Abstract
The characteristics of crystallization, melting and spherulitic growth of a random propylene copolymer (PRC) containing small amount of ethylene were studied in the presence of a selective Β-nucleating agent (calcium pimelate). It was established that the products of isothermal and non-isothermal crystallization are very rich in Β-modification but have mixed polymorphic composition. The formation of α-modification may be attributed to Βα-transition on the surface of growing Β-spherulites resulting in αΒ-twin-spherulites. During melting of PRC of Β-modification, the characteristics observed with Β-nucleated propylene homopolymers, namely, a Βα-recrystallization of recooled samples and separated melting of non-recooled samples (i.e. the melting memory effect), as well as a ΒΒ-recrystallization leading to a perfection of the structure within the Β-modification, are also demonstrated. The disturbance of regularity of the polymer chain highly reduces the tendency to Β-crystallization. In contrast to the observations with propylene homopolymers, the growth rate of α-modification (G α) is higher than that of Β-modification (G β) and no critical crossover temperature can be found (T(Βα)=413 K) below whichG α>G β. The experimental results show that a partial disturbance of chain regularity by incorporation of comonomer units considerably reduces the tendency to Β-crystallization.
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This research was supported by the National Scientific Research Fund (OTKA), the author is grateful for it. Thanks are due to Professor Géza Bodor for his help in X-ray diffractometric investigations and to Ms. Tünde Lócska for her prudential technical assistance in the optical experiments.
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Varga, J., Schulek-Tóth, F. Crystallization, melting and spherulitic structure of Β-nucleated random propylene copolymers. Journal of Thermal Analysis 47, 941–955 (1996). https://doi.org/10.1007/BF01979441
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DOI: https://doi.org/10.1007/BF01979441