GB1592012A

GB1592012A - Suspension polymerization method using a stabilizer system

Info

Publication number: GB1592012A
Application number: GB627/78A
Authority: GB
Original assignee: Kemanobel AB
Current assignee: Kemanobel AB
Priority date: 1977-01-18
Filing date: 1978-01-09
Publication date: 1981-07-01
Also published as: DK154302C; NO780170L; NO152010C; FI63766B; FI63766C; SE431221B; FI780094A; DK154302B; NO152010B; DE2802063C2; DE2802063A1; SE7700488L; DK23278A

Description

(54) SUSPENSION POLYMERIZATION METHOD USING A STABILIZER SYSTEM (71) We, KEMANOBEL AB formerly known as KEMANORD AB, a Swedish Body Corporate, of Box 11005 S-100 61 Stockholm, Sweden do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to improvements in polymerization or copolymerization of vinyl chloride in aqueous suspension.

Processes for the polymerization of ethylenically unsaturated compounds in aqueous suspensions are known. Suspending agents and, optionally, emulsifiers along with initiators of the free radical type are used for such processes. The thus-obtained products are in the form of particles. The effect of the suspension stabilizer is to maintain the polymerized monomer in suspension and to prevent or reduce the tendency to agglomerate. The effect of the emulsifier is to lower the surface tension between the water and the monomer and thereby reduce the droplet size of the monomer dispersion. The emulsifier is primarily used when a porous and easily gelatinizable resin is desired. Furthermore, the amount of fish-eyes (compact polymer grains which are not capable of absorbing plasticizers) in the thus-produced resin is reduced when an emulsifier is used.

Generally emulsifiers of anionic character, such as long-chain alkyl sulphates and sulphonates, metal alkyl phosphates or ammonium and sodium salts of fatty acids, are used.

Nonionic emulsifiers are also commonly used for suspension polymerization.

During the selection of a method for suspension polymerization of vinyl chloride great importance is attached to obtaining a vinyl chloride polymerizate which has a good capacity for absorption of plasticizers and which gives good gelatinization properties. Furthermore, a low degree of polymer build-up is important for accomplishing the polymerization. This is often difficult to achieve when emulsifiers are used.

A further disadvantage of the utilization of emulsifiers is that residues of these remain in the thus-produced polymer. This means that the electric properties of the polymerizate become poor and that there is a risk that the emulsifier will migrate from the finished products. In order to avoid these side effects the polymerizate must be carefully washed which makes the process more expensive.

One object of the present invention is the realization of a method for suspension polymerization of vinyl chloride or copolymerization of monomers including vinyl chloride by utilization of particular suspension stabilizers which give polymerizates having superior properties without the necessity of using emulsifiers.

The thus-obtained polymerizates have very good properties with respect to uniform particle size distribution, absorption capacity for plasticizers and processability. Pictures of cut sections of the polymerizates show a good inner structure and essentially an absence of scales.

The present invention provides a process for suspension polymerization of vinyl chloride and up to 20 per cent of copolymerizable ethylenically unsaturated compound(s) based on the weight of vinyl chloride by utilization of a suspension stabilizing system comprising both (a) a polyvinyl acetate having a degree of hydrolysis of 30-60, suitably 30-55, and preferably 35-55 mol % and (b) a polyvinyl acetate having a degree of hydrolysis of 61-80, suitably 65-80, and preferably 65-75 mol %.

The amount of the above-mentioned suspension stabilizing system is preferably from 0.01 to 0.5 per cent by weight, more preferably from 0.03 to 0.2 per cent by weight, based on the monomer or the mixture of monomers. The weight ratio of polyvinyl acetate (a) to polyvinyl acetate (b) is preferably 1:10 to 10:1, suitably 1:5 to 9:1, and more preferably The thus-obtained polymerizates are porous and have excellent processing properties, such as good plasticizer absorption and good gelatinizability. The polymerizates have a uniform particle size distribution and they contain no glassy particles. The suspension stabilizing system brings about a very low degree of polymer build-up or none at all.

The invention includes an article which has been made from a polymer produced by the present process.

In polymerizing using the present suspension stabilizing system methods known per se can be used. The weight ratio of monomer to water is preferably within the range of from 1:1 to 1:2.5 and the polymerization is suitably carried out at a temperature of 20 to 800C, preferably 40 to 700C at a pressure corresponding to the saturation pressure of the vinyl chloride or the monomer mixture. Known monomer-soluble free radical-forming initiators such as acyl peroxides, dialkyl peroxydi-carbonates, or mixtures of these can be used. As examples of suitable comonomers, which are used in amounts up to 20 per cent by weight based on the vinyl chloride, can be mentioned alkenes, vinyl acetate, vinylidene chloride, acrylic and methacrylic acids or their esters and nitriles, other vinyl esters and maleic or fumaric acid.

The suspension stabilizing system defined above is included per se in the present invention and may be employed in alternative polymerizations. The invention includes an article which has been produced by such a polymerization.

The invention is further described and embodiments illustrated in detail in the following Examples which however are not intended to limit the invention. In the Examples parts and per cent are parts by weight and per cent by weight, respectively, unless othrwise stated.

Example 1 Into a 15 1 steel reactor equipped with a propeller agitator were charged:130 parts of demineralized water 0.08 part of polyvinyl acetate having a degree of hydrolysis of 72 mol % 0.04 part of a polyvinyl acetate having a degree of hydrolysis of 47 mol % (charged as a 25% solution in methanol) 0.06 part of cetyl peroxydicarbonate After evacuation at 400C for 15 minutes 100 parts of vinyl chloride were charged.

The mixture was polymerized at 55"C. When the pressure had dropped to 6 the polymerization was interrupted. The thus-obtained polymerizate was dewatered on a filter and washed with demineralized water. No crust-formation was obtained in the reactor.

Example 2 The polymerization of Example 1 was repeated but with the difference that the ratio between the different polyvinyl acetates was varied according to the following: TABLE I Example Polyvinyl acetate having a Comments hydrolysis degree of (mol-%) 47 72 88 2 a 50 50 - Free from crusts, particle size according to Table II 2 b 40 60 - same as 2 a 2 c 30 70 - same as 2 a 2 d 20 80 - same as 2 a 2 e 33 66 - same as 2 a Comparative tests 2 f 50 - 50 Crust formation, agglomer ates with particle size 100-600 llm 2 g - 50 50 Severe crust-formation 2 h 100 - - Severe crust-formation 2 i - 100 - Almost free from crusts, agg lomerates with particle size 500-1000 ijm 2 j - - 100 Almost free from crusts, agglomerates having a par ticle size of 2000 Fm Examples f) and g) are concerned with the use of polyvinyl acetates including a polyvinyl acetate having a high degree of hydrolysis (88 mol-%), a common suspension stabilizer in the polymerization of vinyl chloride. Example j) shows the result from using polyvinyl acetates having low and medium degrees of hydrolysis, respectively, as the sole suspension stabilizer.

As can be seen from Table I, polymerizates obtained by not using the present combination either appear in the form of crusts or in the form of agglomerates having a broad particle size distribution not suitable for use.

Polymerizates obtained according to the present process were analysed with respect to bulk density and the particle size distribution was determined by sieve analysis.

The results are shown in Table II (also referred to in Table I, above).

TABLE II Example Sieve analysis Ecm > 315 250/315 200/250 160/200 100/160 63/100 < 63 Bulk density (kill) 2 a 0 0 0,4 4 89 7 0,2 0,48 2 b 0 0 2 11 80 6 0,8 0,50 2 c 0 0 6 17 70 5 0,4 0,52 2 d 0 1 12 52 34 1 0,3 0,53 As can be seen from Table II, a polymerizate having a narrow particle size distribution is obtained by polymerization according to the present process. Furthermore, there are no problems of rust formation during polymerization.

WHAT WE CLAIM IS: 1. A method for polymerizing vinyl chloride and, optionally, up to 20 per cent by weight of copolymerizable ethylenically unsaturated monomer(s) based on the weight of vinyl chloride, which method comprises subjecting the monomer or monomer mixture to suspension polymerization using a suspension stabilizing system comprising (a) a polyvinyl acetate having a degree of hydrolysis of from 30 to 60 mol % and (b) a polyvinyl acetate having a degree of hydrolysis of from 61 to 80 mol %.

2. A method of polymerizing vinyl chloride and up to 20 per cent by weight of

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Claims

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TABLE I Example Polyvinyl acetate having a Comments hydrolysis degree of (mol-%)

47 72 88

2 a 50 50 - Free from crusts, particle size according to Table II

2 b 40 60 - same as 2 a

2 c 30 70 - same as 2 a

2 d 20 80 - same as 2 a

2 e 33 66 - same as 2 a Comparative tests

2 f 50 - 50 Crust formation, agglomer ates with particle size 100-600 llm

2 g - 50 50 Severe crust-formation

2 h 100 - - Severe crust-formation

2 i - 100 - Almost free from crusts, agg lomerates with particle size 500-1000 ijm

2 j - - 100 Almost free from crusts, agglomerates having a par ticle size of 2000 Fm Examples f) and g) are concerned with the use of polyvinyl acetates including a polyvinyl acetate having a high degree of hydrolysis (88 mol-%), a common suspension stabilizer in the polymerization of vinyl chloride. Example j) shows the result from using polyvinyl acetates having low and medium degrees of hydrolysis, respectively, as the sole suspension stabilizer.

As can be seen from Table I, polymerizates obtained by not using the present combination either appear in the form of crusts or in the form of agglomerates having a broad particle size distribution not suitable for use.

Polymerizates obtained according to the present process were analysed with respect to bulk density and the particle size distribution was determined by sieve analysis.

The results are shown in Table II (also referred to in Table I, above).

TABLE II Example Sieve analysis Ecm > 315 250/315 200/250 160/200 100/160 63/100 < 63 Bulk density (kill) 2 a 0 0 0,4 4 89 7 0,2 0,48 2 b 0 0 2 11 80 6 0,8 0,50 2 c 0 0 6 17 70 5 0,4 0,52 2 d 0 1 12 52 34 1 0,3 0,53 As can be seen from Table II, a polymerizate having a narrow particle size distribution is obtained by polymerization according to the present process. Furthermore, there are no problems of rust formation during polymerization.

WHAT WE CLAIM IS: 1. A method for polymerizing vinyl chloride and, optionally, up to 20 per cent by weight of copolymerizable ethylenically unsaturated monomer(s) based on the weight of vinyl chloride, which method comprises subjecting the monomer or monomer mixture to suspension polymerization using a suspension stabilizing system comprising (a) a polyvinyl acetate having a degree of hydrolysis of from 30 to 60 mol % and (b) a polyvinyl acetate having a degree of hydrolysis of from 61 to 80 mol %.
2. A method of polymerizing vinyl chloride and up to 20 per cent by weight of

copolymerizable ethylenically unsaturated monomer(s) based on the weight of vinyl chloride, which method comprises dispersing the monomer or monomer mixture in water using a suspension stabilizer comprising a mixture of (a) a polyvinyl acetate having a degree of hydrolysis of from 30 to 60 mol % and (b) a polyvinyl acetate having a degree of hydrolysis of from 61 to 80 mol % and polymerizing with a monomer-soluble free radical-forming initiator.
3. A method as claimed in claim 2, wherein polyvinyl acetate (a) has a degree of hydrolysis of from 35 to 55 mol %.
4. A method as claimed in claim 2 or claim 3, wherein polyvinyl acetate (b) has a degree of hydrolysis of from 65 to 75 mol %.
5. A method as claimed in claim 2, wherein the suspension stabilizer comprises a mixture of polyvinyl acetate having a degree of hydrolysis of from 30 to 55 mol % and polyvinyl acetate having a degree of hyrolysis of from 65 to 80 mol %.
6. A method as claimed in any one of claims 2 to 5, wherein the weight ratio of polyvinyl acetate (a) to (b) is from 1:10 to 10:1.
7. A method as claimed in any one of claims 2 to 5, wherein the weight ratio of polyvinyl acetate (a) to (b) is from 1:5 to 9:1.
8. A method as claimed in any one of claims 2 to 5, wherein the weight ratio of polyvinyl acetate (a) to (b) is from 1:5 to 2:1.
9. A method as claimed in any one of claims 2 to 8, wherein the total amount of polyvinyl acetate used is from 0.01 to 0.5 per cent by weight based on the amount of monomer(s).
10. A method as claimed in any one of claims 2 to 8, wherein the total amount of polyvinyl acetate used is from 0.03 to 0.2 per cent by weight based on the amount of monomer(s).
11. A method as claimed in any one of claims 2 to 10, wherein the weight ratio of monomer(s) to water is from 1:1 to 1:2.5.
12. A method as claimed in any one of claims 2 to 11, wherein the polymerization is effected at a temperature of from 20 to 800C.
13. A method as claimed in claim 12, wherein the temperature is from 40 to 70"C.
14. A method as claimed in any one of claims 2 to 13, wherein the polymerization is effected at a pressure corresponding to the saturation pressure of the vinyl chloride or the monomer mixture.
15. A method as claimed in any one of claims 2 to 14, wherein the initiator is an acyl peroxide, a dialkyl peroxydicarbonate, or a mixture thereof.
16. A method as claimed in any one of claims 2 to 15, wherein the copolymerizable monomer(s) is/are selected from alkenes, vinyl acetate, vinylidene chloride, acrylic and methacrylic acids or their esters and nitriles, other vinyl esters and maleic or fumaric acid.
17. A method as claimed in claim 1 and substantially as hereinbefore described in any one of Examples 1, 2a, 2b, 2c, 2d or 2e.
18. A polymer of vinyl chloride and, optionally copolymerizable ethylenically unsaturated monomer(s) which has been prepared by a method as claimed in any one of claims 1 to 17.
19. An article which has been made from a polymer as claimed in claim 18.
20. A suspension stabilizing system as defined in any one of claims 2 to 8.
21. A suspension polymerization process in which a system as claimed in claim 20 is employed during the suspension polymerization.
22. A polymer which has been produced by a process as claimed in claim 21.
23. An article which has been made from a polymer as claimed in claim 22.