KR20030042207A - Continuous process for producing polystyrene with broad molecular weight distribution by anionic polymerization - Google Patents

Abstract

PURPOSE: Provided is a method for producing a polystyrene which has relatively broad molecular weight distribution by continuous anion polymerization and thus is suitable for food packaging material. CONSTITUTION: The method for producing polystyrene suitable for food packaging material which has molecular weight distribution of 1.1-20 and number average molecular weight of 10,000-1,000,000, in high viscosity anion polymerization, is characterized in that 0.01-1 M of polymerization initiator(with respect to 100 M of styrene monomer) is introduced into a polymerization system, provided that used amount of hydrocarbon which is a polymerization solvent, is less than weight of the introduced styrene monomer.

Description

Continuous process for producing polystyrene with broad molecular weight distribution by anionic polymerization

The present invention relates to a method for producing high purity polystyrene for food packaging materials using a small amount of reaction solvent and continuous anion solution polymerization, and to polystyrene used for cup ramen containers, disposable cups and general trays.

In general, polystyrene resins used in cup noodle containers and disposable dishes are obtained by radical polymerization of styrene, and in this case, various side reactions are likely to occur, and styrene dimers and styrene trimers, which are classified as suspected environmental hormones, are produced. (FR Mayo, J. Am. Chem. Soc. 90, 1968, p1289) Polystyrene containing these substances causes problems with dissolution into food contents when used for food packaging, such as cup noodle containers.

As is well known, styrene dimers and trimers are classified as susceptible to environmental hormones, and in the US World Fund for Nature, styrene dimers and trimers are also defined as endocrine disruptors, ie environmental hormones.

The prevailing theory is that these environmental hormones are harmful in light of repeated ecosystem abnormalities and animal test results.

According to WO 00/15678, this problem has been solved by anionic polymerization of styrene. However, because it is a batch polymerization, it is a low-viscosity polymerization that uses a large amount of reaction solvent to control the heat of polymerization, and the resulting linear polystyrene has a narrow molecular weight distribution.

In general, the molecular weight distribution in the production of polystyrene polymers by a batch low viscosity anionic polymerization method with a large amount of solvent is used to obtain a polymer having a narrow molecular weight distribution (near monodispersion), which has a high processing temperature and a low melt index. (Melt Index) and the like poor workability, there is a difficulty in obtaining the dimensional stability and physical properties of the final molded product molded therefrom.

In addition, batch polymerization has the disadvantage that productivity is too low to obtain commercial scale productivity, and a large amount of energy is consumed to remove the reaction solvent.

US Pat. No. 5,391,655, US Pat. No. 4,883,846, and US Pat. No. 4,748,222 are known as methods for producing continuous polystyrene to solve this problem of batch polymerization. It is a low viscosity anionic polymerization system.

These patents have a higher productivity than the batch type because of adopting a continuous polymerization method, and also produce a polymer having a wide molecular weight distribution, but not an optimized productivity and molecular weight distribution.

In another prior art relating to a process for producing continuous polystyrene, U.S. Patent 5,902,865 and U.S. Patent 4,016,348 disclose a tube loop reactor to control the heat of reaction and mixing of the polymer.

The present invention has been made in view of the above points, and furthermore, the production of polymerization by-products such as styrene dimers and trimers is suppressed, and in addition to the known continuous anion polymerization method with high productivity, It is an object of the present invention to propose a novel polystyrene production method which is easy to remove the heat of polymerization.

The present invention also provides a novel method of preparing polystyrene suitable for food packaging materials having a relatively wide molecular weight distribution.

The object of the present invention as described above is achieved by polymerizing the viscosity of the polymerization system to a certain degree or more.

In other words, the method of the present invention is that increasing the viscosity of the polymerization system can limit the flow (activity) of the resulting polymer and that the resulting polymer polystyrene has a molecular weight and molecular weight distribution suitable for use in food packaging materials It is based on the finding that the polymerization process is easy to control the heat of polymerization due to the slow polymerization rate.

Specifically, the present invention is a method for continuously preparing polystyrene for food packaging materials having a molecular weight distribution of 1.1 to 20 and a number average molecular weight of 10,000 to 1,000,000 by a high viscosity anion polymerization method, and polymerizing polymerization initiator 0.01 to 1M with respect to 100M of styrene monomer. It can be summarized as a method of producing polystyrene, which is added to the system and reacted, but the amount of hydrocarbon used as a polymerization solvent is less than or equal to the weight of the injected styrene monomer.

That is, the method of the present invention suppresses the production of styrene dimers and trimers, which are polymerized side reactions, and commercializes polystyrene having a molecular weight distribution of 1.1 to 20 and a number average molecular weight of 10,000 to 1,000,000 suitable for use in polystyrene for food packaging materials. The polymerization is carried out by a continuous high viscosity anion polymerization method in order to obtain, but it is characterized in that the amount of styrene monomer, polymerization initiator and hydrocarbon solvent introduced into the polymerization system is properly adjusted.

According to the experiments of the present inventors, the polymerization solvent to be added was confirmed to be less than the styrene monomer input amount. Therefore, the high viscosity used in the claims of the present application is understood that the amount of the polymerization solvent introduced into the polymerization system is less than or equal to the styrene monomer input amount.

The method of the present invention is distinguished from Korean Patent Publication No. 2000-19517, which is a well-known invention regarding low-viscosity polystyrene polymerization method in that it is a high viscosity polymerization method, and is a method for producing polystyrene polymers for food packaging having polydispersion, that is, wide molecular weight distribution. It is also distinguished from Korean Patent Publication No. 92-808, which is limited to being used as a standard sample of the analyzer as a high molecular weight polymer close to monodisperse in this respect.

Herein, polystyrene having a wide molecular weight distribution refers to having a wide molecular weight distribution of 1.1 or more, and has a merit of improving physical properties and processability by acting as a plasticizer of a low molecular weight polymer.

Hereinafter, the present invention will be described in detail.

According to the method of the present invention, polymerization is carried out by simultaneously introducing a hydrocarbon solvent, a styrene monomer, and a polymerization initiator into a continuous reactor according to an anionic polymerization method of a high viscosity continuous method, and having a number average molecular weight of 10,000 to 1,000,000 and a dispersion of 1.1 to It is to prepare a polystyrene polymer of 20.

In the case of high viscosity polymerization, it is easy to control the heat of polymerization due to the poor molecular fluidity and the wide molecular weight distribution and the slow polymerization rate.

Reaction solvents used in the process of the invention include nonpolar or polar hydrocarbon compounds. For example, cyclohexane, benzene, n-hexane, n-heptane, toluene, ethylbenzene, xylene, tetrahydrofuran, diethyl ether or mixtures thereof and the like can be used. In addition, the usage-amount of these reaction solvents is required to be below the amount of styrene monomer put into the polymerization system.

The initiator used in the present invention is a compound substituted with an aliphatic or aromatic from C1 to C6, for example n-butyllithium, sec-butyllithium, tert-butyllithium, methyllithium, ethyllithium, phenyllithium or Mixtures and the like may be used, and the amount of the mixture is continuously added in an amount corresponding to 0.01 to 1 Mol% per 100 mol of the monomer added.

As the monomer, all kinds of styrene substituents capable of anionic solution polymerization, for example, styrene, alphamethylstyrene, bromostyrene, or a mixture thereof may be used.

The polymerization is carried out under normal anionic polymerization conditions, in which air and moisture are removed, at a temperature in the range of 10 to 160 ° C., more preferably at 30 to 150 ° C.

In the process of the present invention, a coupling agent may be used after the polymerization reaction to obtain a spherical polymer. Coupling agents that can be used are halogens, isocyanates, esters, anhydrides, lactones, aldehydes, epoxides or ketones, and the like, as well as mixtures thereof. The amount of the coupling agent used is 0.01 to 5% by weight based on the amount of monomer added.

The polymerization is terminated by the addition of terminator. As a reaction terminator, methanol, ethanol, isopropanol, water, or a mixture thereof may be used, and carbon dioxide may be used simultaneously to effectively remove the lithium compound. The amount of carbon dioxide used is generally greater than or equal to the number of moles of initiator used.

Examples of the present invention will now be described, but the present invention is not limited thereto.

(Example 1)

In a continuous reactor in which two 6-liter jacketed stainless steel reactors were connected continuously, high-purity nitrogen was added and 50 ml of ethylbenzene per minute, 50 ml of styrene, and 10 ml of 0.05-mL solution of n-butyllithium were added continuously. The polymerization was carried out.

The temperature of the first reactor was maintained at 110 ° C and the second reactor was maintained at 100 ° C. The number average molecular weight of the produced polystyrene was 120,000, and a prepolymer solution having a molecular weight distribution of 2.3 was obtained.

The prepolymer solution was terminated with carbon dioxide and water and the melt index of the product was 10 g / 10 min (measured by ASTM D-1238).

Example 2

In a continuous reactor in which two 6-liter jacketed stainless steel reactors were connected continuously, high-purity nitrogen was added and 50 ml of ethylbenzene per minute, 50 ml of styrene, and 15 ml of n-butyllithium 0.05 M solution were continuously added. The polymerization was carried out by charging.

The temperature of the first reactor was maintained at 100 ° C and the second reactor was maintained at 90 ° C. The number average molecular weight of the produced polystyrene was 78,000, and a linear prepolymer solution having a molecular weight distribution of 2.23 was obtained.

The reaction was terminated with carbon dioxide and water in the prepolymer solution and the melt index of the product was 17 g / 10 min (as measured by ASTM D-1238).

Example 3

50 ml of ethylbenzene per minute, 50 ml of styrene, and 10 ml of a 0.2 M n-butyllithium 0.2 M solution were continuously added to the 6 liter continuous reactor of Example 1 for polymerization.

The temperature of the first reactor was maintained at 110 ° C and the second reactor was maintained at 100 ° C. The number average molecular weight of the resulting polystyrene was 35,000, to prepare a prepolymer solution having a dispersion degree of 2.2.

After reacting this solution for 20 minutes by adding a coupling agent of silicon tetrachloride (0.05 M solution), the molecular weight distribution was 2.75, linear and radial with a melt index of 6 g / 10 min (ASTM D-1238). A final polymer with mixed forms was obtained. The number average molecular weight of the polymer was 118,000.

(Comparative Example 1)

60 ml of ethylbenzene per minute, 30 ml of styrene, and 15 ml of n-butyllithium 0.05 M solution were continuously added to the 6 liter continuous reactor of Example 1 for polymerization.

The temperature of the first reactor was maintained at 100 ° C and the second reactor was maintained at 90 ° C. The number average molecular weight of the polymerized polystyrene was 75,000, and a prepolymer solution having a molecular weight distribution of 1.5 was prepared.

Terminating the reaction with carbon dioxide and water in the prepolymer solution gave a final polymer having a melt index of 14 g / 10 min (measured by ASTM D-1238).

The polystyrene produced by this comparative example had a narrower molecular weight distribution than the example, and a relatively large amount of solvent was consumed to remove the heat of polymerization.

(Comparative Example 2)

600 g of ethyl benzene and 300 g of styrene monomer were added to a 2-liter batch reactor, and 4 mmol of butyllithium was added at 20 ° C. for polymerization for 40 minutes. The molecular weight distribution of the polymer produced after polymerization was 1.03, and a final polymer having a melt index of 6 g / 10 min (ASTM D-1238) and a number average molecular weight of 91,000 was obtained.

This comparative example also had a narrower molecular weight distribution than the polystyrene prepared in Example, and a large amount of reaction solvent was consumed to remove the heat of polymerization.

According to the method of the present invention described above, it is possible to produce polystyrene on a commercial scale, and it is possible to obtain a polystyrene polymer having excellent processability as well as styrene dimer and styrene trimer, which are suspected environmental hormones due to polymerization reaction.

In addition, if the cup is formed by thermoforming, foaming or other injection molding using high purity polystyrene prepared according to the above method as a raw material, it can be used for containers, disposable cups and general trays.

Claims (5)

A method for continuously preparing polystyrene for food packaging materials having a molecular weight distribution of 1.1 to 20 and a number average molecular weight of 10,000 to 1,000,000 by a high viscosity anion polymerization method, in which 0.01 to 1 M of a polymerization initiator is added to a polymerization system based on 100 M of styrene monomer. A method of preparing polystyrene for food packaging material by a high viscosity anion polymerization method, wherein the amount of hydrocarbon used as a polymerization solvent is less than or equal to the weight of the injected styrene monomer. The method of claim 1, wherein the polymerization initiator is a high viscosity, characterized in that one or more mixtures selected from the group consisting of n-butyllithium, sec-butyllithium, tert-butyllithium, methyllithium, ethyllithium and phenyllithium Polystyrene manufacturing method for food packaging material by anion polymerization method. The mixture according to claim 1, which is selected from the group consisting of halogens, isocyanates, esters, anhydrides, lactones, aldehydes, epoxides and ketones with respect to styrene monomer 0.01 to 5 A method for producing polystyrene for food packaging materials by using a high viscosity anion polymerization method, characterized by using a weight part as a coupling agent. The mixture according to claim 1, which is selected from the group consisting of halogens, isocyanates, esters, anhydrides, lactones, aldehydes, epoxides and ketones with respect to the styrene monomer 0.01 to 5 A method for producing polystyrene for food packaging, characterized in that the weight part is added with a coupling agent. The polystyrene polymer manufactured by the method of any one of Claims 1-4 used for manufacture of a cup noodles container, a disposable cup, and a general tray.