Methyl methacrylate syrup and production thereof

Details Methyl methacrylate syrup and production thereof Methyl methacrylate syrup and production thereof

2000-10-27

2002-09-10

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...

C526S227000, C526S229000, C526S309000, C526S323200, C526S328500, C526S329200, C526S329300, C526S329500, C526S329700, C526S219600

Reexamination Certificate

active

06448354

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methyl methacrylate syrups containing a monomer component mainly comprising methyl methacrylate and a polymer component resulted from the polymerization of methyl methacrylate or a monomer mixture mainly comprising methyl methacrylate, and a production process thereof.
2. Description of the Prior Art
Acrylic syrups have been used as intermediate materials for methacrylic cast products, optical materials such as photo-transmitting fibers and optical wave-guide; acrylic artificial marble; artificial seal materials; floor materials; adhesives; restoration materials for cultural assets and stuffed animals; and medical materials.
Methods of producing syrups mainly comprising methyl methacrylate are described in various patent documents such as Japanese Patent Publication Nos. 36-3392, 40-3701, 46-40693 and 53-2189, and Japanese Patent Application Laid-Open Nos. 55-43111 and 9-255714. Japanese Patent Publication No. 1-11652 and Japanese Patent Application Laid-Open Nos. 49-104937, 3-111408, 9-67495 and 9-194673 disclose carboxy-functional methyl methacrylate syrups.
The production methods of acrylic syrups are classified roughly into two main methods. One is a so-called partial polymerization method where a portion of acrylic monomer is bulk-polymerized, as disclosed in Japanese Patent Publication Nos. 36-3392: and 1-11652. The partial polymerization method is sub-classified into a batch method and a continuous method. In the other method, an acrylic polymer separately prepared is dissolved in acrylic monomer, as disclosed in Japanese Patent Application Laid-Open Nos. 49-104937 and 9-194673. This method is basically different from the production method of the present invention, and is disadvantageous in view of energy consumption and production cost because an acrylic polymer separately prepared must be taken out of a production apparatus and then dissolved in acrylic monomer.
In the methods other than bulk polymerization, for example, solution polymerization and emulsion polymerization, in addition to a batch process and a continuous process, employed is a semi-batch process where a starting monomer containing a polymerization initiator is added to a solvent in portions as described in Kuwano, “Kobunshi Kako”, 47(3), 125, 1998. However, the semi-batch solution polymerization requires a solution for dissolving the monomer, and the semi-batch emulsion polymerization requires a dispersion medium and an emulsifying agent. There is no report about industrial production of methyl methacrylate, syrups by non-solvent semi-batch process under high monomer concentration.
As the semi-batch partial polymerization, Japanese Patent Publication No. 36-3392 discloses a production method of methyl methacrylate syrups. In the method, after heating a starting material containing a monomer component mainly comprising methyl methacrylate and a chain transfer agent to 80° C., a small amount of azobisisobutyronitrile or benzoyl peroxide is added as a polymerization initiator to the starting mixture, and simultaneously the mixture is heated to 100° C. to conduct polymerization for 27 to 50 minutes under reflux. When reaching a predetermined viscosity, the reaction mixture is rapidly cooled by adding a cold methyl methacrylate containing hydroquinone as a polymerization inhibitor, thereby obtaining methyl methacrylate syrups.
In this method, however, since the polymerization is stopped before the polymerization initiator is completely decomposed, the polymerization initiator still remains in the syrups thus produced. Therefore, the storage stability of the syrups is poor even if the polymerization inhibitor is added. In consideration that the half-life of benzoyl peroxide used as the polymerization initiator is about 22 minutes at 100° C., about 20 to 42% of the polymerization initiator based on the total amount added remains in the reaction mixture at the time when the viscosity reaches the predetermined value. In addition, since all the amount of polymerization initiator necessary for the reaction is added in one portion, the control of the reaction is difficult. Therefore, the syrups cannot be stably produced by the proposed method.
Japanese Patent Publication No. 1-11652 discloses the production of syrups as an intermediate material for sheet molding compositions (SMC) and bulk molding compositions (BMC). In the proposed method, a starting material containing 100 parts of a; monomer mixture comprising 89% by weight of methyl methacrylate, 5% by weight of methacrylic acid and 6% by weight of trimethylolpropane trimethacrylate, 0.4 part of n-dodecylmercaptan and 0.05 part of 2,2′-azobisisobutyronitrile are charged into a reaction vessel equipped with a stirrer, a thermometer and a nitrogen inlet tube. The polymerization is conducted at 80° C. under nitrogen atmosphere. When the reaction liquid reaches the predetermined viscosity, hydroquinone and p-methoxyphenol as the polymerization inhibitor is added to the reaction liquid which is then rapidly cooled to room temperature to inhibit the polymerization, thereby producing carboxy-functional acrylic syrups.
In this method, however, since the polymerization is forced to stop by adding the polymerization inhibitor at the time when the reaction mixture reaches the predetermined viscosity, a portion of the polymerization initiator remains in the resultant syrups. Therefore, the storage stability of the syrups is poor even if the polymerization inhibitor is added. In addition, since all the amount of polymerization initiator necessary for the reaction is added in one portion, the control of the reaction is difficult. After the addition of the polymerization initiator, there is no effective means for controlling the reaction except for keeping the temperature constant. Since the slight change of the temperature, etc. largely affects the rate of polymerization and viscosity, the syrups cannot be stably produced by the proposed method.
One method of preventing the polymerization initiator from remaining in the products is to use a polymerization initiator having a short half-life at the polymerization temperature. However, this method requires a large amount of the polymerization initiator, and as a result thereof, the polymerization proceeds so rapidly that the control of the reaction becomes very difficult. Thus, the batch process faces the dilemma that usable polymerization initiator is limited to those having a long half-life at the polymerization temperature.
Japanese Patent Application Laid-Open No. 9-67495 discloses another method of producing syrups as intermediate materials for SMC and BMC. In the proposed method, a monomer mixture comprising 90 parts of methyl methacrylate and 10 parts of methacrylic acid is heated to 90° C. under nitrogen atmosphere, and then, 0.05 part of 2,2′-azobisisobutyronitrile as the polymerization initiator and 0.8 part of n-dodecylmercaptan as the chain transfer agent are added to conduct the polymerization. The reaction mixture is rapidly cooled by adding 50 parts of methyl methacrylate at the time when the reaction mixture reaches the predetermined viscosity, thereby obtaining methyl methacrylate syrups containing carboxy-functional polymers.
In this method, however, since the polymerization is forced to stop by rapid cooling with the addition of the monomer at the time when the reaction mixture reaches the predetermined viscosity, a portion of the polymerization initiator remains in the resultant syrups. Therefore, the storage stability of the syrups is poor. In addition, since all the amount of polymerization initiator necessary for the reaction is added in one portion, the control of the reaction is difficult. After the addition of the polymerization initiator, there is no effective means for controlling the reaction except for keeping the temperature constant. Since the slight change of the temperature, etc. largely affects the rate of polymerization and viscosity, the syrups cannot be stably produced by the proposed method

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