CS195326B2 - Process for preparing non-softened and porous polyvinylchloride - Google Patents

Description

The invention relates to processes for the production of vinyl chloride polymers by slurry polymerization, whereby a product with a low content of residual unreacted vinyl chloride monomer is obtained.

The vinyl chloride polymers obtained by suspension polymerization have so far been subjected to steam stripping to reduce the unreacted vinyl chloride monomer content. Recent legal restrictions require that the level of residual monomer in these products be generally lower than that achieved by conventional steam scrubbing.

It has been found that by introducing a small amount of at least one C 1 -C 12 alkyl ester, C 1 -C 12 alkylbenzyl ester or phthalic acid dibenzyl ester into a suspension polymerization medium containing vinyl chloride monomer and / or comonomer (s), a high porosity polymer product is obtained. considerably reduced content of residual vinyl chloride monomer (VCM). Although the phthalic esters described herein are used in larger amounts as particle size regulators (U.S. Patent No. 2,823,200), as non-polymerizable additives for controlling the molecular weight of the product (U.S. Patent No. 2,719,143) and as in situ plasticizers (patents) U.S. Pat. Nos. 2,322,309 and 2,689,836), it has not been found that using the lower amounts of the present invention yields a product of higher porosity and lower VCM content after steam stripping.

The suspension polymerization process underlying the invention is well known. The process comprises forming an aqueous reaction mixture containing about 25 to about 45% by weight of a monomeric vinyl chloride feed. The reaction batch is composed of vinyl chloride monomer, either alone or in admixture with up to about 50% by weight _and any of the known monomers are copolymerized with vinyl chloride. They are, for example, ethylenically unsaturated monomers, such as vinyl esters of aliphatic acids, for example vinyl acetate, vinylidene halides, for example vinylidene chloride, alkyl acrylates, for example ethyl or methyl acrylate, alkyl methacrylates, for example vinyl toluene, acrylonitrile and the like. The base suspension polymerization medium further comprises about 0.01 to about 5% by weight, preferably about 0.05 to about 1% by weight of the suspension stabilizer and about 0.01 to about 3% by weight, preferably about 0.1 to about 1% by weight of a monomer soluble initiator, the amounts refer to the weight of the monomer or monomers. Examples of suitable suspending agents include methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, talc, clay, polyvinyl alcohol, gelatin and the like. Suitable initiators are, for example, azobisisobutyronitrile, lauroyl peroxide, benzoyl peroxide, isopropyl peroxydicarbonate and the like. The polymerization is carried out by heating the described reaction medium to a temperature of from about 45 to about 75 ° C for about 2 to about 12 hours with stirring throughout the reaction.

SUMMARY OF THE INVENTION The present invention provides a process for the production of substantially unplasticized and porous polyvinyl chloride having a reduced monomer vinyl chloride content by polymerizing vinyl chloride in an aqueous medium in the presence of a suspension stabilizer and a monomer soluble initiator. % by weight based on the weight of monomeric vinyl chloride, a phthalic acid ester selected from the group consisting of C1-C12 dialkyl phthalic acid esters, C1-C12 alkylbenzyl phthalic acid esters, and phthalic dibenzyl ester.

Preferred are C 4 -C 6 dialkyl esters and C 4 -C 8 alkylbenzyl esters. For example, dibutyl phthalate, dioctyl phthalate and butylbenzyl phthalate can be used. The compound is introduced into the reaction medium in an amount which results in a substantially unplasticized and porous vinyl chloride polymer having a very low residual vinyl chloride monomer content after steam stripping. The product of the invention typically has a residual VCM content of less than 10 ppm by weight, for example about 1 to about 7 ppm, after steam removal, as described below. Preferred amounts are from about 0.4 to about 1.6%.

The polymerization reaction product of the invention is subjected to conventional steam stripping processes, either in the reactor or after it has been transported therefrom. Acceptable results can be obtained by steaming the product for a time ranging from about 10 to about 180 minutes, preferably from about 30 to 60 minutes. The temperature during steam stripping, while leaving the reaction slurry in the reactor, should be from about 76.7 to about 82.3%.

The invention is illustrated by the following examples.

Examples 1 to 2

These examples illustrate the improved and lower level of residual VCM obtained according to the invention (Example 1) compared to the procedure (Example 2) in which the invention is not applied.

In both examples, the same general polymerization procedure was used:

1. Charge deionized water (6048 L) into the reactor.

2. Slow speed turns on. stirring and 2.27 kg of ethylenediaminetetraacetic acid (under the trade name " Questex " from Stauffer Chemical Company) are added as a complexing agent.

3. Add an additional 6048 L of water and 1701 L of methylcellulose solution (under the trade name "Methocel-K-35" from Dow Chemical Co.) as a suspension stabilizer.

4. Stir the mixture for at least 15 minutes and adjust the temperature to 65.6 ° C.

5. Switch off mixing and add 40.86 kg of epoxidized soybean oil (under the trade name "G-62" from Rohm and Haas Co.) as a modifier.

6. Add azobisisobutyronitrile (under the trade name "Vase 64" from E.J. Du Pont de Nemeurs & Co.) as initiator in the amount shown in Table 1, divided into four approximately equal additions.

7. Subject the reactor to maximum vacuum once.

8. The monomer vinyl chloride monomer is then metered into the reactor in the amount shown in Table 1 and the reaction is carried out at 72.6 ° C and 1.26 MPa gauge pressure.

9. The reaction is carried out until either a pressure drop of 0.315 MPa or a temperature rise of 5.6 ° C occurs. When the first of these phenomena occurs, 10.9 kg of butylated hydroxytoluene are added.

10. The reactor is rapidly evacuated to minimum pressure and once vacuum reaches min. values.

The jacket temperature is set at 79.5 ° C, a slow pressure equalization connection is established and steam is introduced directly into the reactor to raise the batch temperature to 79.5 ° C. The stick is maintained at this temperature for as long as necessary to slowly equalize the pressure, which is 45 minutes from the beginning of the equalization.

11. The batch is discharged from the reactor at a temperature of 60 ° C and a solids content of 37.5% by weight.

Table 1 shows the residual VCM values (in ppm) obtained by gas chromatography.

Table 1

Example Initiator (kg) VCM (kg) Residual VCM in product .___ (PPm) _

1 *) 12.3 8.317 6.7

12.3 8.317 302 **)

*) in step 5, 126.2 kg of dioc- **) averaged over two experiments; one gave tylphthalate 187 ppm VCM, the other 417 ppm VCM,

19S32B

Examples 3a4

The same general procedure is used as; in Examples 1 and 2. In Example 3, the inventions are followed, while in Example 4, they are not.

The differences from the procedure described in Examples 1 and 2 are as follows:

1. In step 5, the -mpdiflifier is not added.

2. In step 8, the polymerization temperature is 62.6 ° C and 1.015 MPa overpressure. ',.

3. In step 9, add 5.5 kg of butyl. hydroxytoluene.

4. Stage 10 differs. The temperature of the jacket was 87.8 ° C; The reactor is rapidly, eyed, immediately started to drive off the steam in which it is. continues for 10 minutes at minimum pressure. In the reactor, the pressure is then slowly equalized and steam stripping is continued for an additional 45 minutes.

5. Drain the batch at 65.6 ° C. and has a solids content of 38%.

Table 2 shows the residual VCM values (in ppm) of the product.

TABLE 2.

Example

Initiator (kg)

VCM (kg)

Residual VCM in product (ppm)

3 *) 16.8

16.8

*) in step 5, 126.2 kg of dioctyl phthalate was added

") Average of three attempts; individual results were 145, 219 and 248 ppm VCM.

Examples 5 to 8

These examples show the effect of varying the amount of dibutyl phthalate on the amount of residual vinyl chloride monomer in the product in the form of a wet cake and in the form of a dry resin without steam stripping.

The polymerization was carried out at 72.8 ° C, at a stirrer speed of 460 rpm and at a pressure drop of 0.14 MP, the pressure was equalized using the following reactants.

8,367 2,0

8.417 204 **)

Substance Quantity

monomer vinyl chloride 9.99 kg suspension stabilizer - solution methylcelluloses *) 4,5 kg Initiator - azobisisobutyro- nitrile 5 G deionized water 17 liters

*) contains 3 g of methylcellulose on a dry weight basis.

Next, dibutyl phthalate (in the amount shown in Table 3) is added, which is pre-homogenized with a small amount of suspension stabilizer prior to introduction into the reactor. As a result of the reaction, the residual vinyl chloride content in the wet cake and dry resin is measured. The wet cake is formed by simply removing the water from the reaction slurry by filtration. A dry resin is prepared by removing 5 g of wet resin and placing it in a vacuum oven at 50.8 kPa and 100 ° C for 1 hour.

TABLE 3

Example

Dibutyl phthalate *)

VCM (ppm) Dry resin **) wet cake

control 0 5 0, -1 6 0.25 7 0.50 8 1.00 *) Quantity in%, based on mass of vinyl chloride monomer. **) residual VCM content is conditional

factors such as particle size, the amount of water removed during filtration and drying, and other variables that cannot be accurately controlled. Residual content

7383 10.9 1000 19.6 640 5.3 1051 23.1 1145 13.8

VCM in a wet cake allows a more accurate measurement of the effect of the present invention.

These examples are to be construed as merely illustrative of certain embodiments of the invention and are not to be construed as limiting.

Claims (5)

CLAIMS 1. A process for producing substantially unplasticized and porous polyvinyl chloride having a reduced monomeric vinyl chloride content of vinyl chloride polymerate in an aqueous medium in the presence of a suspension stabilizer and a monomer soluble initiator, wherein the polymerization is carried out in the presence of 0.1 to 5% by weight. to a weight of monomer vinyl chloride, a phthalic acid ester selected from the group consisting of C 1 -C 12 dialkyl phthalic acid esters, C 1 -C 12 alkylbenzyl phthalic acid esters and dibenzyl phthalic acid ester. 2. A process according to claim 1, wherein the phthalic acid ester of the invention is C4 -C6 dialkyl phthalate, preferably dioctyl phthalate. 3. The process according to claim 1, wherein the phthalic acid ester is dibutyl phthalate. 4. The process according to claim 1, wherein the phthalic acid ester is C4-C6 alkylbenzyl phthalate, preferably butylbenzyl phthalate. 5. A process according to claim 1, wherein the phthalic acid ester is used in an amount of 0.4 to 1.6% by weight based on the weight of the monomer vinyl chloride.