CA1038548A - Process for copolymerizing styrene and acrylonitrile - Google Patents
Process for copolymerizing styrene and acrylonitrileInfo
- Publication number
- CA1038548A CA1038548A CA221,081A CA221081A CA1038548A CA 1038548 A CA1038548 A CA 1038548A CA 221081 A CA221081 A CA 221081A CA 1038548 A CA1038548 A CA 1038548A
- Authority
- CA
- Canada
- Prior art keywords
- acrylonitrile
- styrene
- copolymer
- residual
- alkaline
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Landscapes
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
- Graft Or Block Polymers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for producing a copolymer of styrene and acrylonitrile substantially free of acrylonitrile which comprises copolymerizing styrene and acrylonitrile and treating the resulting copolymer with an aqueous solution of a sulphur compound selected from the group consisting of alkaline sulfides and alkaline disulfides. Thus copolymers of styrene and acrylonitrile are useful for molding purposes and provide lower thermal deformation, better aging, high gloss and improved mechanical properties in comparison to homopolymers of styrene.
A process for producing a copolymer of styrene and acrylonitrile substantially free of acrylonitrile which comprises copolymerizing styrene and acrylonitrile and treating the resulting copolymer with an aqueous solution of a sulphur compound selected from the group consisting of alkaline sulfides and alkaline disulfides. Thus copolymers of styrene and acrylonitrile are useful for molding purposes and provide lower thermal deformation, better aging, high gloss and improved mechanical properties in comparison to homopolymers of styrene.
Description
B ~
BACKGROUND OF T~l~ INYENTION
The present invention relates to a process -for producing styrene and acrylonitrile based copolyml?rs. More particularly, the present invention relates to a process for producing co-polymers of styrene and acrylonitrile (SAN) and copolymers of styrene and acrylonitrile containing an elastomer (ABS). ;~
By comparison with homopolymers of styrene, SAN resins o~fer many advantages, such as a lower thermal dePormation, better aging, high gloss and improved mechanical propèrties.
.
This improvement in several properties becomes apparent when the acrylonitrile content in SAN resins is as low as 5% of weight. However, SAN resins usually are prepared with an acrylonitrile content varying between 25 and 90% by weight.
By polymerizing vinyl compounds, more particularly a mixture o~ styrene and acrylonitrile, in the presence o~ an elastomer, particularly a polybutadiene rubber, ABS compositions are obtained which consist of said rubber and acrylonitrlle~
styrene copolymers, a part of said copolymers being grafted on ~ ~ -the rubber particles. Such ABS resins have good mechanical ~properties, particularly high-impact resistance, when the rubber is gra~ted by at least 5% o~ its own weight o~ styrene-acrylonitrile copolymers, the remainder of these copolymers iorming a continuous phase wherein the particles o~ grafted rubber are dispersed. ~'9:~;
.: ' ~` .':
For preparing ABS or SAN resins, usual polymerization processes may be used, either mass, suspension or emulsion polymerizati~n. In commercial practice, however, a two-step copolymerization is most often used, such two step process comprising a mass precopolymerization step followed by a sus-pension copolymerization step. The resins so obtained are beads which are easily separated from the reaction mixture and may then be washed and dried. However, when using any one of ~ .
,s,, t S4~
these processcs, the ratio o~ styrene ~'o acrylonitrile in the copolymers is al~v~ys lo~er than the ratio of styrene to acrylonitrile in the starting monomers mixture if the acryloni-trile content in said monomer mixture is higher than 25%.
Consequently, in such case, residual acrylonitrile remains in the resin wl;en the copolymerization is not completed at 100%.
It is not advisable, however, to carry out the copolymerization to the very end with a view ofa~oiding the presence of residual acrylonitrile in the copolymer. The reaction rate is lo~er ;~
10 and lower when the monomer concentration decreases. Further, by carrying on the copolymerization when the total amoun-t of styrene is a]ready copolymerized results in production of the homopolymer of acrylonitrile and this homopolymer h~s a detri-mental effect on the color of the ~BS resins. The presence of residual acrylonitrile (which is very toxic) in the resins is harmful when these resins are handled and worked. Further, .
acrylonitrile is water soluble and the residual process water . . ~
contains acrylonitrile which has to be removed. For instance, ABS resins which are manufactured from a mixture of styrene and acrylonitrile with an acrylonitrile content of 29% may contain 1 to 1.5~ of residual acrylonitrile and the waste process water may contain about 0.5% of acrylonitrile when the content o~ residual styrene is 0.5%.
The object of the present invention is to provide a . ~:
new and improved process for producing ABS and SAN resins which are practically free ~rom residual acrylonitrile.
SUM~IARY OF THE IN~ENTION
The present invention is a process for treating SAN and ABS resins to remove residual acrylonitrile,-said process ; 30 comprising treating SAN and ABS polym~rs with an aqueous solution of a sulphur compound selected from the group r~
, : ;: : ,. .: . . .-, .. .. . .. ..... . .
consisting of the sul~ides and disulfides of alkaline metals, and mlxtures thereof.
Acrylonitrile reacts with these sulfides or ~isulfides and the reaction products which are non-toxic and which would not have been removed by further washing, have no detrimental effect on the properties of the resins The treated resin, which is free from residual acrylonitrile, also has some properties which are better than the properties of similar resins which have not been treated by the present process.
For instance, an ABS resin which has been washed by a sulfide or a bisulfide of an alkaline metal has a higher tensile strength and a higher softening temperature.
DESCRIPTION OF T~ PREFERRED EM~ODIMENTS
The sul~ide or disulfide treating agent o~ the present invention does nQt need to be used in an amount exactly corres-ponding to the stoechiometric amount based on the residual , acrylonitrile. By adding such a sulfide or disulfide, the hydrolysis reaction of the acrylonitrile with formation of;
3,3'-oxydipropionitrile is improved. One reaction of the sul~ide ~ or disulfide, for instance Na2S, with acrylonitrile is the following:
water Na2S + 2 CH2 = CH-CN ~ (NC-CH2-CH2)2 S + 2 NaOH-The basicity of the reaction mixture resulting from the ~orma~tion of NaOH promotes the hydrolysis of the rest of residual acrylonitrile. Accordingly, the amount of sulfide or disulfide may be as low as 25% of the stoechiometric amount. On the other hand, the sulfide or disulfide may be used in excess of this stoechiometric amount, however, use of such amounts is without improvement in the results. ABS or SAN resins, ~30 containing products resulting from the hydrolysis of acryloDi-trile, are yellow Therefore, it is preferable to remove the _3_ ~0~548 residual acrylonitrile by reacting it with a sulfide or di~
sulfide and to avoid or at least to minimize the hydrolysis reaction. Consequently, the sul~ide or disulfide pre~erably is used in an amount of between about 50 and 100%, more particular~
ly between 70 and 100% of the stoechiometric amount~ i The following examples are presented in order to illustrate the presen~ invention but are not to be ~onsidered as limiting thereof.
BXA~PLE 1 The process described in Belgian patent No. 811,750 was ;~
used for manufacturing an ABS resin from 23.27 kg of s~yrene, 9.50 kg of acrylonitrile and 4.92 kg of rubber ~Stereon 703A, a product of Firestone Tire and Rubber Co.). The process is a two step process comprising a mass copolymerization step followed by a suspension polymerization step. Beads of ABS resin were so obtained. The content of residual acrylonitrile was 1.6~ by weight of resin and 0.5% by weight of water (analysis by vapor phase chromatrography with ionization by hydrogen flame). `
Comparatlve experiments were carried out by adding various Compounds known to react with acrylonitrile. These compounds were added at the end of the suspension polymerization, the beads having a temperature of between 100 and 110C attsuah time. The beads were not yet hard and the reaction, therefore, was improved.
The reaction time between the beads and these compounds was one hour. The results of these comparative experiments were as follows: ;-`' ~': ~
, ~'..~
*Trademark Acrylonitrile con tent (% by weight) after treatment Reactant in the water in the beads - ~ , ~
NaH~03 0.08 0.28 Diethanolamine 0.05 0.17 Na~S 0.04 0.01 Na2S 0.03 not detectable These results clearly show that sodium sulfide and sodium disulfide are more active than the other compounds in reactlng ~;
with the acrylonitrile.
By using Na2S in an amount corresponding to about 25%
o~ tbe stoechiometric amount, the content o~ resldual acryloni-trile in the ABS resin does not decrease below 0.06% and the product prepared by molding this ABS resin is yellow. By using ~;~
Na2S in an amount corresponding to 80% of the stoechiometric amount, the content of residual acrylonitrile is decreased to 0.01% and the molded product is not yellow, EXAMPLE 2 `
SAN resin was prepared ~rom 2,300 litres o~ styrene and 865 litres o~ acrylonitrile. The process used was a mass co-polymerization with ~ormatlon o~ a mixture having a viscosity o~ 2,000 centipoises. This mixture has then been polymerized by a suspension process at a temperature of 115 to 135C. The ~;
beads were slowly cooled to a temperature o~ 110 C. and then washed by an aqueous solution containing 8 kg of Na2S in 40 litres o~ water. A~ter this washing, the beads were substan-tially ~ree from residual acrylonitrile.
' ~,
BACKGROUND OF T~l~ INYENTION
The present invention relates to a process -for producing styrene and acrylonitrile based copolyml?rs. More particularly, the present invention relates to a process for producing co-polymers of styrene and acrylonitrile (SAN) and copolymers of styrene and acrylonitrile containing an elastomer (ABS). ;~
By comparison with homopolymers of styrene, SAN resins o~fer many advantages, such as a lower thermal dePormation, better aging, high gloss and improved mechanical propèrties.
.
This improvement in several properties becomes apparent when the acrylonitrile content in SAN resins is as low as 5% of weight. However, SAN resins usually are prepared with an acrylonitrile content varying between 25 and 90% by weight.
By polymerizing vinyl compounds, more particularly a mixture o~ styrene and acrylonitrile, in the presence o~ an elastomer, particularly a polybutadiene rubber, ABS compositions are obtained which consist of said rubber and acrylonitrlle~
styrene copolymers, a part of said copolymers being grafted on ~ ~ -the rubber particles. Such ABS resins have good mechanical ~properties, particularly high-impact resistance, when the rubber is gra~ted by at least 5% o~ its own weight o~ styrene-acrylonitrile copolymers, the remainder of these copolymers iorming a continuous phase wherein the particles o~ grafted rubber are dispersed. ~'9:~;
.: ' ~` .':
For preparing ABS or SAN resins, usual polymerization processes may be used, either mass, suspension or emulsion polymerizati~n. In commercial practice, however, a two-step copolymerization is most often used, such two step process comprising a mass precopolymerization step followed by a sus-pension copolymerization step. The resins so obtained are beads which are easily separated from the reaction mixture and may then be washed and dried. However, when using any one of ~ .
,s,, t S4~
these processcs, the ratio o~ styrene ~'o acrylonitrile in the copolymers is al~v~ys lo~er than the ratio of styrene to acrylonitrile in the starting monomers mixture if the acryloni-trile content in said monomer mixture is higher than 25%.
Consequently, in such case, residual acrylonitrile remains in the resin wl;en the copolymerization is not completed at 100%.
It is not advisable, however, to carry out the copolymerization to the very end with a view ofa~oiding the presence of residual acrylonitrile in the copolymer. The reaction rate is lo~er ;~
10 and lower when the monomer concentration decreases. Further, by carrying on the copolymerization when the total amoun-t of styrene is a]ready copolymerized results in production of the homopolymer of acrylonitrile and this homopolymer h~s a detri-mental effect on the color of the ~BS resins. The presence of residual acrylonitrile (which is very toxic) in the resins is harmful when these resins are handled and worked. Further, .
acrylonitrile is water soluble and the residual process water . . ~
contains acrylonitrile which has to be removed. For instance, ABS resins which are manufactured from a mixture of styrene and acrylonitrile with an acrylonitrile content of 29% may contain 1 to 1.5~ of residual acrylonitrile and the waste process water may contain about 0.5% of acrylonitrile when the content o~ residual styrene is 0.5%.
The object of the present invention is to provide a . ~:
new and improved process for producing ABS and SAN resins which are practically free ~rom residual acrylonitrile.
SUM~IARY OF THE IN~ENTION
The present invention is a process for treating SAN and ABS resins to remove residual acrylonitrile,-said process ; 30 comprising treating SAN and ABS polym~rs with an aqueous solution of a sulphur compound selected from the group r~
, : ;: : ,. .: . . .-, .. .. . .. ..... . .
consisting of the sul~ides and disulfides of alkaline metals, and mlxtures thereof.
Acrylonitrile reacts with these sulfides or ~isulfides and the reaction products which are non-toxic and which would not have been removed by further washing, have no detrimental effect on the properties of the resins The treated resin, which is free from residual acrylonitrile, also has some properties which are better than the properties of similar resins which have not been treated by the present process.
For instance, an ABS resin which has been washed by a sulfide or a bisulfide of an alkaline metal has a higher tensile strength and a higher softening temperature.
DESCRIPTION OF T~ PREFERRED EM~ODIMENTS
The sul~ide or disulfide treating agent o~ the present invention does nQt need to be used in an amount exactly corres-ponding to the stoechiometric amount based on the residual , acrylonitrile. By adding such a sulfide or disulfide, the hydrolysis reaction of the acrylonitrile with formation of;
3,3'-oxydipropionitrile is improved. One reaction of the sul~ide ~ or disulfide, for instance Na2S, with acrylonitrile is the following:
water Na2S + 2 CH2 = CH-CN ~ (NC-CH2-CH2)2 S + 2 NaOH-The basicity of the reaction mixture resulting from the ~orma~tion of NaOH promotes the hydrolysis of the rest of residual acrylonitrile. Accordingly, the amount of sulfide or disulfide may be as low as 25% of the stoechiometric amount. On the other hand, the sulfide or disulfide may be used in excess of this stoechiometric amount, however, use of such amounts is without improvement in the results. ABS or SAN resins, ~30 containing products resulting from the hydrolysis of acryloDi-trile, are yellow Therefore, it is preferable to remove the _3_ ~0~548 residual acrylonitrile by reacting it with a sulfide or di~
sulfide and to avoid or at least to minimize the hydrolysis reaction. Consequently, the sul~ide or disulfide pre~erably is used in an amount of between about 50 and 100%, more particular~
ly between 70 and 100% of the stoechiometric amount~ i The following examples are presented in order to illustrate the presen~ invention but are not to be ~onsidered as limiting thereof.
BXA~PLE 1 The process described in Belgian patent No. 811,750 was ;~
used for manufacturing an ABS resin from 23.27 kg of s~yrene, 9.50 kg of acrylonitrile and 4.92 kg of rubber ~Stereon 703A, a product of Firestone Tire and Rubber Co.). The process is a two step process comprising a mass copolymerization step followed by a suspension polymerization step. Beads of ABS resin were so obtained. The content of residual acrylonitrile was 1.6~ by weight of resin and 0.5% by weight of water (analysis by vapor phase chromatrography with ionization by hydrogen flame). `
Comparatlve experiments were carried out by adding various Compounds known to react with acrylonitrile. These compounds were added at the end of the suspension polymerization, the beads having a temperature of between 100 and 110C attsuah time. The beads were not yet hard and the reaction, therefore, was improved.
The reaction time between the beads and these compounds was one hour. The results of these comparative experiments were as follows: ;-`' ~': ~
, ~'..~
*Trademark Acrylonitrile con tent (% by weight) after treatment Reactant in the water in the beads - ~ , ~
NaH~03 0.08 0.28 Diethanolamine 0.05 0.17 Na~S 0.04 0.01 Na2S 0.03 not detectable These results clearly show that sodium sulfide and sodium disulfide are more active than the other compounds in reactlng ~;
with the acrylonitrile.
By using Na2S in an amount corresponding to about 25%
o~ tbe stoechiometric amount, the content o~ resldual acryloni-trile in the ABS resin does not decrease below 0.06% and the product prepared by molding this ABS resin is yellow. By using ~;~
Na2S in an amount corresponding to 80% of the stoechiometric amount, the content of residual acrylonitrile is decreased to 0.01% and the molded product is not yellow, EXAMPLE 2 `
SAN resin was prepared ~rom 2,300 litres o~ styrene and 865 litres o~ acrylonitrile. The process used was a mass co-polymerization with ~ormatlon o~ a mixture having a viscosity o~ 2,000 centipoises. This mixture has then been polymerized by a suspension process at a temperature of 115 to 135C. The ~;
beads were slowly cooled to a temperature o~ 110 C. and then washed by an aqueous solution containing 8 kg of Na2S in 40 litres o~ water. A~ter this washing, the beads were substan-tially ~ree from residual acrylonitrile.
' ~,
Claims (4)
1. A process for producing a copolymer of styrene and acrylonitrile substantially free of acrylonitrile which comprises copolymerizing styrene and acrylonitrile and treating the resulting copolymer with an aqueous solution of a sulphur compound selected from the group consisting of alkaline sulfides and alkaline disulfides.
2. The process of Claim 1 wherein the sulphur compound is used in an amount corresponding to 25 to 100% of the stoechiometric amount required to react with the residual acrylonitrile in said copolymer.
3. The process of Claim 1 wherein the treatment is carried out at a temperature of between 100 and 110°C.
4. The process of Claim 1 wherein said copolymer includes an elastomer.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BE149845A BE821435A (en) | 1974-10-24 | 1974-10-24 | PROCESS FOR PREPARING COPOLYMERS. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038548A true CA1038548A (en) | 1978-09-12 |
Family
ID=3842711
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA221,081A Expired CA1038548A (en) | 1974-10-24 | 1975-03-03 | Process for copolymerizing styrene and acrylonitrile |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU7870475A (en) |
| CA (1) | CA1038548A (en) |
| IT (1) | IT1048753B (en) |
-
1975
- 1975-02-28 AU AU78704/75A patent/AU7870475A/en not_active Expired
- 1975-03-03 CA CA221,081A patent/CA1038548A/en not_active Expired
- 1975-10-21 IT IT2852575A patent/IT1048753B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| AU7870475A (en) | 1976-09-02 |
| IT1048753B (en) | 1980-12-20 |
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