Showing papers by "DSM published in 1978"

Viscoelasticity of ABS samples differing in thermal history

Abstract: An important parameter in the various molding techniques used in polymer processing is the rate of cooling the object. The effect of the thermal history on the linear viscoelastic properties was studied, mainly by means of stress relaxation experiments on ABS samples in which the influence of other process variables was eliminated. In agreement with recent literature data, it appeared that the time dependence of the stress can be represented by a universal formula, provided that no perceptible change in temperature or relaxation of volume takes place during the experiment. The position of the momentary relaxation curve along the time scale can therefore be described by one characteristic mechanical relaxation time tr. The value of tr is affected by the temperature T, but even more by the thermal history, i.e., by the rate of cooling, q, and the annealing time, ta, at the measuring temperature previous to recording of the relaxation curve. In the case of very rapidly quenched samples, exact proportionality was found to exist between tr and ta at temperatures below Tg −15°C. In slowly cooled samples tr can be longer by a factor of ten than in quenched samples, at the same T and at annealing times of about 1 h. The difference decreases with increasing ta, but remains substantial up to ta values much longer than the total cooling time.

Process of polymerizing {60 -olefins in the liquid phase

Abstract: A process for polymerizing alpha -olefins in the liquid phase is disclosed, wherein the olefins are polymerized in the presence of a catalyst prepared by first reacting as aluminum-halogen compound with an organomagnesium compound and thereafter reacting the resulting reaction mixture with a transition metal compound and then activating the resulting catalyst system with an organo-aluminum compound. The homopolymers and copolymers of alpha -olefins produced by this process find use in the normal applications of such polymers.

Catalyst on a support for the polymerization of 1-alkenes, particularly ethene

Abstract: An improved process and catalyst is described for polymerizing α-alkenes using a catalyst obtained by reacting a chromium-1,3-diketo complex compound having the general formula Cr(OCR.sub.1 CR.sub.2 CR.sub.3 O).sub.3, with an organometallic compound, of a metal from Group II or III of the Periodic Table, contacting the reaction product with an inert inorganic support material, heating said reaction product on said support at a temperature of between about 200° and 1200° C. in a non-reducing atmosphere, combining the resulting product with an organometal compound of a metal from Group II or III of the Periodic Table. The catalysts are highly active and give high yields of polymer. By a proper selection of the pore volume and the particle size of the catalyst support polyalkenes of improved handling properties are obtained.