Abstract: A process is described for the two-stage mass polymerization of vinyl chloride, in which 0.1 to 3% by weight, relative to the monomer employed, of one or more of the following compounds which are known as heat stabilizers for polyvinyl chloride: monoalkyltin-IV or dialkyltin-IV compounds in which the residual valencies of the tin are attached to organic radicals via sulfur atoms, and/or aminocrotonic acid esters, are added to the polymerization mixture when a conversion of 65 to 85% has been reached. After thorough removal of the unreacted vinyl chloride from the resulting polymer, preferably at temperatures above the glass transition point of the polymer, products are obtained which have an improved color in comparison with polyvinyl chloride produced by conventional mass polymerization.

Abstract: In a calender the nip between a pair of rollers, of which one is obliquely adjustable, is bounded at the sides by plates adapted to the geometrical shape of the nip region and provided with slots, into which a control beam, parallel to the obliquely adjustable roller, engages, the ends of the beam are joined to the bearings of this roller, and the plates are arranged on supporting plates so as to be displaceble by means of a guide device, so that the plates, on oblique adjustment of the roller, are moved along a path which is concentric with the surface of the roller which is not obliquely adjustable.