<P> Isotactic polypropylene can exist in various crystalline modifications which differ by the molecular arrangement of the polymer chains . The crystalline modifications are categorized into the α -, β - and γ - modification as well as mesomorphic (smectic) forms . The α - modification is predominant in iPP . Such crystals are built from lamellae in the form of folded chains . A characteristic anomaly is that the lamellae are arranged in the so - called "cross-hatched" structure . The melting point of α - crystalline regions is given as 185 to 220 ° C, the density as 0.936 to 0.946 g cm . The β - modification is in comparison somewhat less ordered, as a result of which it forms faster and has a lower melting point of 170 to 200 ° C. The formation of the β - modification can be promoted by nucleating agents, suitable temperatures and shear stress . The γ - modification is hardly formed under the conditions used in industry and is poorly understood . The mesomorphic modification, however, occurs often in industrial processing, since the plastic is usually cooled quickly . The degree of order of the mesomorphic phase ranges between the crystalline and the amorphous phase, its density is with 0.916 g cm comparatively . The mesomorphic phase is considered as cause for the transparency in rapidly cooled films (due to low order and small crystallites). </P> <P> Syndiotactic polypropylene was discovered much later than isotactic PP and could only be prepared by using metallocene catalysts . Syndiotactic PP has a lower melting point, with 161 to 186 ° C, depending on the degree of tacticity . </P> <P> Atactic polypropylene is amorphous and has therefore no crystal structure . Due to its lack of crystallinity, it is readily soluble even at moderate temperatures, which allows to separate it as by - product from isotactic polypropylene by extraction . However, the aPP obtained this way is not completely amorphous but can still contain 15% crystalline parts . Atactic polypropylene can also be produced selectively using metallocene catalysts, atactic polypropyleneproduced this way has a considerably higher molecular weight . </P> <P> 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 bitumen . </P>

What are the properties of isotactic polypropylene at 30 ∘c