Metallocenic Copolymers of Isotactic Propylene and 1‐Octadecene: Crystalline Structure and Mechanical Behavior

Abstract

Summary: A set of copolymers of isotactic propylene and 1‐octadecene (CiPOD) and the corresponding isotactic poly(propylene) homopolymer (iPP) have been synthesized using a metallocene catalyst. The influence of the incorporation of this long chain comonomer on the structure and final properties exhibited by iPP has been examined. Wide‐angle X ray diffraction and optical microscopy have been used to analyze the effect of introducing 1‐octadecene comonomer within the iPP backbone. The initial monoclinic crystal lattice with a well‐developed lamellar morphology is transformed into a mesomorphic modification showing very small entities. All these structural changes significantly influence the mechanical behavior of these copolymers. Thus, stiffness and microhardness are diminished and the brittle‐ductile transition can be observed by simply varying composition when deformation takes place at room temperature. On the other hand, the intensity of the process associated with cooperative movements within the amorphous phase (β relaxation) significantly goes up with the incorporation of 1‐octadecene and its location is shifted to lower temperature because of the decrease in the crystallinity content.X‐ray diffraction patterns at room temperature, with increasing comonomer content.magnified imageX‐ray diffraction patterns at room temperature, with increasing comonomer content.

Metallocenic Isotactic Poly(propylene) and its Copolymers with 1‐Hexene and Ethylene

“…isotactic propylene and 1-octadecene with molar fractions of around 5 and higher, [14] and under moderate quenching conditions, similar to those applied in the current investigation. Therefore, it seems that the presence of some comonomers in the propene copolymers increases the ability of producing the mesomorphic modification, since it is observed even at rather mild quenching conditions.…”

“…Another alternative for modifying the iPP structure and, therefore its properties, without the necessity of blending it with other polymers, comprises copolymerization of propene with a-olefins of different chain lengths. [14][15][16] The interest in these copolymers is two-fold: firstly, they might improve the final behavior of iPP; and secondly, these new materials obtained by this synthetic route could exhibit interesting novel properties. Contrary to the previouslymentioned approach as to the development of soft and hard domains, this methodology primarily changes the iPP crystalline structure and, therefore, a good rigidity/ toughness balance and better transparency can be attained at a given, optimum comonomer content.…”

“…It has to be said that determination of the viscoelastic behavior was not possible for the CiPE copolymers since fracture of all the specimens occurred at low temperature due, probably, to their relatively low molecular weight. The viscoelastic response of iPP and the copolymers is influenced by variables that affect their crystalline structure, [14] such as comonomer content, degree of crystallinity and thermal treatment. [4] Isotactic poly(propylene) obtained with Ziegler-Natta catalysts, as well as metallocenic poly(propylene), show three viscoelastic relaxations, [24,33] as observed in Figure 9, designated as g, b…”

Rheological and structural details of biocidal iPP-TiO2 nanocomposites

“…The corresponding values obtained at room temperature are listed in Table 1. The degree of crystallinity is within the range of that found in analogous quenched metallocenic iPP specimens [26][27][28][29][30]. Under the quenching conditions imposed during film preparation, crystallization takes place at conditions far from equilibrium and the fast cooling applied limits even more the development of crystallites and their perfection.…”

Influence of structure on the properties of polypropylene copolymers and terpolymers

“…This relaxation is very little visible in copolymers and terpolymers studied in this work, and also has a very low intensity in 1-hexene and 1-octadecene copolymers reported by Palza et al, probably due to the fact that the incorporation of a comonomer into the polypropylene chain leads to a reduced steric hindrance between methyl groups. [50] At low temperatures, the presence of a relaxation, named as ', is observed in the temperature range of -130 to -120 °C. This relaxation is especially noticeable in the case of copolymers of 1-butene, whereas the ethylene is the one with less intensity.…”