Polymer obtained by emulsion polymerization method

A polymer of a low molecular weight having a very little odor is produced by emulsion-polymerizing a radical-polymerizable unsaturated monomer at a temperature of 115.degree. C. or higher in the presence or absence of a chain transfer agent.

CROSS-REFERENCE TO RELATED APPLICATION
 This application is the national phase of International PCT application
 PCT/JP96/02941, filed Oct. 11, 1996.
 TECHNICAL FIELD
 The present invention relates to a polymer of a low molecular weight
 obtained by an emulsion polymerization method, more specifically to a
 polymer of a low odor and a low molecular weight obtained by an emulsion
 polymerization method and a production process for the same.
 BACKGROUND ART
 The size of a molecular weight of a polymer exerts a strong influence on
 the chemical properties and the physical properties of the polymer.
 In general, as the molecular weight of a polymer grows larger, shown are
 tendencies such as an increase in the strength of the polymer, a reduction
 in blocking and an improvement in the weatherability. On the other hand,
 as the molecular weight of a polymer decreases, shown are tendencies such
 as an improvement in a heat-melting property, a heat fluidity, an adhesive
 property to various materials and a penetrability of the polymer and a
 gloss of the paint film formed.
 Making use of these characteristics of polymers having a low molecular
 weight, the polymers having a low molecular weight are used in large
 quantities for molding resins having a good fluidity, electrophotographic
 toners, base materials for hot melt type coating agents, coating
 resin-modifying agents having good penetrability and wetting property
 against substrates, and tackifiers. Further, since the polymers having a
 low molecular weight have a good mixing property or dispersibility in
 various materials, they are useful for specific uses such as pigment
 dispersants, mineral dispersants, water-treating agents in boilers,
 cooling tower, reverse osmosis treatment, sugar refining, paper making,
 geothermal treatment, oil wells and the like, and detergent additives
 acting as builders, film-forming preventives, sequestering agents and
 adhesion-inhibiting agents.
 Such polymers having a low molecular weight are obtained by polymerizing
 various monomers by methods such as bulk polymerization, solution
 polymerization, suspension polymerization, emulsion polymerization and the
 like, and they are produced preferably by emulsion polymerization because
 of the reasons that polymerization can easily be controlled and the
 resulting polymers are easy to handle.
 Usually, when polymers having a low molecular weight are obtained by
 emulsion polymerization, the polymerization has so far been carried out in
 the coexistence of a chain transfer agent in order to reduce the molecular
 weight. In general, in this case, aliphatic mercaptan base and halogenated
 hydrocarbon base chain transfer agents are mainly used as chain transfer
 agents for industrial purposes.
 However, a polymer dispersion obtained in the presence of mercaptans has
 undesired specific odor even if the remaining mercaptan content is small.
 When halogenated organic compounds (for example, carbon tetrachloride,
 bromoform, bromotrichloromethane and the like) are used as a chain
 transfer agent, the content of the chain transfer agent remaining in the
 polymer dispersion is relatively much remained, so that problems on air
 pollution and toxicity are brought about.
 A principal object of the present invention is to produce a polymer of a
 low molecular weight having no or little odor by an emulsion
 polymerization method.
 Intensive researches continued by the present inventors have resulted in
 finding that a polymer of a low molecular weight having no or little odor
 can readily be produced by emulsion-polymerizing a radical-polymerizable
 unsaturated monomer on a higher polymerization temperature condition than
 a polymerization temperature usually used for emulsion polymerization, and
 thus have come to complete the present invention.
 DISCLOSURE OF INVENTION
 Thus, the present invention provides a polymer obtained by
 emulsion-polymerizing a radical-polymerizable unsaturated monomer in the
 presence or absence of a chain transfer agent, wherein the above polymer
 has a weight average molecular weight falling in a range shown by the
 following equation (1):
EQU 3.ltoreq.log Mw&lt;1.50-1.18.times.log (S+0.001) (1)
 wherein
 Mw represents the weight average molecular weight of the polymer, and
 S represents an equivalent number of a polyatomic radical part of the chain
 transfer agent bonded to the end of the polymer chain per 100 g of the
 polymer.
 Further, the present invention provides a production process for a polymer,
 characterized by emulsion-polymerizing a radical-polymerizable unsaturated
 monomer at a temperature of 115.degree. C. or higher in the presence or
 absence of a chain transfer agent, wherein the polymer has a weight
 average molecular weight falling in a range shown by the following
 equation (2):
EQU 3.ltoreq.log Mw&lt;4.11-0.93.times.log (T+0.1) (2)
 wherein
 Mw represents the weight average molecular weight of the resulting polymer,
 and
 T represents parts by weight of the chain transfer agent used for the
 polymerization per 100 parts by weight of the unsaturated monomer.
 The polymer and the production process according to the present invention
 shall be explained below in detail.
 The polymer of the present invention is produced by emulsion polymerization
 in the absence of a chain transfer agent or the presence of a small
 amount, though used, of the chain transfer agent, and it is characterized
 by having a low molecular weight and a small content of chain transfer
 agent fragments introduced into the polymer as compared with those of
 polymers produced by conventional emulsion polymerization methods.
 That is, the polymer of the present invention has a weight average
 molecular weight and a content of a polyatomic radical part of the chain
 transfer agent falling in a range in which a relation shown by the
 following inequality is set up between the weight average molecular weight
 (Mw) and an equivalent number (S; S=0 when the chain transfer agent is not
 used in emulsion polymerization) per 100 g of the polymer, of a polyatomic
 radical part (hereinafter referred to as a chain transfer agent fragment)
 of the remaining chain transfer agent bonded to the end of the polymer
 chain as a result of emulsion polymerization:
EQU 3.ltoreq.log Mw&lt;1.50-1.18.times.log (S+0.001) (1)
 preferably
EQU 3.18.ltoreq.log Mw&lt;1.24-1.18.times.log (S+0.001) (1-1)
 and more preferably
EQU 3.3.ltoreq.log Mw&lt;1.06-1.18.times.log (S+0.001) (1-2)
 The chain transfer agent is split at a part where it is most easily cleaved
 in a chain transfer reaction and is turned into a monoatomic radical and a
 polyatomic radical which is composed of plural atoms, or two polyatomic
 radicals, wherein one of them is bonded to a polymer radical to terminate
 a chain propagation reaction, and the other becomes a starting point for a
 new chain propagation reaction to be bonded to a newly formed polymer. "S"
 used in the inequality described above is an equivalent number per 100 g
 of the polymer, of .left brkt-top.a polyatomic radical.right brkt-bot.
 bonded to the polymer as a result of such reaction. In general, it falls
 preferably in a range of 0 to 0.05, particularly 0 to 0.015 and above all,
 0 to 0.005.
 For example, trichloromethane (CHCl.sub.3) is cleaved at a part of C--H in
 emulsion polymerization into a monoatomic radical (H.) and a polyatomic
 radical (CCl.sub.3.). When emulsion polymerization is carried out using as
 a chain transfer agent, mercaptans (RCH.sub.2 SH) or dimercaptans
 (RCH.sub.2 S--SCH.sub.2 R'), bromotrichloromethane (CCl.sub.3 Br) or
 carbon tetrachloride (CCl.sub.4), or dichlorodibromomethane (CCl.sub.2
 Br.sub.2), polyatomic radical parts (chain transfer agent fragments)
 introduced into the chain terminals of the resulting polymer are .left
 brkt-top.RCH.sub.2 S..right brkt-bot., .left brkt-top.CCl.sub.3..right
 brkt-bot. and .left brkt-top.CCl.sub.2 Br..right brkt-bot. respectively.
 An amount of the chain transfer agent fragments bonded to the chain
 terminals of the polymer of the present invention can be determined in the
 following manner.
 First, a polymer dispersion is allowed to stand overnight -20.degree. C. to
 be frozen and then molten at a room temperature. Further, the polymer is
 separated by means of an ultracentrifuge. The separated polymer is
 dissolved or swollen in a good solvent such as toluene and then
 precipitated again in a poor solvent such as methanol or water and washed.
 In this case, it is to be confirmed that the polymer is not contained in
 the poor solvent.
 The number of chain transfer agent fragments in the resulting polymer is
 determined by elemental analysis such as ion chromatography according to a
 combustion method or ICP (high frequency plasma emission analysis) or NMR
 (nuclear magnetic resonance analysis).
 The polymer of the present invention having a weight average molecular
 weight and a content of chain transfer agent fragments satisfying the
 inequality described above is of a low molecular weight and has a small
 odor originating in the chain transfer agent, so that it can
 advantageously be used for the uses described above.
 The polymer of the present invention has preferably a weight average
 molecular weight Mw falling in a range of 1000 to 100,000, a number
 average molecular weight Mn falling in a range of 500 to 35,000 and a
 molecular weight (molecular weight peak) Mp which shows a maximum value in
 a gel permeation chromatography (GPC) chart falling in a range of 500 to
 80,000, more preferably a weight average molecular weight Mw falling in a
 range of 1,500 to 70,000, a number average molecular weight Mn falling in
 a range of 1,000 to 30,000 and a molecular weight peak Mp falling in a
 range of 1,000 to 50,000, and particularly preferably a weight average
 molecular weight Mw falling in a range of 2,000 to 50,000, a number
 average molecular weight Mn falling in a range of 1,000 to 25,000 and a
 molecular weight peak Mp falling in a range of 2,000 to 40,000.
 In the present invention, the weight average molecular weight Mw, the
 number average molecular weight Mn and the molecular weight peak Mp can be
 determined by the following method.
 First, 50 ml of the polymer dispersion is put in a beaker of 100 ml, and
 about 10 ml of about 1N diluted sulfuric acid is dropwise added to
 precipitate the polymer or separate and precipitate it by means of an
 ultracentrifuge. The polymer thus precipitated is filtered off and washed.
 Then, moisture on the surface is removed with a filter paper, and about
 0.2 g thereof is weighed out and dissolved in about 50 ml of
 tetrahydrofuran (THF). Then, a solid content concentration of the
 resulting THF solution of the polymer is measured according to JIS K 6839.
 THF is further added to this solution to adjust the solid content to 0.2%
 by weight, and this is used as a sample to carry out gel permeation
 chromatography (GPC analysis). A high speed liquid chromatography
 apparatus .left brkt-top.HCL-8020.right brkt-bot. (manufactured by Toso
 Co., Ltd.) is used for a measuring instrument, and the molecular weight is
 based on a polystyrene-converted value.
 The polymer of the present invention includes, for example, polymers
 capable of being synthesized by radical polymerization, such as styrene
 base resins, (meth)acrylic base resins, fatty acid vinyl ester base
 resins, alkyl vinyl ether base resins and halogenated vinyl base resins.
 In particular, the styrene base resins and the (meth)acrylic base resins
 are preferred because various physical properties of the polymers are
 excellent.
 The polymer of the present invention can be produced by
 emulsion-polymerizing a radical-polymerizable unsaturated monomer at a
 temperature of 115.degree. C. or higher in the presence or absence of a
 chain transfer agent.
 The radical-polymerizable unsaturated monomers capable of being
 emulsion-polymerized in the present invention shall not specifically be
 restricted as long as they are usually used for emulsion-polymerization.
 The following ones can be given as the examples thereof, and these
 monomers can be used alone or in combination of two or more kinds thereof.
 Styrene base monomers: included are, for example, styrene, o-methylstyrene,
 m-methylstyrene, p-methylstyrene, .alpha.-methylstyrene,
 .alpha.-methylstyrene dimer (2,4-diphenyl-4-methyl-1-pentene),
 p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-t-butylstyrene,
 p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene,
 p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene,
 3,4-dichlorostyrene and p-chloromethylstyrene. Styrene is particularly
 preferred.
 (Meth)acrylate base monomers: included are, for example, methyl acrylate,
 ethyl acrylate, n-butyl acrylate, i-butyl acrylate, propyl acrylate,
 n-octyl acrylate, dodecyl acrylate, lauryl acrylate, 2-ethtyl-hexyl
 acrylate, stearyl acrylate, 2-chloroethtyl acrylate, methyl
 .alpha.-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl
 methacrylate, n-butyl methacrylate, i-butyl methacrylate, n-octyl
 methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-ethylhexyl
 methacrylate and stearyl methacrylate. Among them, (meth)-acrylates of
 C.sub.1 to C.sub.12, preferably C.sub.2 to C.sub.8 aliphatic alcohols can
 be used alone or in combination of two or more kinds thereof.
 Aliphatic acid vinyl ester base monomers: for example, C.sub.1 to C.sub.12
 saturated aliphatic acid vinyl monomers such as vinyl formate, vinyl
 acetate, vinyl propionate and vinyl versatate.
 Alkyl vinyl ether base monomers: included are alkyl vinyl ethers such as,
 for example, methyl vinyl ether, ethyl vinyl ether, i-propyl vinyl ether,
 n-butyl vinyl ether, i-butyl vinyl ether, n-amyl vinyl ether, i-amyl vinyl
 ether, 2-ethylhexyl vinyl ether and octadecyl vinyl ether; and cycloalkyl
 vinyl ethers such as, for example, cyclohexyl vinyl ether,
 2-methylcyclohexyl vinyl ether and 3,3,5-trimethylcyclohexyl vinyl ether.
 Halogenated vinyl base monomers: included are halogenated vinyl base
 monomers such as, for example, vinyl chloride, vinylidene chloride, vinyl
 fluoride and vinylidene fluoride.
 In addition to the monomers described above, monomers capable of being used
 for producing the polymer of the present invention include C.sub.1 to
 C.sub.12 dialkyl ester monomers of C.sub.4 to C.sub.5 unsaturated .alpha.,
 .beta.-dicarboxylic acids such as, for example, dibutyl maleate, dioctyl
 maleate, dibutyl fumarate, dioctyl fumarate, dibutyl itaconate and dioctyl
 itaconate; and cyanized vinyl base monomers such as, for example,
 acrylonitrile and methacrylonitrile.
 Further, there can also be used as monomers capable of constituting the
 polymer of the present invention, in addition to the various monomers
 described above, for example, monomers containing carboxyl groups,
 monomers containing hydroxyl groups, monomers containing amino groups or
 substituted amino groups, monomers containing amide groups or substituted
 amide groups, monomers containing nitrogen atoms other than amino groups
 or amide groups, monomers containing epoxy groups, monomers containing
 acetoacetyl groups, and silane base monomers.
 The foregoing monomers containing carboxyl groups include unsaturated mono-
 or di-carboxylic acid monomers such as, for example, acrylic acid,
 methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic
 acid, itaconic acid, citraconic acid and cinnamic acid; unsaturated
 dicarboxylic acid monoalkyl ester monomers such as, for example, monobutyl
 maleate and mono-2-ethylhexyl fumarate; (meth)acrylates of dicarboxylic
 acid mono-polyhydric alcohol esters such as, for example, monohydroxyethyl
 succinate (meth)acrylate, monohydroxyethyl maleate (meth)acrylate,
 monohydroxyethyl fumarate (meth)acrylate, monohydroxyethyl phthalate
 (meth)acrylate and 1,2-dicarboxycyclohexane mono-hydroxyethyl
 (meth)acrylate; and for example, (meth)-acrylic acid dimer and
 .omega.-carboxy-polycaprolactone mono-(meth)acrylate.
 The foregoing monomers containing hydroxyl groups include, for example,
 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,
 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate,
 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate,
 2-hydroxyethyl (meth)allyl ether, 2-hydroxypropyl (meth)allyl ether,
 3-hydroxypropyl (meth)allyl ether, 4-hydroxybutyl (meth)allyl ether and
 allyl alcohol.
 The foregoing monomers containing amino groups or substituted amino groups
 include, for example, aminoethyl (meth)acrylate, dimethylaminoethyl
 (meth)acrylate, diethylaminoethyl (meth)acrylate and butylaminoethyl
 (meth)acrylate.
 The foregoing monomers containing amide groups or substituted amide groups
 include, for example, (meth)acrylamide, N-methylacrylamide,
 N,N-dimethylacrylamide, N-methylolacrylamide, N-methoxymethylacrylamide,
 N-butoxymethylacrylamide and N-dimethylaminopropylmethacrylamide.
 The foregoing monomers containing nitrogen atoms other than amino groups or
 amide groups include, for example, monomers such as 2-vinylpyridine,
 4-vinylpyridine, N-vinylpyrrolidone, N-vinylformamide and
 N-vinylimidazole.
 The foregoing monomers containing epoxy groups include, for example,
 glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate,
 glycidyl vinyl ether, 3,4-epoxycyclohexyl vinyl ether, glycidyl
 (meth)-allyl ether and 3,4-epoxycyclohexyl (meth)allyl ether.
 The foregoing monomers containing acetoacetyl groups include alkenyl esters
 of vinyl acetoacetate such as, for example, vinyl acetoacetate and
 (meth)allyl acetoacetate; diesters of alkylene glycols with (meth)-acrylic
 acid and (substituted) acetoacetic acid such as, for example,
 2-acetoacetoxyethyl (meth)acrylate, 2-acetoacetoxypropyl (meth)acrylate,
 3-acetoacetoxypropyl (meth)acrylate, 2-acetoacetoxybutyl (meth)acrylate,
 3-acetoacetoxybutyl (meth)acrylate and 4-cyanoacetoacetoxyethyl
 (meth)acrylate; diesters of alkylene glycols with crotonic acid and
 acetoacetic acid such as, for example, 2-acetoacetoxyethyl crotonate,
 2-acetoacetoxypropyl crotonate and 3-acetoacetoxypropyl crotonate; and
 acetoacetates of N-alkylol (meth)acrylamide such as, for example,
 N-acetoacetoxymethyl (meth)acrylamide and N-acetoacetoxyethyl
 (meth)acrylamide.
 Further, there can be used as the monomers described above, methacrylic
 acid acetoacetic acid diesters of lactone-modified hydroxyalkyl glycols
 obtained by esterifying lactone-modified hydroxyalkyl (meth)acrylates
 comprising adducts of hydroxyalkyl (meth)acrylates and lactones such as
 caprolactam with acetoacetic acid or acetoacetylating the above
 lactone-modified hydroxyalkyl (meth)acrylates with diketene.
 The foregoing silane base monomers include, for example,
 3-(meth)acryloxypropyltrimethoxysilane,
 3-(meth)acryloxypropylmethyidimethoxysilane,
 3-(meth)-acryloxypropyltriethoxysilane,
 3-(meth)acryloxypropylmethyldiethoxysilane,
 3-(meth)acryloxypropylethyldi-ethoxysilane,
 3-crotonyloxypropyltrimethoxysilane, vinyltrimethoxysilane,
 vinyltriethoxysilane, vinyl tris(3-methoxyethoxy)silane,
 vinylmethyldimethoxysilane, vinylmethyldiethoxysilane,
 vinyidimethylmethoxysilane, vinyldimethylethoxysilane,
 vinyltriacetoxysilane, vinyltriisocyanatesilane, vinyltrichlorosilane,
 vinylmethyldichlorosilane, vinyldimethylchlorosilane,
 allyltrimethoxysilane and styrylethyltrimethoxysilane.
 In addition to the radical-polymerizable unsaturated monomers described
 above, compounds having two or more polymerizable double bonds can be used
 in combination for the purpose of providing the low molecular weight
 polymers with a cross-linking structure to carry out emulsion
 polymerization. Such compounds having two or more polymerizable double
 bonds include, for example, aromatic divinyl compounds such as
 divinylbenzene and divinyinaphthalene; diethylenical carboxylic esters
 such as ethylene glycol dimethacrylate, tetraethylene glycol
 dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol diacrylate
 and aryl methacrylate; N,N-divinylaniline, divinyl ether, divinyl sulfide
 and triallyl cyanurate.
 The emulsion polymerization in the present invention is carried out usually
 in the absence of the chain transfer agent but can be carried out as well,
 if necessary, in the presence of the chain transfer agent. Agents
 conventionally used for emulsion polymerization can be used likewise as
 the chain transfer agent capable of being used in such case and include,
 for example, sulfur-containing chain transfer agents such as
 n-dodecylmercaptan, t-dodecylmercaptan, n-butylmercaptan, 2-ethylhexyl
 thioglycolate and 2-mercaptoethanol; halogen-containing chain transfer
 agents such as trichlorobromomethane, carbon tetrachloride and bromoform;
 nitrogen-containing chain transfer agents such as N,N-di-methyl-formamide
 and pivalonitrile; in addition thereto, turbinolene, myrcel, limonene,
 .alpha.-pinene and .beta.-pinene.
 The chain transfer agent can usually be used according to a weight average
 molecular weight (Mw) desired to the resulting polymer in an amount (T
 represents parts by weight of the chain transfer agent used for the
 polymerization per 100 parts by weight of the radical-polymerizable
 unsaturated monomer, and when the chain transfer agent is not used, T is
 zero) falling in a range in which a relation shown by the following
 inequality is set up:
 3.ltoreq.log Mw&lt;4.11-0.93.times.log (T+0.1) (2)
 preferably
EQU 3.18.ltoreq.log Mw&lt;3.85-0.93.times.log (T+0.1) (2-1)
 more preferably
EQU 3.3.ltoreq.log Mw&lt;3.67-0.93.times.log (T+0.1) (2-2)
 To be more specific, the use amount (T) of the chain transfer agent falls
 preferably in a range of:
EQU 0.ltoreq.T.ltoreq.3
 particularly
EQU 0.ltoreq.T.ltoreq.1
 above all
EQU 0.ltoreq.T.ltoreq.0.1
 According to the present invention, the polymer having a low molecular
 weight which is equivalent to or lower than those of polymers obtained by
 emulsion polymerization using conventional chain transfer agents can be
 produced by using much smaller amounts of the chain transfer agents, and
 even when the chain transfer agents are used, the use amounts thereof can
 be reduced to a large extent.
 The emulsion polymerization in the present invention is characterized by
 being carried out at higher temperatures which have not so far been used.
 In the present invention, the emulsion polymerization is carried out at a
 temperature falling in a range of 115.degree. C. or higher, preferably 120
 to 250.degree. C., more preferably 130 to 200.degree. C. and particularly
 preferably 140 to 190.degree. C. When the polymerization temperature is
 lower than 115.degree. C., it is difficult to obtain the polymer having a
 low molecular weight which is intended in the present invention.
 Thus, since a high polymerization temperature is used in the present
 invention, the emulsion polymerization is preferably carried out usually
 under pressure at which the reaction mixture is not vaporized and
 volatilized. In general, the polymerization is carried out preferably
 under a pressure (gauge pressure) of about 1 to about 50 kg/cm.sup.2,
 preferably about 1 to 10 kg/cm.sup.2. To be specific, for example, a
 pressure proof polymerization vessel is used, and the reaction can be
 carried out in a sealed state while controlling the pressure.
 The emulsion polymerization in the present invention can be carried out by
 polymerizing the radical-polymerizable monomers described above in an
 aqueous medium in the presence of the chain transfer agent on the
 polymerization temperature condition described above using an emulsifier,
 an initiator and the like.
 Usually, deionized water is used as the polymerization medium, but a mixed
 solvent of a water miscible organic solvent such as alcohol and water can
 be used in a certain case. The reaction can be carried out in the air but
 may be carried out, if necessary, under an atmosphere of inert gas such as
 nitrogen and argon.
 The emulsifier capable of being used in the emulsion polymerization may be
 any of anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers and
 amphoteric emulsifiers, and these emulsifiers may be used alone or can be
 used in combination of two or more kinds thereof.
 Examples of the nonionic emulsifiers described above include
 polyoxyethylene alkyl ethers such as, for example, polyoxyethylene lauryl
 ether and polyoxyethylene stearyl ether; polyoxyethylene alkylphenyl
 ethers such as, for example, polyoxyethylene octylphenyl ether and
 polyoxyethylene nonylphenyl ether; sorbitan higher fatty acid esters such
 as, for example, sorbitan monolaurate, sorbitan monostearate and sorbitan
 trioleate; polyoxyethylene sorbitan higher fatty acid esters such as, for
 example, polyoxyethylene sorbitan monolaurate; polyoxyethylene higher
 fatty acid esters such as, for example, polyoxyethylene monolaurate and
 polyoxyethylene monostearate; glycerin higher fatty acid esters such as,
 for example, monoglyceride oleate and monoglyceride stearate; in addition
 thereto, polyoxyethylene.polyoxypropylene.block copolymers.
 Examples of the anionic emulsifiers described above include higher fatty
 acid salts such as, for example, sodium oleate; alkylarylsulfonic acid
 salts such as, for example, sodium dodecylbenzenesulfonate; alkylsulfuric
 acid salts such as, for example, sodium laurylsulfate; polyoxyethylene
 alkyl ethersulfuric ester salts such as, for example, sodium
 polyoxyethylene lauryl ethersulfate; polyoxyethylene alkylaryl
 ethersulfuric ester salts such as, for example, sodium polyoxyethylene
 nonylphenyl ethersulfate; and alkylsulfosuccinic ester salts and
 derivatives thereof such as sodium monooctylsulfosuccinate, sodium
 dioctylsulfosuccinate and sodium polyoxyethylene laurylsulfosuccinate.
 The amphoteric emulsifiers described above include, for example, alkyl
 betaines such as lauryl betaine.
 Further, fluorine base emulsifiers obtained by substituting at least a part
 of hydrogen atoms of the alkyl groups of these emulsifiers with fluorine
 can be used as well.
 Examples of the cationic emulsifiers described above include
 octadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride,
 hexadecyltrimethylammonium chloride, dioctadecyidimethylammonium chloride,
 didodecyldimethylammonium chloride, dodecylbenzyidimethylammonium
 chloride, tetradecylbenzyldimethylammonium chloride,
 octadecylbenzyldimethylammonium chloride, tetradecyltrimethylammonium
 chloride, dihexadecyidimethylammonium chloride,
 dioctadecyldimethylammonium chloride, hexadecylbenzyldimethylammonium
 chloride, palmityltrimethylammonium chloride, oleyltrimethylammonium
 chloride, dipalmitylbenzyltrimethylammonium chloride and
 dioleylbenzyltrimethylammonium chloride.
 Further, there can be used cationic emulsifiers using as starting
 materials, natural vegetable oils such as coconut oil, palm oil, safflower
 oil, cotton seed oil, rape seed oil and linseed oil, and these cationic
 emulsifiers include coconut oil alkylbenzyldimethylammonium chloride and
 coconut oil alkyltrimethylammonium chloride. Amine acetates and
 hydrochlorides include dodecylamine acetate, tetradodecylamine acetate,
 octadecylamine acetate, dodecylamine acetate, tetradodecylamine
 hydrochloride, octadecylamine hydrochloride and hardened beef tallow amine
 acetate.
 Further, reactive emulsifiers having polymerizable double bonds in
 molecular structures can be used as well, and examples of these reactive
 emulsifiers include a reactive emulsifier represented by the following
 formula (1) or (2):
 ##STR1##
 wherein R.sup.1 and R.sup.2 represent independently hydrogen or a methyl
 group; R.sup.3 represents an alkyl group having 6 to 18 carbon atoms, an
 alkenyl group, an aryl group or an aralkyl group; EO is --CH.sub.2
 CH.sub.2 O--; X represents a single bond or a methylene group; Z
 represents hydrogen or SO.sub.3 M, in which M represents alkaline metal,
 ammonium or organic ammonium; and m is a natural number of 1 to 50.
 Among the reactive emulsifiers represented by the formula (1) described
 above, specific examples of the anionic reactive emulsifiers in which Z is
 SO.sub.3 M include, for example, .left brkt-top.Adeka Reasoap SE-10N.right
 brkt-bot. (manufactured by Asahi Denka Ind. Co., Ltd.), and specific
 examples of the anionic reactive emulsifiers in which Z is hydrogen
 include, for example, .left brkt-top.Adeka Reasoap NE-10.right brkt-bot.,
 .left brkt-top.Adeka Reasoap NE-20.right brkt-bot. and .left
 brkt-top.Adeka Reasoap NE-30.right brkt-bot. (all manufactured by Asahi
 Denka Ind. Co., Ltd.).
 Among the reactive emulsifiers represented by the formula (2) described
 above, specific examples of the anionic reactive emulsifiers in which Z is
 SO.sub.3 M include, for example, .left brkt-top.Aquaron HS-10.right
 brkt-bot. and .left brkt-top.Aquaron HS-20.right brkt-bot. (all
 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and specific examples of
 the nonionic reactive emulsifiers in which Z is hydrogen include, for
 example, .left brkt-top.Aquaron RN-10.right brkt-bot., .left
 brkt-top.Aquaron RN-20.right brkt-bot., .left brkt-top.Aquaron RN-30.right
 brkt-bot. and .left brkt-top.Aquaron RN-50.right brkt-bot. (all
 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).
 Anionic reactive emulsifiers other than those described above include
 alkylsulfosuccinic acid alkenyl ether salt base reactive emulsifiers such
 as, for example, .left brkt-top.Latemul S-120.right brkt-bot., .left
 brkt-top.Latemul S-120A.right brkt-bot., .left brkt-top.Latemul
 S-180.right brkt-bot. and .left brkt-top.Latemul S-180A.right brkt-bot.
 (all manufactured by Kao Corp.); alkylsulfosuccinic acid alkenyl ester
 salt base reactive emulsifiers such as, for example, .left
 brkt-top.Eleminol JS-2.right brkt-bot. (manufactured by Sanyo Kasei Ind.
 Co., Ltd.); methylenebispolyoxyethylene alkylphenylalkenyl ether sulfuric
 acid ester salt base reactive emulsifiers such as, for example, .left
 brkt-top.Antox MS-60.right brkt-bot. (manufactured by Nippon Nyukazai Co.,
 Ltd.); alkylalkenylsulfosuccinic acid ester salt base reactive emulsifiers
 such as, for example, .left brkt-top.Latemul ASK.right brkt-bot.
 (manufactured by Kao Corp.); polyoxyalkylene (meth)-acrylate sulfuric acid
 ester salt base reactive emulsifiers such as, for example, .left
 brkt-top.Eleminol RS-30.right brkt-bot. (manufactured by Sanyo Kasei Ind.
 Co., Ltd.); polyoxyalkylene alkyl ether aliphatic unsaturated dicarboxylic
 acid ester salt base reactive emulsifiers such as, for example, .left
 brkt-top.RA-1120.right brkt-bot. and .left brkt-top.RA-2614.right
 brkt-bot. (all manufactured by Nippon Nyukazai Co., Ltd.); (meth)acrylic
 acid sulfoalkyl ester salt base reactive emulsifiers such as, for example,
 .left brkt-top.Antox MS-2N.right brkt-bot. (manufactured by Nippon
 Nyukazai Go., Ltd.); phthalic acid dihydroxyalkyl (meth)acrylate sulfuric
 acid ester salt base reactive emulsifiers; and mono- or
 di(glycerol-1-alkylphenyl-3-allyl-2-polyoxyalky lene ether)phosphoric acid
 ester salt base reactive emulsifiers such as, for example, .left
 brkt-top.H-3330PL.right brkt-bot. (manufactured by Daiichi Kogyo Seiyaku
 Co., Ltd.).
 Nonionic reactive emulsifiers other than those described above include
 polyoxyalkylene alkylphenyl ether (meth)acrylate base reactive emulsifiers
 such as, for example, .left brkt-top.RMA-564.right brkt-bot. and .left
 brkt-top.RMA-568.right brkt-bot. (all manufactured by Nippon Nyukazai Co.,
 Ltd.); and polyoxyalkylene alkylphenyl ether (meth)acrylate base reactive
 emulsifiers such as, for example, .left brkt-top.RMA-1114.right brkt-bot.
 (manufactured by Nippon Nyukazai Co., Ltd.).
 Water soluble protective colloid can be used in combination with the
 anionic and/or nonionic emulsifiers described above.
 The water soluble protective colloid capable of being used includes
 polyvinyl alcohols such as, for example, partially saponified polyvinyl
 alcohol, fully saponified polyvinyl alcohol and modified polyvinyl
 alcohol; cellulose derivatives such as, for example, hydroxyethyl
 cellulose, hydroxypropyl cellulose and carboxymethyl cellulose; and
 natural polysaccharides such as gua gum. They can be used in a mode of
 single use or combined use of plural kinds.
 The use amount of the emulsifiers described above can be set usually in a
 range of 0.03 to 10 parts by weight, preferably 0.05 to 7 parts by weight
 and more preferably 0.1 to 5 parts by weight per 100 parts by weight of
 the total of the monomers to be used.
 Further, optional water soluble initiators which have so far been used for
 emulsion polymerization can be used likewise as the initiator capable of
 being used for emulsion polymerization in the present invention.
 A group of suitable initiators are free radical initiators such as hydrogen
 peroxide, some specific alkyl hydroperoxides, dialkyl peroxides,
 persulfates, peresters, percarbonates, ketone peroxides and azo
 initiators. Specific examples of the suitable free radical initiators
 include hydrogen peroxide, t-butyl hydroperoxide, di-tert-butyl peroxide,
 ammonium persulfate, potassium persulfate, sodium persulfate, tert-amyl
 hydroperoxide, methyl ethyl ketone peroxide, 2,2'-azobis(2-amidinopropane)
 and 2,2'-azobis(4-cyanovaleric acid). From the viewpoint that the water
 resistance of the polymer is not reduced, preferred are nonionic catalysts
 such as hydrogen peroxide, alkyl hydroperoxides, dialkyl peroxides,
 peresters, percarbonates, ketone peroxides and azo initiators, and
 hydrogen peroxide is particularly preferred.
 In general, the use amount of such free radical initiator falls preferably
 in a range of 0.05 to 50 parts by weight, more preferably 0.2 to 30 parts
 by weight and particularly preferably 1 to 10 parts by weight per 100
 parts by weight of the total of the monomers used. The reaction
 temperature and the use amount of the free radical initiator are
 controlled according to the molecular weight desired to the intended
 polymer.
 A water soluble redox initiator obtained by combining a water soluble
 peroxide with a water soluble reducing agent can be used as well. The
 peroxide used for the water soluble redox initiator includes the peroxides
 described above, and there can be used as the reducing agent, for example,
 sodium bisulfite, sodium pyrosulfite, sodium sulfite, hypophosphites,
 ascorbic acid and formaldehyde-sodium sulfoxylate.
 In general, the use amount of the reducing agent in the redox catalyst can
 fall in a range of 0.05 to 50 parts by weight per 100 parts by weight of
 the total of the monomers used.
 Further, in addition to the redox catalysts described above, a trace amount
 of transition metal, for example, ferrous sulfate and Mohr's salt copper
 sulfate can be used in combination.
 The radical-polymerizable unsaturated monomer, the chain transfer agent,
 the emulsifier, the initiator and the aqueous medium each described above
 can be added gradually to a polymerization vessel in one lot to be
 reacted, or at first, a part of them is added and heated to start
 polymerization, and then the remainder can be added to carry out the
 polymerization. In general, the latter method is preferred from the
 viewpoint that the polymerization temperature can readily be controlled.
 Further, the radical-polymerizable unsaturated monomer is mixed in advance
 with the emulsifier and the aqueous medium to prepare an emulsion of the
 monomer, and this emulsion is added to the polymerization vessel to carry
 out polymerization, whereby the emulsion polymerization can safely be
 advanced.
 Further, the emulsion polymerization can be carried out by a so-called
 power feed polymerization method in which polymerization is carried out
 while changing the composition of monomers and a so-called seed
 polymerization method in which a polymer emulsion is added in advance and
 then polymerization is started.
 Further, the initiator may be added at first in one lot, or first a small
 amount, for example, 0.1 to 2 parts by weight, preferably 0.5 to 1 part by
 weight per 100 parts by weight of the total of the monomer is added, and
 then the remainder may be added intermittently, semi-continuously or
 continuously after starting the polymerization. The addition thereof can
 be finished usually in 5 minutes to 5 hours, preferably 30 minutes to 4
 hours and more preferably 1 to 3 hours.
 The emulsion polymerization described above turns usually a great part of
 the monomer fed into a polymer and allows the unreacted monomer to
 scarcely remain. However, if it is desired to further reduce the content
 of the residual monomer, the residual monomer can be reduced by a method
 in which the initiator is added to the reaction mixture after the
 polymerization to further promote the polymerization of the residual
 monomer or nitrogen or air is blown to thereby remove the residual
 monomer.
 Thus, an emulsified dispersion containing a polymer having a low molecular
 weight is obtained. Polymer particles contained in the above emulsified
 dispersion can have usually a particle diameter falling in a range of 0.01
 to 2 .mu.m, preferably 0.02 to 1 .mu.m and more preferably 0.05 to 0.5
 .mu.m. The polymer contained in the above emulsified dispersion has a
 concentration (solid matter concentration) falling usually in a range of
 20 to 80% by weight, preferably 30 to 70% by weight and more preferably 40
 to 65% by weight, and the viscosity (BH type rotary viscometer, 25.degree.
 C., 20 rpm; herein-after the same viscosity measuring conditions apply)
 falls usually in a range of 10,000 cps or less, particularly 5 to 5,000
 cps.
 Further, the polymer-emulsified dispersion has a pH falling usually in a
 range of 2 to 10, particularly preferably 2 to 9, and the pH of the
 dispersion may be adjusted, if necessary, by adding aqueous ammonia, an
 amine aqueous solution and an alkali hydroxide aqueous solution.
 There can further be added to and mixed with the polymer-emulsified
 dispersion, if necessary, defoaming agents such as silicon base compounds;
 thickeners and viscosity-improving agents such as polycarboxylic acid base
 resins and surfactants; film-forming aids such as ethylene glycol, butyl
 cellosolve, butyl carbitol, butyl carbitol acetate and
 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate; antioxidants;
 preservatives; fungicides; UV-absorbers; and antistatic agents.
 The resulting polymer-emulsified dispersion can be used as it is in a
 dispersion state according to uses thereof, or the polymer separated from
 the above dispersion can be used. The polymer can be separated from the
 dispersion, for example, by putting the polymer-emulsified dispersion
 directly into a flash dryer or a spray dryer to dry it or adding an
 electrolyte to salt out the polymer or adding a solvent such as alcohol to
 precipitate the polymer by solvation and then centrifuging and drying it.
 The polymer-emulsified dispersion obtained according to the present
 invention can advantageously be used as it is for a thermoplastic or
 thermosetting coating composition (for example, paint and adhesive).
 Further, the above composition can be blended, if necessary, with
 conventional polymers, cross-linking agents or modifiers to thereby
 obtain, for example, a polymer composition with a wide molecular weight
 distribution containing the low molecular weight polymer obtained by the
 emulsion polymerization in the present invention and a polymer having a
 high molecular weight, a polymer composition having plural molecular
 weight peaks and a polymer composition in which polymers having different
 compositions are blended. The use of such composition can improve the
 properties of the film such as, for example, appearance, gloss, build
 feeling, water resistance, alkali resistance, acid resistance, solvent
 resistance, weatherability, strength and the like. Blending may be carried
 out by dissolving or dispersing the additives described above in the
 polymerizable monomers before emulsion polymerization or by blending them
 in the form of a suitable aqueous dispersion in the middle or after the
 emulsion polymerization. Specific examples and use amounts of such
 additives are as follows:
 (1) Cellulose derivatives (for example, cellulose acetate butyrate,
 cellulose acetate propionate and nitrocellulose): they can provide the
 film with excellent properties such as gloss, a color and a gloss-holding
 property, weatherability, heat stability, a heat flow property and
 hardness, and the use amount thereof can fall in a range of 5 to 50 parts
 by weight per 100 parts by weight of the polymer.
 (2) Acryl resin and alkyd resin: used usually in an amount of 150 parts by
 weight or less per 100 parts by weight of the polymer.
 (3) Cross-linking agents such as aminoplast resin, blocked polyisocyanate
 compounds, compounds having two or more carboxyl groups or acid anhydrides
 thereof and epoxy compounds:
 Such cross-liking agents can contribute to an improvement in appearance,
 gloss and physical and chemical properties of the film. The aminoplast
 resin described above includes condensation products of amino compounds
 such as urea, melamine and guanamines with formaldehyde, and
 alcohol-etherified compounds thereof.
 They can be used in a range of 5 to 40 parts by weight per 100 parts by
 weight of the polymer, and the baking temperature falls preferably in a
 range of 80 to 200.degree. C. The blocked polyisocyanate compounds
 described above include, for example, addition products of diisocyanates
 or polyisocyanates and blocking agents (phenols, alcohols, lactams, active
 methylene compounds, amines and oximes), and they can be used in a range
 of 5 to 60 parts by weight per 100 parts by weight of the polymer. In
 using this blocked polyisocyanate, dissociation catalysts such as bases
 (triethylamine, N-methylmorpholine and the like) and metal compounds
 (dibutyltin dilaurate, stannous chloride and the like) are preferably used
 in combination. The baking temperature falls suitably in a range of 120 to
 220.degree. C.
 The foregoing compounds having two or more carboxyl groups or acid
 anhydrides thereof include, for example, polycarboxylic acids (adipic
 acid, sebacic acid, phthalic acid, trimellitic acid and the like) and acid
 anhydrides thereof (phthalic anhydride, trimellitic anhydride, polyester
 resins obtained by condensation reaction of excess polycarboxylic acids
 with polyols, and the like), and they can be used in a range of 3 to 50
 parts by weight per 100 parts by weight of the polymer. The baking
 temperature falls suitably in a range of 120 to 220.degree. C.
 The epoxy compounds described above include, for example, copolymers of
 triglycidyl isocyanurate, glycidyl acrylate, glycidyl methacrylate,
 methylglycidyl acrylate, methylglycidyl methacrylate and the like with
 other copolymerizable monomers, a condensation product of bisphenol A and
 epichlorohydrin, a condensation product of novolak and epichlorohydrin,
 diepoxy compounds having a polyalkyl ether chain structure, alicyclic
 epoxy compounds and the like. They can be used in a range of 5 to 40 parts
 by weight per 100 parts by weight of the polymer. In use, there may be
 used in combination, if necessary, hardening-accelerating catalysts such
 as Lewis acids (boron trifluoride and the like), bases
 (benzyldimethylamine, 2-ethyl-5-methylimidazole, triethyleneamine,
 N-methylmorpholine and the like) and salts (boron
 trifluoride-monoethylamine complex salt and the like). The baking
 temperature falls suitably in a range of 140 to 220.degree. C.
 (4) Other ester gums, maleic acid resins and phenol resins.
 A coating composition obtained by using the polymer-emulsified emulsion of
 the present invention can be colored with organic pigments (for example,
 phthalocyanine blue and phthalocyanine green) and inorganic pigments (for
 example, carbon black, titanium oxide and aluminum flake) usually used for
 coloring paints. Such pigments can be added to water or the polymerizable
 monomers in the emulsion polymerization. Further, the above coating
 composition can be blended as well with additives such as conventional
 wetting agents, film surface-controlling agents, curing aids and
 antioxidants.
 The polymer of the present invention can be used, for example, as a toner
 binder for an electronic copying machine, a binder resin for paints, a
 tackifier, a sealant, a plasticizer, a pigment dispersant, various
 treating agents and the like.
 When the polymer of the present invention is used as the toner binder for
 an electronic copying machine, the kind of the polymer is preferably a
 styrene resin or an epoxy resin. The toner for an electronic copying
 machine does not have to cause blocking between the toners during storage.
 On the other hand, the toner transferred on paper is requested to be
 quickly fixed on the paper in the course of fixation. A toner comprises
 particles which are present in the form of a homogeneous mixture of carbon
 black, a binder resin, an anti-static agent and the like, and if the
 binder resin is soft, the toners are liable to cause blocking between them
 but have a good fixing property. In contrast with this, if the binder
 resin is hard, blocking is hardly brought about but the fixing property is
 inferior. In order to satisfy these required characteristics which are
 contrary to each other, a resin-mixed composition obtained by mixing a
 resin having a high molecular weight with a resin having a low molecular
 weight is usually used as a resin for a toner binder in many cases. The
 polymer of the present invention is particularly useful as a resin
 component of a low molecular weight in such resin mixed composition and
 can be used in combination with a resin having a high molecular weight
 obtained by suspension polymerization and emulsion polymerization.
 Further, the polymer of the present invention can be turned into a paint
 composition by blending with various pigments and the like. A paint
 containing the polymer of the present invention provides a paint film
 having good gloss and adhesive property. A functional group such as
 carboxyl group and a hydroxyl group can be introduced into the polymer of
 the present invention used for a paint, and making use of this functional
 group, the polymer is cross-linked with a curing agent such as an
 isocyanate compound and melamine, whereby the paint film which is
 excellent in a water resistance and a mechanical strength can be formed.
 The kind of the polymer used for a paint shall not specifically be
 restricted, and in general, styrene base polymers or acryl base polymers
 are preferred. Further, the polymer of the present invention produced
 using a monomer having a carboxyl group such as acrylic acid and
 methacrylic acid in a proportion of 30% by weight or more based on the
 whole monomers can be solubilized in water by neutralizing with, for
 example, organic amine and can be used for water base paints. Further, the
 paint film performances such as an adhesive property and gloss can be
 raised as well by adding a hydrophobic polymer such as polystyrene
 produced by the method of the present invention in a proportion of 5 to
 30% by weight as an additive to a paint.
 The polymer of the present invention having a weight average molecular
 weight falling in a range of 1000 to 10000 can be used as a plasticizer, a
 dispersant and various treating agents.
 The polystyrene base resin obtained by the method of the present invention
 is excellent in not only affinity with pigments but also compatibility
 with resins and therefore can be used as a master batch for coloring a
 styrene resin and polyvinyl chloride.

EXAMPLES
 The present invention shall more specifically be explained below with
 reference to examples and comparative examples.
 Example 1
 First, a vessel equipped with a dropping pump was charged with 31 parts by
 weight of deionized water and 5 parts by weight of an anionic reactive
 emulsifier .left brkt-top.Aquaron HS-10.right brkt-bot. [sodium
 polyoxyethylene (n=about 10) nonylpropenylphenyl ethersulfate; effective
 ingredient about 100% by weight; manufactured by Asahi Denka Ind. Co.,
 Ltd.] and stirred to dissolve them. Then, a monomer mixed solution
 comprising 42.7 parts by weight of methyl methacrylate (MMA), 52.3 parts
 by weight of 2-ethylhexyl acrylate (EHA) and 5 parts by weight of acrylic
 acid (AA) was dropwise added under stirring to obtain a monomer emulsion.
 Next, a pressure proof reactor equipped with a stirrer, a pressure gauge, a
 thermometer and a dropping pump was charged with 120 parts by weight of
 deionized water and substituted with nitrogen. Then, it was heated to
 150.degree. C. after sealing, and 10% by weight of the monomer emulsion
 described above was added to the pressure proof reactor. Further, 3 parts
 by weight of a 5 weight % hydrogen peroxide aqueous solution was added to
 carry out initial polymerization at 150.degree. C. After finishing the
 initial polymerization, the temperature was elevated to 155.degree. C.,
 and the remaining monomer emulsion and 19 parts by weight of the 5 weight
 % hydrogen peroxide aqueous solution were added in 3 hours. Thereafter,
 the same temperature was maintained for 2 hours to obtain an aqueous acryl
 base polymer dispersion. The polymer dispersion thus obtained had a high
 polymerization conversion rate and could stably be polymerized.
 The polymer dispersion was analyzed after separating by means of an ultra
 centrifuge, and as a result thereof, it had a weight average molecular
 weight (Mw) of 39,000, a number average molecular weight (Mn) of 14,000, a
 molecular weight peak (Mp) of 33,000 and Mw/Mn of 2.8. Also, it had a very
 little odor.
 Example 2
 A vessel equipped with a dropping pump was charged with 31 parts by weight
 of deionized water, 2.5 parts by weight of .left brkt-top.Neogen R.right
 brkt-bot. and 0.8 part by weight of .left brkt-top.STK-199.right brkt-bot.
 [polyoxyethylene (n=about 30) nonylphenyl ether; effective ingredient
 about 70% by weight; manufactured by Kao Corp.] and stirred to dissolve
 them. Then, a monomer mixed solution comprising 95 parts by weight of
 styrene and 5 parts by weight of 2-hydroxyethyl acrylate was dropwise
 added while stirring to obtain a monomer emulsion.
 The same reactor as used in Example 1 was charged with 120 parts by weight
 of deionized water and 0.3 part by weight of an anionic emulsifier .left
 brkt-top.Neogen R.right brkt-bot. [sodium alkylbenzenesulfonate; effective
 ingredient about 60% by weight; manufactured by Daiichi Kogyo Ind. Co.,
 Ltd.] and substituted with nitrogen. Then, it was heated to 185.degree. C.
 after sealing.
 Added to the pressure proof reactor was 5 parts by weight of a 5 weight %
 hydrogen peroxide aqueous solution, and then the monomer emulsion
 described above and 75 parts by weight of the 5 weight % hydrogen peroxide
 aqueous solution were added at 185.degree. C. in 3 hours. Thereafter, the
 same temperature was maintained for 2 hours to obtain an aqueous styrene
 polymer.
 The polymer was analyzed in the same manner as in Example 1, and as a
 result thereof, it had a weight average molecular weight (Mw) of 3,400, a
 number average molecular weight (Mn) of 1,500, a molecular weight peak
 (Mp) of 3,000 and Mw/Mn of 2.3. Also, it had a very little odor.
 Example 3
 The same operation as in Example 2 was carried out, except that 52 parts by
 weight of styrene, 15 parts by weight of methyl methacrylate, 30 parts by
 weight of butyl acrylate and 3 parts by weight of acrylic acid were used
 as monomers and the 5 weight % hydrogen peroxide aqueous solution was
 changed in an amount from 75 parts by weight to 95 parts by weight and
 that the reaction temperature was changed from 185.degree. C. to
 145.degree. C. The polymer thus obtained was analyzed, and as a result
 thereof, it had a weight average molecular weight (Mw) of 12,500, a number
 average molecular weight (Mn) of 5,200, a molecular weight peak (Mp) of
 11,000 and Mw/Mn of 2.4.
 Example 4
 The same operation as in Example 3 was carried out, except that 25 parts by
 weight of a 2.5 weight % potassium persulfate aqueous solution was
 substituted for 75 parts by weight of the 5 weight % hydrogen peroxide
 aqueous solution and that the reaction temperature was changed to
 160.degree. C.
 The polymer thus obtained was analyzed, and as a result thereof, it had a
 molecular weight peak (Mp) of 21,000, a weight average molecular weight
 (Mw) of 25,000, a number average molecular weight (Mn) of 9,300 and Mw/Mn
 of 2.7. Also, the odor was scarcely present.
 Comparative Example 1
 A polymer was synthesized on the same conditions as in Example 4, except
 that the reaction temperature was changed to 90.degree. C.
 The polymer thus obtained was analyzed, and as a result thereof, it had a
 molecular weight peak (Mp) of 270,000 and a weight average molecular
 weight (Mw) of 340,000.
 Example 5
 The same operation as in Example 2 was carried out, except that 0.3 part by
 weight of bromotrichloromethane as a chain transfer agent was added to 95
 parts by weight of styrene and 5 parts by weight of 2-hydroxyethyl
 acrylate and the 5 weight % hydrogen peroxide aqueous solution was changed
 in an amount from 75 parts by weight to 15 parts by weight and that the
 reaction temperature was changed from 185.degree. C. to 160.degree. C.
 The polymer thus obtained was analyzed, and as a result thereof, it had a
 weight average molecular weight (Mw) of 7,000, a number average molecular
 weight (Mn) of 2,800, a molecular weight peak (Mp) of 6,100 and Mw/Mn of
 2.5. Also, the odor was very small. The polymerization conversion rate was
 high, and the polymerization could stably be carried out.
 After separating, the resulting polymer was washed with methanol to be
 refined and dried, and then an equivalent number S of chain transfer agent
 fragments originating in bromotrichloromethane bonded to the end of the
 polymer chain was determined by ion chromatography according to a
 combustion method, and as a result thereof, the value of S was 0.00212
 (equivalent/100 g of the polymer).
 Comparative Example 2
 The same operation as in Example 5 was carried out, except that the chain
 transfer agent was changed to 7 parts by weight of bromotrichloromethane
 and vitamin C was added as a reducing agent for hydrogen peroxide at the
 same time in the same amount as that of hydrogen peroxide and that the
 reaction temperature was changed from 160.degree. C. to 90.degree. C.
 The polymer thus obtained was analyzed, and as a result thereof, it had a
 weight average molecular weight (Mw) of 7,200, a number average molecular
 weight (Mn) of 2,600, a molecular weight peak (Mp) of 6,100 and Mw/Mn of
 2.8. The polymerization conversion rate was low, and the odor containing
 halogen was very strong. Further, block matters were produced during the
 polymerization, and the polymer was adhered to the polymerization vessel
 and lacking in polymerization stability.
 After separating, the resulting polymer was washed with methanol to be
 refined and dried, and then an equivalent number S of chain transfer agent
 fragments originating in bromotrichloromethane used was determined by ion
 chromatography, and as a result thereof, the value of S was 0.0346
 (equivalent/100 g of the polymer).