Characterization of metallocene ethylene‐1‐octene copolymers with high comonomer content cross‐linked by dicumyl peroxide or β‐radiation

Abstract

Two metallocene ethylene-1-octene copolymers differing in comonomer content were cross-linked either by dicumyl peroxide (DCP) or b-radiation with doses ranging from 0.5 to 4% DCP and 25 to 200 kGy, respectively. The effect of cross-linking on the crystalline morphology was analyzed by differential scanning calorimetry (DSC). Slight alterations in the crystalline structure were found, which were more severe in the case of peroxi modification. Through infrared spectroscopy (FTIR analysis), oxidation during the cross-linking process was detected on the DCP cross-linked samples, while b-irradiated samples do not exhibited significant degrees of oxidation. The state of cure was studied following the changes in the rheological properties in small-amplitude oscillatory shear mode, and the evolution of the molecular weight and molecular weight distribution through size exclusion chromatography. Irradiation doses below 200 kGy increased the molecular weight and branching of both copolymers but were not sufficient to reach gelation. All the peroxide modified samples resulted in a post-gel condition. Optimal mechanical properties were obtained with concentration of about 1% DCP. At higher doses, scission reactions diminish the tensile strength and the elongation at break. When polymers with equivalent amounts of gel fraction obtained by the two modification procedures studied in this work are compared, higher tensile strength and elongation at break are obtained with irradiation.

Study on the influence of electron beam irradiation on the thermal, mechanical, and rheological properties of ethylene‐octene copolymer with high comonomer content

“…EOC has been successfully crosslinked using techniques like peroxide crosslinking,7–10 silane water crosslinking,11–14 and electron beam (β) or gamma (γ) irradiation 15–19. Irradiation is very powerful form of energy which can produce deep changes in the polymers.…”

Influence of Branching Density in Ethylene-Octene Copolymers on Electron Beam Crosslinkability

“…One possibility is careful mixing with peroxide (the temperature must be kept low to avoid premature crosslinking during mixing) followed by high-temperature crosslinking of the moulded article [8,11]. Another method includes grafting by vinyltrimethoxy silane followed by exposure to water or humidity at elevated temperatures [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26].…”

Cross‐linking of ethylene‐octene copolymer (EOC) by dicumyl peroxide (DCP)

“…While other olefin rubbers, such as EPDM (ethylene-propylene-diene monomer) have a double bond in the chain and can be crosslinked by traditional sulfur systems, EOC without a double bond cannot be crosslinked by sulfur and one has to use other methods. There are several possibilities how to crosslink EOC, such as electron beam exposure, [1][2][3][4][5][6] silane grafting followed by water cross-linking [7][8][9][10][11][12][13] and peroxide cross-linking. [14][15][16][17][18][19] All of these methods have practical importance.…”