Change in fine structures of isotactic polpropylene during isothermal crystallization

Abstract

The objects of this study were to examine the change of the fine structure in isotactic polypropylene during isothermal crystallization and to determine whether the theory of molecular weight fractionation induced by crystallization or the lamellae thickening, due t o longitudinal translation or sliding diffusion of polymer chains in a crystal state (sliding diffusion theory) is important in the crystallization process. As crystallization proceeds, low melting crystals are produced, irrespective of molecular weight and molecular weight distribution. For high molecular weight polymers, the peak of the thermogram shifts t o higher temperatures, and the high melting components are produced mainly by the sliding diffusion mechanism. If the difference between the molecular weights of both components in a polymer blend is not too great, a peak is found in the DSC thermogram of such a crystallized blend which occurs roughly midway between those of each separately component crystallized under the same conditions as the blend. If the molecular weights of the two components differ greatly the DSC thermograms of the blend show that each component tends to crystallize separately. The experimental evidences, obtained by KAWAI, HOSOI, and KAMIDE in the case of linear polyethylene, against the fractionation theory are examined in detail for isotactic polypropylene. ZUSAMMENFASSUNG:Gegenstand dieser Arbeit war die Untersuchung der Anderung der Feinstruktur von isotaktischem Polypropylen wahrend der isothermen Kristallisation und die Feststellung, ob die Theorie der durch die Kristallisation induzierten Molekularfraktionierung oder die der durch die Translationsdiffusion der Polymerkette im Kristallzustand hervorgerufenen Lamellenverdichtung (Translationsdiffusionstheorie) bei dem KristallisationsprozeB die entscheidende Rolle spielt. Mit fortschreitender Kristallisation entstehen unabhangig vom Molekulargewicht und der Molekulargewichtsverteilung bei niedriger Temperatur schmelzende Kristalle. Bei Polymeren mit hohem Molekulargewicht wird das Maximum der Warmekapazitat zu hoheren Temperaturen hin verschoben ; die hoch schmelzenden Komponenten entstehen im wesentlichen uber den Translationsdiffusionsmechanismus. Sofern der Unterschied der Molekulargewichte zweier Komponenten einer Polymermischung nicht zu grog ist, findet man im DSC-Thermogramm einer solchen auskristallisierten Mischung ein Maximum, das in erster Naherung in der Mitte zwischen den Maxima der unter den gleichen Bedingungen wie die Mischung auskristallisierten getrennten Komponenten liegt. Sofern sich die Molekulargewichte der beiden Komponenten wesentlich unterscheiden, zeigt das DSC-Thermogramm der Mischung, dal3 beide Komponenten die Tendenz getrennt zu kristallisieren aufweisen. Die von KAWAI, HOSOI und KAMIDE fur lmeares Polyathylen auf experimentellem Wege erhaltenen Hinweise gegen die Fraktionierungstheorie werden am Beispiel des isotaktischen Polypropylens im Detail untersucht.

Dilatometric study on the melting of polypropylene at elevated pressure

“…5). Finally, Reinshagen and Dunlap give 0.08 g/cm a (17) for a partially crystalline sample with a heat of fusion of 24 cal/g (20). With our AHthis gives a A Vof 0.18 g/cm a. Wilski (21) found about 0.21 g/cm a.…”

Highly active thermally stable ?-nucleating agents for isotactic polypropylene

“…Nevertheless, a similar melting behavior was found and intensively studied for ␣-iPP. 1,[13][14][15][16][17][18][19] Due to the high ␤-nucleating activity of Ca-Sub, this high melting temperature peak widening can be studied up to a T c of ϳ145°C. The intensity of the shoulder of the melting peak seems to increase up to 142°C.…”

“…Based on the results of several research groups, four separate ranges of T c can be distinguished for ␣-iPP, resulting in different melting profiles. 1,[13][14][15][16][17][18][19] The samples crystallized isothermally at low temperature (T c Ͻ 112°C) showed strong peak duplication. When increasing the T c between 112 and 132°C, a single melting peak was observed at even lower heating rates.…”

Characterization and properties of ethylene-propylene copolymers synthesized with homogeneous and supported metallocene catalyst in the whole range of compositions

“…64,65 However, it has to be considered that, as commented in the WAXS section, the propylene rich copolymers exhibit a polymorphic behavior, so that the splitting might be due to the melting of the different polymorphs. 10,14,66 Microhardness Measurements.…”