JPH0225925B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a vinyl chloride polymer, and particularly to a method for obtaining a vinyl chloride polymer having a large bulk specific gravity. Many reports have been made for a long time regarding gas phase polymerization of vinyl chloride monomers, and when carried out without using a solid support, only vinyl chloride polymers with poor general properties are often obtained. Are known. Therefore, many attempts have been made to develop solid supports. For example, special public service in 1977-
No. 30290 and JP-A-47-596 disclose a method of gas phase polymerization of vinyl chloride monomer in the presence of a vinyl chloride polymer, asbestos, silica, perlite, etc. as a solid support. It has been stated that it is advantageous to use vinyl chloride polymers as However, it is extremely inefficient to use a prepolymerized and dried vinyl chloride polymer as a solid support, and the heat history and drying characteristics of the vinyl chloride polymer used as a solid support during gas phase polymerization This adds to the thermal history of the vinyl chloride polymer, which impairs the properties of the vinyl chloride polymer. Therefore, these methods cannot necessarily be said to be satisfactory techniques. The present inventors have conducted research on obtaining vinyl chloride polymers with high bulk specific gravity by gas phase polymerization of vinyl chloride monomers. It has become clear that known methods are extremely difficult. A method of obtaining a vinyl chloride polymer by gas phase polymerization of vinyl chloride monomers is described, for example, in U.S. Pat. A superior gas-phase continuous polymerization method for use is described. It has been reported that alcohol, aliphatic hydrocarbons, aromatic hydrocarbons, etc. may be added as long as the amount is 5% by weight or less when obtaining vinyl chloride polymer seeds in the bulk polymerization. However, although these methods are excellent, when implemented industrially,
It was found that the bulk specific gravity of the obtained polymer was not sufficiently large, and that how to increase the bulk specific gravity was a major technical problem. In order to obtain a vinyl chloride polymer with a high bulk specific gravity without losing the advantages of the gas phase polymerization method, the inventors of the present invention have conducted extensive research, and as a result, the composition of the polymerization system when obtaining seeds of the vinyl chloride polymer has been determined. They obtained the knowledge that the bulk specific gravity of the resulting vinyl chloride polymer is greatly affected, and after further research, they completed the present invention. In the present invention, a vinyl chloride monomer or a vinyl monomer mixture mainly consisting of a vinyl chloride monomer is added to an organic solvent in which the volume ratio of the vinyl chloride monomer or the vinyl monomer mixture mainly composed of vinyl chloride monomer to the organic solvent is in the range of 5/95 to 90/10. Adding vinyl chloride monomer or a vinyl monomer mixture mainly consisting of vinyl chloride monomer and polymerizing in the presence of a catalyst to obtain seeds of vinyl chloride polymer,
Next, polymerization is carried out in the presence of the vinyl chloride polymer seeds while continuously supplying a vinyl chloride monomer or a vinyl monomer mixture mainly composed of vinyl chloride monomers at a pressure lower than the saturated vapor pressure. The present invention provides a method for producing a vinyl chloride polymer. The present invention is obtained without losing the advantages of gas phase polymerization. It not only has the characteristic of increasing the bulk specific gravity of the vinyl chloride polymer, but also has the advantage that the polymerization can be extremely easily controlled during polymerization of the vinyl chloride polymer seed. The vinyl monomer that can be used in the present invention in combination with the vinyl chloride monomer is a vinyl monomer that can be copolymerized with the vinyl chloride monomer. The copolymerizable vinyl monomer is not particularly limited and any known vinyl monomer can be used, but typical examples include olefin compounds such as ethylene and propylene; vinyl acetate, vinyl propionate, etc. Vinyl esters; unsaturated monocarboxylic acids such as acrylic acid and α-acrylic acid, and their alkyl esters, amides such as acrylic acid, methacrylic acid, ethyl acrylate, methyl methacrylate, acrylic acid amide, and methacrylic acid. Acid amide;
Unsaturated nitrites such as acrylonitrile; unsaturated dicarboxylic acids such as maleic acid and fumaric acid, their alkyl esters, and their anhydrides; vinyl alkyl ethers such as vinyl methyl ether and vinyl ethyl ether; and various other known compounds. Examples include polymerizable monomers. The organic solvent used in the present invention may be any organic solvent as long as it does not dissolve the vinyl chloride polymer. Such organic solvents generally exclude ethylene glycol, and the organic solvent used in the present invention is not particularly limited as long as it does not dissolve the vinyl chloride polymer. In particular, organic solvents that do not dissolve the vinyl chloride polymer and have a smaller ability to swell the vinyl chloride polymer are generally more suitable. Such organic solvents can generally be defined using the following scale: x = (Vs/RT) (δ _s − δ _p ) ² −(1) where x is the Flory-Huggins interaction constant, which is a unique value between polymer and solvent (Journal of Chemical Physics, Vol. 9, 440 p. 660 (1941), Vol. 10, p. 51 (1942)). Further, V _s is the molar volume of the solvent, R is the gas constant, and T is the absolute temperature. Furthermore, δ _s and δ _p are the solubility parameters of the solvent and the polymer compound, respectively, and are derived from the Hildebrand-Scatchard solution theory (JHHildebrand, “The
Solubility of Nonelectrolytes.”3rd ed.,
Reinhold Publishing Corporation, New;
York, 1979; G. Scatchard, Chemical Review,
Volume 8, page 321 (1931)). However, since it is very difficult to experimentally determine the solubility parameter of the above-mentioned polymer compound, the calculation may generally be performed using the following calculation formula proposed by Hoy.
(KLHoy, Journal of Paint Technology Vol. 42 , p. 76 (1970)). δ _p = δΣFi/M − (2) where ρ is the density, M is the molecular weight, and is the value of the repeating unit in a polymer compound. In addition, Fi is the molar attraction force for constituent groups such as atoms, atomic groups, bond types, etc. that make up the molecule. The solubility parameters of organic solvents and vinyl chloride polymers in the present invention can be found in the Polymer Handbook (John Wiley & Sons, New
York, 1975), and those not mentioned above were calculated and used from the above formula (2). For example, the solubility parameter of the vinyl chloride polymer calculated from equation (2) was 9.54 (Cal/mole) ^1/2 . The solubility parameter of a vinyl chloride copolymer can be easily calculated using equation (2) by determining the density of the copolymer and the copolymer monomer composition ratio, so if necessary, use the equation (2) above. It can be calculated from. As the value of x in formula (1) increases, the vinyl chloride polymer becomes less soluble in organic solvents. That is,
Poor solvent property increases. The present inventors systematically investigated the value of x of the organic solvent and the bulk specific gravity of the vinyl chloride polymer obtained by the production method of the present invention, and found that x
When the value of is 0.3 or more, preferably 0.4 or more, the vinyl chloride polymer becomes substantially insoluble in the organic solvent, and when such an organic solvent is used, a vinyl chloride polymer with a large bulk specific gravity can be obtained. I found it. Therefore, the organic solvent used in the present invention is preferably an organic solvent that does not dissolve the vinyl chloride polymer or has an extremely small swelling ability.For example, the value of x in the above formula (1) is 0.3 or more, preferably 0.4. The above is desirable. However, even if the value of x is 0.3 or more, ethylene glycol has a significantly large swelling ability for vinyl chloride polymers and is therefore preferably not used as an organic solvent in the present invention. Typical organic solvents particularly preferably used in the present invention include:
For example, alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol; aliphatic hydrocarbons such as butane, pentane, and heptane;
Examples include alicyclic hydrocarbons such as cyclopentane, cyclohexane and methylcyclopentane; ethers such as diethyl ether and methyl ethyl ether. Further, a mixed solvent of two or more organic solvents can also be used as long as x in the above formula (1) is 0.3 or more, preferably 0.4 or more. In the present invention, when polymerizing vinyl chloride polymer seeds, the volume ratio of vinyl chloride monomer (VCM) or a vinyl monomer mixture (VCMIX) mainly consisting of vinyl chloride monomer to organic solvent (ORSOL), that is, (VCM or
VCMIX)/ORSOL is 5/95 to 90/10, preferably 20/80 to 80/20. When the above (VCM or VCMIX)/ORSOL is greater than 90/10, not only does the bulk specific gravity of the resulting vinyl chloride polymer decrease significantly, but it also becomes difficult to remove the heat generated during polymerization, which often results in the formation of particulate vinyl chloride. This is not preferred because a polymer cannot be obtained. Also mentioned above (VCM
If the value of VCMIX)/ORSOL is less than 5/95, not only the bulk specific gravity will be markedly lowered but also the polymerization rate will be slow, making it necessary to add a large amount of catalyst, which is not preferable. The method of supplying vinyl chloride monomer is as follows:
Liquid vinyl chloride monomer may be charged so that the volume ratio of organic solvent to vinyl chloride monomer is 5/95 to 90/10, or a method may be adopted in which gas phase vinyl chloride monomer is supplied and dissolved in the organic solvent. do it. Therefore, the following method can be preferably employed as the method for producing the vinyl chloride polymer in the present invention. (1) When the amount of vinyl chloride monomer added is large relative to the organic solvent, polymerization occurs in the presence of a catalyst, and after the organic solvent has apparently disappeared, the vinyl chloride monomer in the gas phase is heated to a pressure lower than the saturated vapor pressure. A method in which polymerization is carried out while continuously supplying. (2) When the amount of vinyl chloride monomer added to the organic solvent is small, polymerize for a certain period of time in the presence of a catalyst, and then continuously supply the vinyl chloride monomer in the gas phase at a pressure lower than the saturated vapor pressure. A method in which polymerization is carried out while (3) After preparing the organic solvent and catalyst in advance,
A method in which polymerization is carried out while continuously supplying vinyl chloride monomer at a pressure lower than the saturated vapor pressure. Adopting these methods not only makes it very easy to control the polymerization of the vinyl chloride polymer used as a seed, but also increases the bulk specific gravity of the resulting vinyl chloride polymer. The method of polymerizing a vinyl chloride monomer or a vinyl chloride monomer mixture mainly consisting of a vinyl chloride monomer in the presence of the vinyl chloride polymer seed is performed in a manner that the vinyl chloride monomer is in a gas phase, that is, a saturated vapor of the vinyl chloride monomer. As long as the polymerization is carried out under a pressure lower than the above pressure, known polymerization techniques can be employed as they are. Furthermore, the method for separating the organic solvent used in the present invention from the vinyl chloride polymer is not necessarily limited. Examples include methods for separating it from vinyl polymers. In the present invention, the polymerization temperature is not particularly limited, and generally -30°C to 80°C when vinyl chloride polymer seeds are polymerized, preferably 0°C to 70°C, followed by gas phase polymerization of vinyl chloride monomer. In other words, when polymerization is carried out while continuously supplying vinyl chloride monomer at a pressure lower than the saturated vapor pressure, 40
Polymerization temperatures from 0.degree. C. to 80.degree. C. are preferably employed. Further, the polymerization time is generally preferably 1 hour to 10 hours. The polymerization pressure in the gas phase polymerization of the present invention must be lower than the saturated vapor pressure of the vinyl chloride monomer to be polymerized. Generally relative pressure (Pr)
(Pressure of vinyl chloride monomer in polymerization system/saturation pressure of vinyl chloride at polymerization temperature) is 0.5<Pr<1
It is sufficient to satisfy the following conditions. When an organic solvent is present in the polymerization system, the relative pressure can be easily set to be less than or equal to the saturated vapor pressure of the vinyl chloride monomer based on the amount of the organic solvent and the vapor pressure at the polymerization temperature. As the catalyst used in the present invention, any known catalyst can be used. For example, radical catalysts, ie catalysts which generate free radicals, are used.
More specific examples include organic peroxides such as lauroyl peroxide, tert-butyl peroxypivalate, benzoyl peroxide, isopropyl dioxycarbonate, etc.; azo compounds such as azobisisobutyronitrile, α,
α'-Azobis-4-methoxy-2,4-dimethylvaleronitrile and the like can be preferably used. The amount of catalyst used is preferably 0.01 to 5% by weight of the monomers used. Although the entire amount of the catalyst can be added at the beginning of the polymerization, a method of successive addition is also suitably employed. The bulk specific gravity of the vinyl chloride polymer obtained by the present invention is significantly larger than that of the vinyl chloride polymer obtained by conventional known gas phase polymerization. The reason for this is not necessarily clear, but it is due to the amount of organic solvent present in the polymerization system when producing seeds made of vinyl chloride polymer. When producing seeds made of vinyl chloride polymer, the ratio of vinyl chloride monomer or vinyl monomer mixture mainly consisting of vinyl chloride monomer to organic solvent has a significant influence on the bulk specific gravity of the vinyl chloride polymer obtained. The phenomenon that gives this can be said to be astonishing. The present invention was completed based on the knowledge of the above-mentioned unexpected phenomenon, and the industrial contribution of the present invention will be immeasurable. EXAMPLES In order to explain the present invention more specifically, the following Examples and Comparative Examples will be given and explained, but the present invention is not limited to these Examples. The measured values shown in Examples and Comparative Examples were based on the following measuring method. (1) Weight average degree of polymerization and bulk specific gravity Determined according to the method of JIS K-6721. (2) Particle size distribution The vinyl chloride polymer was sieved through a 16-mesh sieve (1000 μm) and a 42-mesh sieve (350 μm), and its weight was measured. Example 1 In a glass autoclave equipped with a stirrer, n-pentane, vinyl chloride monomer, 1.0 g of diisopropyl peroxydicarbonate (hereinafter simply abbreviated as IPP), and tertiary butyl peroxy pivalate ( (hereinafter simply abbreviated as PV)
0.7 g was charged and polymerized at 55° C. for 1 hour and 30 minutes to obtain vinyl chloride polymer seeds in which apparently liquid n-pentane had disappeared. Next, a gaseous vinyl chloride monomer was continuously supplied at a pressure of 6.2 Kg/cm ² to maintain the pressure inside the autoclave at 6.2 to 6.5 Kg/cm ² for polymerization for 3 hours. After that, the vinyl chloride polymer was recovered and 40
It was dried under reduced pressure at ℃ overnight. Table 1 shows the properties of the vinyl chloride polymer obtained. As a comparative example, Table 1 shows the results of polymerization under conditions other than those of the present invention. In addition, in Comparative Examples 1' to 4', after the polymerization of the seeds made of vinyl chloride polymer was completed,
The remaining monomer was purged, and then the polymerization was carried out while supplying the vinyl chloride monomer in the gas phase.

[Table] Example 2 A glass autoclave equipped with a stirrer was charged with an organic solvent in the proportions shown in Table 2, 1.0 g of diisopropyl peroxydicarbonate, and 0.7 g of tertiary butyl peroxyvivalate, and then the autoclave was heated to 55°C. It was warm. Then, gaseous vinyl chloride monomer was continuously introduced at a pressure of 6.2 kg/cm ² to maintain the autoclave pressure at 6.2 to 6.4 kg/cm ² and polymerization was carried out for one hour as shown in Table 2. After about 1.5 hours of polymerization, the apparently liquid organic solvent disappeared. After the polymerization, the vinyl chloride polymer was recovered and dried under reduced pressure at 40°C all day and night. Table 2 shows the characteristics of the vinyl chloride polymer obtained. As a comparative example, Table 2 shows the results of polymerization using organic solvents other than those of the present invention.

【table】

[Table] Under the polymerization conditions shown in Table 2, the vinyl chloride monomer dissolved in the organic solvent before the start of polymerization is organic solvent: vinyl chloride monomer = 30:70 to 60:40 (volume ratio). Example 3 A glass autoclave equipped with a stirrer was charged with 100 ml of n-pentane, 10 mmol of diisopropyl peroxycarbonate, and 10 mmol of tertiary butyl peroxyvivalate, and then the temperature of the autoclave was raised to 50°C. Next, gaseous vinyl chloride monomer at a pressure of 6.2 Kg/cm ² was continuously injected, and the autoclave was kept at a pressure of 6.2 to 6.5 Kg/cm ² for polymerization for 2 hours (until the polymerization started, as measured by a gas flow meter). The amount of vinyl chloride monomer dissolved was 110 ml). Then, while stirring the autoclave,
- Recovered pentane. Then autoclave
The temperature was raised to 60°C, and gaseous vinyl chloride monomer was continuously injected at a pressure of 7.0 kg/cm ² to polymerize for 3 hours.
After the polymerization, the vinyl chloride polymer was recovered and dried under reduced pressure at 40°C all day and night. The weight of the obtained vinyl chloride polymer was 320 g, and the weight average degree of polymerization was 730. The bulk specific gravity was 0.65 g/cc, and the amount passing through a 40-mesh sieve was 85% by weight. Example 4 50 ml of n-pentane, 0.5 g of triethyl boron, and hydrogen peroxide in a glass autoclave equipped with a stirrer.
After cooling to 0°C, 50ml of vinyl chloride monomer was added, and the mixture was stirred and polymerized at 0°C for 3 hours. Next, the temperature of the autoclave was raised to 55°C, 0.8 g of diisopropyl peroxydicarbonate and 0.5 g of tertiary butyl peroxypivalate were charged, and then gaseous vinyl chloride monomer was continuously injected at a pressure of 6.2 Kg/cm ² . Autoclave pressure 6.2
Polymerization was carried out for 4 hours while maintaining the temperature at ~6.5 Kg/cm ² . 55℃
Thirty minutes after the temperature was raised to , the apparently liquid n-pentane disappeared. The vinyl chloride polymer thus obtained was dried under reduced pressure at 40°C all day and night. The weight of the obtained vinyl chloride polymer was 270 g, and the weight average degree of polymerization was 850. Also, the bulk specific gravity is 0.67g/cc,
The amount passing through the 40 mesh sieve was 80% by weight. Example 5 After charging 50 ml of n-pentane, 50 ml of vinyl chloride monomer, 0.5 g of diisopropyl peroxycarbonate, and 0.5 g of tertiary butyl peroxy pivalate into a glass autoclave equipped with a stirrer,
The temperature was raised to 55°C and polymerization was carried out with stirring for 2 hours to obtain vinyl chloride polymer seeds. Then, 0.5 g of diisopropyl peroxycarbonate and 0.5 g of tertiary butyl peroxy pivalate were added while continuously pressurizing the autoclave with gaseous vinyl chloride monomer at 6.2 Kg/cm ² pressure to maintain the autoclave at 6.2-6.4 Kg/cm ² . Polymerization was carried out for 4 hours by sequentially adding 20 c.c. of the dissolved n-pentane solution to the autoclave at a rate of 5 c.c. per hour. After the polymerization, the vinyl chloride polymer was recovered and dried under reduced pressure at 40°C all day and night. The weight of the obtained vinyl chloride polymer was 330 g, and the bulk specific gravity was 0.69 g/cc. Example 6 A glass autoclave equipped with a stirrer was charged with 50 ml of n-pentane, 10 g of vinyl acetate monomer, 50 ml of vinyl chloride monomer, and 1.0 g of diisopropyl peroxy carbonate and 1.0 g of tertiary butyl peroxy pivalate, and then heated to 55°C. Raise the temperature 2
Polymerization was carried out by stirring for hours. The apparently liquid n-pentane disappears. Next, a gaseous vinyl chloride monomer was continuously supplied at a pressure of 6.5 Kg/cm ² to maintain the autoclave pressure at 6.5 to 6.8 Kg/cm ² and polymerization was carried out with stirring for 3 hours. Thereafter, the vinyl chloride polymer was collected and dried under reduced pressure at 40° C. all day and night. The yield of the vinyl chloride polymer obtained was 210 g, the bulk specific gravity was 0.57 g/cc, and the vinyl acetate content was 4% by weight. Example 7 A glass autoclave equipped with a stirrer was charged with 50 ml of n-pentane, 50 ml of vinyl chloride monomer, 0.7 g of azobisisobutyronitrile, and 1.0 g of tertiary butyl peroxypivalate, and heated to 65°C. Polymerization was carried out with stirring for 1 hour and 30 minutes to obtain seeds of vinyl chloride polymer free of liquid n-pentane. Next, an equimolar mixed gas of vinyl chloride monomer and ethylene was continuously injected into the autoclave at a pressure of 7.0 Kg/cm ² , and the polymerization pressure of the autoclave was adjusted.
Polymerization was carried out with stirring for 5 hours while maintaining the pressure at 7.0 to 7.8 Kg/cm ² . The vinyl chloride polymer thus obtained was
It was dried under reduced pressure at ℃ overnight. The bulk specific gravity of the obtained vinyl chloride polymer was 0.62 g/cc, and the ethylene content was 1.1% by weight.

Claims (1)

[Scope of Claims] 1. In an organic solvent that does not dissolve a vinyl chloride polymer, the volume ratio of a vinyl chloride monomer or a vinyl monomer mixture mainly consisting of a vinyl chloride monomer to the organic solvent is 5/95 to 90/ 10, a vinyl chloride monomer or a vinyl monomer mixture mainly composed of vinyl chloride monomers is added and polymerized in the presence of a catalyst to obtain vinyl chloride polymer seeds, and then the vinyl chloride polymer is of a vinyl chloride polymer, characterized in that the polymerization is carried out while continuously supplying a vinyl chloride monomer or a vinyl monomer mixture mainly composed of vinyl chloride monomers at a pressure lower than the saturated vapor pressure in the presence of seeds of Production method. 2. The method according to claim 1, wherein the organic solvent does not dissolve the vinyl chloride polymer and has a small ability to swell the vinyl chloride polymer. 3 _The organic solvent _{has the} ^formula :
T is the absolute temperature, δ _s is the solubility parameter of the solvent, δp
is the solubility parameter of vinyl chloride polymer. )
3. The method according to claim 2, wherein X represented by is an organic solvent of 0.3 or more.