Syndiotactic polystyrene /poly vinyl

S. Cimmino, E. D. Pace, E. Martuscelli, C. Silvestre, D. M. Rice, and F. E. Karasz, Miscibility of syndiotactic polystyrene/poly(vinyl methyl ether) blends. Polymer, Vol. 34, 214-217, 1993. 

Draw a short segment of each polymer (a) isotactic poly(vinyl chloride) (b) syndiotactic polyacrylonitrile (c) atactic polystyrene. 

The differences in reactivities in poly(vinyl alcohol)s between isotactic meso) and syndiotactic (trans acetals [26-28] is another example. In extending this to model compounds, reactions of stereo isomers of pentane-2,4-diol and heptane-1,4,6-triol with formaldehyde take place much faster for the meso than for the dl-diol portions [26-28]. Even more important are the steric effects imposed by restricted rotations. For instance, quatemizations of chloromethylated polyether sulfmies exhibit decreasing rates at high degrees of substitution. This can be attributed to restricted rotations of the polymeric chains, because this phenomenon is not observed with more flexible chloromethylated polystyrene under identical conditions [23, 24]. 

It is well-known that many polymers, synthetic and natural, form physical, thermoreversible aggregates in dilute solutions, whereas in moderately concentrated solutions gels can be formed. Examples are poly(vinyl chloride), polyacrylonitrile, poly(vinyl alcohol), atactic polystyrene, mixtures of syndiotactic and isotactic poly(methyl methacrylates), liquid crystalline polymers, gelatin, agarose, carrageenans etc. 

Until 2003, Chen s [28], Qu s [29-31], and Hu s [32] groups independently reported nanocomposites with polymeric matrices for the first time the. In Hsueh and Chen s work, exfoUated polyimide/LDH was prepared by in situ polymerization of a mixture of aminobenzoate-modified Mg-Al LDH and polyamic acid (polyimide precursor) in N,N-dimethylactamide [28]. In other work, Chen and Qu successfully synthesized exfoliated polyethylene-g-maleic anhydride (PE-g-MA)/LDH nanocomposites by refluxing in a nonpolar xylene solution of PE-g-MA [29,30]. Then, Li et al. prepared polyfmethyl methacrylate) (PMMA)/MgAl LDH by exfoliation/adsorption with acetone as cosolvent [32]. Since then, polymer/LDH nanocomposites have attracted extensive interest. The wide variety of polymers used for nanocomposite preparation include polyethylene (PE) [29, 30, 33 9], polystyrene (PS) [48, 50-58], poly(propylene carbonate) [59], poly(3-hydroxybutyrate) [60-62], poly(vinyl chloride) [63], syndiotactic polystyrene [64], polyurethane [65], poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] [66], polypropylene (PP) [48, 67-70], nylon 6 [9,71,72], ethylene vinyl acetate copolymer (EVA) [73-77], poly(L-lactide) [78], poly(ethylene terephthalate) [79, 80], poly(caprolactone) [81], poly(p-dioxanone) [82], poly(vinyl alcohol) [83], PMMA [32,47, 48, 57, 84-93], poly(2-hydroxyethyl methacrylate) [94], poly(styrene-co-methyl methacrylate) [95], polyimide [28], and epoxy [96-98]. These nanocomposites often exhibit enhanced mechanical, thermal, optical, and electrical properties and flame retardancy. Among them, the thermal properties and flame retardancy are the most interesting and will be discussed in the following sections. 

Table 17.4 shows the well-known fiber polymers, and a few which seem unsuitable as fiber material, namely polystyrene and poly(vinyl chloride). The latter finds limited fiber application, but a special syndiotactic grade with some crystallinity is then used. Polypropylene has a fairly low melting point but is nevertheless a large fiber product, because the material is cheap and versatile. Polyethylene is even lower melting and is used only as a superstrong fiber at ambient temperature. 

There are other important commercial thermoplastics beyond polyolefins. There are the various vinyl polymers. Both atactic polystyrene and syndiotactic polystyrene have a Tg of 100 C. Syndiotactic polystyrene has a crystalline melting point of 270 °C. Poly(vinyl chloride) has both atactic (-85%) and syndiotactic (-15%) sections of chains depending upon polymerization conditions. Its Tg is 65 C and is higher than 200 °C. In addition to vinyl polymers, there is poly(methyl methacrylate), which is atactic and has Tg about 110 °C. 

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