GB2051835A - Aqueous free-radical polymerisation - Google Patents

Abstract

Homopolymers or copolymers are produced by radical polymerisation in an aqueous phase at 273 DEG to 373 DEG K, the aqueous phase being a solution or dispersion containing at least one monomer chosen from vinyl halides, vinyl esters, vinyl ethers, vinylidene halides, acrylic and methacrylic monomers and ethylenically unsaturated bicarboxylic acids and their esters, by maintaining a monomer or total monomer concentration corresponding to the solubility of the or each monomer in the aqueous solution or dispersion, the partial vapour pressure of the or each monomer being maintained below the respective partial saturation vapour pressure of the respective monomer. Preferably at least one of the monomers is a vinyl monomer. Advantageously the aqueous phase contains at least one additive chosen from specified hydrocarbons and esters.

Description

SPECIFICATION Method for producing polymers by radial polymerisation The invention relates to a method for producing homo polymers and copolymers, for example using vinyl chloride hereinafter referred to as VC, by radial polymerisation in an aqueous phase, optionally containing one or more surface-active substances, in a temperature range of 273 to 3730K.

As is known, vinyl monomers and other monomers, especially VC, can be polymerised in the aqueous phase either by the addition of emulsifiers (in general 1 to 5% with respect to the total monomeric weight to be polymerised) preferably in the soap micelles, or in the presence of suspension stabilisers in the dispersed monomer droplets.

In this way porous VC polymers with bulk densities in general of between 0.48 and 0.58 g/cm3 can be obtained.

Apart from specific dispersing systems (DE-OS 26 10 021, DE-OS 27 02 771, US-PS 3 630 976) there also exist so-called porosity modifiers such as sorbitol derivatives DEOS, 2603025), phthalic acid esters (DE-OS 27 01 971) as well as selected organic acids and salts (US-PS 3642744)-the use of porosity enhancing substances is known, but this results only in limited improvements in the polymer porosity and apart from that is generally associated with a lowering or limitation of the bulk density.

Furthermore, the emulsion and suspension polymers obtained in this way, because of their morphology and particularly because of the residual emulsifier or protective colloidal content which acts in a detrimental way in a number of applications, can only be used in a limited way.

In contrast to this, polymers which are prepared by procedures not involving additional emulsifiers or protective colloids and compared with aqueous phase polymerisation methods require considerably less preparation. Also, in order to eliminate the polymer deposits occurring in connection with the difficult heat transfer in the reactor, it is known to polymerise the VC below its saturation vapour pressure (PS) in the presence of suitable carriers, preferably the polymers (PVC) themselves, by using monomer-soluble radical-forming initiators (DD-AP 63170, DD-WP 117021, DE-PS975823, DS-AS 1942823, US-PS 3622553).

Apart from the production of special graft copolymers using mostly elasticising polymer carriers, where the development of specific two-phase structures is paramount (DD-WP 122686, 124051, 131752; DE-OS 2133606,2344553), the vinyl homo chloride polymers and vinyl copolymers produced below P0 have the disadvantage that the quality of the polymer carrier, particularly its morphological parameters, to a considerable degree affect the properties of the end product. For this reason it is difficult to obtain homogeneous polymer products of high porosity (E.M. Sorvik and T. Hjertberg, J.

Macromol Sci. Chem. All (1977)7, page 1349-1378).

It is the primary object of this invention to provide by means of a more simplified technology, preferably porous, homo and copolymers from certain monomers, for example from VC, having improved properties both forthe hard as well as soft processing industry.

According to this invention there is provided a method for producing a homopolymer or copolymer by radical polymerisation in an equeous phase within a temperature range of 273 to 373"K, wherein the homopolymerisation or copolymerisation is conducted in an aqueous solution or dispersion containing at least one radical-forming initiator and at least one monomer chosen from vinyl halides, vinyl esters, vinyl ethers, vinylidene halides, acrylic and methacrylic monomers and ethylenically unsaturated dicarboxylic acids, their an hydrides and their esters by maintaining a monomer or total monomer concentration corresponding to the solubility of the or each monomer in the aqueous solution or dispersion, the partial vapour pressure of the or each monomer being maintained below the respective partial saturation vapour pressure of the respective monomer. At least one of the monomers may be vinyl chloride, vinyl acetate, vinylisobutyl ether, an acrylic or methacrylic monomer chosen from acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethyl hexyl acrylate, glycolmonoacrylate, methacrylic acid and methyl methacrylate, vinylidene chloride, maleic acid anhydride, maleinate or fumarate.If desired, the aqueous solution or dispersion may contain at least one surface-active substance andlor may contain less than 1% by weight of at least one suspension stabiliser based on the water present and/or less than 1% by weight of at least one emulsifier based on the water present, the preferred amountofsuspension being 10-' to 10-6% by weight based on the water present and/or the preferred amountofemulsifier(s) present being 10-' to 106% by weight based on the water present. The aquebus solution or dispersion may contain at least one water-soluble peroxide and/or at least one partially water-soluble peroxide and/or at least one diazo compound and/or at least one redox-initiator.

When monomer mixtures are used for producing specific co-and terpolymers, the partial vapour pressures may be replaced by the fugacities resulting from the respective vapour pressure measurements. The polymerisation may be initiated by known radical-forming substances in the usual concentrations, particularly water-soluble peroxides such as potassium and ammonium peroxide disulphate or hydrogen peroxide, diazo compounds such as 2,2' - azo - bis [isobutyronitrilea and 2,2' - azo - bis [2,4 dimethylvaleronitrilej, but also peroxides having less or almost non-existent water-solubility, such as alkyl perpivalate, diacylperoxide and dialkylperoxidic carbonate, the latter particularly in combination with water-soluble or partially water-soluble initiators.

Also there may be used redox initiators such as peroxidic sulphate sulphite or peroxidisulphate mercaptan systems and others, in order to produce at temperatures from 293 to 323 K at relatively high reaction rates polymers having higher Fikentsch K values (60-75).

The effectiveness and efficiency of the initiators also depends upon the type and concentration of the surfactant. Whereas the use of typical soaps (alkyl sulphonates, fatty acid salts, ethylene oxide adducts etc.) partially water-soluble initiators (diazo com pounds, perpivalates) and water-soluble initiators (e.g. K2S2OB) shows a high degree of effectiveness, the use of high molecular surfactants (cellulose ether, styrene maleic acid anhydride copolymers) causes a conflict of interest with regard to their effectiveness between the water-soluble and almost water-insoluble initiators.

Advantageously the aqueous solution or dispersion contains at least one additive chosen from hydrocarbons having 5 to 16 carbon atoms and/or esters of higher molecular fatty acids or aliphatic and aromatic dicarboxylic acids in a total quantity of less than or equal to 20% by weight based on the water present.

From the group of hydrocarbons and/or esters and higher molecular fatty acids or aliphatic and aromatic dicarbonic acids which can be added to the polymerisation mixture in orderto enhance the bulk density, n-hexane, cyclohexane, n-heptane and n-octane and/or the n-octyl or 2-ethylhexyl esters of the coconut fatty acid and other natural fatty acids or adipic and phthalic acids preferably in a quantity of 0.5-20%, especially 1 to 10% by weight with respect to the water present, are particularly well suited.

If desired, polymerisation may be effected in a main polymerisation stage and then in a subsequent stage, not more than 30% by weight of the mono mer(s) being polymerised in the subsequent stage.

With such multi-stage polymerisation the mono mer(s) islare preferably chosen from vinyl acetate or other vinyl esters, methacrylic acid, acrylic acid, methacrylate, acrylmitrite and other acrylic and methacrylic monomers, maleic anhydride, maleinite, fumanate and vinylidine chloride.

Since dissolved surfactants are not usually required for suspension and/or emulsification of liquid monomer droplets, considerably lower surfactant concentrations are usually required as compared to the conventional polymerisation techniques using aqueous dispersion.

If water-soluble initiators such as K2S206 are employed, the use of surfactants generally can be dis pensed with.

Example In a reaction vessel provided with agitators which can be broughtto a specific temperature and which can be rendered free of oxygen and containing an aqueous solution of 0.006% by weight of Na-alkyl sulphonate (molecular weight MG -300g/mol) and 0.1% by weight of K2S2O8, VC is added in such a quantity that, after heating to a polymerisation temperature (T) of 333 K, a pressure (p) of 8.5 bar is reached which is maintained throughout the entire conversion process by continuous after filling of gaseous VC from a reservoir directly connected with the reactor.

Polymerisation is maintained until a solid content of 41% by weight is achieved.

After separation of the precipitated polymers, washing and drying, a product is obtained which has a consistency of a porous PVC suspension, which does not have a pericellular skin, has a K value according to Fikentscher of 56 and a bulk density of 0.47 g/cm3. (see No. 1 in Table I). By varying the starting mixture (different monomers or monomer mixtures, type and concentration of the initiators, surfactants and additives) and the polymerisation conditions (T, p or p/ps) and by adhering to the specific polymerisation conversions or rates (solid content/unit or time) further homovinyl polymers and vinyl copolymers are produced according to the above example.In Table I is shown a selection of differentVC homopolymers and in Table II is shown a series af representative VC copolymers; from the large number of possible starting substances the following have been selected: Monomers - VC, vinylacetate (VAc), acrylic acid (AS), ethyl acrylate (EA), n-butylacrylate (BA), glycol mono acrylate (EMA), methyl methacry late (MMA), acrylonitrile (AN), vinyl isobutyl ether (VIBE), vinylidene chloride (VDC), maleic acid anhyd ride (MSA);; Surfactants - Sodium - alkylsulphonate (MG 300g/mol, Na-AS), sodium laurate (Na - L), nonylphenolethylenoxide adductwith 20 ethylene oxide units (NOP 20), a styrene-maleic acid anhydride copolymer saponified with NaOH (S/MSA), polyvinyl alcohol (PVA), hydroxypropyl methyl cellulose (HPMC);; Initiators - K2S2O6 2,2' - AZO - bis isobutyronitrile (AlBN) 2,2' - AZO - bis 2,4 - dimethyl valeronitrile (AMVN), tert.-butylperpivalate (tBPP) dilaroyl peroxide (DLPO) diisopropyl peroxidicarbonate (DIPP) dicetyl peroxidicarbonate (DCP) K2S2O, + Na2S20s K2S208 + dodexylmercaptan (DM) Additives - n-heptane (C7) Cyclohexane (cC6) dioctylphthalate (DOP) di-n - ethylhexyladipate (DEHA) coconut oil acid ethylhexyl ester (KFEH).

All percentages stated in Tables I and II related to the quantity of water. Concentrations for the initiators used (column 2) without reference to the type of initiator always relate to K2S2)8.

In addition, the following abbreviations are used: MT - parts per mass SD - bulk density TS - thermostat stability (according to TGL 28475).

The vinyl polymers obtained are characterised by high rates of plasticiser absorption (2 20 mass % DOP) and plasticiser absorption rates (0-5 min and 5-10 min for more compact products - according to the so-called "fat spot method", TGL 28475), the high degree of porosity remaining even in products which have particularly high bulk densities as a result of hydrocarbon or ester additives.

A specific injection of comonomers produces coand terpolymers which because of their good solubility in ordinary solvents, their good weldability, high transparency and surface gloss for coatings, are particularly useful as raw materials for adhesives and paints. Furthermore, the VCNAC copolymers, because oftheir high homogeneity and low melting range, make them particularly useful as melt adhesives. By adding special acrylic monomers to the VC/VAC-mixture it is possible to adjust the hardness of the particularterpolymers (e.g. by adding small quantities of EA- hard transparent shiny surfaces are produced and softer shiny surface layers are produced by adding (BA), and/or adhesion (by adding small quantities of AS).

By varying the composition of VC/acrylic monomer-copolymers further possibilities of application become available (e.g. softer crease resistant sheets from VC/BA and VC/VIBE copolymers, and hard sheets from VC/AS copolymers).

Table I: Production of PVC under various conditions

No. Initiator Surfactant Polym.-conditions Conversion PVC-properties []"/4j additive T p MT PVC K-value SD TS [%] [KJ [bar] / hd [9/ld [min] 100 MT H20 1 0.1 Na-AS 0.006 333 8.5 13.0 56 510 35 2 0.1 - 333 8.5 14.0 50.5 470 25 3 0.1 + l 318 6.8 11.5 68 362 28 0.04 Na2S2OsJ 6.10 333 8.5 6.5 61.7 495 48 4 0.05 5 0.1 + 0.04 Na2S2Os - 323 8.0 12.2 65.5 370 45 6 0.1 + 0.04 Na2S2O - 298 3.7 3.8 79.2 395 22 7 0.02 NOP20 1.5.10~5 333 8.5 5.0 63.0 305 46 8 0.2 1.5.10-3 333 8.5 20.2 54.5 305 25 9 0.1 - 343 12.2 18.3 44.8 370 21 10 0.05+ 1.5.10 333 9.0 8.5 55.5 493 27 0.2 0. AIBIN 1.5.10-5 333 9.0 8.5 55.5 493 . 27 11 0.1 Na-L 2.10" 335 9.0 8.0 58.5 480 .32 12 0.15tBPP 2.10-4 335 9.0 3.5 52.3 415 20 13 0.15 HPMC 0.08 333 9.0 9.0 47.0 412 22 14 0.15AMVN 0.25 333 9.0 7.5 53.2 445 27 15 0.15AIBN Slmsa 0.09 333 9.0 4.8 57.0 505 34 16 0.5 C7 5 328 7.5 13.5 58.6 625 45 17 0.2 cC6 5" 333 9.5 15.0 57.5 582 56 18 0.2 cC6 8" 333 9.5 16.4 58.8 685 45 19 0.2 DOP 8 338 10.5 14.0 64.5 522 47 20 0.1 + 0.04Na2S2C5J cC6 5 318 6.6 12.3 63.8 570 46 21 0.5 DEHA 10 333 9.5 13.2 60.8 724 43 22 0.2 + DEHA 5 318 6.8 10.9 65.2 552 46 0.05 DEHA 5 318 6.8 10.9 65.2 552 DM 23 0.5 KFEH 10 338 11.0 17.2 56.5 730 40 24 0.2+ 0.04 Na2S2OsJ DEHA 5 308 4.7 20.0 70.2 538 58 1) additionally 0.008 % NOP 20 in solution Table II: Production of vinylchloride copolymers under various conditions

No. Initiator Surfactant Monomers Polym. - conditions Polymer properties [O/ol L MOJ Proportions by T p L-value SD weight LKJ LbarJ L9,,0 Na-A S 1 0.05 0.06 7VC/3VAc 333 6.0 53.0 430 2 0.05 7VC/3VAc 333 5.5 50.5 445 3 0.1 6.106 3VC/7VAc 338 5.0 53.0 475 4 0.2 9VC/1 EA 328 8.5 54.7 495 5 0.15 0.08 7VC/3VAc 333 6.0 53.3 435 6 0.15AIBN +0.05 DIPP J 0.08 7VC/3AS 333 7.5 62.3 505 7 0.15 AIBN 0.08 7VC/3BA 333 6.5 64.7 485 8 0.15AIBN 0.08 3VC/3VIBE 333 7.0 54.1 452 9 2(0.15 AIBN 0.08 7VC/3BA/0.3AS 333 6.5 68.6 496 10 0.15 AlBN 0.08 7VC/3VAc/0.3GMA 333 6.0 53.6 475 Na-L 11 0.05 +0.03 DlPP 0.002 7VC/3VAc 338 6.5 52.5 462 12 0.05 +0.05 DLPOi 2.10-5 9VC/1VAc/0.5BA 333 9.1 59.6 455 NOP20 13 0.1 0.0015 9VC/1BA 333 9.2 63.0 452 14 0.1 - 7VC/3VAc/0.5VDC 333 6.2 57.0 415 15 0.1 +0.03 DCPI 1.5.10-5 7VC/3VAc/0.3MMA 338 7.2 60.3 465 16 0.15A1B 0.015 7VC/3VAc/0.5AS 338 7.0 56.5 428 17 0.05 +0.15 DIPP 0.09 9VC/1VAc/0.5AN 338 9.8 55.6 465 HPMC 18 0.15AIBN 0.08 9VC/1VAc 333 9.3 55.1 454 19 0.1 tBPP 0.05 7VC/3VAc/0.5GMA 333 4.2 60.2 522 SIMSA 20 0.15 AMVN 0.05 7VC/3VAc/1 BA 328 4.8 65.2 480 PVA 21 0.15 AlBN 0.05 9VC/1VAc/0.5MSA 335 9.5 54.3 505 22 0.1 Al B +0.03 DIPPY 0.02 9VC/1 Boa10.5 EA 338 7.3 58.8 496 23 0.2 C7 8 9VC/iBA 333 9.5 543 24 0.2 KFEH 5 8VC/2VAc 338 10.8 520 25 0.2 DEHA6" 9VC/1As 333 10.0 578 1) additionally 0.02 weight-% HPMC in solution

Claims (20)

1. A method for producing a homopolymer or copolymer by radical polymerisation in an aqueous phase within a temperature range of 273 to 3730K, wherein the homopolymerisation or copolymerisation is conducted in an aqueous solution or dispersion containing at least one radical-forming initiator and at least one monomer chosen from vinyl halides, vinyl esters, vinyl ethers, vinylidene halides, acrylic and methacrylic monomers and ethylenically unsaturated dicarboxylic acids, their an hydrides and their esters by maintaining a monomer or total monomer concentration corresponding to the solubility of the or each monomer in the aqueous solution or dispersion, the partial vapour pressure of the or each monomer being maintained below the respective partial saturation vapour pressure of the respective monomer.

2. A method according to Claim 1, wherein at least one of the monomers is vinyl chloride.

3. A method according to Claim 1 or Claim 2, wherein at least one of the monomers is vinyl acetate.

4. A method according to any preceding claim, wherein at least one of the monomers is vinylisobutyl ether.

5. A method according to any preceding claim, wherein at least one of the monomers is an acrylic or methacrylic monomer chosen from acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethyl hexyl acrylate, glycomonoacrylate, methacrylic acid and methyl methacrylate.

6. A method according to any preceding claim, wherein at least one of the monomers is chosen from vinylidene chloride, maleic acid an hydride, maleinate and fumarate.

7. A method according to any preceding claim, wherein the aqueous solution or dispersion contains at least one surface-active substance.

8. A method according to any preceding claim, wherein the aqueous solution or dispersion contains less than 1% by weight of at least one suspension stabiliser based on the water present and/or less than 1% by weight of at least one emulsifier based on the water present.

9. A method according to Claim 8, wherein the amount of suspension stabiliser(s) present is/are 10-' to 106% by weight based on the water present and/orthe amount of emulsifier(s) present is/are 10-' to 106% by weight based on the water present.

10. A method according to any preceding claim, wherein the aqueous solution or dispersion contains at least one water-soluble peroxide and/or at least one partially water-soluble peroxide.

11. A method according to any preceding claim, wherein the aqueous solution or dispersion contains at least one diazo compound.

12. A method according to any preceding claim, wherein the aqueous solution or dispersion contains at least one redox-initiator.

13. A method according to any preceding claim, wherein the aqueous solution or dispersion contains at least one additive chosen from hydrocarbons having 5 to 16 carbon atoms and/or esters of higher molecular fatty acids or aliphatic aromatic dicarboxylic acids in a total quantity of less than or equal to 20% by weight based on the water present.

14. A method according to Claim 13, wherein the said additive(s) is/are chosen from n-hexane, cyclohexane, n-heptane and n-octane and/or the n-octyl or 2-ethyl hexyl esters of the coconut fatty acid and other natural fatty acids or adipic and phthalic acids.

15. A method according to any one of Claims 12 to 14, wherein the aqueous solution or dispersion contains at least one said additive in a total quantity of 0.5 to 20% by weight based on the water present.

16. A method according to Claim 15, wherein the aqueous solution or dispersion contains at least one said additive in total quantity of 1 to 10% by weight based on the water present.

17. A method according to any preceding claim, wherein polymerisation is effected in a main polymerisation stage and then in a subsequent stage, not more than 30% by weight of the total monomer(s) being polymerised in the subsequent stage.

18. A method according to Claim 17, wherein the monomer(s) is/are chosen from vinyl acetate or other vinyl esters, methacrylic acid, acrylic acid, methacrylate, acrylmitrite and other acrylic and methacrylic monomers, maleic anhydride, maleinite, fumanate and vinylidine chloride.

19. A method according to Claim 1 substantially as herein described and exemplified.

20. Ahomopolymerorcopolymerwhich has been obtained by the method claimed in any preceding claim.