By twofold extrusion

Olefin Synthesis by Twofold Extrusion Carbon dioxide,thio-extrusion... 

T ris( diethy lamino)phosphine Ethylene derivs. by twofold extrusion... 

Thermolysis of diferrocenyltellone,250 as well as its reaction with M(CO)6 (M=Cr, Mo, W),221 yields the tetraferrocenylethylene by a twofold extrusion process from a preformed cyclic dimer of diferrocenyltelluroketone (Scheme 45). 

The twofold extrusion of nitrogen and sulfur and selenium and sulfur from 1-thia- and l-selena-3,4-diazolines(77), readily available from the reaction of diazoalkanes with thio- and selenaketones, respectively, as well as from the reductive coupling of carbonyl compounds such as 78, is the preferred method for preparation of olefins of type I and II (98,99). Examples of the extrusion method, developed by Barton (100), and the McMurry reaction (101) are given in Scheme 1. 

Several convenient olefin syntheses have been reported. N-Carbalkoxysulfamate esters undergo elimination to olefins at room temperature. Epoxides afford olefins by reductive elimination under the influence of MgBr2 and magnesium amalgam. A twofold extrusion process for the construction of complex olefins has also been described. In the example shown, the highly hindered olefin shown was obtained in 80% yield. 

Purpose of the screens is primarily twofold (1) to change the melt s spiraling motion, caused by the screw rotation and (2) to filter contaminants out of the melt. Most plastics contain contaminants and these particles can be conveniently removed by means of a screen placed after the extruder barrel and before the melt flow reaches the extrusion die. The simplest means for filtering plastic melts are woven wire mesh disks of about the same diameter as that of the extruder barrels. Several... 

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