| Abstract
| - A structural characterization of copolymers of syndiotactic polypropylene containing ethylenecomonomeric units (PPET) in a wide range of concentrations (0.4−60 mol %) is presented. The copolymersamples are crystalline up to an ethylene content of 18−20 mol %. Ethylene units are partially includedin the crystals of both as-prepared and melt-crystallized samples. As-prepared PPET samples basicallycrystallize in conformationally disordered modifications of form II of syndiotactic polypropylene (sPP)containing kink bands. The amount of kink bands defects, represented mainly by T6G2 sequences, increaseswith the ethylene content. These modifications are metastable and transform by crystallization from themelt into the most stable form I or form II, depending on the ethylene concentration. PPET sampleshaving low ethylene content (up to 6−7 mol %) crystallize from the melt into the antichiral form I, eventhough disordered modifications of form I are always obtained. For higher ethylene contents, mixtures ofcrystals of forms I and II are obtained by crystallization from the melt. The fraction of form II increaseswith increasing the crystallization temperature and the ethylene content. The form II obtained by meltcrystallizations does not present kink-band disorder, all chains being in the more stable (T2G2)n helicalconformation. This is the first example of crystallization of the isochiral form II of sPP from the melt atatmospheric pressure.
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