Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F112/00—Homopolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring
  • C08F112/02—Monomers containing only one unsaturated aliphatic radical
  • C08F112/04—Monomers containing only one unsaturated aliphatic radical containing one ring
  • C08F112/06—Hydrocarbons
  • C08F112/08—Styrene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F12/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring
  • C08F12/02—Monomers containing only one unsaturated aliphatic radical
  • C08F12/04—Monomers containing only one unsaturated aliphatic radical containing one ring
  • C08F12/06—Hydrocarbons
  • C08F12/08—Styrene

Definitions

• the present invention relates to a highly pure polystyrene, and more particularly to a highly pure polystyrene prepared by anionic polymerization and a disposable food container using the same.
• the polystyrene, from which styrene dimers and trimers do not substantially migrate, is particularly useful as food containers, such as disposable noodle cups, disposable trays etc.
• a polystyrene used as polystyrene paper for noodle cups and a wide variety of disposable food containers such as cups, trays etc.
• styrene monomers styrene dimers and trimers, which are reaction by-products of two or more monomers, and have been recently suspected as the chemicals being responsible for endocrine disruptions, are produced due to the numerous side reactions.
• the styrene dimers and trimers which were incorporated in the polystyrene, tend to migrate from the polystyrene into the food.
• the Environmental Protection Agency(EPA) in U.S. which has already established DDT insecticide and dioxin released from incinerators of industrial waste treatment facilities as endocrine disrupting chemicals, also classified the styrene dimers and trimers as being possible agents of endocrine disrupting chemicals.
• Worldwide Fund for Nature(WWF) in Canada classified the styrene dimers and trimers as endocrine disrupting chemicals. From various tests on the abnormal influence of the styrene dimers and trimers on animal life, there is a general consensus of their adverse endocrine effects.
• Japan Food and Drug Agency released a report on April 25, 1998, confirming the presence of styrene dimers and trimers in the polystyrene food containers such as noodle cups.
• the report showed that in 25 different types of disposable food containers using polystyrene papers, 9509/,g of styrene dimers and trimers are found in a gram of polystyrene papers. Few months later, Korea Food and Drug Agency confirmed the same finding.
• the polystyrene can also be produced through an anionic polymerization of styrene monomer in an organic solvent, where an initiator is used to activate styrene monomers to initiate polymerization.
• the activated monomer continuously combines with other monomer to form a polymer until stopped by a terminator.
• This anionic polymerization process for producing polystyrene are disclosed in the U.S. Patent Nos. 5,391 ,655; 5,089,572; 4,883,846; 4,748,222; 4,205,016; 4,200,713; 4,016,348; and 3,954,894. More particularly, U.S.
• Patent '846 discloses an anionic polymerization process for producing polystyrene having a narrow molecular-weight distribution
• U.S. Patents '348, '222, and '655 disclose apparatus for continuous anionic polystyrene polymerization process rather than a batch process
• U.S. Patents '016 and '572 disclose process for preparing initiators and their use in the polystyrene polymerization process.
• none of the above prior arts recognize their adverse endocrine effects when the polystyrene paper is used as disposable food containers.
• the present invention provides a process for preparing highly pure polystyrene for food container by an anionic polymerization wherein the polystyrene has a number-average molecular weight of from 10,000 to 1 ,000,000, and a polydispersity of from 1.1 to 20, styrene dimer content of less than 50ppm and styrene trimer content of less than 500ppm, characterized in that the anionic polymerization is carried out by adding a styrene monomer, a solvent whose amount is more than 100 weight part to 100 weight part of the monomer, and an initiator whose amount is from 0.01 to 1 mol part to 100 mol part of the monomer to initiate polymerization of the monomer into a batch-wise or a continuous-wise reactor, and reacting them at a reaction temperature of 10
• the present invention provides a process for preparing highly pure polystyrene for food container by an anionic polymerization wherein the polystyrene has a number-average molecular weight of from 10,000 to 1 ,000,000, and a polydispersity of from 1.1 to 20, styrene dimer content of less than 50ppm and styrene trimer content of less than 500ppm, characterized in that the anionic polymerization is carried out by adding a styrene monomer, a solvent whose amount is more than 100 weight part to 100 weight part of the monomer, an initiator whose amount is from 0.01 to 1 mol part to 100 mol part of the monomer to initiate polymerization of the monomer, and a coupling agent whose amount is from 0.01 to 5 weight part to 100 weight part of the monomer into a batch-wise or a continuous-wise reactor, and reacting them at a reaction temperature of 10 ⁇ 160 ° C and, wherein the initiator is added
• a polymer produced by a radical polymerization contains a lot of low-molecular weight compounds due to various side reactions. Especially, it contains a lot of styrene dimers and styrene trimers classified as being possible agents of endocrine disrupting chemicals. Therefore, it is undesirable to use the polystyrene obtained by a radical polymerization as the food container.
• the present invention minimizes the above-mentioned side reaction and reduces the production of low-molecular weight compounds such as styrene dimers and styrene trimers by a batch-wise or continuous-wise anionic polymerization process.
• styrene monomer and polymerization initiator are reacted in a solvent at a temperature of from 10 to 160 ° C to provide the a highly pure polystyrene having a number-average molecular weight of from 10,000 to 1 ,000,000, and a polydispersity of from 1.1 to 20, styrene dimer content of less than 50ppm and styrene trimer content of less than 500ppm.
• the amount of the initiator to initiate polymerization is preferably from 0.01 to 1 mol part to 100 mol part of the styrene monomer, and the initiator is preferably added in two or more steps, and more preferably in multiple steps of 2 to 10 steps.
• the amount of the solvent used is preferably more than 100 weight part to 100 weight part of the styrene monomer, and more preferably from 150 to 600 weight part to 100 weight part of the styrene monomer.
• a coupling agent is preferably added to produce the highly pure polystyrene.
• the highly pure polystyrene is produced by reacting the styrene monomer, the solvent whose the amount is more than 100 weight part, preferably from 150 to 600 weight part to 100 weight part of the styrene monomer, the initiator whose amount is from 0.01 to 1 mol part to 100 weight part of the styrene monomer.
• the initiator is added in one step and a coupling agent whose amount is from 0.01 to 5 weight part to 100 weight part of the styrene monomer is added to the reactants, and the reaction is carried out at a temperature of from 10 to 160 ° C .
• the styrene monomer is purified just before use.
• the purification of the styrene monomer is carried out by distilling it at the temperature of 25 ° C under reduced pressure in the presence of reaction inhibitor such as p-tert-butylcatecol, hydroquinone, p-benzoquinone, trinitrobenzene, or passing it through an activated neutral alumina column.
• the polymerization reaction is also preferably carried out at a temperature of 10 to 160 ° C in the absence of air and moisture. If the polydispersity of the polystyrene is less than 1.1 , there is a processing problem due to low melt flow rate, and if the polydispersity of the polystyrene is more than 20, the physical properties of the polystyrene are deteriorated.
• the preferable melt-index of the polystyrene of the present invention is from 0.5 to 50.
• melt-index of the polystyrene is less than 0.5, it is difficult to manufacture the final products with the polystyrene, and if the melt-index is more than 50, the physical properties of the polystyrene are deteriorated.
• the amount of the initiator used in the present invention to initiate polymerization is from 0.01 to 1 mol part to 100 mol part of the styrene monomer.
• the initiator can be added in one or more steps.
• the polydispersity of the produced polystyrene can be controlled by controlling the initiator adding steps and adding time.
• the preferable maximum adding time (duration) of the initiator is 30 minutes for each adding step.
• organomonoalkali metal initiator is preferably used.
• the more preferable initiator includes n-butyllithium, sec-butyllithium, tert-butyllithium, methyllithium, ethyllithium, phenyllithium or mixtures thereof.
• the added amount of the initiator is less than 0.01 mol part, there is a processing problem due to extremely high molecular weight of the polystyrene, and in the case that the amount of the initiator is more than 1 mol part, physical properties of the polystyrene are deteriorated.
• the solvent used in the present invention does not react with other reactants.
• the preferable amount of solvent is more than 100 weight part to 100 weight part of the styrene monomer and the more preferable amount of the solvent is from 150 to 600 weight part to 100 weight part of the styrene monomer.
• the preferable solvent includes non-polar or polar hydrocarbon compounds, such as cyclohexane, n-hexane, benzene, ethyl benzene, n-heptane, toluene, tetrahydrofuran, diethylether or mixtures thereof.
• a coupling agent can be further added in the present invention. The roles of the coupling agent are to shorten reaction time and broaden the polydispersity of the produced polystyrene, and also some coupling agent is used as terminator.
• the amount of the coupling agent used in the present invention is from 0.01 to 5 weight part to 100 weight part of the styrene monomer.
• the coupling agent used in the present invention includes epoxidized soybean oil, epoxidized linseed oil, divinyl benzene, epoxidized liquid polybutadiene, silicon tetrahalide, silicon tetrachloride or mixtures thereof. If the amount of the coupling agent is less than 0.01 weight part, the preferable coupling reaction is not obtained. If the amount of the coupling agent is more than 5 weight part, the excess coupling agent deteriorates the physical properties of the produced polystyrene.
• reaction terminator can be further added in the present invention.
• the reaction terminator used in the present invention includes methanol, ethanol, isopropanol, and water.
• CO 2 can be simultaneously added with water.
• the amount of the CO 2 in mol is preferably equivalent or more than the amount of the initiator in mol.
• the polystyrene produced in the present invention is processed into a polystyrene paper preferably by an extrusion process, and the polystyrene paper is thermoformed to disposable food containers.
• the present invention also provides disposable food containers, such as noodle cups, disposable cups, food trays using the polystyrene.
• the disposable food containers of the present invention do not or much less release styrene dimer and styrene trimer which are classified as being possible endocrine disrupting chemicals than conventional food containers.
• Polymerization was carried out in pure nitrogen atmosphere in a two- gallon stainless steel jacket reactor. To the reaction chamber of the reactor, were added 3.8 liter of cyclohexane, 10cc of tetrahydrofuran, and 0.05 mole of n-butyllithium.
• a prepolymer having a number-average degree of polymerization of 340 and a polydispersity of 1.02 was obtained.
• the above prepolymer was coupled by adding 0.05 mole of epoxidized soybean oil and the reaction was terminated after reacting it for 35 minutes at a temperature of 75 ° C , and then the product was neutralized by adding water and CO 2 .
• a prepolymer having a number-average degree of polymerization of 400 and a polydispersity of 1.02 was obtained.
• the mixture was allowed to react for 20 minutes at a temperature of 50 ° C .
• a prepolymer having a polydispersity of 1.54 was obtained.
• Example 3 To a two-gallon reactor, were added 3.8 liter of cyclohexane, 5cc of tetrahydrofuran, and 0.01 mole of sec-butyllithium. Then, 9 mole of the styrene monomer, which was passed through an activated neutral alumina column just before use, was added to the mixture and allowed to react for 25 minutes at a reaction temperature of 15 ° C . A prepolymer having a number-average degree of polymerization of 900 and a polydispersity of 1.04 was obtained.
• a prepolymer having a number-average degree of polymerization of 1600 lo and a polydispersity of 1.02 was obtained.
• the mixture was allowed to react for 10 minutes at a temperature of 80 ° C .
• the reaction was terminated by adding methanol.
• the above prepolymer was coupled by adding 0.02 mole of epoxidized linseed oil and the reaction was terminated by reacting it for 10 minutes at a temperature of 95 ° C , and then the product was neutralized by adding water and CO 2 .
• Example 7 To a two-gallon reactor, were added 3.8 liter of ethylbenzene, 12cc of tetrahydrofuran, 10 mole of the styrene monomer which was distilled at 25 ° C under reduced pressure in the presence of 0.005% p-tert-butylcatecol just before use, 3 mole of alpha-methylstyrene monomer and 0.05 mole of n-butyllithium.
• the mixture was allowed to react for 5 minutes at a reaction temperature of 35 ° C .
• a prepolymer having a number-average degree of polymerization of 260 and a polydispersity of 1.03 was obtained.
• the mixture was reacted for 10 minutes at a temperature of 80 ° C , then the reaction was terminated and neutralized by adding methanol, CO 2 , and water.
• Comparative example 1 __ To a two-gallon reactor, were added 50 mole of purified styrene monomer and 0.002 mole of benzoyl peroxide as an initiator for heat polymerization.
• the mixture was allowed to react for 20 minutes at a reaction temperature of 70 ° C under nitrogen atmosphere.
• the monomer was allowed to react without using any heat polymerization initiators for 120 minutes at a temperature of 100 ° C under nitrogen atmosphere. Residual monomers in the polymerization solution were removed by vacuum, followed by addition of methanol, and the remaining solution was filtered with a filter paper.
• a final polymer was obtained by drying the filtrate in an oven under vacuum at 100 ° C .
• the mixture was allowed to react for 20 minutes at a reaction temperature of 38 ° C , then the reaction was terminated and neutralized by adding isopropanol, CO 2 and water.
• 100 g of the polystyrene obtained from Examples 1 to 7 and Comparative examples 1 to 2 was extruded by using a twin screw extruder at a speed ranging- from 50 to 200 rpm and at the temperature of from 70 to 200 ° C .
• the temperature of extruded polystyrene increases to from 80 to 130 ° C
• the polystyrene was kneaded by injecting butane gas as a forming agent through side conveying path installed at the two thirds of the twin screw extruder with a injection pressure of from 10 to 100kg/cm 2 , and then the melted polystyrene is extruded by using T-die to form a polystyrene paper.
• the polystyrene paper was thermoformed to a food container at the temperature of from 100 to 170 ° C .
• the polystyrene of Comparative example 3 was processed to produce a formed sheet, but the preferable food container was not obtained due to its low melting index and low melting stress.
• the polystyrene obtained from Examples 1 to 7 and Comparative examples 1 and 2 were made into a foamed sheet and manufactured into a food container.
• 0.5g of the food container was pulverized and added into 10ml solution of 1 :1 cyclohexane and 2-propanol mixture, and the solution was allowed to stand for a day.
• 5ml of the solution was concentrated down to 0.2 ml under nitrogen atmosphere.
• 4.5ml of acetonitrile was added into the solution and stirred for 10 minutes.
• acetonitrile was further added into the solution until total volume of the solution is 5ml.
• the solution was filtered by 5 m filter and the styrene dimer and the styrene trimer contents were measured by GC-Mass. The results obtained are shown in the following Table 1.
• Table 1 Table 1
• the amounts of the styrene dimers and the styrene trimers which are products of side reactions of a radical polymerization process are greatly reduced by preparing the polystyrene by the anionic polymerization according to the present invention.
• the polystyrene obtained from Examples 1 to 7 and Comparative Examples 1 to 2 were made into a foamed sheet and thermoformed into a food container.
• the final product was subjected to an migration test by utilizing water, 20% ethanol, 50% ethanol and n-heptane.
• ND represents “non-detected” and a migrated amount below 0.01 ⁇ g/c ⁇ 2 was designated to be “non-detected”.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Polymerisation Methods In General (AREA)
• Polymerization Catalysts (AREA)

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Citations (8)

• 1998
  • 1998-09-12 KR KR1019980037650A patent/KR20000019517A/ko not_active Application Discontinuation
• 1999
  • 1999-01-05 JP JP11000343A patent/JP2000143725A/ja active Pending
  • 1999-09-11 WO PCT/KR1999/000536 patent/WO2000015678A1/en active Application Filing
  • 1999-09-11 AU AU57612/99A patent/AU5761299A/en not_active Abandoned

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