise detailed. 

It may be of interest that isotactic polystyrene formed by styrene polymerisation with Ziegler Natta catalysts [13] did not appear to be a polymer that could exhibit significantly better usable properties compared with atactic polystyrene produced in free radical styrene polymerisation processes. 

Morphology, Viscoelastic Properties, and Stress-Strain Behavior of Blends of Polycarbonate of Bisphenol-A (PC) and Atactic Polystyrene (PST)... 

Li et al. [44] found that the addition of the zinc salt of sulfonated atactic polystyrene to sPS in amounts lower than 10wt% decreases both the crystallization rate and the crystallite size and perfection of sPS. On the other hand, above this content, only minor influences on the properties of sPS are observed. The authors concluded that in the latter case interpolymer association of the ionic groups causes greater liquid-liquid separation, so supporting the hypothesis of substantial incompatibility between such polymers. 

Before BASF investigated this product, Quirk and Hsieh [1], Yuki and coworkers [2,3] and Fischer [4] carried out investigations with this monomer. The first two used the anionic polymerization mechanism and Fischer tried to copolymerize this monomer using free radical polymerization. In the latter case the yields were very low. The use of S/DPE blocks in thermoplastic elastomers [5] has also been briefly described. Some of the work carried out at BASF has been published in a recent review article [6], Owing to the enhanced thermal properties of this copolymer in comparison with atactic polystyrene - the glass transition temperature increases up to 180 °C, depending... 

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... 

However, as we shall see, the results in the asymptotic domain should reveal a different property of polymer chains. Criticism came from Yoon and Flory,10 disturbed by the absence of local chemical structure effects. These authors modelled the atactic polystyrene chain of N beads as realistically as they could (see Chapter 1). Thus, Yoon and Flory accounted for interactions between nearest neighbour monomers in particular, these interactions are responsible for the fact that the three orientations of a bond j, relative to bonds j — 1,/ — 2, are weighted differently in relation to the stereochemical composition. Moreover, we have seen in Chapter 1 that, for atactic polystyrene, pairs of successive benzene rings are slightly more frequent in syndiotactic than in isotactic positions. 

THE EFFECT OF ORIENTATION OF SOME THERMALLY DEPENDENT PROPERTIES OF ATACTIC POLYSTYRENE. PH.D. THESIS. BRITTON P N JR STEVENS INSTITUTE OF TECHNOLOGY HOBOKEN NEW JERSEY UNIV MICROFILMS PUBL... 

ATACTIC POLYSTYRENE. THERMODYNAMIC PROPERTIES OF POLYMERS-PART 7. 

The mutual repulsion between substituents may cause some displacement. As a result, the plane of symmetry is bent in the form of a helix. This occurs also in biopolymers (double-helix of deoxyribonucleic acid (DNA)). Different stereoisomers have different mechanical and thermal properties. For example, atactic polystyrene is an amorphous polymer whereas syndiotactic polystyrene is a crystalline substance. The chemical design of macromolecules determines their properties as extent of crystallization, melting point, softening (glass transition temperature), and chain flexibility which in turn strongly influence mechanical properties of the materials. 

Fully amorphous polyethylene is rather difficult to make because of its fast crystallization. By superfast quenching it was, however, possible to make small amounts of polyethylene glass of phase area 11 [6]. Glassy polymers are much more easily available for macromolecules that crystallize slowly, such as poly(ethylene terephthalate) and poly(oxy-l, 4-phenyleneoxy-1,4-phenylenecarboxy-1,4-phenylene) or macromolecules that have structural irregularities which prohibit crystallization completely, such as atactic polystyrene andpoly(methyl methacrylate). More details about the special properties of the transition 11— are discussed in Sect. 6.3. 

The position of the side group R has a very important influence on the polymer properties. Since crystallinity depends on the regularity of the structure, isotactic polymers may be very crystalline whereas atactic polymers are non-crystalline. Thus, atactic polystyrene and polypropylene are completely amorphous, whereas isotactic polystyrene and polypropylene are partially crystalline. Crystallinity not only affects the mechanical properties of the polymer but also its permeability. 

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