Method of producing vinyl-based polymer

Details Method of producing vinyl-based polymer Method of producing vinyl-based polymer

2002-04-16

2004-01-13

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C524S804000, C524S834000, C524S459000

Reexamination Certificate

active

06677409

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a vinyl-based polymer, and in particular to a method using a reaction inhibitor during the polymerization of a vinyl monomer by a radical reaction.
2. Description of the Prior Art
In conventional radical polymerization reactions of vinyl monomers, reaction inhibitors (also known as reaction suppressants) have typically been added to the polymerization system, and examples of such reaction inhibitors include phenol based compounds, sulfur compounds, N-oxide compounds, phosphorus compounds, and unsaturated hydrocarbon compounds. Specific examples of the phenol based compounds include 2,2-di-(4′-hydroxyphenyl)propane, hydroquinone, p-methoxyphenol, t-butylhydroxyanisole, n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate, t-butylhydroquinone, 2,5-di-t-butylhydroquinone, 4,4′-butylidenebis-(3-methyl-6-t-butyl)phenol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2′-methylene-bis-(4-ethyl-6-t-butyl)phenol, triethyleneglycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenol)propionate], t-butylcatechol, 4,4′-thiobis-(6-t-butyl)-m-cresol, and tocopherol.
These reaction inhibitors may either be added to the polymerization system prior to commencement of the polymerization reaction in order to reduce the occurrence of fish eyes within the product polymer (Japanese Laid-open publication (kokai) No. 48-49990 (JP48-49990A), Japanese Post-Examination Publication (kokoku) No. 60-50366 (JP60-50366B)), added during the polymerization reaction in order to suppress heat kick, or alternatively added at or after the completion of the polymerization reaction in order to prevent postpolymerization and prevent deterioration in the anti-initial discoloration property resulting from heat history (U.S. Pat. No. 3,642,756, Japanese Laid-open publication (kokai) No. 57-185302 (JP57-185302A), and Japanese Laid-open publication (kokai) No. 62-503 (JP62-503A)). Furthermore, such reaction inhibitors are also used for halting rapid reactions which occur during abnormal reactions.
Amongst the above reaction inhibitors, 2,2-di-(4′-hydroxyphenyl)propane displays excellent reaction inhibiting properties, enables the production of high quality polymers, and also produces very little adhesion of scale to the polymerization vessel, and has consequently been widely used at the completion of polymerization reactions.
However, 2,2-di-(4′-hydroxyphenyl)propane is a solid at room temperature, and unless the material is dissolved in an organic solvent such as methanol prior to use, then the operation of supplying the reaction inhibitor to the reaction vessel via the supply line is problematic. Consequently, because this method requires the use of an organic solvent, not only are there associated physical dangers for the operators exposed to the fumes, but these fumes also become a source of environmental pollution.
Consequently, in Japanese Post-Examination Publication (kokoku) No. 7113041 (JP7-113041B) a reaction inhibitor represented by a general formula (1) shown below was disclosed as an alternative to 2,2-di-(4′-hydroxyphenyl)propane.
(wherein, R represents an alkyl group of 3 or more carbon atoms)
Specifically, the compound in which the R group is a sec-butyl group, namely, 2,6-di-t-butyl-4-sec-butylphenol is currently used. This compound is a liquid at room temperature, and so is able to be supplied to the polymerization vessel via the supply line without requiring the use of a solvent.
However, the solidifying point of this reaction inhibitor is between 18 and 20° C., and so in cases in which the external temperature is cold, namely 10° C. or lower, the compound enters a supercooled state, and as a result, the reaction inhibitor may begin to crystallize, thereby blocking the supply piping. Consequently, in those cases in which the reaction inhibitor is introduced from the supply line to the polymerization vessel within a low temperature external environment, an organic solvent such as methanol must be used to dissolve the reaction inhibitor, and consequently this compound does not completely resolve the aforementioned problems of physical danger for the operators and environmental pollution.
Furthermore, in cases in which cold temperatures result in the reaction inhibitor solidifying and blocking the supply piping, a device for heating the supply piping to melt any solidified reaction inhibitor and prevent blocking of the piping can be installed, although if this heating is overly vigorous, the reaction inhibitor may undergo thermal decomposition causing a reduction in the reaction inhibiting property and increasing the likelihood of a discolored product polymer. Furthermore, in terms of operating efficiency, the heating operation using a heating device or the like increases the complexity of the process.
SUMMARY OF THE INVENTION
The present invention takes the above factors in consideration, with an object of providing a method of producing a vinyl-based polymer in which problems such as the blocking of piping resulting from solidification of a reaction inhibitor do not arise even if the operation of supplying the reaction inhibitor is conducted at low temperatures and without the use of an organic solvent.
As a result of intensive research aimed at resolving the issues described above, the inventors of the present invention discovered that when polymerizing a vinyl monomer, if the reaction inhibitor is dispersed in an aqueous medium prior to use, then the polymerization can be performed without the occurrence of pipe blockage problems and the like resulting from solidification of the reaction inhibitor, and were hence able to complete the present invention.
In other words, the present invention provides a method of producing a vinyl-based polymer by polymerizing a vinyl monomer via a radical reaction, wherein a reaction inhibitor comprising a compound represented by a general formula (1), shown below, is added to the polymerization system in the form of an aqueous dispersion.
wherein, R represents an alkyl group of 3 to 6 carbon atoms.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As follows is a more detailed description of the present invention.
The terminology “polymerization system” herein means an aqueous mixture of materials charged in a polymerization vessel before the initiation of polymerization reaction or an aqueous reaction mixture in the polymerization vessel during, or at or after the completion of polymerization reaction.
In the present invention, in the polymerization of a vinyl monomer via a radical reaction, a reaction inhibitor represented by the aforementioned general formula (1) (wherein, R represents an alkyl group of 3 to 6 carbon atoms) is dispersed in an aqueous medium prior to being added to the polymerization system. In order to add the reaction inhibitor to the polymerization system, a dispersion such as an emulsion or a suspension is first prepared by dispersing the reaction inhibitor in an aqueous medium, with the aid of a dispersant such as an emulsifier or a suspension agent, and this dispersion is then added to the polymerization system. This dispersion comprises fine particles of the reaction inhibitor of diameter from 1 to 30 &mgr;m dispersed in water, in other words, an oil in water type emulsion, and should preferably comprise protective colloids.
In cases in which the reaction inhibitor retains a liquid form despite being cooled below melting point, in other words, cases in which the reaction inhibitor is in a supercooled state, crystallization is accelerated by factors such as the presence of crystal nuclei or the surface state of the storage vessel and the piping. For example, if the reaction inhibitor is 2,6-di-tert-butyl-4-sec-butylphenol, then the melting point is approximately 20° C., and so at temperatures below 20° C., the addition of a small amount of solid 2,6-di-tert-butyl-4-sec-butylphenol to the liquid 2,6-di-tert-butyl-4-sec-but

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