Search results
Results from the WOW.Com Content Network
[citation needed] The two materials have very different properties because the irregular structure of the atactic version makes it impossible for the polymer chains to stack in a regular fashion: whereas syndiotactic PS is a semicrystalline material, the more common atactic version cannot crystallize and forms a glass instead.
Therefore, the polypropylene product generally did not require additional purification steps to remove the atactic or low crystalline fraction. This meant that the APP supply from polypropylene plants using standard first- and early second-generation Z-N catalysts decreased as commercial plants adopted the new catalysts.
Atactic polypropylene has lower density, melting point and softening temperature than the crystalline types and is tacky and rubber-like at room temperature. It is a colorless, cloudy material and can be used between −15 and +120 °C. Atactic polypropylene is used as a sealant, as an insulating material for automobiles and as an additive to ...
For example, atactic polypropylene is usually amorphous and transparent while syndiotactic polypropylene, which has crystallinity ~50%, is opaque. [30] Crystallinity also affects dyeing of polymers: crystalline polymers are more difficult to stain than amorphous ones because the dye molecules penetrate through amorphous regions with greater ease.
Radical polymerization is a key synthesis route for obtaining a wide variety of different polymers and materials composites. The relatively non-specific nature of radical chemical interactions makes this one of the most versatile forms of polymerization available and allows facile reactions of polymeric radical chain ends and other chemicals or ...
A polymer that lacks any regular arrangement in the position of its alkyl substituents (R) is called atactic. Both isotactic and syndiotactic polypropylene are crystalline, whereas atactic polypropylene, which can also be prepared with special Ziegler–Natta catalysts, is amorphous.
Polyamorphism is also an important area in pharmaceutical science. The amorphous form of a drug typically has much better aqueous solubility (compared to the analogous crystalline form) but the actual local structure in an amorphous pharmaceutical can be different, depending on the method used to form the amorphous phase.
Polymer morphology is a microscale property that is largely dictated by the amorphous or crystalline portions of the polymer chains and their influence on each other. Microscopy techniques are especially useful in determining these microscale properties, as the domains created by the polymer morphology are large enough to be viewed using modern ...