1. Field of the Invention
The present invention relates to a polymer scale preventive agent useful in polymerization of a monomer having an ethylenically unsaturated double bond, and a process of producing a polymer using said agent.
2. Description of the Prior Art
As a method of polymerizing a monomer having an ethylenically unsaturated double bond, there have hitherto been known suspension polymerization, emulsion polymerization, solution polymerization, gas phase polymerization and bulk polymerization. In any type of the polymerizations, polymer scale is liable to be deposited on the areas with which the monomer comes into contact during polymerization, such as inner walls, agitation equipment, etc. of a polymerization vessel.
Deposition of the polymer scale results in disadvantages that the yield of the polymer and cooling capacity of the polymerization vessel lowers; that the polymer scale may peel off and mix into the resulting polymer, thereby impairing the quality of formed products obtained by forming the polymer; and that the removal work of such a polymer scale not only is extremely laborious and hence time-consuming, but also may cause physical disorders, which are serious problems among the operators in recent years, due to unracted monomers which are contained in the polymer scales.
Heretofore, with regard to preventing the polymer scale deposition on inner walls, etc. of polymerization vessels during polymerization of a monomer having an ethylenically unsaturated double bond, there is known a method of coating a polymer scale preventive agent consisting of an organic polar compound, such as an amine compound, a quinone compound or an aldehyde compound, on the inner walls, etc. of the polymerization vessel to form a coating film, and a method of adding these compounds into an aqueous medium where suspension polymerization is effected, as locally practiced, for example, in suspension polymerization of vinyl chloride [Japanese Patent Publication (KOKOKU) No. 45-030343 (1970)].
However, such methods have the disadvantages that although a polymer scale preventive effect is exhibited while polymerization is repeated for up to about 5 or 6 batches, the preventive effect decreases (is inferior in durability) when the numbers or times of repeated batches of polymerization exceed 5 or 6. The decrease in the preventive effect is remarkable especially when used a water-soluble catalyst in polymerization, so that these methods can not be satisfied from the industrial view.
In order to overcome the above disadvantages, there are proposed, for example, methods of coating a polymer scale preventive agent containing, as an effective component, such as a condensation product of an aromatic amine compound with an aromatic nitro compound [Japanese Patent Publication (KOKOKU) No. 60-30681], a reaction product of a phenolic compound with an aromatic aldehyde [Japanese Pre-examination Patent Publication (KOKAI) No. 57-192414], a reaction product of a polyhydric phenol with an aliphatic aldehyde [Japanese Patent Publication (KOKOKU) No. 57-502169], and a reaction product of 1-naphthole with formaldehyde [Japanese Patent Publication (KOKOKU) No. 01-31523], and the like.
In case where each of these polymer scale preventive agents is coated on the areas, with which the monomer comes into contact during polymerization, such as inner walls, etc. of a polymerization vessel to thereby form a coating film, polymer scale deposition on the areas in the liquid phase of the polymerization vessel does not occur, even if polymerization batches are repeated about 100 to 200 times. Similarly, also in case where said water-soluble catalyst is used, polymer scale deposition on the liquid phase areas is prevented.
However, said polymer scale preventive agents have a drawback that polymer scale deposition is liable to occur at and in the vicinity of the interface between a gas phase and a liquid phase which is located at the upper of the polymerization vessel, even if a coating film of a polymer scale preventive agent containing, as the effective component, the condensation product of said aromatic amine compound with said aromatic nitro compound and the like is formed.
Once polymer scale is deposited at or in the vicinity of the interface between the gas phase and the liquid phase, the deposited scale will grow gradually as polymerization runs are repeated, and at last peel off from the inner wall, etc. to get mixed with the polymeric product. If the polymeric product containing the polymer scale is processed into formed products such as sheets or the like, the polymer scale causes increase in fish eyes in the formed products, thereby lowering seriously the quality of the products.
Meanwhile, where polymeric products obtained by polymerization are processed into formed products such as sheets, etc., the formed products are required to have a high whiteness. When a polymeric product is formed into a sheet or the like without adding any coloring agent, the resulting formed product is more or less colored. Such coloration is called initial coloration, which is desired to be as low as possible. However, when a coating film containing, as the effective component, the condensation product of said aromatic amine compound with said aromatic nitro compound, etc. is formed, the coating film may be peeled or dissolved during polymerization and mix into polymeric products, the resulting formed products will exhibit a low whiteness, that is, an inferior initial whiteness.