Maximilian Dorn’s scientific contributions

The present study was carried out to examine the effectiveness of an addition of triethylaluminium to tert ‐butyl perpivalate which is frequently used in industrial applications for initiating the copolymerisation of ethylene with vinyl acetate. For this purpose, polymerisation tests were carried out in the laboratory on a continuous basis at 1900 bar and 150°C. Vinyl acetate was added in concentrations of up to 36 wt.‐% in the feed to the reactor. The organic peroxide concentration was 50 mole ppm; the concentration of organoaluminium alkyl was varied within the range of 0–75 mole ppm. The effects observed, namely an increase in the conversion and a decrease in the peroxide consumption were more marked than with the homopolymerisation of ethylene. This is attributable to the increased rate of chain growth in addition to the increased amount of radicals available. The properties of the copolymers obtained are changed only moderately by aluminium alkyl. Apart from a decrease in density and an increase in the melting point, a decrease in the polydispersity was observed.

In the course of this study, an activator system consisting of an aluminium trialkyl compound and a Lewis base was tested for its suitability for the radical polymerisation of ethylene at high pressure. The aim of reducing the initiator consumption and the polymerisation temperature was achieved with aluminium trialkyl alone without the use of a Lewis base. Among the aluminium trialkyl compounds examined, triethyl aluminium proved to be the most effective. This effectiveness is due to the increased rate of decomposition of the peroxide as a result of which a larger amount of free radicals becomes available thus increasing the rate of polymerisation. By using an addition of 50 mole ppm triethyl aluminium to 50 mole ppm tert‐butyl‐perpivalate in the ethylene feed it was possible to almost double the monomer conversion at a given polymerisation temperature and to reduce by half the consumption of peroxide initiator per kg polyethylene produced. Compared with the non‐activated polymerisation, the polymerisation temperature was reduced from 150°C to 125°C, the initiator consumption remaining the same. The costs of the triethyl aluminium activator are more than offset by the increased yield and the decrease in initiator consumption.

In this study, the terpolymerisation, under high pressure, has been examined for the ethylene-methyl acrylate-vinyl acetate system. The polymerisations were carried out in a high pressure polymerisation facility designed for continuous operation. To assess the effect of pressure and temperature on the reaction, polymerisation was carried out at two different pressures of 1 900 and 1 100 bar and at temperatures of 180 and 230 degrees C. By varying the concentration of the ethylene, methyl acrylate and vinyl acetate monomers in the feed, polymers of different composition were obtained. The ratio of the monomer concentrations in the reactor was calculated from the amount of polymer weighed out and its comonomer content as well as the composition of the feed, using the mass balance for the ideal stirred tank reactor. The result was used to determine the reactivity ratios of the three possible binary copolymerisation systems ethylene/methyl acrylate, ethylene/vinyl acetate and methyl acrylate/vinyl acetate. This made it possible to predetermine, by calculation, the composition of a product obtained by continuous polymerisation in a stirred autoclave.