Various methods have heretofore been used for the preparation of homopolymers or copolymers from vinyl monomers or mixtures of vinyl monomers. In the past, such homopolymers or copolymers have generally been used in the form of solutions, suspensions or emulsions containing a liquid phase, for example, water. The preparation of polymers or copolymers from vinyl monomers or compositions having a high solids concentration of such homopolymers or copolymers presents problems due to the fact that polymerization reactions are highly exothermic, thereby causing run-away reactions which are difficult to control. This problem applies in general to polymer production or the production of high polymer solid compositions by well recognized methods such as thin film polymerization, "jello" polymerization and suspension polymerization.
In U.S. Pat. No. 4,164,612 solid water soluble polymers in a grindable glassy state are prepared by reacting a mixture of a specific type of vinyl monomer and water in an amount of 7% to 18% by weight based on the total weight of the monomer, and adding a water soluble salt in a powdery form. Various types of water soluble salts are employed. The water content is said to be critical. If the water content is less than 7% by weight, the polymerization operation becomes difficult to carry out resulting in a non-uniform polymerization while, if the water content in the polymerization system exceeds 18% by weight, the solubility of the salt is increased to give an adverse effect in the polymerization. Also, the softening point of the polymer is lowered to make the polymer difficult to grind. Sodium chloride and crystals of anhydrous sodium sulfate are used in the examples to illustrate the practice of the process. The reaction is carried out under anaerobic conditions in a container placed in a bath designed to allow the bath temperature to accord with the internal temperature of the container and the bath temperature is adjusted so as to remain equal to the internal temperature of the container. In a typical polymerization the initial temperature was 20.degree. C. The polymerization started 30 minutes after the addition of polymerization initiator. Seventy-five minutes elapsed before the maximum temperature of 114.degree. C. was reached. The polymerization system was maintained at this temperature for one hour. The container was then taken out of the bath and allowed to stand at room temperature for two days and two nights. Then the polymer was crushed by a jaw crusher for rough grinding and then by a hammer mill for fine grinding. It is apparent that this type of process requires a considerable amount of control of temperature conditions. Furthermore, the amount of water present must also be controlled.
It will be apparent that there is a need for a process of preparing polymers from a vinyl monomer or monomers by a homopolymerization or a copolymerization reaction wherein the temperature of reaction can be controlled more readily and wherein solid polymers or compositions containing a high percentage of solid polymers can be produced.
USPTO Backgrounds
USPTO Backgrounds