SYNOPSISGrafting dicarboxylic anhydrides onto polyolefins has great practical importance. The process of grafting maleic anhydride onto high-density polyethylene in the presence of various comonomers in an intermeshing corotating twin-screw extruders was studied. Three types of comonomers were investigated (i) vinyl monomers, including styrene and methacrylic acid; (ii) esters of dicarboxylic acids forming succinic groups after grafting, such as fumaric acid; and (iii) esters of fumaric and maleic acid and ethylenically unsaturated cyclic dicarboxylic anhydrides, such as Diels-Alder adducts of maleic anhydride; and (iv) dienes and dodecenyl succinic anhydride. 0 1995 John Wiley & Sons, Inc.

In the thermal oxidation of low density polyethylene (PE) in the melt phase and isotactic polypropylene (PP) in the solid phase, the changes in molecular weight distribution (MWD), weight average molecular weights (Mω), and average number of chain scissions have been studied by gel permeation chromatography (GPC). It has been established that in the case of PP degradation, there is an increase in molecular weight during the induction period both at 80 and 760 torr with simultaneous scission of the macromolecules. In contrast, a similar tendency can be observed in the degradation of PE only at very low (20 torr) pressures, i.e., the degree of molecular weight increases proportional to the length of induction period. For both polymers at the temperature of investigations, considerable molecular weight decrease can be detected both at reduced and atmospheric pressures at the onset of measurable oxygen absorption. In the maximum rate oxidation of PE and PP, the increase of temperature, oxygen pressure, and degradation time each causes a shift of the MWD curves towards lower molecular weights. The average number of chain scissions against the amount of absorbed oxygen was also studied. It has been found that the average number of chain scissions per 1 mole absorbed oxygen is considerably higher for PE than for PP. Molecular weight studies performed in the kinetic range of thermal oxidation show that under given conditions, Intermolecular combination reactions and chain scissions may occur simultaneously.

Weight average molecular weights were calculated for several sets of polymer Sdmpk from GPC chromatograms using different evaluation methods. The results were compared with light scattering data in order to check the reliability of individual evaluation procedures: data obtained using the direct calibration were compared with those calculated via the Benoit universal calibration employing (i) directly measured Kuhn-Mark-Houwink constants and (ii) Weiss-Cohn-Ginsberg iterative calculation. ZUSAMMENFASSUNG:Gewichtsmittlere Molekulargewichte wurden fur eine Reihe von Polymerproben aus Gelchromatogrammen ermittelt, wobei verschiedene Auswertemethoden verwandt wurden. Die Ergebnisse wurden rnit Lichtstreuungsmessungen verglichen, um die Zuverlassigkeit der einzelnen Auswertungen zu uberpriifen. Erhaltene Daten uber die Direkt-Kalibrierung wurden mit solchen aus der Benoit-Universalkalibrierung einmal unter Anwendung der direkt gemessenen Kuhn-Mark-Houwink-Konstanten, zum anderen aus der Weiss-Cohn-Ginsberg-Naherungsmethode verglichen.

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