JPH04183703A - Method of preparing copolymer of alpha-methyl styrene and acrylonitrile - Google Patents

Abstract

PURPOSE: To obtain a copolymer of α-methylstyrene and acrylonitrile having good composition uniformity and impact strength by subjecting α-methylstyrene and acrylonitrile to the emulsion polymerization under such a specific condition that excess unreacted α-methylstyrene is present and then, adding the entire monomers to complete the emulsion polymerization.

CONSTITUTION: A first monomer feed flow containing α-methylstyrene and acrylonitrile at a weight ratio of 77/25-85/15 is filled in a reactor containing 0.05-5.0 wt.% polymer seed latex under the emulsion polymerization condition until, based on the total weight of the monomers and a polymer, the amount of unreacted α-methylstyrene and acrylonitrile comes to 20-45% and, at the same time, the amount of unreacted α-methylstyrene comes to 670-5,000 wt.% based on unreacted acrylonitrile and subsequently, a second feed monomer flow containing acrylonitrile in the absence of α-methylstyrene is filled in the reactor until the amount of unreacted monomers comes to 5-15% based on the total monomer weight, and until the conversion reaches 90 wt.%, the emulsion polymerization is continued to obtain the desired copolymer.

COPYRIGHT: (C)1992,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application W) The present invention relates to a method for producing a copolymer of alpha-methylstyrene and acrylonitrile. More particularly, the present invention relates to an emulsion polymerization process for the production of such copolymers that have improved uniformity of monomer content, thereby yielding polymers with improved physical properties.

Batch emulsion polymerization of α-methylstyrene and acrylonitrile in which both monomers a-methylstyrene and acrylonitrile are added at the beginning or one or both monomers are added during the course of polymerization. The variations in monomer content experienced in the present invention result in compositions with varying monomer contents. Fluctuations or compositional biases such as those shown in B are the result of differences in the reactivity of both monomers. In particular, acrylonitrile was found to be highly reactive under standard polymerization conditions and was consumed faster than Q-methylstyrene monomer. As a result, copolymers made from an initial charge of both monomers, or made using reaction conditions that do not take into account the differences in reactivity of the two monomers, are polymer mixtures with widely varying monomer contents. Configure.

It is believed that optimal polymer properties are obtained from copolymers consisting of a-methylstyrene/acrylonitrile with a weight ratio of polymerized monomers of 70/30 to 85/15. Copolymer products containing only small amounts of polymer products with compositions outside this range tend to lack desirable physical properties such as toughness or impact strength.

No. 4,526,928 states that at any time during polymerization
A process is described for the preparation of copolymers of α-methylstyrene/acrylonitrile that maintains an α-methylstyrene/acrylonitrile ratio greater than 0/10. Although such a process results in the production of a copolymer with a high glass transition point, a process that involves polymerizing both monomers while maintaining such a high ratio of a-methylstyrene/acrylonitrile disadvantageously results in the production of copolymers with high glass transition points. It has now been discovered that the excessive amount of α-methylstyrene, which has a relatively low reaction rate, requires long reaction times. Consequently, it is desirable to achieve a reduction in reaction time in order to provide a commercially acceptable polymerization process. Moreover, the glass transition temperature of polymers produced by the above method is not necessarily better than those produced using reduced ratios, and the toughness Z of the resulting polymers is
It has now been discovered that, in many cases, the impact value is inferior (as measured by the Notsuchi-Izotsu impact value). This undesirable result is believed to be due to compositional bias, ie, the production of a small amount of polymer with inferior properties due to variations in the ratio of monomers during polymerization.

U.S. Pat. No. 4,294,946 also describes a method for producing copolymers of alpha-methylstyrene and acrylonitrile.

In the method described therein, the reaction is not completed until the conversion of monomer exceeds 99%. In this method, a-methylstyrene is charged in a patch manner and acrylonitrile is added to the reactor by a secondary addition step. Although this patent suggests that the process may be operated in a continuous manner, no teaching is suggested regarding relative monomer addition rates over time for such a continuous process. Moreover, this patent does not provide any teaching regarding the existence and effect of compositional bias in the copolymer and how to alleviate it.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, it would be desirable to provide an improved method for producing copolymers of α-methylstyrene and acrylonitrile that yields polymers with improved uniformity and physical properties. That would be highly desirable. The problem to be solved by the present invention is to provide such an improved manufacturing method.

(Means for Solving the Problems) According to the present invention, as means for solving the above problems, the following steps 1) to 4) are included.
A method for producing a copolymer of alpha-methylstyrene and acrylonitrile with a total monomer ratio of (alpha-methylstyrene/acrylonitrile) from 0/30 to 85/15 is provided: 1) 77/25 to 85/Is
A first monomer feed stream containing alpha-methylstyrene and acrylonitrile in a weight ratio of 0.005 to 50% by weight (based on the final copolymer weight) polymer species is operated under emulsion polymerization conditions. Add the latex to the well-mixed reactor in a continuous or semi-continuous manner until the amount of unreacted alpha-methylstyrene and acrylonitrile in the reactor is 20-45% based on the total weight of monomer and polymer. 2) Then, add it to the above reactor while mixing under emulsifying conditions. ? - a feed stream of a second monomer containing acrylonitrile in the absence of alpha-methylstyrene, such that the amount of unreacted alpha-methylstyrene and acrylonitrile in the reactor is between 5 and 15, based on the weight of the combined monomer and polymer; 3) then continue the emulsion polymerization until the total monomer conversion reaches at least 90% by weight;
and 4) recovering the copolymer of alpha-methylstyrene and acrylonitrile.

(Effects of the Invention) The copolymers produced by the above method according to the present invention have improved compositional uniformity and concomitant improvements in physical properties, especially improved toughness (as compared to polymers produced without the above constraints). (measured by Izot impact). As a result, copolymer products made using the compositions of the present invention can achieve improved levels of performance without concomitantly sacrificing other physical properties. More specifically, melt flow rates, which are normally adversely affected by increasing the level of rubbery additives, are improved due to the inherent improved toughness of compositions made by the method of the present invention. High standards can be maintained by using reduced amounts of additives.

Aspects of the Invention The methods of the invention include the use of emulsifying agents such as sodium lauryl sulfate, potassium oleate, sodium oleate, potassium or sodium salts of fatty acids, potassium or sodium salts of rosin acids, and sodium alkylbenzene sulfonates. Utilizes well-known emulsion polymerization techniques. A particularly desirable emulsifier is sodium n-dodecylbenzenesulfonate. All components used in the polymerization process of the present invention are purified prior to use.

Moreover, the reaction is carried out under an inert atmosphere such as nitrogen for 5 to 20 min.
It is preferably carried out under slightly increased pressure of psig (140-240 kPa).

The reaction is carried out at a temperature of about 35-95°C, preferably about 50-90°C. Use stirring to keep the reaction mixture homogeneous. Free radical initiators such as the well-known sodium peroxydisulfate or potassium peroxydisulfate initiators can be used. Molecular weight regulators such as mercaptans or other suitable chain transfer agents may also be used.

In a preferred embodiment of the invention, the alpha-methylstyrene and acrylonitrile are initially 80/20 to 85/
Add at a monomer weight ratio of 15 alpha-methylstyrene/acrylonitrile. Although it is preferred that the reaction be carried out continuously, semi-continuous addition of monomers can also be used. Semi-continuous addition means that the monomer charge is added in portions and then the reaction is carried out for a period of about 1710 minutes or less of the total reaction time.

Typically, alpha-methylstyrene and acrylonitrile are added continuously under polymerization conditions over a period of 1 to 6 hours.

Generally speaking, the initial charge of the first monomer feed stream is between 600 and 500% by weight based on the weight of unreacted acrylonitrile.
00% by weight, preferably 670-5000% by weight excess of unreacted alpha-methylstyrene is reached. Addition of acrylonitrile monomer alone begins immediately after stopping comonomer addition and preferably continues under polymerization conditions for 1 to 4 hours. Although the addition of acrylonitrile usually results in a reduction in the total amount of unconverted monomer, generally from 600 to 5000% by weight based on the weight of unreacted acrylonitrile.
Preferably an excess of 670-5000% by weight of unreacted alpha-methylstyrene remains. Polymerization is generally allowed to continue for 15 minutes to 1 hour after monomer addition is complete.

In a highly preferred embodiment, the initial monomer concentration and acrylonitrile monomer addition rate are adjusted to
A polymer product having an (alpha-methylstyrene/acrylonitrile) monomer weight ratio of 25 to 78/22 is obtained. Conversions of 90-96% based on total monomer weight are generally employed to achieve commercially practical reaction times. The product is recovered by conventional recovery techniques including steam stripping to remove volatile components, coagulation, and pelletizing the product.

If additional improvement in impact properties is desired, rubbers such as styrene- or styrene/acrylonitrile grafted polybutadiene rubbers, or styrene/butadiene copolymer rubbers may be used. In a preferred embodiment, the alpha-methylstyrene/acrylonitrile copolymer is coated with rubber prior to coagulation and pelletization.
Latex is added.

The resulting rubber-modified polymer product can be dried and used as an injection molding resin.

As previously mentioned, the continuous or semi-continuous addition of acrylonitrile monomer after the initial period of copolymer formation is carried out such that the monomer concentration in the reaction mixture is within the limited ranges described above.

Adding acrylonitrile too quickly results in composition imbalance due to the formation of a copolymer containing excessive amounts of acrylonitrile and having poor impact properties.

The seed latex used for initial polymerization is 100-1.00
Preferably, it comprises any compatible polymer latex having a particle size of 0' angstroms. Highly preferred are polymer latexes consisting of polystyrene, polybutadiene, copolymers of styrene and butadiene, or copolymers of alpha-methylstyrene and acrylonitrile.

(Examples) Examples are shown below to further specifically explain the present invention described above, but these examples are for illustrating the present invention and do not limit the present invention. It should not be interpreted as such.

A 1 gallon glass-lined latex reactor was charged with 1149 g deionized water, 107 g polystyrene seed latex (number average particle size 400 angstroms) (30% active, thereby reducing the final polymer weight). 0.3 g disodium ethylenediaminetetraacetate, 10 g sodium bicarbonate, and 20 g 43% aqueous sodium n-dodecylbenzenesulfonate.

The reactor was purged with nitrogen and then evacuated with a three-water aspirator at room temperature. After the final evaporation, the reactor was
It was pressurized with nitrogen at psi (69 kPa). 85 reactor
℃ and stirred at 2000 rpm. An aqueous feed consisting of 141 g water, 41.8 g 43% aqueous sodium n-dodecylbenzenesulfonate, and 14 g sodium persulfate; and 750 g a-methylstyrene, 187 g acrylonitrile (80/20 a-methyl a monomer feed consisting of styrene/acrylonitrile ratio) and 20 g of n-octyl mercaptan (first monomer feed) were simultaneously stirred to
．． were added to the reactor at a rate of 4 g/hr and 234.6 g/hr, respectively. After 4 hours, addition of the first monomer feed was stopped. The proportion of unreacted monomers based on the total monomers and polymer was 314%. The amount of unreacted a-methylstyrene/acrylonitrile was 2070%.

A second monomer feed consisting of 41 g of acrylonitrile and 0.59 g of n-octyl mercaptan was introduced at 10.
Started at a rate of 4 g/hr. The aqueous feed liquid is 7.
Filled at a rate of 8 g/hr.

Addition of the aqueous feed stream and second monomer stream continued for an additional 4 hours.

The total monomer feed yielded an α-methylstyrene/acrylonitrile ratio of 77/23. The amount of unreacted monomers relative to the total monomers and polymer is 136
%Met. The amount of α-methylstyrene based on acrylonitrile was 650%. The second monomer feed was then stopped, the aqueous stream feed continued for an additional 15 minutes, and the mixture was held at 85° C. for 15 minutes. Antifoam (Antifoam; 15% active, obtained from Dow Corning Corporation) was added and volatile components were steam distilled from the mixture. The reaction progressed to 90% conversion.

The polymerized α-methylstyrene/acrylonitrile ratio in the final latex was 76/24.

Examples 2-4 and Comparative Examples Additional latex samples were prepared substantially according to the technique of Example 1 using various ratios of monomers in the first monomer feed stream. These latexes were blended with bimodal styrene/acrylonitrile grafted butadiene rubber using the following rubber manufacturing method.

Rubber Production 61.979 g of bimodal butadiene rubber latex (75% 1400 Å, 25% 8
000 angstroms, 33% active). The mixture was purged with nitrogen and then evacuated with a three-water aspirator at room temperature. The reactor was heated to 80°C and 150°C
Stir with rp@. 6618 g water, 22.1 g sodium persulfate, and 529.4 g aqueous 43% n-
Aqueous feed consisting of sodium dodecylbenzenesulfonate; and 8603 g styrene and 2427 g
of acrylonitrile were added to the reactor at rates of 1792 g/hr and 2757 g/hr, respectively, starting simultaneously. The addition was completed in 4 hours and the reaction product was held at 80° C. for an additional 15 minutes. Add antifoam agent (Antiform H-10, 15% active),
650 ml of volatile reaction by-products were steam stripped from the mixture. The reaction proceeded to a conversion of 92%.

A blend containing 15% by weight rubber was prepared by latex blending the resins, coagulating, dewatering and pelletizing. Test samples are manufactured by injection molding the product. These samples are tested using ASTM standard methods.

The results obtained are shown in Table 1.

From Table 1, it can be seen that by observing the processing conditions specified in the present invention, a composition with improved toughness and a uniform or improved melt fluorate is produced. Ru.

Patent applicant f! ') 'y E *tk
#>t<=, ;.

Claims (1)

[Claims] A method for producing a copolymer of alpha-methylstyrene and acrylonitrile having a monomer weight ratio of (alpha-methylstyrene/acrylonitrile) from 1.70/30 to 85/15, comprising the steps of: Namely: 1) A first monomer feed stream containing alpha-methylstyrene and acrylonitrile in a weight ratio of 77/25 to 85/15 is operated under emulsion polymerization conditions and initially (based on the final copolymer weight). ) A well-mixed reactor containing 0.05 to 5.0 wt. % and the excess unreacted alpha-methylstyrene is 67% based on unreacted acrylonitrile.
0 to 5000% by weight in a continuous or semi-continuous manner; 2) thereafter containing acrylonitrile substantially free of alpha-methylstyrene into the above reactor while mixing under emulsifying conditions; The second monomer feed stream is adjusted such that the amount of unreacted alpha-methylstyrene and acrylonitrile remaining in the reactor is between 5 and 1, based on the total monomer weight.
3) continuous or semi-continuous charging until the total monomer conversion is at least 90%;
4) recovering the copolymer of alpha-methylstyrene and acrylonitrile; and 4) recovering the copolymer of alpha-methylstyrene and acrylonitrile. 2. The method of claim 1, wherein the first monomer stream has an alpha-methylstyrene/acrylonitrile weight ratio of 80/20 to 85/15. 3. The method according to claim 1, wherein the total monomer conversion reaches 90-96% by weight.