CA1250395A - Method of reducing the formation of unprocessable particles and incrustations in the polymerization and copolymerization of vinyl monomers - Google Patents
Method of reducing the formation of unprocessable particles and incrustations in the polymerization and copolymerization of vinyl monomersInfo
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- CA1250395A CA1250395A CA000458525A CA458525A CA1250395A CA 1250395 A CA1250395 A CA 1250395A CA 000458525 A CA000458525 A CA 000458525A CA 458525 A CA458525 A CA 458525A CA 1250395 A CA1250395 A CA 1250395A
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- copolymerization
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
- C08F2/002—Scale prevention in a polymerisation reactor or its auxiliary parts
- C08F2/005—Scale prevention in a polymerisation reactor or its auxiliary parts by addition of a scale inhibitor to the polymerisation medium
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- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
- Polymerisation Methods In General (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed is a method for reducing the formation of unprocessible particles or incrustations in process equipment in connection with the aqueous suspension polymerization and copolymerization of vinyl monomers, said vinyl monomer polyme-rization and copolymerization including homopolymerization adn copolymerization of vinyl chloride, and polymerization of vinyl chloride with additives, wherein the said polymeriza-tion and copolymerization is carried out in the presenc of one or more ethers selected from the group consisting of dime-thylether, methylethylether, diethylether, di-n-butylether, tert-butylmethylether and diisopropylether.
Disclosed is a method for reducing the formation of unprocessible particles or incrustations in process equipment in connection with the aqueous suspension polymerization and copolymerization of vinyl monomers, said vinyl monomer polyme-rization and copolymerization including homopolymerization adn copolymerization of vinyl chloride, and polymerization of vinyl chloride with additives, wherein the said polymeriza-tion and copolymerization is carried out in the presenc of one or more ethers selected from the group consisting of dime-thylether, methylethylether, diethylether, di-n-butylether, tert-butylmethylether and diisopropylether.
Description
~250395 METHOD FOR REDUCINC ~HE FORMATION OF
-UNPROCESSIBLE PARTICLES AND INCRUSTATIONS
IN THE POLYMERIZATION AND COPOLYMERIZATION
_ VINYL MONOMERS
The invention pertains to a method for reducing the formation of unprocessible particles and incrustations of a polymerization equipment in the polymerization and copolymerization of vinyl monomers, in particular in the homopolymerization of vinyl chloride, polymerization of vinyl chloride with additives, above all with low-molecular-weight and high-molecular-weight plasticizers and with an ethylene -vinyl acetate copolymer, and in the copolymerization of vinyl chloride.
The homopolymerizations and copolymerizations of vinyl chloride in aqueous dispersions, known as su~pensi~on, micro-suspension or emulsion polymerizations are the most known polymerization procedures in the prod~ction of poly(vinyl chloride) (PVC) and copolymers of vinyl chloride. The most important of these polymerization procedures is the suspension homopolymerization and copolymerization of vinyl chloride, because the physico-chemical properties of the homopolymers and copolymers of vinyl chloride may be varied within broad limits by changing the polymerization conditions in this procedure.
;t ` ' '~25~0395 Z
Polymer deposits are formed during the homopolymerization and copoly~erization of vinyl chloride on the walls of reactors as well as on stirrers and on the surface of vinyl chloride reflux condensers. This process, called incrustation of polymerization equipment, pronouncedly reduces the intensity of heat transfer between the heating medium in reactor walls and stirrers and the polymerization m$xture during repeated production cycles, and ~owers the cooling efficiency of vinyl chloride condensers.
Consequently, vinyl chloride homopolymerization and copolymerization becomes less temperature controlled and the quality of th~ produced product deteriorates.
The growing incrustation alao harmfully affect~ the hydrodynamics of agitation of the polymerization mixture and causes the formation of heterogeneous particles, which may behave as unprocessible particles, so called l'Eish Eyes", in the processing of homopolymers and copo~ymers. Their presence in the proces-qed polymers deteriorates above all mechanical properties, the quality of surface, appearance, and transparency of the final products. Incrustations cau~e periodically putting the equipment out of operation for the period of time necessary for cleaning 25 and thus highly influence the economy Or the polymerization process in the given production line.
Incrustat;on of the polymerization equipment occurs ~25039 in the free radical and in the anionic and complex-coordination homopolymerization and copolymerization of vinyl chloride. It is obvious, that the physical phenomenon, which leads to incrustations, -is an adsorption of reaction components of the polymerization system. However, the heterogeneous system of vinyl chloride homopolymerization and copolymerization consists of numerous polymerization components, and it is therefore difficult to detèrmine which one of 10 components i3 directly responsible for incrusSation and which component only conduces to this phenomenon, or whether a combined parallel adsorption of several components should be considered.
The reaction components, in the suspension process 15 are dispersed in a water phase and the dispersions are stabilized with inorganic or organic dispersants e.g., the calcium salt of hydroxy-apatite, gelatin, ether derivatives of cellulose, high-molecular-weight poly(ethylene oxide), partially or completely 20 hydrolyzed poly(vinyi acetate), or a copolymer of qtyrene with maleic anhydride. These agents, called protective colloids, are not typical surface-active compounds (emulsifiers) ~nd their stabilization effect conaists in the adsorption on the surface of dispersed 25 organic phase, so that both monomer droplets and polymer particles are covered by them on the surface.
The adsorption characteristics for individual ~50~39~i components of the vinyl chloride homopolymerization and copolymerization are not known. However, it has been proved that vinyl chloride is sorbed on the metallic surface of reactor walls (Behrens H.: Angew. Makromol.
Chem. 47, 97, 1975). It is supposed that the dispersants adsorption depends on their chemical composition and molecular weight (Kaltwasser H. et all.: Plaste Kaut. 26, 552, 1979). High-molecular-weight compounds containing in their molecules polar groups~ wh~ch enable sorption on the wall surface by means of d~pole-dipole bonds, are preferably adsorbed on the reactor walls. The thick incrustations generally occurr~ng on metallic surfaces, in comparison with enamelled surfaces of reactors, may be explained by stronger adsorption of vinyl chloride and polymeric particles swollen with monomers on the metallic surface in the presence of dispersants. The adsorption of di~per~ants was ~xperimentally proved with hydroxypropylmethyl oe~lulose (Methocel - Registered 20 Trade Mark) by observations that Methocel is concentrated in the layer of deposited PVC near the metallic surface of walls (Cluck P. et all.: Mater.
Pla~tics 13, 46, 1976). The adsorption of polymer macromolecules on the walls of the reactor is very strong if the macromolecules have a lower temperature than the reactor wall; the adsorbed amount increases linearly with the molecular weight and high-molecular-, .. .
, ~ .
~Z~039~;
weight particles are preferably adsorbed in co~parisonwith low-molecular-weight particles Insufficient coalescent stability of the polymerization system assist~ in adsorption of the polymerization components.
S The aggregation of swollen polymer particles and the coalescence of ~nonomer droplets occur with changes in - the stability of whole polymerization system or some of its parts. Considering the formation of a new phase by precipitation of polymer in the ~onomer droplets at the conversion about 1% and disappearance of a p,hase by absorption of free monomers into polymer particles at the conversion about 70% during the homopolymerization and copolymerization of vinyl chloride, it is evident that the interpha~e tension and the stability of the polymerization system vary during polymerization.
It may be assumed that incrustations are originated and formed by creating a thin layer of ~orbed vinyl chloride on the ~urface of the reactor walls immediately after addition of vinyl chloride (or further comonomers), which polymerizes into a primary polymer layer on the walls. A secondary layer is formed on the primary layer during polymerization by a deposition of monomer-swollen particles. The polymerization of vinyl chloride proceeds within the layers formed on the walls depending on the diffusion of monomer. The patented procedures reducing the incrustation suppress the origin and growth of the - 6 - ~2~0~9S
primary and secondary layers built on the reactor walls by the effect of inorganic and organic compounds, which are adsorbed on metal walls more strongly than vinyl chloride or comonomers. Such compounds are, for example, alkaline hydroxides, aluminum oxide (Ger. pat. 2,709,053), phosphoric and polyphosphoric acid (Jap. pat. 69,287, 1978), or their salts (Jap. pat. 116,571, 1976), alkaline silicates (Ger.
pat. 2,632,469), silica (Jap. pat. 14,789, 1978), siloxanes (Pat. GDR 118,287), cellulose derivatives (Ger. pat.
-UNPROCESSIBLE PARTICLES AND INCRUSTATIONS
IN THE POLYMERIZATION AND COPOLYMERIZATION
_ VINYL MONOMERS
The invention pertains to a method for reducing the formation of unprocessible particles and incrustations of a polymerization equipment in the polymerization and copolymerization of vinyl monomers, in particular in the homopolymerization of vinyl chloride, polymerization of vinyl chloride with additives, above all with low-molecular-weight and high-molecular-weight plasticizers and with an ethylene -vinyl acetate copolymer, and in the copolymerization of vinyl chloride.
The homopolymerizations and copolymerizations of vinyl chloride in aqueous dispersions, known as su~pensi~on, micro-suspension or emulsion polymerizations are the most known polymerization procedures in the prod~ction of poly(vinyl chloride) (PVC) and copolymers of vinyl chloride. The most important of these polymerization procedures is the suspension homopolymerization and copolymerization of vinyl chloride, because the physico-chemical properties of the homopolymers and copolymers of vinyl chloride may be varied within broad limits by changing the polymerization conditions in this procedure.
;t ` ' '~25~0395 Z
Polymer deposits are formed during the homopolymerization and copoly~erization of vinyl chloride on the walls of reactors as well as on stirrers and on the surface of vinyl chloride reflux condensers. This process, called incrustation of polymerization equipment, pronouncedly reduces the intensity of heat transfer between the heating medium in reactor walls and stirrers and the polymerization m$xture during repeated production cycles, and ~owers the cooling efficiency of vinyl chloride condensers.
Consequently, vinyl chloride homopolymerization and copolymerization becomes less temperature controlled and the quality of th~ produced product deteriorates.
The growing incrustation alao harmfully affect~ the hydrodynamics of agitation of the polymerization mixture and causes the formation of heterogeneous particles, which may behave as unprocessible particles, so called l'Eish Eyes", in the processing of homopolymers and copo~ymers. Their presence in the proces-qed polymers deteriorates above all mechanical properties, the quality of surface, appearance, and transparency of the final products. Incrustations cau~e periodically putting the equipment out of operation for the period of time necessary for cleaning 25 and thus highly influence the economy Or the polymerization process in the given production line.
Incrustat;on of the polymerization equipment occurs ~25039 in the free radical and in the anionic and complex-coordination homopolymerization and copolymerization of vinyl chloride. It is obvious, that the physical phenomenon, which leads to incrustations, -is an adsorption of reaction components of the polymerization system. However, the heterogeneous system of vinyl chloride homopolymerization and copolymerization consists of numerous polymerization components, and it is therefore difficult to detèrmine which one of 10 components i3 directly responsible for incrusSation and which component only conduces to this phenomenon, or whether a combined parallel adsorption of several components should be considered.
The reaction components, in the suspension process 15 are dispersed in a water phase and the dispersions are stabilized with inorganic or organic dispersants e.g., the calcium salt of hydroxy-apatite, gelatin, ether derivatives of cellulose, high-molecular-weight poly(ethylene oxide), partially or completely 20 hydrolyzed poly(vinyi acetate), or a copolymer of qtyrene with maleic anhydride. These agents, called protective colloids, are not typical surface-active compounds (emulsifiers) ~nd their stabilization effect conaists in the adsorption on the surface of dispersed 25 organic phase, so that both monomer droplets and polymer particles are covered by them on the surface.
The adsorption characteristics for individual ~50~39~i components of the vinyl chloride homopolymerization and copolymerization are not known. However, it has been proved that vinyl chloride is sorbed on the metallic surface of reactor walls (Behrens H.: Angew. Makromol.
Chem. 47, 97, 1975). It is supposed that the dispersants adsorption depends on their chemical composition and molecular weight (Kaltwasser H. et all.: Plaste Kaut. 26, 552, 1979). High-molecular-weight compounds containing in their molecules polar groups~ wh~ch enable sorption on the wall surface by means of d~pole-dipole bonds, are preferably adsorbed on the reactor walls. The thick incrustations generally occurr~ng on metallic surfaces, in comparison with enamelled surfaces of reactors, may be explained by stronger adsorption of vinyl chloride and polymeric particles swollen with monomers on the metallic surface in the presence of dispersants. The adsorption of di~per~ants was ~xperimentally proved with hydroxypropylmethyl oe~lulose (Methocel - Registered 20 Trade Mark) by observations that Methocel is concentrated in the layer of deposited PVC near the metallic surface of walls (Cluck P. et all.: Mater.
Pla~tics 13, 46, 1976). The adsorption of polymer macromolecules on the walls of the reactor is very strong if the macromolecules have a lower temperature than the reactor wall; the adsorbed amount increases linearly with the molecular weight and high-molecular-, .. .
, ~ .
~Z~039~;
weight particles are preferably adsorbed in co~parisonwith low-molecular-weight particles Insufficient coalescent stability of the polymerization system assist~ in adsorption of the polymerization components.
S The aggregation of swollen polymer particles and the coalescence of ~nonomer droplets occur with changes in - the stability of whole polymerization system or some of its parts. Considering the formation of a new phase by precipitation of polymer in the ~onomer droplets at the conversion about 1% and disappearance of a p,hase by absorption of free monomers into polymer particles at the conversion about 70% during the homopolymerization and copolymerization of vinyl chloride, it is evident that the interpha~e tension and the stability of the polymerization system vary during polymerization.
It may be assumed that incrustations are originated and formed by creating a thin layer of ~orbed vinyl chloride on the ~urface of the reactor walls immediately after addition of vinyl chloride (or further comonomers), which polymerizes into a primary polymer layer on the walls. A secondary layer is formed on the primary layer during polymerization by a deposition of monomer-swollen particles. The polymerization of vinyl chloride proceeds within the layers formed on the walls depending on the diffusion of monomer. The patented procedures reducing the incrustation suppress the origin and growth of the - 6 - ~2~0~9S
primary and secondary layers built on the reactor walls by the effect of inorganic and organic compounds, which are adsorbed on metal walls more strongly than vinyl chloride or comonomers. Such compounds are, for example, alkaline hydroxides, aluminum oxide (Ger. pat. 2,709,053), phosphoric and polyphosphoric acid (Jap. pat. 69,287, 1978), or their salts (Jap. pat. 116,571, 1976), alkaline silicates (Ger.
pat. 2,632,469), silica (Jap. pat. 14,789, 1978), siloxanes (Pat. GDR 118,287), cellulose derivatives (Ger. pat.
2,930,757), starch (Ger. pat. 2,522,473), isobutylenemaleic anhydride copolymer (Jap. pat. 52,986, 1977), sulfonated dicarboxylic acids (Jap. pat. 116,242, 1977~. The rate of homopolymerization or copolymerization of vinyl chloride, in the formation of primary layer and in the boundary layer wall-liquid, is suppressed by the action of inorganic or organic inhibitors of the free radical polymerization of vinyl chloride, e.g., alkaline nitrites (Jap. pat. 71,584, 1977) or o~ -methylstyrene (US pat. 3,778,423). To lncrease the effect, these compounds are used in combinations and are either applied onto the inner surfaces of polymerization equipment or added to the polymerization mixture at the beginning or even during polymerization. Such compounds are, e.g., aromatic polyols (Jap. pat. 77,290, 1978) diindole derivatives (Jap. pat. 85,282, 1977), triazole derivatives (Jap.
~
/
pat. 119,783, 1976), various types of dyes, above all Nigrosine (Ger. pat. 2,801,219; Jap. pat. 73, 887, 1979), oxidized aromatic amines (Jap. pat. 13, 689, 1978), condensation products of amines with phenols (Jap. pat. 7,920,089, 1979), polyamides (Jap. pat. 124, Oa6, 1977), polyimides and polyamideimides (Jap. pat.
108 473 1977), or gases, such as carbon monoxide, dinitrogen monoxide, nitrogen oxide, sulfur dioxide, or also butadiene (Jap. pat. 10,391, 1979; Jap. pat.
10 97,397, 1975).
A close relation exists between the degree of ~ncru~tation of the polymerization equipment and the occurence of difficultly proce~sible or unprocessible partic~es in the polymer powder. Their presence in proce~ed polymers deteriorates above all the mechanical properties, surface quality, appearance, and transparency of final products.
The structure and mechanism of formation of unprocessible particles, defined as particles which, during the polymer processing with plasticizers,change into the gel-like state either with difficulty or not at all, have not yet been unambiguously explained, because usually one ur.~rocessible particle appears in the powdered polymer per some 105 of ordinary particles.
Irrespective of the so far unknown mechanism of the formation of unprocessible particles, the patent 1 ~,j ~ .
~z50395 `
literature describes numerous procedures leading to a reduced amount of unprocessible particles in polymer~.
These procedures lower, at the same time, the incrustation of polymerization equipment and comprise, 5 for example: the iodine or bromine addition, addition - of alkali metal iodides, bromides~ thiocyanates, and isothiocyanates to polymerization mixtures (Jap. pat.
12,291, 1977), addition of acetylenic alcohols, e.g., propargyl alcohol, to polymerization mixtures (Jap.
pat. 69,195,1979), organic dyes and ~ùgars (Ger. pat.
2,631,325), also with the addition of metal salts, e.g. Nigrosine base with copper(I) chloride (Cer. pat.
2,632,469), the addition of potassium dimethyldithiocarbamate with sodium nitrite, or iodine 15 with dithiophosphoric acid or its salt (Jap. pat.
76,379, 1976; Jap. pat. 135,991, 1976), the addition of sodium polyphosphate and an inhibitor, e.g., N-nitrophenylhydroxylami~ne, into the polymerization mixture (Jap. pat. 87~491, 1977), the addition of diazabicycloalkanes, tetrazaadamantans or tetrazatricycloalkanes into the polymerization mixture (Cer. pat. 2,806,649), application of phosphoric or polyphosphoric acid with sorbitol monoesters of fatty acids on the surface of the polymerization equipment 25 (Jap.` pat. 69,287, 1978) or also a modification of the polymerization process,e.g., polymerization up to the conversion of 30% at pH 12.8 of the reaction mixture ~ !
g ~.~s039~i (Ger. pat. 2,208,796).
Most of the above mentioned compounds, which are used so far to suppress the incrustations and to reduce the amount of unprocessible particles, have a disadvantage that they remain in the final product and thus more or less influence its physicochemical properties. In addition, they act negatively on the rate of polymerization. The said shortcomings are unfavourably manifested in the economy of polymerisation process.
According to the invention we provide a method for reducing formation of unprocessable particles or incrustations in process equipment in connection with the aqueous suspension polymerization and copolymerization of vinyl monomers, said vinyl monomer polymerization and copolymerization including homopolymerization and copolymerization of vinyl chloride, and polymerization of vinyl chloride with additives, said additives including low-molecular-weight plasticizers, high-molecular-weight platiclzers and ethylene-vinyl acetate co-polymer, wherein the said polymerization and copolymerization is carried out in the presence of one or more of dimethylether, methylethylether, diethylether, di-n-butylether, tert-butylmethylether, and diisopropylether.
The amount of ether added into polymerization mixture depends, on the one hand, on whether only : - 1 o ~2S~)395 incrustations or both incrustations and the formation of unprocessible particles are suppressed in the given polymerization process, and on the solubility of the ether in the polymerization mixture and on the inner surface area of polymerization equipment.
~Z~O~9~
The said method of suspension homopolymerization and copolymerization of vinyl monomers in the presence of the specified ethers is applicable for homopolymerization and/or copolymerization of known vinyl monomers, for example, alkyl acrylates (methyl, ethyl, butyl acrylate), alkyl methacrylates (methyl methacrylate), vinyl esters of carboxylic acids tvinyl acetate), 1-alkenes (propene, 1- and 2-butene), acrylonitrile, styrene, ~inylidene chloride, N-vinylpyrrolidone, and above all vinyl chloride, under known polymerization conditions, the produced polymers being isolated and processed by ~nown procedures.
The invention is further illu~trated in examples of performance, without limiting the scope of the invention to them.
The results obtained in the examples are surveyed in Table~ , which show the effect of quality and quantity of the ethers, used accordirg to the invention, on suppressing the incrustations and i;0395 ! : - 12 decreasing the amount of unprocessible particles.
Also the effect of ethers on physico~hemical properties can be seen.
Example 1 - Ceneral Formula A stainless-steel jacketed reactor was charged with 250 g vinyl chloride, 437 g distilled water, 15 g aqueous solution containing 3.8 wt.%
hydroxypropylmethyl cellulose, 12 g aqueous solution containing 1 wt.% sodium hydroxide, 0.7 g dilauroyl peroxide, and 0.223 g dicetylperoxydicarbonate (Liladox). The polymerization was carried out at 51 degrees C and a stirring speed of 300 r.p.m. for 6.5 h.
After the polymerization was completed, the resulting polymer was three times decanted with 3 dm3 distilled water, filtered on a sintered-glass filter S1, and dried in stainless-steel dishes lined with filter paper at 50 degrees C to a constant weight.
Incrustations were determined by weighing the polymer mechanically removed from the reactor walls and stirrer after drying and are related to the weight of vinyl chloride in the polymerization batch. Molecular weights, intrinsic viscosity and the K-values were determined by common methods. Thermal stability was measured in nitrogen at 180 degrees C as the amount of split-off hydrogen chloride, which was determined potentiometrically. The amount of unprocessible particles was determined by the method according to ~%~9~
Czechoslovak standard CSN 64 3~00.
Example 2 - 1~
The polymerization was carried out in the same way as in Example 1, with the distinction that various amounts of di~nethylether, methylethylether, diethylether, tert-butylmethylether, di-n-butylether, and diisopropylether, were added to the polymerization batch. The polymerizations and resulting polymers were evaluated similarly as in Examp~e 1. The results and the added amounts of ethers are surveyed in Table I, II
and I~.
Examples 15 - 17 The polymerizations were carried out in the same way as in E~ample 1, with the distinction that the polymerization batch contained an addition of 50 g polyester plasticizer based on adipic acid and 1,4-butanediol (Palamoll) - example 15. The polymerization batches in examples 16 and 1~ further contained 18 g diethylether and 21.4 g tert-butylmethylether, respectively. The results were evaluated similarly as in Example 1 ard are surveyed in Table III.
Example 1 a 22 The polymerizations were carried out in the same way as in Example 1, with the distinction that the polymerization batch contained 14.4 g ethylene- vinyl acetate copolymer texample 18, Table III). The ~ _ 14 _ ~2~39~
polymerization batches in examples 19 - 22 (Table III) also contained 18 and 36g diethylether and 21.4 and 42.8 g tert-butylmethylether, respectively. In examples 20 and 22, the ethylene-vinyl acetate copolymer was previously dissolved in the said ethers.
The results were evaluated similarly as in Example and are surveyed in Table III.
Example 23 A stainlescS-steel jacketed reactor was charged wlth 1O 250 g vinyl chloride, 22.5 g propene, 1.65 g Liladox, and other components in the ~ame amounts as in Example 1. The polymerization was carried out at 51 degrees C
and stirring speed 500 r.p.m. for f3.5 h. The processing of copolymer and determinations of incrustations, the amount of unprocessible particles, ; and K-values were identical to example 1. The results are ~urveyed in Table III and IV.
Examplecs 24 and 25 The polymerizations were carried out in the same way as in Example 23 with the di~tinction that the polymerization batches contained an addition of 18 g diethylether and 21.4g tert-butylmethylether, respectively. The polymerizations and resulting copolymers were evalu~ated analogously as in Examples and 23. The results are surveyed in Tables III and IV.
25i0~5 TABLE I
The effect of concentrations of diethylether (DEE) and tert-butylmethylether (t-BME) on the size of incrustation and amount of unprocessible particles in the suspension polymerization of vinyl chloride xample Ether Conversion Incrustation Fish Eyes per Type Amount 1 g polymer .
~g] [wt.~ ~ %] ~ %]
~ _ _ _ 76.2 7.84 41 4 DEE 5 1.2 72.3 i.22 21 DEE 6 2.4 64.9 1.10 6 6DEE 12 4.8 61.4 0.92 7 7DEE 18 7.2 54.4 0.12 7 8t-BME 4 1.6 75.l 1.61 8 9t-BME 8 3.2 73.2 l.30 6 10t-BME 16 6.4 70.8 0.83 0 11 t-BME 21.4 8.6 64.0 0.24 o aRelated to the weight of vinyl chloride.
TABLE II
The effect of various types of dialkyl and aiicyclic ethers on the size of incrustation and amount of unprocessible particles in the suspension ~Z~03~3S
polymerization of vinyl chloride.
Example Ether Conversion Incrustation Fish Eyes . per Type Amount . 1 g polymer g] [w~-~b~ tmol %C~ [%b~ ~%]
~ - 76 2 7.84 . 4~
2 DME 11.2 4.5 6 72.1 ~mponderable 20
~
/
pat. 119,783, 1976), various types of dyes, above all Nigrosine (Ger. pat. 2,801,219; Jap. pat. 73, 887, 1979), oxidized aromatic amines (Jap. pat. 13, 689, 1978), condensation products of amines with phenols (Jap. pat. 7,920,089, 1979), polyamides (Jap. pat. 124, Oa6, 1977), polyimides and polyamideimides (Jap. pat.
108 473 1977), or gases, such as carbon monoxide, dinitrogen monoxide, nitrogen oxide, sulfur dioxide, or also butadiene (Jap. pat. 10,391, 1979; Jap. pat.
10 97,397, 1975).
A close relation exists between the degree of ~ncru~tation of the polymerization equipment and the occurence of difficultly proce~sible or unprocessible partic~es in the polymer powder. Their presence in proce~ed polymers deteriorates above all the mechanical properties, surface quality, appearance, and transparency of final products.
The structure and mechanism of formation of unprocessible particles, defined as particles which, during the polymer processing with plasticizers,change into the gel-like state either with difficulty or not at all, have not yet been unambiguously explained, because usually one ur.~rocessible particle appears in the powdered polymer per some 105 of ordinary particles.
Irrespective of the so far unknown mechanism of the formation of unprocessible particles, the patent 1 ~,j ~ .
~z50395 `
literature describes numerous procedures leading to a reduced amount of unprocessible particles in polymer~.
These procedures lower, at the same time, the incrustation of polymerization equipment and comprise, 5 for example: the iodine or bromine addition, addition - of alkali metal iodides, bromides~ thiocyanates, and isothiocyanates to polymerization mixtures (Jap. pat.
12,291, 1977), addition of acetylenic alcohols, e.g., propargyl alcohol, to polymerization mixtures (Jap.
pat. 69,195,1979), organic dyes and ~ùgars (Ger. pat.
2,631,325), also with the addition of metal salts, e.g. Nigrosine base with copper(I) chloride (Cer. pat.
2,632,469), the addition of potassium dimethyldithiocarbamate with sodium nitrite, or iodine 15 with dithiophosphoric acid or its salt (Jap. pat.
76,379, 1976; Jap. pat. 135,991, 1976), the addition of sodium polyphosphate and an inhibitor, e.g., N-nitrophenylhydroxylami~ne, into the polymerization mixture (Jap. pat. 87~491, 1977), the addition of diazabicycloalkanes, tetrazaadamantans or tetrazatricycloalkanes into the polymerization mixture (Cer. pat. 2,806,649), application of phosphoric or polyphosphoric acid with sorbitol monoesters of fatty acids on the surface of the polymerization equipment 25 (Jap.` pat. 69,287, 1978) or also a modification of the polymerization process,e.g., polymerization up to the conversion of 30% at pH 12.8 of the reaction mixture ~ !
g ~.~s039~i (Ger. pat. 2,208,796).
Most of the above mentioned compounds, which are used so far to suppress the incrustations and to reduce the amount of unprocessible particles, have a disadvantage that they remain in the final product and thus more or less influence its physicochemical properties. In addition, they act negatively on the rate of polymerization. The said shortcomings are unfavourably manifested in the economy of polymerisation process.
According to the invention we provide a method for reducing formation of unprocessable particles or incrustations in process equipment in connection with the aqueous suspension polymerization and copolymerization of vinyl monomers, said vinyl monomer polymerization and copolymerization including homopolymerization and copolymerization of vinyl chloride, and polymerization of vinyl chloride with additives, said additives including low-molecular-weight plasticizers, high-molecular-weight platiclzers and ethylene-vinyl acetate co-polymer, wherein the said polymerization and copolymerization is carried out in the presence of one or more of dimethylether, methylethylether, diethylether, di-n-butylether, tert-butylmethylether, and diisopropylether.
The amount of ether added into polymerization mixture depends, on the one hand, on whether only : - 1 o ~2S~)395 incrustations or both incrustations and the formation of unprocessible particles are suppressed in the given polymerization process, and on the solubility of the ether in the polymerization mixture and on the inner surface area of polymerization equipment.
~Z~O~9~
The said method of suspension homopolymerization and copolymerization of vinyl monomers in the presence of the specified ethers is applicable for homopolymerization and/or copolymerization of known vinyl monomers, for example, alkyl acrylates (methyl, ethyl, butyl acrylate), alkyl methacrylates (methyl methacrylate), vinyl esters of carboxylic acids tvinyl acetate), 1-alkenes (propene, 1- and 2-butene), acrylonitrile, styrene, ~inylidene chloride, N-vinylpyrrolidone, and above all vinyl chloride, under known polymerization conditions, the produced polymers being isolated and processed by ~nown procedures.
The invention is further illu~trated in examples of performance, without limiting the scope of the invention to them.
The results obtained in the examples are surveyed in Table~ , which show the effect of quality and quantity of the ethers, used accordirg to the invention, on suppressing the incrustations and i;0395 ! : - 12 decreasing the amount of unprocessible particles.
Also the effect of ethers on physico~hemical properties can be seen.
Example 1 - Ceneral Formula A stainless-steel jacketed reactor was charged with 250 g vinyl chloride, 437 g distilled water, 15 g aqueous solution containing 3.8 wt.%
hydroxypropylmethyl cellulose, 12 g aqueous solution containing 1 wt.% sodium hydroxide, 0.7 g dilauroyl peroxide, and 0.223 g dicetylperoxydicarbonate (Liladox). The polymerization was carried out at 51 degrees C and a stirring speed of 300 r.p.m. for 6.5 h.
After the polymerization was completed, the resulting polymer was three times decanted with 3 dm3 distilled water, filtered on a sintered-glass filter S1, and dried in stainless-steel dishes lined with filter paper at 50 degrees C to a constant weight.
Incrustations were determined by weighing the polymer mechanically removed from the reactor walls and stirrer after drying and are related to the weight of vinyl chloride in the polymerization batch. Molecular weights, intrinsic viscosity and the K-values were determined by common methods. Thermal stability was measured in nitrogen at 180 degrees C as the amount of split-off hydrogen chloride, which was determined potentiometrically. The amount of unprocessible particles was determined by the method according to ~%~9~
Czechoslovak standard CSN 64 3~00.
Example 2 - 1~
The polymerization was carried out in the same way as in Example 1, with the distinction that various amounts of di~nethylether, methylethylether, diethylether, tert-butylmethylether, di-n-butylether, and diisopropylether, were added to the polymerization batch. The polymerizations and resulting polymers were evaluated similarly as in Examp~e 1. The results and the added amounts of ethers are surveyed in Table I, II
and I~.
Examples 15 - 17 The polymerizations were carried out in the same way as in E~ample 1, with the distinction that the polymerization batch contained an addition of 50 g polyester plasticizer based on adipic acid and 1,4-butanediol (Palamoll) - example 15. The polymerization batches in examples 16 and 1~ further contained 18 g diethylether and 21.4 g tert-butylmethylether, respectively. The results were evaluated similarly as in Example 1 ard are surveyed in Table III.
Example 1 a 22 The polymerizations were carried out in the same way as in Example 1, with the distinction that the polymerization batch contained 14.4 g ethylene- vinyl acetate copolymer texample 18, Table III). The ~ _ 14 _ ~2~39~
polymerization batches in examples 19 - 22 (Table III) also contained 18 and 36g diethylether and 21.4 and 42.8 g tert-butylmethylether, respectively. In examples 20 and 22, the ethylene-vinyl acetate copolymer was previously dissolved in the said ethers.
The results were evaluated similarly as in Example and are surveyed in Table III.
Example 23 A stainlescS-steel jacketed reactor was charged wlth 1O 250 g vinyl chloride, 22.5 g propene, 1.65 g Liladox, and other components in the ~ame amounts as in Example 1. The polymerization was carried out at 51 degrees C
and stirring speed 500 r.p.m. for f3.5 h. The processing of copolymer and determinations of incrustations, the amount of unprocessible particles, ; and K-values were identical to example 1. The results are ~urveyed in Table III and IV.
Examplecs 24 and 25 The polymerizations were carried out in the same way as in Example 23 with the di~tinction that the polymerization batches contained an addition of 18 g diethylether and 21.4g tert-butylmethylether, respectively. The polymerizations and resulting copolymers were evalu~ated analogously as in Examples and 23. The results are surveyed in Tables III and IV.
25i0~5 TABLE I
The effect of concentrations of diethylether (DEE) and tert-butylmethylether (t-BME) on the size of incrustation and amount of unprocessible particles in the suspension polymerization of vinyl chloride xample Ether Conversion Incrustation Fish Eyes per Type Amount 1 g polymer .
~g] [wt.~ ~ %] ~ %]
~ _ _ _ 76.2 7.84 41 4 DEE 5 1.2 72.3 i.22 21 DEE 6 2.4 64.9 1.10 6 6DEE 12 4.8 61.4 0.92 7 7DEE 18 7.2 54.4 0.12 7 8t-BME 4 1.6 75.l 1.61 8 9t-BME 8 3.2 73.2 l.30 6 10t-BME 16 6.4 70.8 0.83 0 11 t-BME 21.4 8.6 64.0 0.24 o aRelated to the weight of vinyl chloride.
TABLE II
The effect of various types of dialkyl and aiicyclic ethers on the size of incrustation and amount of unprocessible particles in the suspension ~Z~03~3S
polymerization of vinyl chloride.
Example Ether Conversion Incrustation Fish Eyes . per Type Amount . 1 g polymer g] [w~-~b~ tmol %C~ [%b~ ~%]
~ - 76 2 7.84 . 4~
2 DME 11.2 4.5 6 72.1 ~mponderable 20
3 MEE 15.0 .6.0 6 68.8 imponderable 15 7 DEE 18.0 7.2 6 54.4 0.12 7 11 t-BME 21.4 8.6 6 64.0 0.84 0 12 DBE 31.6 12.6 6 25.6 0.28 0 13 DIPE 24.8 9.9 6 42.5 0.63 0 aDME - dimethylet~er. MEE - methylethylether, DEE
diethyl-ether, t-BME - tert-butylmethylether, DBE - di-n-butylether, DIPE - diisopropylether, ~elated to the weight of vinyl chloride ~elated to moles of ~inyl chloride TABLE III
The effect of diethylether (DEE~ and tert-butylmethylether (t-BME) on the size of incrustation and amount of unprocessible particles in the presence ~ ~0 39 of polymeric plasticizer Palamoll , ethylene-vinyl Example Additive Ether - type Conversion Inc~station Fish g wt.% g wt.% % % per polymer 15 Palamoll _ 64.9 4.2 370 16 Palamoll DEE 52.9 1.4 6 5~- 20 18 7.2 17 Palamoll t-BME 58.2 0.7 0 21.4 8.6 18 EVA - 81.0 12.1 many 19 EVA DEE ~8.7 1.0 Approx. 1200
diethyl-ether, t-BME - tert-butylmethylether, DBE - di-n-butylether, DIPE - diisopropylether, ~elated to the weight of vinyl chloride ~elated to moles of ~inyl chloride TABLE III
The effect of diethylether (DEE~ and tert-butylmethylether (t-BME) on the size of incrustation and amount of unprocessible particles in the presence ~ ~0 39 of polymeric plasticizer Palamoll , ethylene-vinyl Example Additive Ether - type Conversion Inc~station Fish g wt.% g wt.% % % per polymer 15 Palamoll _ 64.9 4.2 370 16 Palamoll DEE 52.9 1.4 6 5~- 20 18 7.2 17 Palamoll t-BME 58.2 0.7 0 21.4 8.6 18 EVA - 81.0 12.1 many 19 EVA DEE ~8.7 1.0 Approx. 1200
4 4 t-BME ' 74 5 4 36 approx. 600 14 4 5 7 21 4 8.6 66 9 6 2 296 t4 4 5.7 42.8 17.2 83.5 0.12 small a~ze 23 Zr25ene 9~0 36 2 2P2 S 9 18 7.Z small size 25 propene 9 0 21 4 8.6 small ~lze aPalamoll - polyester from adipic acid and 1,4-butanedlol bRelated to the weight of vinyl chloride CEV~ was previously dissolved in the corresponding amount of DEE or t-BME
Table I~
The e~ect of ethers on physicochemical properties Or ~uspension poly(vinyl chloride~
. .j .
f` ~.~5~39~
_ 18 -:. .. .
. .
Example Ether M x10-3 M /M K-value Specific Type~Amount 7~cX10 2 area [wt.%]b ~cm3.g~l] ~m2/g]
1 _ _ 89 2.3 0.91 70.2 1.0 2 DME 4-5 92 - 3.3 0 95 67.3 0.88 3 I~E 6.o 85 3.4 0.97 66.2 1.12 4 - DEE 1.2 110 3.4 1.04 69.9 0.56 ~
DEE 2.4 92 3.4 0.95 69.2 a.gs `
6 DEE 4.8 110 3.5 1.03 . 66.9 1.18 7 DEE 7.2 88 . 3-5 0.87 60.5 1.15 8 t-BME 1.6 113 2.5 1.05 10.0 1.31 g t-BME 3.2105 . Z.5 1.01 69.4 1.43 10t-B~E 6.4 115 Z.5 1.08 68.5 1.54 11t-BME 8.6 122 2.6 1.14 68.0 1.68 12. DBE12.6 80 3.4 0.82 61.2 3.70 13DIPE 9.9 113 .. 2.9 . 1.08 66.4 2.52 23d _ _ : _ _ _53.8 _ 24dDEE 7 2 - ~ ~49 3 25dt-BME 8.6 - - ~52.4 _ aDME-dimethylether, MEE-methylethylether, DEE-diethylether, t-BME - tert-butylmeth.ylether, DBE - di-n-butylether, DIPE - diisopropylethbr;, bRelated to the weight of vinyl chloride CIntrinsic viscosity dCopolymer of vinyl chloride with propene Examples 4 - 11 (Table I), with various concentrations of diethylether and tert-butylmethylether in the polymerization mixture for vinyl chloride homopolymerization, prove that a strong suppression of ~L2~03~
~incrustation and of formation of unprocessable particles takes place with the addition of these ethers into polymerization mixture in the concentration range up to 20 wt.%, preferably 7 - 9 wt.%, related to the weight of vinyl chloride. Diethylether suppresses incrustations somewhat better than tert-butylmethylether, which, on the other hand, suppreSses the formation of unprocessable particles a little more than the former. ~ert-butylmethylether Iesq reduces the conversion of vinyl chloride and the values of molecular parameters of PVC. Examples 2- 13 (Tables I and II) reveal that the -~traight-chain dialkylethers suppress the incrustation more than branched dialkylethers.
According to the invention, vinyl chloride may be advantageously polymerized in the presence of further add~tive~, for example, low- and high-molecular-weight plasticizers or a ethylene~vinyl acetate copolymer. Example 15 - 17 (Table III) show the effect of diethylether and tert-butylmethylether on the extent of incrustation and the number of unprocessable particles in the suspension polymerization of vinyl chloride in the presence of the polymer plasticizer Palamoll, which is a polyester of adipic acid and 1,4-butanediol. Tert-butylmethylether is more effecti~e than diethylether in this case. On the contrary, diethylether is more effective in the ~`" .
'~ - 20 - 12~395 ~suspension polymerization of vinyl chloride in the presence of an ethylene-vinyl acetate copolymer (Examples 18 - 22, Table III). In the copolymerization of vinyl chloride with propene, tert-butylmethylether is more effective and also more suitable from the standpoint of retaining the K-value (Examples 23 - 25, Tables III and IV).
The time dependence of conversion ~ of the dehydrochlorination of PVC samples, which was measured in a nitrogen atmosphere at 180 C, is shown in the appended drawing.
The curve 1 corresponds to PVC prepared according to the formula used in the invention, but without the addition of ether (Example 1) and the curve~ 2-3 correspond to the application of ethers according to the invention, where the curve 2 corresponds to PVC
prepared according to Example 11 (tert-butylmethylether), the curve 3 according to Example 7 (diethylether), anq t~he curve 4 according to example~ 12, 13 (di-n-butylether, diisopropylether).
As follows from these measurements of . dehydrochlorination, the thermal stability of the , 1 .
, :~"-~, . ~ .
)395 suspension PVC prepared in the presence of ethers is not deteriorated.
, , i ~ . . ... .. .
. , ;~.,, ., ,, :', . , ,:
: ... .~, . . , ' . . .. ~ .
: ~:
I
.
Table I~
The e~ect of ethers on physicochemical properties Or ~uspension poly(vinyl chloride~
. .j .
f` ~.~5~39~
_ 18 -:. .. .
. .
Example Ether M x10-3 M /M K-value Specific Type~Amount 7~cX10 2 area [wt.%]b ~cm3.g~l] ~m2/g]
1 _ _ 89 2.3 0.91 70.2 1.0 2 DME 4-5 92 - 3.3 0 95 67.3 0.88 3 I~E 6.o 85 3.4 0.97 66.2 1.12 4 - DEE 1.2 110 3.4 1.04 69.9 0.56 ~
DEE 2.4 92 3.4 0.95 69.2 a.gs `
6 DEE 4.8 110 3.5 1.03 . 66.9 1.18 7 DEE 7.2 88 . 3-5 0.87 60.5 1.15 8 t-BME 1.6 113 2.5 1.05 10.0 1.31 g t-BME 3.2105 . Z.5 1.01 69.4 1.43 10t-B~E 6.4 115 Z.5 1.08 68.5 1.54 11t-BME 8.6 122 2.6 1.14 68.0 1.68 12. DBE12.6 80 3.4 0.82 61.2 3.70 13DIPE 9.9 113 .. 2.9 . 1.08 66.4 2.52 23d _ _ : _ _ _53.8 _ 24dDEE 7 2 - ~ ~49 3 25dt-BME 8.6 - - ~52.4 _ aDME-dimethylether, MEE-methylethylether, DEE-diethylether, t-BME - tert-butylmeth.ylether, DBE - di-n-butylether, DIPE - diisopropylethbr;, bRelated to the weight of vinyl chloride CIntrinsic viscosity dCopolymer of vinyl chloride with propene Examples 4 - 11 (Table I), with various concentrations of diethylether and tert-butylmethylether in the polymerization mixture for vinyl chloride homopolymerization, prove that a strong suppression of ~L2~03~
~incrustation and of formation of unprocessable particles takes place with the addition of these ethers into polymerization mixture in the concentration range up to 20 wt.%, preferably 7 - 9 wt.%, related to the weight of vinyl chloride. Diethylether suppresses incrustations somewhat better than tert-butylmethylether, which, on the other hand, suppreSses the formation of unprocessable particles a little more than the former. ~ert-butylmethylether Iesq reduces the conversion of vinyl chloride and the values of molecular parameters of PVC. Examples 2- 13 (Tables I and II) reveal that the -~traight-chain dialkylethers suppress the incrustation more than branched dialkylethers.
According to the invention, vinyl chloride may be advantageously polymerized in the presence of further add~tive~, for example, low- and high-molecular-weight plasticizers or a ethylene~vinyl acetate copolymer. Example 15 - 17 (Table III) show the effect of diethylether and tert-butylmethylether on the extent of incrustation and the number of unprocessable particles in the suspension polymerization of vinyl chloride in the presence of the polymer plasticizer Palamoll, which is a polyester of adipic acid and 1,4-butanediol. Tert-butylmethylether is more effecti~e than diethylether in this case. On the contrary, diethylether is more effective in the ~`" .
'~ - 20 - 12~395 ~suspension polymerization of vinyl chloride in the presence of an ethylene-vinyl acetate copolymer (Examples 18 - 22, Table III). In the copolymerization of vinyl chloride with propene, tert-butylmethylether is more effective and also more suitable from the standpoint of retaining the K-value (Examples 23 - 25, Tables III and IV).
The time dependence of conversion ~ of the dehydrochlorination of PVC samples, which was measured in a nitrogen atmosphere at 180 C, is shown in the appended drawing.
The curve 1 corresponds to PVC prepared according to the formula used in the invention, but without the addition of ether (Example 1) and the curve~ 2-3 correspond to the application of ethers according to the invention, where the curve 2 corresponds to PVC
prepared according to Example 11 (tert-butylmethylether), the curve 3 according to Example 7 (diethylether), anq t~he curve 4 according to example~ 12, 13 (di-n-butylether, diisopropylether).
As follows from these measurements of . dehydrochlorination, the thermal stability of the , 1 .
, :~"-~, . ~ .
)395 suspension PVC prepared in the presence of ethers is not deteriorated.
, , i ~ . . ... .. .
. , ;~.,, ., ,, :', . , ,:
: ... .~, . . , ' . . .. ~ .
: ~:
I
.
Claims (3)
1. Method for reducing the formation of unprocessible particles or incrustations in process equipment in connection with the aqueous suspension polymerization and copolymerization of vinyl monomers, said vinyl monomer polymerization and copo-lymerization including homopolymerization and copolymerization of vinyl chloride, and polymerization of vinyl chloride with additives, wherein the said polymerization and copolymerization is carried out in the presence of one or more ethers selected from the group consisting of dimethylether, methylethylether, diethylether, di-n-butylether, tert-butylmethylether and dii-sopropylether.
2. Method as claimed in claim 1 wherein said additi-ves are selected from low-molecular-weight plasticizers, high-molecular-weight plasticizers and ethylene-vinyl acetate co-polymer.
3. A method as claimed in claim 1 or 2, wherein said ether is present in an amount of 7 to 9 weight percent based on the amount of vinyl monomers.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CSPV5213-83 | 1983-07-11 | ||
| CS835213A CS245419B1 (en) | 1983-07-11 | 1983-07-11 | Method of untreated particles' and incrustations' formation reduction during polymerization and copolymerizationof vinyl monomers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1250395A true CA1250395A (en) | 1989-02-21 |
Family
ID=5396591
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000458525A Expired CA1250395A (en) | 1983-07-11 | 1984-07-10 | Method of reducing the formation of unprocessable particles and incrustations in the polymerization and copolymerization of vinyl monomers |
Country Status (7)
| Country | Link |
|---|---|
| CA (1) | CA1250395A (en) |
| CS (1) | CS245419B1 (en) |
| DE (1) | DE3425539A1 (en) |
| FR (1) | FR2549071B1 (en) |
| GB (1) | GB2143244B (en) |
| IT (1) | IT1178490B (en) |
| NL (1) | NL8402170A (en) |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU7654274A (en) * | 1973-09-27 | 1976-06-17 | Goodrich Co B F | Process for producing heat stable vinyl chloride polymers |
| JPS5150989A (en) * | 1974-10-31 | 1976-05-06 | Shinetsu Chemical Co | Enkabiniru mataha enkabiniruoshutaitosuru tanryotaikongobutsuno jugohoho |
| JPS5214688A (en) * | 1975-07-24 | 1977-02-03 | Shin Etsu Chem Co Ltd | A process for polymerizing vinyl chloride |
-
1983
- 1983-07-11 CS CS835213A patent/CS245419B1/en unknown
-
1984
- 1984-07-03 GB GB08416952A patent/GB2143244B/en not_active Expired
- 1984-07-09 NL NL8402170A patent/NL8402170A/en not_active Application Discontinuation
- 1984-07-10 IT IT21829/84A patent/IT1178490B/en active
- 1984-07-10 CA CA000458525A patent/CA1250395A/en not_active Expired
- 1984-07-11 FR FR8411033A patent/FR2549071B1/en not_active Expired
- 1984-07-11 DE DE19843425539 patent/DE3425539A1/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| DE3425539A1 (en) | 1985-01-24 |
| GB2143244A (en) | 1985-02-06 |
| FR2549071A1 (en) | 1985-01-18 |
| GB8416952D0 (en) | 1984-08-08 |
| IT8421829A0 (en) | 1984-07-10 |
| FR2549071B1 (en) | 1987-10-16 |
| CS245419B1 (en) | 1986-10-16 |
| GB2143244B (en) | 1987-12-23 |
| NL8402170A (en) | 1985-02-01 |
| IT1178490B (en) | 1987-09-09 |
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