Browsing by Author "Galland, Griselda B."

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    Publication
    Nonisothermal crystallization and melting behavior of syndiotactic polypropylenes of different microstructure
    (2008) Vanegas Peña, María Eulalia; Quijada, Raúl; Serafini, Daniel; Galland, Griselda B.; Palza, Humberto
    Syndiotactic polypropylenes and their copolymers with 1-olefins were synthesized using two metallocene/MAO catalytic systems, and the effect of the different microstructures on nonisothermal crystallization and subsequent melting was studied. Using differential scanning calorimetry (DSC) it was observed that samples with lower content of defects showed crystallization on cooling from the melt, and a double melting peak in the subsequent heating scan, the latter associated with melt, recrystallization and remelt processes that it was confirmed by its nonreversing exothermic process found by means of temperature modulated DSC (MDSC). However, polymers with high amount of defects showed cold crystallization on heating followed by a melting process, that it was observed by MDSC. Wide angle X-ray diffraction was used for characterizing the changes of crystalline forms in relationship with crystallization process.
  • Thumbnail Image
    Publication
    Syndiotactic poly (propene-co-norbornene): synthesis and properties at low norbornene incorporation
    (2010) Vanegas Peña, María Eulalia; Quijada, Raúl; Galland, Griselda B.
    Copolymerizations of propene with norbornene were carried out using a syndiotactic metallocene catalyst at low initial comonomer concentrations for different polymerization times. The influence of the norbornene concentration on the catalytic activity and on the resulting material properties has been analyzed. The copolymer molecular weight decreased drastically when small amounts of norbornene were added in reactions which lasted 30 min. When longer reaction times were used the molecular weight increased with time, however living polymerizationwas ruled out because the polydispersity was ca. 2. The DSC measurements showed copolymers with low crystallinity or which were completely amorphous.