Evolution of a Metallocenic sPP with Time: Changes in Crystalline Content and Enthalpic Relaxation

Abstract

Summary: The structural evolution of a metallocenic syndiotactic poly(propylene), sPP, with time has been studied. Due to the low syndiotactic content, the analyzed sPP sample can be easily quenched to a completely amorphous state. This amorphous sample, when left at room temperature is able to crystallize at relatively long times. The degree of crystallinity, as a function of time, has been analyzed by X‐ray diffraction and DSC. The DSC melting curves show the presence of a very important low‐temperature endotherm, besides the main melting peak. Real‐time variable–temperature synchrotron experiments have been performed in order to analyze the origin of the two melting peaks. They seem to arise from the melting of two populations of sPP crystals with different size and/or perfection, rather than from the melting of different polymorphs. The changes in the crystalline regions are accompanied by important variations in the mechanical behavior, as revealed by DMTA and microhardness (MH) measurements. In addition, the sPP crystallization has been analyzed by MH measurements, showing the importance that a relative low crystallinity has on the stiffness of a polymeric material at temperatures above Tg. On the other hand, the kinetics of the enthalpic recovery of quenched amorphous sPP specimens has been analyzed by DSC with temperature modulation. It was found that this enthalpic relaxation can be described by the KWW model, and the relaxation times and shape parameters at three different aging temperatures have been determined, with the corresponding apparent activation energy of this process.Variation with temperature of the most probable long spacing of sPP.imageVariation with temperature of the most probable long spacing of sPP.

Biodegradable Polycaprolactone-Titania Nanocomposites: Preparation, Characterization and Antimicrobial Properties

“…This multiple melting behavior in polymers has been explained by assuming successive melting-recrystallization processes [23–26], existence of dual lamellar populations [27,28] or presence of two or more polymorphs [29–32]. The former assumption seems to be the cause for this thermal response in the specimens under study, since a unique PCL crystalline structure is developed, as deduced from WAXS measurements and two crystallite populations have not been apparently observed, as revealed in the SAXS profiles within the temperature range of interest.…”

Effect of Polymer Structure and Incorporation of Nanoparticles on the Behavior of Syndiotactic Polypropylenes

“…The intensity of tan δ for the present sPP sample (0.15) corresponds to a semicrystalline polymer (tan δ amorphous phase > 1.2) . The γ relaxation is observed in Figure at around −80 °C attributed to local motions of methyl groups directly connected to the main backbone in sPP and its copolymers . This relaxation is quite less broad than that with similar molecular origin found in iPP.…”

“…The β relaxation is identified with the glass transition of sPP, related to generalized motions in the amorphous region, with intensity and location depending on the presence of crystalline phase. The intensity of tan δ for the present sPP sample (0.15) corresponds to a semicrystalline polymer (tan δ amorphous phase > 1.2) . The γ relaxation is observed in Figure at around −80 °C attributed to local motions of methyl groups directly connected to the main backbone in sPP and its copolymers .…”

Effect of different thermal treatments on the mechanical performance of poly(L‐lactic acid) based eco‐composites

“…Analyzing the results of DMTA, it can be observed that at temperatures higher than T g , the values of storage modulus are very low and practically the same for all eco‐composites, but with increasing temperature and reaching the region of the cold crystallization, the moduli are increasing again. Although this behavior is not usual, it has been previously observed in metallocenic syndiotactic polypropylene, as a result of cold crystallization 29…”