Rhone-poulenc Industries

Salomon Soussan

Jean-Bernard Pompon

Francois Erard

Vinyl chloride polymers are prepared by polymerization or copolymerization in mass, in two phases, comprising prepolymerizing vinyl chloride monomers in a first phase under highly turbulent agitation until a degree of conversion thereof between about 5 and 15% is attained, and thence, in a second distinct phase, polymerizing said prepolymerized reaction product through reaction completion under mild agitation, said process being characterized in that [1] there is added to the reaction medium, prior to same attaining a polymer content of about 15% by weight, an additive selected from the group comprising (a) a copolymer of vinyl acetate and an ethylenically unsaturated carboxylic acid monomer copolymerizable therewith, and (b) a condensate of ethylene oxide on a polypropylene glycol backbone, and in that [2] the reaction rate is controlled such that the period of time during which the content by weight of polymer or copolymer in the reaction medium is comprised between 15 and 25% is less than 45 minutes. The reaction product comprises at least 95% by weight of a fraction which will pass through a 250 micron mesh sieve.

Two-phase vinyl chloride polymerization

An improved method of degassing polymers and copolymers prepared by mass polymerizing a monomeric composition, based on vinyl chloride. The polymer is kept under agitation, the monomeric composition to be eliminated is brought from polymerization pressure to a pressure below 120 mm of mercury, the polymer is brought to or kept at a temperature of at least 70.degree. C. and below the temperature at which degradation of the polymer or copolymer commences, and these conditions of pressure and temperature are maintained substantially until the degassing process stops, the polymer being put into contact with a quantity of water representing 0.01 to 0.8% and preferably 0.05 to 0.5% of its weight, after the residual monomeric vinyl chloride content of the polymer or copolymer has been reduced below 2000 ppm. The polymers and copolymers obtained, before being placed in open air, have a residual monomeric vinyl chloride content which is less than 50 ppm, generally less than 20 ppm and may be as little as 1 ppm.

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Saint Symphorien D'Ozon, France

Salomon Soussan