Dispersing stabilizer for suspension polymerization of vinyl chloride

A dispersing stabilizer suitable for suspension polymerization of vinyl chloride or a monomer mixture mainly composed of vinyl chloride which can be used in a hot water charging polymerization process without any problems, and which can produce vinyl chloride homopolymer or copolymers having a good porosity, a large bulk density, a very low content of coarse particles and good physical properties, the dispersing stabilizer comprising a polyvinyl alcohol having a degree of hydrolysis of 75 to 85% by mole, an absorbance of not less than 0.1 measured at a wavelength of 280 m.mu. with respect to the 0.1% by weight aqueous solution, a content of carboxyl group of 0.01 to 0.15% by mole and a cloud point of not less than 50.degree. C. measured with respect to the 0.1% by weight aqueous solution.

BACKGROUND OF THE INVENTION 
The present invention relates to an agent for stabilizing dispersion 
(hereinafter referred to as "dispersing stabilizer") in suspension 
polymerization of vinyl chloride monomer alone or a mixture containing a 
major amount of the monomer, and a process for preparing the same. More 
particularly, the invention relates to a dispersing stabilizer for homo- 
or co-polymerization of vinyl chloride, which enables to produce a vinyl 
chloride resin having good physical properties such as a large porosity, a 
large bulk density and a uniform distribution of particle size with a less 
amount of coarse particles. Further, the invention relates to a process 
for the suspension polymerization of vinyl chloride or its mixture in the 
presence of the stabilizer, particularly the process which is improved in 
producibility by adopting a hot water charging polymerization manner to 
raise the efficiency of polymerization cycle. 
In a suspension polymerization of vinyl chloride or a mixture of vinyl 
chloride and other monomers copolymerizable therewith, it is necessary to 
employ one or more of various dispersing stabilizers, e.g. polyvinyl 
alcohol, methylolcellulose, vinyl acetate/maleic anhydride copolymer, and 
gelatin. Above all, polyvinyl alcohols have excellent properties as the 
dispersing stabilizer, and are the most generally employed. While there 
are various polyvinyl alcohols, it is known that the physical or chemical 
characteristics of polyvinyl alcohols, such as average degree of 
polymerization and average degree of hydrolysis, have a delicate influence 
upon the produced vinyl chloride resins. So, a number of proposals have 
been made for the purpose, for example, (a) a polyvinyl alcohol defined by 
degree of hydrolysis, degree of polymerization, content of carbonyl group 
and content of vinylene group within specified ranges (Japanese Unexamined 
Patent Publication Kokai No. 45189/1976), and (b) a polyvinyl alcohol 
modified by maleic acid and/or an ester of maleic acid (Japanese Examined 
Patent Publication Kokoku No. 59242/1982). 
In general, the suspension polymerization of vinyl chloride has been 
carried out in a batchwise operation, wherein a polymerization vessel is 
charged with a water medium, a dispersing stabilizer, a polymerization 
initiator, vinyl chloride or its mixture, and optionally other necessary 
additives, followed by gradually raising the temperature of the mixture up 
to the polymerization temperature to carry out the polymerization. 
Such a batchwise operation, however, requires a very long time to feed the 
ingredients and to raise the temperature, which may sometimes account for 
10% or more of the polymerization time in one cycle. It is a cause of 
decrease in productivity of the polymerization, which is a problem long 
wanted to be solved in the art. In order to solve the problem, various 
processes have been proposed. Recently, there is proposed a "hot water 
charging polymerization process", in which a hot water heated at 
50.degree. C. or higher temperature is employed. This process has great 
effects in points of process steps for polymerization and shortening of 
time. 
However, when suspension polymerization is carried out in such a hot water 
charging manner employing the above-mentioned polyvinyl alcohol (a) or (b) 
as the dispersing stabilizer, on feeding hot water, the polyvinyl alcohol 
is partly deposited out to make the aqueous solution turbid. Thus, not 
only cannot the polyvinyl alcohol produce its excellent effects as the 
stabilizer, but also it often affect adversely the polymerization 
stability and physical properties of the produced polymers. 
Accordingly, a dispersing stabilizer, suitable for use in the hot water 
charging polymerization process and always capable of yielding vinyl 
chloride resins having good qualities, has been strongly demanded, since 
it would enable to advantageously carry out the suspension polymerization. 
It is an object of the present invention to provide a dispersing stabilizer 
suitable for suspension homo- or co-polymerization of vinyl chloride, 
which can be used in the hot water charging polymerization process without 
causing any problem and give vinyl chloride resins of high quality. 
A further object of the invention is to provide a process for preparing the 
dispersing stabilizer for suspension polymerization of vinyl chloride. 
A still further object of the invention is to provide a process for the 
suspension homo- or copolymerization of vinyl chloride which can stably 
produce vinyl chloride resins having a high porosity, a high bulk density 
and a uniform distribution of particle size in a shortened period of time. 
Another object of the invention is to provide a process for 
suspension-polymerizing vinyl chloride or its mixture with other 
copolymerizable monomers in hot water charging polymerization manner. 
These and other objects of the present invention will become apparent from 
the description hereinafter. 
SUMMARY OF THE INVENTION 
It has been found that when a polyvinyl alcohol which has specific 
properties, i.e. degree of hydrolysis, content of carbonyl group, content 
of carboxyl group and cloud point, which fall within the specified ranges, 
respectively, is used a dispersing stabilizer for suspension 
polymerization of vinyl chloride or its mixture with other copolymerizable 
monomers, the polymerization can be conducted stably, even in a hot water 
charging polymerization manner, without depositing the polyvinyl alcohol 
or making the solution cloudy, and there can be obtained a vinyl chloride 
resin having excellent properties, e.g. a high porosity, and having a 
uniform distribution of particle size without containing coarse particles. 
In accordance with the present invention, there is provided a dispersing 
stabilizer for suspension homopolymerization or copolymerization of vinyl 
chloride, comprising a polyvinyl alcohol having a degree of hydrolysis of 
75 to 85% by mole, an absorbance of not less than 0.1 measured at a 
wavelength of 280 m.mu. with respect to the 0.1% by weight aqueous 
solution, a content of carboxyl group of 0.01 to 0.15% by mole and a cloud 
point of not less than 50.degree. C. measured with respect to the 0.1% by 
weight aqueous solution. 
The polyvinyl alcohol used as the dispersing stabilizer is prepared by 
heat-treating a polyvinyl alcohol, preferably a carbonyl group-containing 
polyvinyl alcohol, in the presence of sodium acetate at a temperature of 
120.degree. C. to 150.degree. C. in an atmosphere containing 1 to 15% by 
volume of oxygen, thereby introducing carboxyl group. 
The dispersing stabilizer of the present invention can be used in 
suspension polymerization of vinyl chloride alone or a monomer mixture 
containing a major amount of vinyl chloride, and is particularly suitable 
for use in producing vinyl chloride resins in a hot water charging manner 
wherein the polymerization is started by adding a hot water to a mixture 
of a monomer, a polymerization initiator and a dispersing stabilizer to 
raise the temperature of the polymerization system to a desired 
polymerization temperature. 
It is important in obtaining the advantageous effects as mentioned above 
that the degree of hydrolysis, content of carbonyl group, content of 
carboxyl group and cloud point of the polyvinyl alcohol fall within the 
specified ranges.

DETAILED DESCRIPTION 
The polyvinyl alcohol used as the dispersing stabilizer according to the 
invention is usually prepared by polymerizing vinyl acetate in the 
presence of a chain transfer agent, such as an aldehyde, a ketone or the 
like, followed by hydrolyzing the obtained vinyl acetate polymer to 
provide a polyvinyl alcohol containing carbonyl group, and heat-treating 
the carbonyl group-containing polyvinyl alcohol in the presence of sodium 
acetate, preferably not more than 2% by weight of sodium acetate based on 
the polyvinyl alcohol, in an atmosphere having a specified oxygen 
concentration to introduce carboxyl groups into the polyvinyl alcohol. The 
production of the carbonyl group-containing polyvinyl alcohol is not 
limited to the above-mentioned process using chain transfer agents such as 
aldehydes or ketones. For example, carbonyl group-containing polyvinyl 
alcohols may be produced by heat-treating usual polyvinyl alcohols 
containing no carbonyl group. It is also known that polyvinyl alcohols 
produced in a usual manner may contain carbonyl group by various causes or 
mechanisms, e.g. acetaldehyde impurity included in vinyl acetate monomer 
and disproportionation termination reaction. Accordingly, any polyvinyl 
alcohols can be used as the starting material in the present invention, so 
long as polyvinyl alcohols containing both carbonyl groups and carboxyl 
group are obtained therefrom by the above-mentioned heat treatment, thus 
providing polyvinyl alcohols having desired properties. 
Examples of the aldehyde used as the chain transfer agent in the 
polymerization of vinyl acetate are for instance, acetaldehyde, 
propionaldehyde, butylaldehyde, benzaldehyde, and the like. Examples of 
the ketone used as the chain transfer agent are, for instance, acetone, 
methyl ethyl ketone, hexanone, cyclohexanone, and the like. The amount of 
the chain transfer agent varies to some extent depending on its chain 
transfer constant or the desired degree of polymerization of polyvinyl 
alcohol. It is usually from 0.1 to 5% by weight, preferably 0.5 to 3% by 
weight, based on the vinyl acetate monomer. 
The polymerization of vinyl acetate can be conducted in any known manner 
without particular restriction. Usually, the polymerization is conducted 
in a solution polymerization manner employing as the solvent an alcohol 
such as methanol, ethanol or isopropanol. Of course, an emulsion 
polymerization and suspension polymerization may also be adopted. In such 
a solution polymerization, vinyl acetate monomer may be fed at one time, 
continuously, intermittently or in any other manner. The solution 
polymerization is conducted in the presence of azobisisobutyronitrile, 
acetyl peroxide, benzoyl peroxide, lauroyl peroxide or other known radical 
polymerization catalysts. The polymerization temperature is selected from 
about 50.degree. C. to the boiling point of the reaction mixture. 
Vinyl acetate may be polymerized alone, or may be copolymerized with other 
monomers copolymerizable with vinyl acetate, e.g. an unsaturated 
carboxylic acid or its alkyl ester, such as acrylic acid, methacrylic 
acid, crotonic acid, maleic acid or a monoalkyl maleate; a nitrile such as 
acrylonitrile or methacrylonitrile, an amide such as acrylamide 
methacrylamide; an olefinsulfonic acid or its salt such as 
ethylenesulfonic acid, allylsulfonic acid or methallylsulfonic acid; a 
vinyl ester other than vinyl acetate; a vinyl ester of a saturated 
branched fatty acid; a vinyl ether; a vinyl ketone; an .alpha.-olefin; a 
vinyl halide; a vinylidene halide; or the like. The amount of the other 
copolymerizable monomers is usually at most 10% by mole, preferable at 
most 5% by mole. 
The hydrolysis of a vinyl acetate polymer is conducted by dissolving the 
vinyl acetate polymer in an alcohol and adding an alkali catalyst or an 
acid catalyst to the solution. As an alcohol are used, for example 
methanol, ethanol and butanol. 
The concentration of the vinyl acetate polymer in the alcohol solution is 
from 20 to 50% by weight. Examples of the alkali catalyst are, for 
instance sodium hydroxide, potassium hydroxide, sodium methylate, sodium 
ethylate, potassium methylate, and other alkali metal hydroxides or 
alcoholates. Examples of the acid catalyst are, for instance, an inorganic 
acid such as hydrochloric acid or sulfuric acid, and an organic acid such 
as p-toluene sulfonic acid. The amount of such a catalyst is needed to be 
1 to 100 millimole equivalents to vinyl acetate unit. The hydrolysis 
temperature is not particularly limited, but usually selected from 
10.degree. to 70.degree. C., preferably from 30.degree. to 40.degree. C . 
The reaction is usually conducted for 2 to 3 hours. 
The heat treatment to introduce carboxyl groups into polyvinyl alcohol is 
conducted in an oxygen atmosphere having an oxygen concentration of 1 to 
15% by volume, preferably 3 to 12% by volume, at a temperature of 
120.degree. to 150.degree. C. for 0.5 to 5 hours. If the oxygen 
concentration is higher than the above range, the carboxyl group is 
introduced in excess, so the obtained polyvinyl alcohol is easy to 
deposite. If the heat treatment temperature is lower than 120.degree. C., 
the desired amount of carboxyl group is not introduced, and if it is 
higher than 150.degree. C., the polymer is cross-linked to form insoluble 
substance causing to develop fish eyes in molded articles of polyvinyl 
chloride resins. 
The polyvinyl alcohol used as the dispersing stabilizer is required to be a 
partially hydrolyzed polyvinyl alcohol having a carbonyl group content 
such that the absorbance of a 0.1% by weight aqueous solution thereof is 
not less than 0.1 at a wavelength of 280 m.mu., and having a degree of 
hydrolysis of 75 to 85% by mole, a content of carboxyl group of 0.01 to 
0.15% by mole, and a cloud point of not less than 50.degree. C. measured 
with respect to a 0.1% by weight aqueous solution thereof. 
When the absorbance is less than 0.1, the stabilizer does not provide vinyl 
chloride resins having a high good plasticizer absorptivity. If the degree 
of hydrolysis is less than 75% by mole, the cloud point is low and, 
therefore, no good effects as dispersing stabilizer are not exhibited when 
used in the hot water charging polymerization process. If the degree of 
hydrolysis is more than 85% by mole, the polyvinyl alcohol lacks in 
dispersing ability, so the obtained vinyl chloride resins are not 
satisfactory in properties such as porosity and distribution of particle 
size. Also, if the content of carboxyl group is lower than 0.01% by mole, 
the polyvinyl alcohol is hard to keep the cloud point at not lower than 
50.degree. C., and if the content is higher than 0.15% by mole, the 
suspension polymerization of vinyl chloride is not stably conducted, 
resulting in lowering of the physical properties of the obtained vinyl 
chloride resins. 
The polyvinyl alcohol having a cloud point lower than 50.degree. C. is not 
suitable for use in the suspension polymerization in the hot water 
charging manner, because there are observed phenomena of depositing 
polyvinyl alcohol from a polymerization system and making the system 
turbid when a hot water above 50.degree. C. is added to the system. The 
term "cloud point" as used herein means the temperature at which a 0.1% by 
weight aqueous solution of a polyvinyl alcohol begins to become cloudy 
when the temperature is raised from about 20.degree. C. at a rate of 
0.5.degree. C. per minute. 
By using a dispersing stabilizer comprising the polyvinyl alcohol as 
mentioned above in a suspension homo- or copolymerization of vinyl 
chloride, there are obtained vinyl chloride homopolymer or copolymers 
having excellent properties such that the polymer particles are porous, 
the distribution of particle size is uniform, and they do not form fish 
eyes in the molded articles. 
In regard to the hot water charging polymerization process, some 
embodiments are given below, specifically to illustrate the present 
invention, but it is to be understood that the invention is not limited to 
these embodiments. 
(1) In an embodiment, a polymerization initiator, a dispersing stabilizer 
for suspension polymerization, other additives and a monomer, namely vinyl 
chloride or a mixture of vinyl chloride with other copolymerized monomers 
(hereinafter referred to as "vinyl chloride monomer") are uniformly mixed 
at a temperature lower than that at which the initiator is substantially 
decomposed. Water heated at a temperature not less than 50.degree. C. is 
then added to the mixture with stirring to initiate the polymerization 
(cf. Japanese Unexamined Patent Publication Kokai No. 5703/1982). 
(2) In a second embodiment, a polymerization vessel is charged with a 
polymerization initiator, a dispersing stabilizer for suspension 
polymerization, other additives, and a cold water not higher than about 
30.degree. C. in an amount of about 5 to about 50% by weight of the whole 
amount of water to be employed for the polymerization system. The order of 
addition of these materials is not particularly limited. After adding 
these components, the polymerization vessel is usually degassed to remove 
air present in the polymerization vessel. Vinyl chloride monomer is then 
fed into the polymerization vessel. At last, the residual amount of water, 
namely about 95 to about 50% by weight of the whole water to be employed, 
which has been heated at a temperature above the polymerization 
temperature (not less than 50.degree. C.), is added to the polymerization 
system (cf. Japanese Unexamined Patent Publication No. 47785/1979). 
(3) In a preliminary mixing vessel, there are fully mixed at a temperature 
below 50.degree. C., a polymerization initiator, a dispersing stabilizer 
for suspension polymerization, other additives, water and a vinyl chloride 
monomer. The preliminary mixture is continuously preheated with a heat 
exchanger and sent to a polymerization vessel so as to heat the mixture 
such that at the moment the mixture is fed to the polymerization vessel, 
the temperature of the mixture reaches the polymerization temperature (cf. 
Japanese Unexamined Patent Publication Kokai No. 158207/1985). 
In these processes, the dispersing stabilizer is added in the form of 
powder or solution. When added in the form of a solution, it is dissolved 
in water, or an organic solvent such as an alcohol, a ketone or an ester, 
or a mixture of an organic solvent with water. The amount of the 
dispersing stabilizer employed is from 0.01 to 0.3% by weight, preferably 
0.03 to 0.1% by weight, based on the vinyl chloride monomer. The polyvinyl 
alcohol according to the invention may be used as the dispersing 
stabilizer in combination with other known dispersing stabilizers. The 
other stabilizers should be used in an amount appropriate in view of the 
desired properties of the vinyl chloride resins to be produced. The other 
stabilizers include, for instance, cellulose derivatives such as methyl 
cellulose, hydroxylethyl cellulose, hydroxypropyl cellulose and 
hydroxypropyl methyl cellulose; partially hydrolyzed polyvinyl alcohols; 
partially hydrolyzed polyvinyl acetates; polyacrylic or polymethacrylic 
acid polymers; gelatin; sorbitan fatty acids; polyethers mixrures; and the 
like. These other stabilizers may be used alone or in admixture thereof. 
As the polymerization initiators, there can be employed those 
conventionally used in the polymerization of vinyl chloride monomer. 
Examples of the initiator are, for instance, percarbonates such as 
di-isopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate and 
diethoxyethyl peroxydicarbonate; peresters such as t-butyl 
peroxyneodecanoate, .alpha.-cumyl peroxyneodecanoate and t-butyl 
peroxyneodecanoate; peroxides such as acetyl cyclohexanesulfonyl peroxide 
and 2,4,4-trimethylpentyl 2-peroxyphenoxyacetate; azo compounds such as 
azobis-(2,4-dimethylvaleronitrile) and 
azobis-(4-methoxy-2,4-dimethylvaleronitrile); and the like. In addition, 
potassium persulfate, ammonium persulfate, hydrogen peroxide or a mixture 
thereof can be employed. 
In the suspension polymerization, known additives conventionally used for 
polymerization of vinyl chloride may be optionally used, e.g. 
polymerization regulator, chain transfer agent, gelation modifier, 
antistatic agent, pH regulator and the like. 
Vinyl chloride may be homopolymerized or copolymerized with other 
copolymerizable monomers by the process according to the invention. The 
comonomers copolymerizable with vinyl chloride is used in an amount of 
less than 50% by weight based on the whole monomers. Examples of the 
comonomer are, for instance, vinyl esters such as vinyl acetate, vinyl 
propionate and the like; acrylate esters or methacrylate esters such as 
methyl acrylate, ethyl acrylate and the like; olefins such as ethylene, 
propylene and the like; maleic anhydride, acrylonitrile, styrene, 
vinylidene chloride, and other monomers copolymerizable with vinyl 
chloride. 
In carrying out the process of the invention, the feeding ratio of 
ingredients, the polymerization temperature and the other conditions can 
be determined according to the conditions that have been adopted in 
conventional suspension polymerizations of vinyl chloride monomer, and 
they are not particularly limited. 
The dispersing stabilizer according to the invention have various 
advantages. For example, it enables to polymerize vinyl chloride monomer 
in a hot water charging polymerization manner. Also it can provide vinyl 
chloride homopolymer or copolymers having a good porosity, a uniform 
distribution of particle size and excellent physical properties, and the 
molded articles prepared therefrom has no or a very few fish eyes. 
The present invention is more specifically described and explained by means 
of the following Examples, in which all % and parts are by weight unless 
otherwise noted. It is to be understood that the present invention is not 
limited to the Examples. 
EXAMPLE 1 
Preparation of dispersing stabilizer! 
A polymerization vessel was charged with 100 parts of vinyl acetate, 1.2 
parts of acetaldehyde, 5 parts of methanol and 0.07% of, based on vinyl 
acetate, azobisisobutyronitrile. After the atmosphere in the 
polymerization vessel was replaced by nitrogen, the mixture was heated to 
a temperature of 50.degree. to 70.degree. C. to initiate polymerization 
and the polymerization was continued at that temperature until the 
polymerization conversion reached 90%. 
Unreacted vinyl acetate was removed, and the obtained polymer was 
hydrolyzed with sodium hydroxide according to a common method to form a 
partially hydrolyzed polyvinyl alcohol. 
Then, 1.5 parts of sodium acetate was added to 100 parts of the obtained 
partially hydrolyzed polyvinyl alcohol. After the mixture was dried at a 
powder temperature of 110.degree. C. for 2 hours, it was placed in a 
reactor, and heat-treated at 145.degree. C. for 2 hours with keeping the 
oxygen concentration at 10% by volume by passing through the reactor a 
mixed gas of nitrogen and air in a volume ratio of 1:1 at a rate of 100 
l/hour. The properties of the obtained polyvinyl alcohol are as follows: 
______________________________________ 
Degree of polymerization 
1000 
Degree of hydrolysis 79.0% by mole 
Absorbance at 280 m.mu. of 0.1% 
0.5 
aqueous solution thereof 
Content of carboxyl group 
0.08% by mole 
Cloud point 60.degree. C. 
______________________________________ 
Suspension polymerization of vinyl chloride! 
Into a 100 l, stainless steel autoclave equipped with a stirrer were 
simultaneously fed with stirring 30 parts of 30.degree. C. cold water, 100 
parts of vinyl chloride, 0.1 part of the polyvinyl alcohol obtained above 
as a dispersing stabilizer and 0.2 part of di-2-ethylhexyl 
peroxydicarbonate as a polymerization initiator, and subsequently 120 
parts of hot water heated at 85.degree. C. was added to the autoclave and 
the suspension polymerization was carried out at 58.degree. C. 
The properties of the obtained polyvinyl chloride were measured according 
to the following methods. The results are shown in Table 1. 
1. Porosity 
Porosity was measured by a mercury porosity meter. 
2. Bulk density 
Bulk density was measured according to JIS K 6721. 
3. Absorption of plasticizer 
A dry up time of a mixture of 6 parts of vinyl chloride resin and. 4 parts 
of diethylhexyl phthalate was measured with a Brabender. The plasticizer 
absorptivity was estimated according to the following criteria. 
A . . . dry up time in 3 minutes 
B . . . dry up time longer than 3 minutes and not longer than 5 minutes 
C . . . dry up time longer than 5 minutes and not longer than 10 minutes 
4. Fish eye 
A mixture of 100 parts of the vinyl chloride resin, 1.0 part of lead 
stearate, 1.0 part of barium stearate, 50 parts of dioctyl phthalate and 
0.8 part of carbon black was kneaded with rolls at 150.degree. C. for 6 
minutes to form into a sheet having a thickness of 0.08 mm. The number of 
fish eyes in the area of 5.times.4 cm of the obtained sheet was counted. 
The estimation was made according to the following criteria. 
A . . . fish eyes from 0 to 4 
B . . . fish eyes from 5 to 10 
C . . . fish eyes exceeding 11 
5. Distribution of particle size 
The particle size distribution is estimated by a content (%) of coarse 
particles which did not pass through the JIS standard 42 mesh sieve. The 
representations are as follows: 
A . . . content of 42 mesh on particles not more than 1% 
B . . . content of 42 mesh on particles more than 1% and not more than 5% 
C . . . content of 42 mesh on particles more than 5% 
EXAMPLE 2 
A dispersing stabilizer was prepared in the manner as in Example 1 except 
that the conditions of the heat treatment in an oxygen atmosphere were 
changed. 
That is to say, a partially hydrolyzed polyvinyl alcohol was prepared by 
using 100 parts of vinyl acetate, 1.2 parts of acetaldehyde, 5 parts of 
methanol and 0.07% of, based on vinyl acetate, azobisisobutyronitrile. 
Then, 1.5 parts of sodium acetate was added to 100 parts of the obtained 
partially hydrolyzed polyvinyl alcohol, and after the mixture was dried at 
a powder temperature of 110.degree. C. for 2 hours, it was thermally 
treated in a reactor at 145.degree. C. for 2 hours with keeping the oxygen 
concentration at 5% by volume by passing through the reactor a mixed gas 
of nitrogen and air in a volume ratio of 1:0.5 at a rate of 100 l/hour. 
The properties of the obtained polyvinyl alcohol are as follows: 
______________________________________ 
Degree of polymerization 
1000 
Degree of hydrolysis 79.0% by mole 
Absorbance at 280 m.mu. of 0.1% 
0.30 
by weight aqueous solution thereof 
Content of carboxyl group 
0.05% by mole 
Cloud point 55.degree. C. 
______________________________________ 
A polyvinyl chloride resin was prepared in the same manner as in Example 1 
except that the thus obtained polyvinyl alcohol was employed as the 
dispersing stabilizer. The properties of the obtained polyvinyl chloride 
are shown in Table 1. 
EXAMPLE 3 
A partially hydrolyzed polyvinyl alcohol was prepared in the same manner as 
in Example 1 except that 100 parts of vinyl acetate, 20 parts of methanol 
and 0.02% of, based on vinyl acetate, azobisisobutyronitrile were used. 
Then, 1.5 parts of sodium acetate was added to 100 parts of the obtained 
partially hydrolyzed polyvinyl alcohol, and after the mixture was dried at 
a powder temperature of 110.degree. C. for 2 hours, it was thermally 
treated in a reactor at 145.degree. C. for 2 hours with keeping the oxygen 
concentration at 10% by volume by passing through the reactor a mixed gas 
of nitrogen and air in a volume ratio of 1:1 at a rate of 100 l/hour. 
The properties of the obtained polyvinyl alcohol are as follows: 
______________________________________ 
Degree of polymerization 
1700 
Degree of hydrolysis 80.5% by mole 
Absorbance at 280 m.mu. of 0.1% 
0.20 
aqueous solution thereof 
Content of carboxyl group 
0.05% by mole 
Cloud point 62.degree. C. 
______________________________________ 
A vinyl chloride resin was prepared in the same manner as in Example 1 
except that the thus obtained polyvinyl alcohol was employed as the 
dispersing stabilizer. The results of the measurement of properties of the 
obtained vinyl chloride resin are shown in Table 1. 
Comparative Example 1 
A partially hydrolyzed polyvinyl alcohol was prepared in the same manner as 
in Example 1 except that 100 parts of vinyl acetate, 1.5 parts of 
acetaldehyde, 5 parts of methanol and 0.08% of, based on vinyl acetate, 
azobisisobutyronitrile were used. 
Then, 2.0 parts of sodium acetate was added to 100 parts of the obtained 
partially hydrolyzed polyvinyl alcohol, and after the mixture was dried at 
a powder temperature of 110.degree. C. for 2 hours, it was thermally 
treated in a reactor at 145.degree. C. for 2 hours with keeping the oxygen 
concentration at 20% by volume by passing through the reactor a mixed gas 
of nitrogen and air in a volume ratio of 1:2 at a rate of 100 l/hour. 
The properties of the obtained polyvinyl alcohol are as follows: 
______________________________________ 
Degree of polymerization 
800 
Degree of hydrolysis 80.1% by mole 
Absorbance at 280 m.mu. of 0.1% 
0.70 
aqueous solution thereof 
Content of carboxyl group 
0.20% by mole 
Cloud point 60.degree. C. 
______________________________________ 
A vinyl chloride resin was prepared in the same manner as in Example 1 
except that the thus obtained polyvinyl alcohol was employed as the 
dispersing stabilizer. The results of the measurement of properties of the 
obtained vinyl chloride resin are shown in Table 1. 
Comparative Example 2 
A dispersing stabilizer was prepared in the manner as in Example 1, except 
that the conditions of the heat treatment in an oxygen atmosphere were 
changed. 
That is to say, a partially hydrolyzed polyvinyl alcohol was prepared by 
using 100 parts of vinyl acetate, 1.2 parts of acetaldehyde, 5 parts of 
methanol and 0.07% of, based on vinyl acetate, azobisisobutyronitrile. 
Then, 1.5 parts of sodium acetate was added to 100 parts of the obtained 
partially hydrolyzed polyvinyl alcohol, and after the mixture was dried at 
a powder temperature of 110.degree. C. for 2 hours. It was thermally 
treated in a reactor at 90.degree. C. for 2 hours with keeping the oxygen 
concentration at 10 % by volume by passing through the reactor a mixed gas 
of nitrogen and air in a volume ratio of 1:1 at a rate of 100 l/hour. 
The properties of the obtained polyvinyl alcohol are as follows: 
______________________________________ 
Degree of polymerization 
1000 
Degree of hydrolysis 71% by mole 
Absorbance at 280 m.mu. of 0.1% 
0.25 
aqueous solution thereof 
Content of carboxyl group 
0.03% by mole 
Cloud point 40.degree. C. 
______________________________________ 
A vinyl chloride resin was prepared in the same manner as in Example 1 
except that the thus obtained polyvinyl alcohol was employed as the 
dispersing stabilizer. The properties of the obtained vinyl chloride resin 
are shown in Table 1. 
Comparative Example 3 
A partially hydrolyzed polyvinyl alcohol was prepared in the same manner as 
in Example 1 except that 100 parts of vinyl acetate, 20 parts of methanol 
and 0.02% of, based on vinyl acetate, azobisisobutyronitrile were used. 
Then 0.3 parts by weight of sodium acetate was added to 100 parts of the 
obtained partially hydrolyzed polyvinyl alcohol, and after the mixture was 
dried at a powder temperature of 110.degree. C. for 2 hours, no heat 
treatment was conducted. 
The properties of the obtained polyvinyl alcohol are as follows: 
______________________________________ 
Degree of polymerization 
1000 
Degree of hydrolysis 79.2% by mole 
Absorbance at 280 m.mu. of 0.1% 
0.03 
aqueous solution thereof 
Content of carboxyl group 
0.01% by mole 
Cloud point 45.degree. C. 
______________________________________ 
A vinyl chloride resin was prepared in the same manner as in Example 1 
except that the thus obtained polyvinyl alcohol was employed as the 
dispersing stabilizer. The results of the measurement of properties of the 
obtained vinyl chloride resin are shown in Table 1. 
TABLE 1 
______________________________________ 
Bulk Distribution 
Porosity 
density of particle 
Fish Plasticizer 
(cc/g) 
(g/ml) size eye absorptivity 
______________________________________ 
Example 1 
0.38 0.56 A A A 
Example 2 
0.35 0.57 A A A 
Example 3 
0.32 0.60 A A A 
Com. Ex. 1 
0.26 0.51 C B B 
Com. Ex. 2 
0.27 0.48 C B B 
Com. Ex. 3 
0.25 0.54 B C C 
______________________________________ 
By using the dispersing stabilizer according to the present invention, it 
is possible to conduct a suspension polymerization in a hot water charging 
manner. The obtained vinyl chloride resins have a good porosity, a uniform 
distribution of particle size such that they provide molded articles 
having no or few fish eye, and have excellent physical properties, so the 
dispersing stabilizer is industrially very advantageous.