NL8102415A - Mfg. alpha-methyl-styrene! acrylonitrile! copolymers in aq. suspension - with controlled rate of temp. rise and defined max. temp., gives prod. for prodn. of heat resistant ABS - Google Patents

Abstract

In a process for the prodn. of a copolymer of alpha-methylstyrene (I) and acrylonitrile (II) in aq. dispersion in the presence of a free radical agent, not all the heat evolved during the polymerisation is removed by cooling, the mean rate of temp. rise per hour being kept at below 60 deg.C, esp. below 30 deg.C per hour and the maximum temp. of the aq. dispersion not being allowed to rise above 110 deg.C, esp. not above 95 deg. c. The rate or monomer conversion is maintained at a maximum. Prods. are useful in the prodn. of ABS polymers with improved heat resistance.

Description

* »# STAMICARBON B.V.

Inventors: Jan TUSSEN in Geleen

Jozef L.M. VAN DER LOOS in Sittard Λ 1 3283

PROCESS FOR PREPARING A COPOLYMER

The invention relates to a process for preparing a copolymer of α-methylstyrene and acrylonitrile in aqueous dispersion, in the presence of a free radical-providing compound, in which the heat of reaction released during the polymerization is not completely removed by cooling, so that the rate of conversion of monomers shows a maximum, as well as on an article made from such a copolymer.

Such a method is known from Dutch patent application 7708002 laid open to public inspection.

When preparing a copolymer by polymerizing a mixture of α-methylstyrene and acrylonitrile, which may still contain a minor amount of styrene, it is important to choose the polymerization conditions in such a way that the highest possible heat resistance is obtained. is becoming.

Measures that result in this include: 1. - a high content of α-methylstyrene, 2. - a very low residual monomer content, and 3. - an increase in molecular weight.

All these measures, individually or in combination, can have a clear influence on the heat resistance. However, it has become apparent from investigations by the applicant that in this way the maximum attainable value for the heat resistance is not yet obtained.

The object of the invention is to provide a process for preparing a copolymer of α-methylstyrene and acrylonitrile, whereby a very good heat resistance is obtained.

The process according to the invention is characterized in that during the polymerization the temperature of the aqueous dispersion is not allowed to exceed 110 ° C, while the rate at which the temperature rises on average per hour to a value of no more than 60 ° C. C is held per hour.

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Preferably, the temperature of the aqueous dispersion is not allowed to rise above 95 ° C, more in particular 90 ° C.

The rate at which the temperature rises on average per hour is determined by the following formula: ^ m ”T0 5 v --- · '“ to where

Tm = maximum temperature of the aqueous dispersion (° C) T0 = temperature of the aqueous dispersion at the start of the polymerization (° C) 10 tra time at which Tm is reached (hours) t0 th time of the start of the polymerization (hours )

Preferably, the temperature rise is limited to a maximum of 30 ° C per hour, more in particular 25 ° C per hour.

It is particularly surprising that a copolymer of α-methylstyrene and acrylonitrile can be obtained in this way with improved heat resistance.

In a semi-adiabatic polymerization, as described above, part of the heat of reaction is removed by cooling. It is important, however, that not all of the released heat of reaction is removed by cooling. There must still be an observable maximum in the temperature-time curve

Preferably, the speed v is kept at a value greater than 5 ° C per hour.

There are various possibilities for realizing the method according to the invention. Depending on the operating range of the chosen initiator or initiators, a specific starting temperature can for instance be chosen for this purpose. In addition, it is also possible to use a cooled liquid continuously or intermittently, e.g. water, monomers and / or an emulsion, optionally provided with additives, to be added to the reaction mixture.

A third possibility is the installation and control of an external cooling system with cooling water or another cooling liquid.

Combinations of these options can also be applied.

8102415

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The copolymers of α-methylstyrene and acrylonitrile to be prepared according to the invention may additionally also contain one or more other monomers. Examples of such monomers are methacrylonitrile, methyl methacrylate, ethyl acrylate and styrene. It is also possible to prepare the copolymer of α-methylstyrene, and acrylonitrile in the presence of a rubber, such as polybutadiene, butadiene-styrene rubber, butadiene-acrylonitrile rubber, polychloroprene, acrylate rubber, ethylene-propylene rubber and / or epdm- rubber.

The method according to the invention can advantageously be applied in polymerization in emulsion or in suspension. Such a polymerization can be carried out batchwise, semi-continuously or continuously.

When the polymerization is carried out semi-continuously, the rate of temperature rise per step is calculated, whereas in a continuous polymerization, the rate is calculated from the average residence time of monomer / copolymer from the start of the polymerization to the time of the polymerization. maximum temperature of the aqueous dispersion.

An additional advantage of the process according to the invention is that during the polymerization in an aqueous emulsion the processing behavior of the obtained copolymer is improved. This is especially evident in the coagulation, centrifugation and drying of the copolymer. In addition, the properties of the obtained copolymer powder are very good, so that it can be processed without problems into granulate or directly into molded products.

In the preferred polymerization in aqueous emulsion, use is made of the necessary conventional auxiliaries, such as emulsifiers, caustic soda, salts, soaps, free radical compounds and chain length regulators.

Suitable chain length regulators are the organosulfur compounds such as the commonly used merpaptans as well as the dialkyl diantogens, diaryl disulfides, mercaptothiazoles, tetraalkylthiurammono- and disulfides, etc., separately or mixed together, as well as hydroxyl compounds such as terpinolenes. The dimer of α-methyl-styrene or α-olefins with relatively long chains can also be used. The commercially most commonly used chain length regulators are mainly the mercaptan compounds, of which currently the hydrocarbyl mercaptans having 8-20 carbon atoms per molecule are often used. More particularly, preference is given to mercaptans with a tertiary alkyl group.

The amount of chain length regulator can vary within wide limits depending on the mixture selected, the specific compound, polymerization equipment, emulsifier, and other recipe related variables.

A good result can be achieved by 0.01-5 wt. parts (per 100 parts by weight of monomer) to use organosulfur compound, whereby 0.05-2 wt. sharing is preferred. Suitable organosulphur compounds comprise n-octyl mercaptan, n-dodecylmercaptan, tertiary dodecylmercaptan, tertiary nonylmercaptan, tertiary hexadecylmercaptan, tertiary octadecylmercaptan, tertiary eicosyl mercaptan, secondary octyl mercaptan, secondary tridecyl mercaptan, cyclododecyl 15, aryl mercaptan such as 1-naphthalene thiol, etc., bis ( tetrahydrofuralxantogen), diphenyl disulfide, tetramethylthiuram disulfide, 2-mercaptobenzathiazole, etc. mixtures of these compounds can also be used.

As an emulsifier, very different compounds can be used, such as disproportionated resin soap, fatty acid soap, mixtures of these compounds aryl sulfonates, alkyl aryl sulfonates and other surface active compounds and mixtures thereof. Nonionic emulsifiers can also be used such as polyethers and polyols.

The amounts of the emulsifiers used depend on the type, as well as on the reaction parameters and the concentrations of polymerizable mouthwash in the emulsion polymerization system.

Suitable compounds providing free radicals for the emulsion polymerization process are organic or inorganic peroxides, hydroperoxides, azo compounds, as well as redox initiator systems. These compounds can be added at the beginning of the polymerization. It is also possible to add these compounds partly at the beginning and partly during the course of the polymerization.

Preferably, alkali or ammuria salts and / or redox systems are chosen as initiators. Particular mention should be made of potassium persulfate, ammonium persulfate and sodium persulfate. Examples of suitable redox systems are persalts (e.g. perchlorates 81 0 2 4 1 5 5 or peraulfates), tertiary butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide and methylcyclohexyl hydroperoxide, combined with reducing agents based on acids containing low valency sulfur, sodium sulfoxide, sodium sulfide 5 pyrosulfide, or with organic bases such as triethanolamine with dextrose, sodium pyrophosphate and mercaptans or combinations thereof, optionally in combination with metal salts such as ferrous sulfate. These initiators or initiator systems can be dosed in one go, stepwise or even gradually. The choice of initiator or initiator system basically determines the temperature at which the polymerization starts.

The method of coagulation depends on the emulsifier used. In the case where an anionic or cationic emulsifier has been used (ie an emulsifier which is active only in a certain pH range), the coagulation can be accomplished by changing the pH of the latex.

When using emulsifiers that become ineffective at elevated electrolyte concentrations, the latex can be coagulated by adding appropriate electrolytes, such as calcium chloride, aluminum chloride, or aluminum sulfate.

After the coagulation, the coagulated latex is separated from the water phase, washed and then dried. The resulting polymer powder can then be further processed into granulate.

The copolymer of α-methylstyrene is mainly used to improve the heat resistance of other plastics, in particular styrene-containing plastics, such as ABS. In addition, the copolymer is also used as such, for example for household and / or electrical items, as well as for certain car parts.

The invention is now illustrated by some non-limiting examples. *

Example I

The polymerization was performed in a 100 L reactor equipped with a fast-acting stirrer (tip speed 5.1 m / s). The reactor was charged under nitrogen with 56 L of oxygen-free deionized water, in which 45 g of KOH and 485 g of resin soap were dissolved. To this was metered 81.024 1 5 6 + according to 7.77 kg of acrylonitrile and 16.51 kg of α-methylstyrene.

The reaction mixture was heated to 50 ° C with stirring, after which 152 g of potassium persulfate (KPS) dissolved in 5 L of deionized oxygen-free water was added. The temperature was kept constant at 50 ° C for 30 min, after which the polymerization temperature was gradually raised to a temperature between 85 ° and 95 ° C over 90 min.

45 g after the start of the polymerization, 228 g of tert was passed over a period of 30 min. dodecyl mercaptan (TDDM) dosed. 105 minutes after raising the temperature, an additional 152 g of KPS dissolved in 5 L of water were added to the reaction medium. The temperature was then kept constant for a further 30 minutes, after which the reaction mixture was cooled to 60 DEG C. in 60 minutes and allowed to drain.

The polymer latex thus obtained was coagulated with H 2 SO 4 at high temperature, about 90 ° C 95 ° C. The resulting powder was separated, washed and dried. 23.4 kg of polymer with a moisture content of 2% and a free monomer content of 0.7% were obtained.

In addition to this good flow value, this product was found to have a high HDT 20 [(tempered at 105 ° C) determined according to ASTM D-648 with a load of 1820 kPa (18.5 bar)] of 117 ° C. The flexural strength determined according to ASTM D-790 was 131 N / mm 2.

Example II

This example is analogous to Example I, however instead of a fast-acting agitator, a slow-rotating agitator was used with a tip speed of 1.1 m / s, and the amount of TDDM used was added in its entirety already at the beginning of the polymerization. In addition, instead of 45 g of KOH, 19 g of Η0Η was added, keeping the pH below 10.5 by the pH.

This product was also found to combine good workability and high HDT while retaining flexural strength (see table).

Example III

This example was analogous to Example II. However, 35 was operated with a varying stirring speed. At the beginning of the polymerization up to about 60 minutes after the first dose of potassium persulfate, 8102415 1 ^ 7 was stirred at a tip speed of 1.0 m / sec. after which the stirring speed was increased to 3.2 m / sec. This method presented less risk of unwanted coagulate formation than in Example II. Results see table.

Example IV

This example was carried out in the same manner as Example I with the difference that at the beginning of the polymerization, 50% of the soap and the water, 25% of the monomers and the initiator and 10% of the TDDM were presented. The rest of the mono-10 lakes, TDDM, initiator, soap and water were added to the reactor as an emulsion over 60 minutes after the start of polymerization over a 60 minute period.

For results see table.

Example V

The polymerization was carried out in a reactor with an effective content of about 28 m3. 15.3 m3 of deionized water at 50 ° C in which dissolved 129.2 kg of emulsifier and 9.1 kg of Κ0Η were added to the reactor. 52 kg of tert were then added. dodecyl mercaptan, 2564 l of acrylonitrile and 4827 l of α-methylsty-20 reen. After the reaction mixture was brought to a temperature of 50 ° C, 51.7 kg of potassium persulfate dissolved in 2.2 m3 of water were added to this. The reaction mixture was stirred at a tip speed of 1.9 m / sec, which is quite low for such a reactor. The temperature was brought to 90 ° G in 2.5 hours. After 25 minutes after reaching the maximum temperature, a further 51.7 kg of potassium persulfate dissolved in 2.2 m 3 of water was added to the reactor. Then, in about 2 hours, the temperature was gradually lowered to 60 eC, after which the resulting polymer latex was passed to a coagulation vessel. The coagulation was performed at about 93 ° C with 30 H 2 SO 4. The resulting powder was centrifuged off, washed and dried to a moisture content of 1%. 6,380 kg of polymer with a free monomer content of 0.4% methyl styrene and 0.02% acrylonitrile were obtained.

For the properties of this product see table.

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Examples according to the invention

I II III IV V

spiral flow length 75 82 71 76 75 S / V 4.7 3.9 4.7 5.1 5.4 5 HDT ° C 1) 117.. 116 118 117 118 bend. N / mm2 2) 131 122 135 140 140 tempered, according to ASTM D-648.

2) ASTM D-790.

From these examples it clearly follows that the products prepared by using the method according to the invention corabinate a good heat resistance with a good processability and a good bending strength * 8102415

Claims (7)

9 3283 1. A process for preparing a copolymer of α-methylstyrene and acrylonitrile in aqueous dispersion, in the presence of a free radical-providing compound, in which the heat of reaction released during the polymerization is not completely dissipated by cooling, so that the rate of monomer conversion has a maximum, characterized in that during the polymerization the temperature of the aqueous dispersion is not allowed to exceed 110 ° C, while the rate at which this temperature rises on average per hour to a value of less than 60 ° C keeps 10 per hour. 2. Process according to claim 1, characterized in that the temperature of the aqueous dispersion is not allowed to exceed 95 ° C. 3. Process according to claim 1 or 2, characterized in that the rate of temperature rise is kept at a value of less than 30 ° C. 4. Process according to any one of claims 1-3, characterized in that the polymerization is carried out in emulsion. 5. Method essentially as described and illustrated by the examples. 6. Object wholly or partly manufactured from a copolymer obtained according to any one of claims 1-5. Use of a copolymer obtained by using the method according to any one of claims 1 to 5 to improve the heat resistance of ABS. MH / WLS 81 0 2 4 1 5