No abstract

The WAXS diffractograms of random ethylene copolymers were analyzed for samples rapidly quenched, annealed, or isothermally crystallized. Comonomers studied include 1-decene, 1-hexene, 4-methylpentene, norbornene, and dicyclopentadiene in a range of concentration that includes semicrystalline and amorphous copolymers at ambient temperature. Only crystalline reflections corresponding to the orthorhombic structure were identified in these copolymers. Focus is given to analyze the contribution of the concentration of comonomer as well as the comonomer type in the angular position of the amorphous halo. For samples quenched to 23 °C the peak value scales linearly and in inverse proportion with the concentration of comonomer in the copolymer reflecting the increase of the average backbone carbon−carbon intermolecular distance associated with the interlamellar region. With increasing temperature, a progressive melting of crystallites changes the comonomer composition of the amorphous region and leads to a temperature coefficient of the peak position of the halo that is a function of the concentration of comonomer in the chain.

No abstract

ABSTRACT:The influences of the type and concentration of ␣-olefin (1-hexene, 1-octene, 1-decene, 1-octadecene, 4-methyl-1-pentene) on the mechanical behavior and crystallinity degree of some ethylene/␣-olefin copolymers obtained by metallocene catalysts were studied by means of stress/strain experiments. The crystallinity degree of these copolymers has been determined by X-ray measurements. It has been observed that the copolymers show less resistance to strain as the comonomer content increases and the crystallinity decreases. Most of the studied copolymers exhibit a significant increase in the crystallinity level after the stress/strain experiments.

In order to improve elongational viscosity of polypropylene, allowing its use in a wide range of applications, different samples of branched polypropylene have been produced by reactive extrusion and evaluated by different techniques. It is known that the long chain branching (LCB) can act as a nucleating agent in the crystallization process. This is confirmed by differential scanning calorimetry (DSC), optical microscopy, and crystallization analysis fractionation (CRYSTAF), where an increase in the crystallization temperature can be observed when comparing linear and branched samples. In the chemical composition distribution profile of the analyzed samples, it is possible to see differences in the amount of crystallized material among the branched PP samples and it is possible to correlate it with the long chain branching content and distribution, measured by Triple Detector Gel Permeation Chromatography (3D-GPC), using the Mark-Houwink plot (MH Plot), conformation plot, and gpcBR methodology. A decrease in dissolution temperature, and an increase in soluble fraction is observed by temperature rising elution fractionation (TREF) at increasing LCB content in the polymer samples. These results indicate that the presence, amount, or distribution of long chain branching affects the crystallization kinetics and the crystal morphology. CRYSTAF and TREF show a good correlation with LCB content measured by GPC.