Synthesis of polyethylenes with high polydispersity

Abstract

For a number of applications the use of polyethylenes with a high polydispersity is recommended. In order to prepare such grades polymerisation tests were performed in a stirred autoclave in laboratory scale. The autoclave was run continuously at 1800 bar in the range of 210 to 285 "C with 60 s residence time. Difunctional peroxides with identical and with different substituents on both 0-0 groups were tested. For comparison, monofunctional compounds from industrial processes were used. The concentration of the peroxides in the feed was varied between 3 and 60 mol ppm.By GPC, polydispersities of 5 to 9, comparable to those of commercial polyethylenes, were measured on the samples produced with the monofunctional peroxides. Distinctly higher polydispersities of up to 13 were achieved by the use of the difunctional peroxides, especially with the symmetrical compound. ZUSAMMENFASSUNG:Polyethylene mit hoher Polydispersitat sind fur bestimmte Anwendungszwecke besonders geeignet. Zu ihrer Synthese wurden Polymerisationsversuche in einem kontinuierlich betriebenen Labor-Ruhrautoklaven bei 1800 bar, 210 bis 285 "C und einer Verweilzeit von 60 s durchgefuhrt. Als Polymerisationsinitiatoren wurden bifunktionelle Peroxide rnit gleichen und ungleichen Substituenten an den 0-0 Gruppen und zum Vergleich gebrauchliche monofunktionelle Peroxide in Konzentrationen von 3 bis 60 mol ppm im Ansatz eingesetzt.Die GPC-Analyse der rnit den monofunktionellen Peroxiden erhaltenen Proben ergab Polydispersitaten von 5 bis 9, die im gleichen Bereich wie die Werte industriell hergestellter Polyethylene liegen. Hohere Polydispersitaten bis zu 13 wurden bei der Polymerisation rnit den bifunktionellen Initiatoren, insbesondere rnit dem symmetrisch substituierten Peroxid erreicht.

Chemical modification of low density polyethylene through reactive extrusion: Part I: Process development and product characterization

“…Analyses were conducted on selected samples that comprised a 2 factorial design, two 3 center points, the control run, and the base resin. The n was not changed appreciably and the max-M imum w obtained was 113 000.…”

“…The dimensions of the channel through which the polymer passes inside the die were: h ϭ 4.1 mm h ϭ 2.05 mm 1 2 h ϭ 1.28 mm w ϭ 14 mm ϭ 0.9Њ 3 Process data were recorded using an Opto 22 data acquisition and control system interfaced to a Pentium personal computer running a DOS program written in C. Measurements of key process parameters were logged at 2-second intervals during each experiment. These parameters were: (1) extruder screw speed, (2) decalin pump pressure, (3) polymer melt temperature at the injection point, and (4) three pressures along the wedge die.…”

“…It is manufactured in 2,3 autoclaves or tubular reactors at high pressures, typically between 150 and 300 MPa, resulting in polydispersities between 5 and 10. It is known that 4 resins produced in autoclave-type reactors have broader molecular weight distributions (MWDs) and different branching structures than those produced in tubular reactors.…”

Hochdruckpolymerisation von Ethylen

“…Weitere Verbesserungen sind von neuen oder modifizierten Initiatorsystemen zu erwarten, z. B. von bifunktionellen Peroxiden [19,20] oder solchen mit tert-Amyl-anstelle von tert-Butyl-Liganden, die die Produkteigenschaften verbessern, oder durch Zusätze wie Aluminiumalkyle, welche den Initiatorverbrauch reduzieren [21].…”

The reactive modification of polyethylene. I: The effect of low initiator concentrations on molecular properties

“…Processes involving low dosage of irradiation (10) and low peroxide concentration (1 1-14) were used to improve the rheological and optical properties of HDPE and LLDPE, while maintaining superior mechanical properties, in applications such as blow molding, blown-film, and coating extrusions. The increases in breadth of molecular weight distribution and degree of long chain branching allows thin wall objects with superior properties to be manufactured at high rate (10)(11)(12)(15)(16)(17)(18).…”