Crystallization kinetics of metallocene type polypropylenes

Abstract

The crystallization kinetics from the melt of metallocene type isotactic poly(propylenes) having the same chain defect concentration and molecular weights ranging from 68480 to 288430 have been studied by differential scanning calorimetry. The crystallization rates and the variation of the rates with crystallization temperature follow a pattern that is basically independent of molecular weight. This result contrasts with the molecular weight dependence on the crystallization rate observed in linear polyethylene, random ethylene copolymers as well as other semierystalline systems.Most significant is the fact that the metalloeene poly(propylenes) show apparently significantly higher o 9 products than do the Ziegler type fractions of matched molecular weight and defect eoneentration. This difference can be interpreted as the metallocene type crystallites having higher effect on surface interfaeial free energies than the Ziegler type, or can result from the two different chain types having different sequence propagation probabilities.

Crystallization behavior of polyethylene/polystyrene AmBnmiktoarm star copolymers

“…The reason being that the heat evolved per unit time was too small to be detected by the calorimeter in isothermal mode. Therefore, we used a DSC technique employed previously by us with block copolymer microphases termed “isothermal step crystallization.” A similar technique has also been used before by Galante et al . The procedure consisted of the following: (i) erasure of crystalline history by heating the sample to 150°C for 3 min; (ii) cooling at a controlled rate of 60°C/min down to T c ; (iii) holding the sample at T c for a time t c , which was later increased in the subsequent steps; (iv) heating at 20°C/min from T c to 150°C—the heat of fusion calculated from this final DSC heating scan should correspond to the crystallization enthalpy of the crystals formed in step “iii” at T c for the specified crystallization time—(v) steps “i”–“iv” were repeated, employing the same T c in step “ii” but increasing t c .…”

Classification of homogeneous copolymers of propylene and 1‐octene based on comonomer content

“…Crystallization of such segments results in well‐ordered crystals and thick lamellae, giving znPP a high melting temperature 17. In contrast, mPP has narrower molecular weight distribution and more homogeneous distribution of chain defects that are excluded from the crystal 16, 18, 19. Shorter crystallizable chain segments results in more defective crystals and a lower peak melting temperature.…”

Review on modification strategies of polyethylene/polypropylene immiscible thermoplastic polymer blends for enhancing their mechanical behavior

“…ZN-derived POEs have high heterogeneity, due to a high number of stereo defects and unwanted side reactions, and a broad molecular weight distribution, leading to very different overall performances, also difficult to control. 17 Consequently, this limits their potential of being used for a wide range of industrial applications. Regarding durable long-term applications, they are used for plastic pipes, wires, and cable coatings, while in terms of consumable short-term applications, they are utilized for garbage bags, packaging, and paper coating.…”