NO170744B - DEVICE FOR SUSPENSING THE PARTS IN A CHAMBER RING OVEN FOR CARBON CONTAINING BLOCKS - Google Patents

Description

Process for the production of polystyrene with high clarity and impact strength.

The invention relates to the production of polystyrene.

Many different applications have been found for polystyrene in industry. One of the important uses is the use as an industrial casting resin. Generally, styrene resins that produce clear casting compositions have low impact strength. High impact polystyrene has been produced in a variety of materials, including graft polymers and blends which necessitate the use of relatively large amounts of rubber, all of which, when molded, form opaque or hazy products.

Styrene is soluble in aliphatic hydrocarbon solvents, such as hexane, pentane, petroleum ether and the like. Polystyrene is not soluble in these solvents. Attempts to polymerize styrene in such solvents result in a polymer that sticks to the equipment and appears as large globules, making such polymerization commercially impractical.

The peculiarity of the present invention appears from the patent claim.

The polymerization according to this invention is carried out in such aliphatic solvents as mentioned above. A small amount of polymer is added as a suspending agent which is soluble in the solvent used, e.g. a polymer or copolymer of a diene containing 4 to 6 carbon atoms, such as 1,3-polybutadiene, polypiperylene, polyisoprene, poly-1,3-(2,3-dimethylbutadiene) and poly-1,3-(2-methylpentadiene) ) or a copolymer of at least 50% of such a diene with styrene, alpha-methylstyrene, para-methylstyrene or other hydrocarbon monomers which results in a polymer which is soluble in the hydrocarbon solvent at the temperature used, although the preferred suspending agents are enumerated above, it is possible to use polymer or copolymers of olefinic hydrocarbons containing from 2 to 10 carbon atoms and which are soluble in the aliphatic hydrocarbon solvent at the temperature used. Such poly-

more include polyisobutylene, polypropylene, polybutene, ethylene-propylene copolymers, isobutylene-isoprene copolymers, isobutylene-styrene copolymers and the like. The use of small amounts of such polymeric suspending agents makes it possible to produce polystyrene in the form of particles with a size that is easily filterable. By varying the amount and molecular weight of the suspending agent, non-aqueous suspensions of particles are obtained which quickly settle and can be easily centrifuged or filtered.

Generally, the particle size in the suspension will increase as the molecular weight of the suspending agent decreases, and usually the molecular weight of the polymeric suspending agent will be above 1500, since materials with lower molecular weights will not usually provide the desired suspension. The particle size will decrease as the amount of the particular suspending agent used increases, i.e. either increase the concentration of the suspending agent in the solvent or increase the quantity per 100 parts styrene. Usually from 0.05 to 3 parts by weight of suspension agent will be used per 100 parts monomer. The quantity of the suspending agent used will determine the size of the particles formed. The more effective the suspending agent is, the smaller amount is needed to produce the desired suspension.

The saturated aliphatic hydrocarbons containing from 3

to 15 carbon atoms, are the preferred solvents for the process and they include propane, butane, isobutane, pentane, isopentane, neopentane, hexane, isohexane, neohexane, 2,3-dimethylbutane, heptane, isoheptane, octane, isooctane, nonane, isononane, decane, undecane, dodecane, trimethyldodecane and mixtures of any of these. In cases where polystyrene is to be isolated from the suspension, the solvents with a lower boiling point are preferable.

Alkyl or aryl lithium catalysts can be used. These include ethyllithium, butyllithium, amyllithium, hexyllithium, 2-ethylhexyllithium, n-decahexyllithium, trimethylenedilithium, tetramethylenedilithium, pentamethylenedilithium, phenyllithium, tolyllitium, xylyllithium, naphthyllithium etc.

The monomer-solvent mixture must be essentially free of contaminants that can react with the catalyst and destroy its activity. The harmful pollutants usually consist of water, air or compounds containing active hydrogen atoms, such as phenyl or alkyl acetylenes, alcohols, phenols, some carbonyl compounds and the like. When these materials are present, some catalyst will react with them and be destroyed. An excess of catalyst must therefore be used when such contaminants are present.

One method of achieving the desired purity of the styrene monomer and solvent required for alkyl or aryl lithium catalysts is to pass a solution of these two through a column containing activated alumina. The resulting solution has a sufficiently low degree

of contaminants to be able to work satisfactorily in the process. The small amounts of impurities, such as water, air or various carbonyl compounds that remain after this treatment, can be removed by a small amount of the anionic catalyst used.

The molecular weight of the suspending agent can be as low as about 1500, but can also be higher such as 15,000 or much higher. There is no critical upper limit for the molecular weight. Larger amounts of high molecular weight gums can produce opacity in the product.

The temperatures in the examples are illustrative, and the temperatures which are known to be used in polymerization with the respective classes of catalysts can be used. A polymerization temperature in the range from -100°C to +250°C is satisfactory, depending on the particular conditions, which will be readily understood by a person skilled in the art.

The properties of polyethylene resins obtained by this process and then injection molded depend on the molecular weight of the polystyrene. This can easily be measured by measuring the viscosity of a 1# solution of the polymer in toluene. Relative viscosities of between 1.5 and 3.0 give the most satisfactory results. If the viscosity is lower than 1.5, the product has reduced impact resistance. If it is above 3.0, it is extremely difficult to injection mold the product in a satisfactory manner. Polystyrenes with such molecular weights, when produced with an alkyl or aryl lithium as a catalyst, have high impact strength.

Methods of regulating the molecular weight of the styrene whip product depend on the particular catalyst used. Usually, an increase in the catalyst concentration will reduce the molecular weight. In polymerizations where an alkyl or aryl lithium catalyst is used, the molecular weight is quite sensitive to the amount of catalyst used and to contaminants present in the solution to be polymerized. Sufficient organo-lithium compound should then be used to provide between about 0.10 and about 1.0 milliatoms of active lithium per 100 grams of monomer, in addition to the amount of catalyst needed to remove the last remnants of harmful contaminants. It is usually desirable to use enough of such a catalyst to provide such an excess of between 0.2 and 0.6 milliatoms of active lithium per 100 grams of monomer, to produce styrene resins in the desired viscosity range for injection molding.

The production of resins with high impact strength which are essentially polystyrene and which do not require the presence of relatively large amounts of high molecular weight rubbers is not previously known. The presence of the relatively large amounts of high molecular weight rubber in the high impact resins, which, as is known in the industry, results in a significant reduction in the modulus and hardness of the resin and likewise destroys its clarity. High impact resins made in accordance with this invention can be made with a flexural modulus in excess of 28,100

p

kg/cm and a hardness on the M scale of over 50, and has a clarity that cannot be achieved by previously known methods. The clarity of the materials is difficult to define quantitatively since much depends on the thickness of the samples and the casting conditions. Material samples produced by methods according to this invention have been formed so that it is possible to read writing

through as much as 1 inch thick samples of injection molded material. . The properties of the resulting polymers can be altered as has been the practice of certain processes in the manufacture of high impact commercial products, such as admixing a rubbery polymer, but this technique is not usually necessary.

As is known in the industry, the impact strength depends to a certain extent on the conditions used in injection molding. Generally, the highest impact strength is achieved when the polymer is molded at the lowest temperature and highest pressure practicable.

The following expressions are used in the examples when describing the properties of the different products.

The impact strength is determined by the Izod notch method, and is stated in cmkg per cm.

The modulus is Young's Modulus and is stated in kg per cm 2.

The hardness is indicated as Rockwell M.

Mooney means the viscosity expressed as ML-4 at 100°G.

The thermal deformation is indicated in degrees Celsius at a load of 18.6 kg/cm <2>.

ASTM methods were used.

Clarity or transparency was determined visually by inspection of injection molded pieces.

Harnesses are weight components unless otherwise stated.

EXAMPLES.

For use as suspending agents in Examples 1-3, a low molecular weight polybutadiene was prepared by polymerizing 100 g of butadiene in 300 g of hexane for 4 hours at 50°C with a 1.75 M solution of butyllithium in hexane in amounts as shown in the following table. The amounts in millimoles are listed directly below the corresponding amounts in ml.

SUSPENSION AGENT SOLUTION.

A preferred suspending agent is obtained by using sufficient lithium catalyst to provide 10 to 60 milliatoms of active lithium per 100 g of butadiene.

These polymer solutions were shaken in air until the characteristic amber color of the active lithium compound had disappeared. The resulting solutions were then used as suspending agent in examples 1-3.

EXAMPLES 1-3.

Butyl lithium and the suspending agent solutions prepared above were added to a solution of 150 g of styrene in 280 g of heptane in accordance with the following table:

The polymerization was carried out in closed bottles which were freed from air and moisture. The reaction was complete after 4-5 hours at 50°C. The characteristic yellow color of the suspension was removed by adding 0.5 ml of water and shaking. The heptane was decanted off and the finely divided polymerizate was washed with iso-propanol and dried in a cabinet at 75°C. The polymers were formed by injection molding, after which they had the following properties:

All of these products had sufficiently high impact resistance to even be useful substitutes for commercial tire compounds, etc., which are now used, and the products of Examples 1 and 2 are particularly advantageous because the products molded therefrom are clear and transparent.

EXAMPLE 4- 11. -

These examples illustrate the use of a selection of polymers and copolymers as suspending agents in the polymerization of styrene 1 an aliphatic hydrocarbon solvent.

In each of the examples given below, 430 g of a

35% solution of styrene in heptane polymerized for 5 hours at 50°C with butyllithium as catalyst, as shown in the table.

Suspension agent declaration:

"C-oil" MD-11 E-11D is a commercial product of Enjay Chemical Company, and is known as a low molecular weight liquid copolymer of butadiene and styrene.

"FE-S 195" is a butadiene-styrene copolymer containing 2596 bonded styrene and is manufactured by The Firestone Tire & Eubber Company.

"PBD" is a 12-Mooney polybutadiene made by polymerizing butadiene with butyllithium in hexane solution.

Polypiperylene was produced by polymerizing piperylene with butyllithium in hexane solution to an intrinsic viscosity of 0.42.

Butyl rubber M-25 is an isoprene-isobutylene copolymer from

Enjay Chemical Company.

Polypropylene is a rubbery atactic polypropylene made with a Ziegler catalyst.

Polyisoprene is a high-molecular polymer produced by polymerizing isoprene in hexane solution with a butyllithium catalyst.

It is clear from examination of the table that a good suspension is obtained with the diene copolymers which contain more than 50% diene rubber. Poorer suspension was achieved with butyl rubber and polypropylene, but in all cases evidence of suspending action can be seen, and this results in improved filterability of the polymeric product. None of the injection molded products had the sparkling clarity observed in the first two examples. Clarity depends on the compatibility of the suspending agent with the product, which in turn depends on the molecular weight and structure of the suspending agent as well as the amount used. By carefully regulating these factors, it is possible to produce products that are more or less clear.

EXAMPLE 12.

This example illustrates the preparation of a copolymer of styrene and α-methyl-styrene. A solution containing 98 g of styrene, 52 g of α-methylstyrene and 1.9 g of polybutadiene in 280 g of heptane was polymerized in the presence of 1.30 ml of 1.75 molar butyllithium in hexane. The polybutadiene was produced by polymerizing butadiene in the hexane solution with butyllithium in a ratio of 40 ml of butyllithium per 100 g of butadiene. The polymerization took place for 16 hours at 50°C. A good suspension was achieved.

Claims (1)

Process for the production of polystyrene with high clarity and impact strength, by polymerization in an aliphatic hydrocarbon solvent, in that the styrene is added to a polymeric suspension agent with a molecular weight of at least 1500 which is dissolved in the solvent, at the temperature at which polymerization takes place, characterized by that the polymerization is carried out in the presence of ionic catalysts until grains of size 10 microns to 5 mm are formed which are insoluble in the solvent at the said temperature.