Composition‐properties relationships in propene‐ethene random copolymers obtained with high‐yield Ziegler‐Natta supported catalysts

Abstract

The crystallization and thermal behaviour of crystallizable random propene/ethene copolymers (P-co-E) was systematically investigated. Index of crystallinity and, index of y-form, enthalpy and entropy of fusion, equilibrium melting temperature, spherulite growth rate, and overall kinetic rate constant were determined and correlated with the overall ethene content and with the concentration of specific chemical defects as determined by "C NMR analysis (PEP, EPP, EPE triads). The samples of the copolymers, obtained with very-high-yield Ziegler-Natta catalysts, were characterized by IR, 13C NMR, wide angle X-ray scattering, and differential scanning calorimetry.

Crystallization of Polypropylene and Poly(Ethylene Terephthalate)

“…24, along with our fitting equations to these data. Figures 24a and 24b show that 7^, A/7 f°, and o e all decrease rapidly with increasing m [70], consistent with inclusion of an appreciable fraction of ethylenic repeat units into iPP crystallites. These data can be fitted reasonably well byEqs.…”

“…Avella et al [70] studied the crystallization of propylene-rich random copolymers of propylene with ethylene, provided by Himont, for which the resins were synthesized with a third-generation, high-yield supported catalyst system (a superactive catalyst). They found trends similar to those they had found earlier [63][64][65][66] for copolymers of propylene and 1-butene.…”

Effect of copolymerized ethylene unit on the crystallization behavior of poly(propylene-co-ethylene)s

“…In the reheating curves (Fig. 3(c) and (d)) for each fraction besides the main melting peak, there exists a weak shoulder peak at low temperature side, which, unambiguously, results from the melting of small amount of g-form crystals [19,24,29,32], as mentioned above. It should be pointed out that the fractions eluted at room temperature (25 8C), PPE1-25 and PPE2-25, exhibit elastomer characteristics.…”

“…It should be pointed out that the introduction of ethylene unit in iPP backbone can modify crystallization behavior of iPP, not only crystal morphology but also crystal structure. Early studies indicated that g-form crystals could be formed by short propylene sequences, while the long sequences crystallizaed into a-form crystals [19,24,[26][27][28][29][30][31][32][33]. Thus, the PPE may exhibit complicated crystallization behavior.…”

“…Although investigation of the latter is not as wide as that of the former, recently, more and more attention has been drawn to the studies on the propylene-rich copolymers. Reports on thermal behavior [12][13][14][15], crystal structure [16][17][18][19], morphology [20][21][22][23], crystallization kinetics [13,14,[22][23][24][25] and polymorphism [19,24,[26][27][28][29][30][31][32][33] of propylene-ethylene copolymers (PPE) with minor ethylene contents have been published. However, the relationships between the chain structure and the crystalline morphology of the PPE have not been studied in detail.…”