A subject-matter of the present invention is a process for the preparation of latices using block copolymers as surfactants and the latex compositions prepared by the said process.
The invention likewise relates to the preparation of latices exhibiting high resistance to water and which can be used in particular as concrete or cement additive in formulations intended for applications in particular in building materials, adhesives, paints or papers.
Latices are products which are well known to a person skilled in the art, as well as the redispersible powders obtained from these latices. They have numerous applications, in particular as additives in paint formulations or paper formulations (coating slips, bulk paper) or in formulations intended to be applied in the construction field (adhesive, pastes, smoothing coats, and the like). They confer important properties on the formulas in the composition of which they participate, by virtue, for example, of their binding capability, of their film-forming capability and of their ability to confer specific Theological properties.
Generally, for all latex applications, the aim is to reconcile good colloidal stability of the aqueous formulas before drying and good resistance to water after drying.
Processes for the preparation of latices have been well known for many years. It is also known to add a surfactant of low molecular weight to the aqueous phase, so as to keep in suspension both the monomers and the polymers in small spheres in suspension in the water, within which spheres the radical polymerization reaction takes place. However, this addition of surfactant has the disadvantage of allowing surfactant residues to remain on the latex particles, which can be harmful to the properties of the compositions comprising the said latices.
One of the aims of the present invention is to provide a process for the preparation of latices which makes it possible to solve the above-mentioned problems.
These aims and others are achieved by the present invention, a subject-matter of which is thus a process for the preparation of latices by radical aqueous emulsion polymerization in the presence:
of at least one ethylenically unsaturated monomer,
of at least one radical polymerization initiator, and
of at least one surface-active block copolymer comprising at least one hydrophilic block and at least one hydrophobic block which is prepared by a “living” preparation process using a transfer agent, the said copolymer exhibiting:
a number-average molecular mass of between 2 000 and 20 000, preferably between 4 000 and 16 000,
a glass transition temperature of the hydrophobic block of less than 30° C., preferably of less than 25° C., and greater than −100° C.,
a surface tension of less than 60 millinewtons per metre (mN/m), preferably of less than 50 mN/m, measured at a concentration in demineralized water of less than or equal to 10−4 mol/l at 20° C. and under one atmosphere, and
the transfer agent having been rendered inert with respect to the said radical polymerization.
The invention also relates to formulations which are intended to be applied in the field of building materials, in that of paints, in that of papers and in that of adhesives and pressure-sensitive adhesives and which comprise the latices prepared by the said process or the redispersible powders capable of being obtained by drying the latices.
It likewise relates to the use of the latices and redispersible powders in formulations intended to be used in particular in the construction field or in the field of paints.
However, other advantages and characteristics of the present invention will become more clearly apparent on reading the description and examples which will follow.
According to the invention, surface-active block copolymers comprising at least one hydrophilic block and at least one hydrophobic block are prepared by a “living” or “controlled” radical polymerization process involving the use of a transfer agent specifically for the purpose of controlling the said radical polymerization. The hydrophilic block preferably derives from hydrophilic monomers, and the hydrophobic block preferably derives from hydrophobic monomers.
Generally, the preceding block copolymers can be obtained by any “living” or “controlled” polymerization process, such as, for example:
radical polymerization controlled by xanthates according to the teaching of Application WO 98/58974,
radical polymerization controlled by dithioesters according to the teaching of Application WO 98/01478,
polymerization using nitroxide precursors according to the teaching of Application WO 99/03894,
radical polymerization controlled by dithiocarbamates according to the teaching of Application WO 99/31144,
atom transfer radical polymerization (ATRP) according to the teaching of Application WO 96/30421,
radical polymerization controlled by iniferters according to the teaching of Otu et al., Makromol. Chem. Rapid. Commun., 3, 127 (1982),
radical polymerization controlled by degenerative transfer of iodine according to the teaching of Tatemoto et al., Jap. 50, 127, 991 (1975), Daikin Kogyo Co Ltd Japan, and Matyjaszewski et al., Macromolecules, 28, 2093 (1995),
group transfer polymerization according to the teaching of Webster O. W., “Group Transfer Polymerization”, p. 580-588, in the “Encyclopedia of Polymer Science and Engineering”, Vol. 7, edited by H. F. Mark, N. M. Bikales, C. G. Overberger and G. Menges, Wiley Interscience, New York, 1987,
radical polymerization controlled by tetraphenylethane derivatives (D. Braun et al., Macromol. Symp., 111, 63 (1996)),
radical polymerization controlled by organocobalt complexes (Wayland et al., J. Am. Chem. Soc., 116, 7973 (1994)).
The preferred transfer agents for implementing the controlled polymerization process are chosen from dithioesters, thioethers-thiones, dithiocarbamates and xanthates.
The preferred polymerization is the living radical polymerization using xanthates.
The invention additionally relates to a process for the preparation of these block polymers. This process consists in:
1—bringing into contact:
at least one ethylenically unsaturated monomer,
at least one source of free radicals, and
at least one transfer agent of formula (I):
R represents an R2O—, R2R′2N—or R3-group with: R2 and R′2, which are identical or different, representing (i) an alkyl, acyl, aryl, alkene or alkyne group or (ii) an optionally aromatic, saturated or unsaturated carbonaceous ring or (iii) a saturated or unsaturated heterocycle, it being possible for these groups and rings (i), (ii) and (iii) to be substituted, R3 representing H, Cl, an alkyl, aryl, alkene or alkyne group, an optionally substituted, saturated or unsaturated (hetero)cycle, an alkylthio, alkoxycarbonyl, aryloxycarbonyl, carboxyl, acyloxy, carbamoyl, cyano, dialkyl- or diarylphosphonato, or dialkyl- or diarylphosphinato group, or a polymer chain,
R1 represents (i) an optionally substituted alkyl, acyl, aryl, alkene or alkyne group or (ii) a carbonaceous ring which is saturated or unsaturated and which is optionally substituted or aromatic or (iii) an optionally substituted, saturated or unsaturated heterocycle or a polymer chain, and
2—repeating, at least once, the above operation of bringing into contact using:
different monomers from the preceding implementation, and
instead of the precursor compound of formula (I), the polymer resulting from the preceding implementation, and
3—rendering the transfer agent inert at the end of the polymerization.
The R1, R2, R12 and R3 groups can be substituted by substituted phenyl or alkyl groups, substituted aromatic groups or the following groups: oxo, alkoxycarbonyl or aryloxycarbonyl (—COOR), carboxyl (—COOH), acyloxy (−O2CR), carbamoyl (—CONR2), cyano (—CN), alkylcarbonyl, alkylarylcarbonyl, arylcarbonyl, arylalkylcarbonyl, isocyanato, phthalimido, maleimido, succinimido, amidino, guanidino, hydroxyl (—OH), amino (—NR2), halogen, allyl, epoxy, alkoxy (—OR), S-alkyl, S-aryl or silyl, groups exhibiting a hydrophilic or ionic nature, such as alkaline salts of carboxylic acids or alkaline salts of sulphonic acid, poly(alkylene oxide) (PEO, PPO) chains, or cationic substituents (quaternary ammonium salts), R representing an alkyl or aryl group.
Preferably, the transfer agent of formula (I) is a dithiocarbonate chosen from the compounds of following formulae (IA), (IB) and (IC):
R2 and R2′ represent (i) an alkyl, acyl, aryl, alkene or alkyne group or (ii) an optionally aromatic, saturated or unsaturated carbonaceous ring or (iii) a saturated or unsaturated heterocycle, it being possible for these groups and rings (i), (ii) and (iii) to be substituted,
R1 and R1′ represent (i) an optionally substituted alkyl, acyl, aryl, alkene or alkyne group or (ii) a carbonaceous ring which is saturated or unsaturated and which is optionally substituted or aromatic or (iii) an optionally substituted, saturated or unsaturated heterocycle or a polymer chain,
p is between 2 and 10.
During Stage 1, a first block of the polymer is synthesized with a hydrophilic or hydrophobic nature, according to the nature and the amount of the monomers used. During Stage 2, the other block of the polymer is synthesized.
The ethylenically unsaturated monomers are chosen from hydrophilic and hydrophobic monomers in the proportions appropriate for obtaining a surface-active block copolymer, the blocks of which exhibit the characteristics of the invention. According to this process, if all the successive polymerizations are carried out in the same reactor, it is generally preferable for all the monomers used during one stage to have been consumed before the polymerization of the following stage begins, therefore before the new monomers are introduced. However, it may happen that the hydrophobic or hydrophilic monomers of the preceding stage are still present in the reactor during the polymerization of the following block. In this case, these monomers generally do not represent more than 5 mol % of all the monomers and they participate in the following polymerization by contributing to the introduction of the hydrophobic or hydrophilic units into the following block.
The surface-active block copolymers prepared according to this polymerization process can be simply diblocks, with a hydrophobic block and a hydrophilic block, or even triblocks, with either a hydrophilic block framed by two hydrophobic blocks or a hydrophobic block framed by two hydrophilic blocks.
More particularly, the surface-active block copolymer can be obtained by employing, as hydrophilic monomer, at least one ethylenically unsaturated monomer chosen from:
unsaturated ethylenic mono- and dicarboxylic acids, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid,
monoalkyl esters of the dicarboxylic acids of the type mentioned with alkanols preferably having 1 to 4 carbon atoms and their N-substituted derivatives, such as, for example, 2-hydroxyethyl acrylate or methacrylate,
amides of unsaturated carboxylic acids, such as acrylamide or methacrylamide,
ethylenic monomers comprising a sulphonic acid group and its alkali metal or ammonium salts, for example vinylsulphonic acid, vinylbenzenesulphonic acid, alpha-acrylamidomethylpropanesulphonic acid or 2-sulphoethyl methacrylate.
However, the most preferred hydrophilic monomers are acrylic acid (AA), acrylamide (AM), 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and styrenesulphonate (SS).
Mention may in particular be made, as illustration of hydrophobic monomers which can be used to constitute the hydrophilic block, of (meth)acrylic esters, vinyl esters and vinyl nitrites.
The term “(meth)acrylic esters” denotes esters of acrylic acid and of methacrylic acid with hydrogenated or fluorinated C1-C12 alcohols, preferably C1-C8 alcohols. Mention may be made, among the compounds of this type, of: methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, t-butyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate or isobutyl methacrylate. The preferred monomers are the esters of acrylic acid with linear or branched C1-C4 alcohols, such as methyl, ethyl, propyl and butyl acrylate.
The vinyl nitriles include more particularly those having from 3 to 12 carbon atoms, such as, in particular, acrylonitrile and methacrylonitrile. The other ethylenically unsaturated monomers, which can be used alone or as mixtures, or which can be copolymerized with the above monomers, are in particular:
carboxylic acid vinyl esters, such as vinyl acetate, vinyl versatate or vinyl propionate,
vinylamine amides, in particular vinylformamide or vinylacetamide,
unsaturated ethylenic monomers comprising a secondary, tertiary or quaternary amino group or a heterocyclic group comprising nitrogen, such as, for example, vinylpyridines, vinylimidazole, aminoalkyl (meth)acrylates and aminoalkyl(meth)acrylamides, such as dimethylaminoethyl acrylate or methacrylate, di-tert-butylaminoethyl acrylate or methacrylate, or dimethylaminomethylacrylamide or -methacrylamide.
It is very obviously possible to include, in the composition of the block copolymers, a certain proportion of hydrophobic monomers in the hydrophilic block and a certain proportion of hydrophilic monomers in the hydrophobic block, provided that the surface-active properties and the limits of the number-average molecular mass, of the glass transition temperature of the hydrophobic group and of surface tension are adhered to.
The polymerization of the copolymer can be carried out in an aqueous and/or organic solvent medium, such as tetrahydrofuran or a linear, cyclic or branched C1-C8 aliphatic alcohol, such as methanol, ethanol or cyclohexanol, or a diol, such as ethylene glycol. An alcoholic solvent is more particularly recommended in the case where the hydrophilic monomers are acrylic acid (AA), acrylamide (AM), 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and styrenesulphonate (SS) and the hydrophobic monomers are n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate or t-butyl acrylate.
At the end of the controlled polymerization stage, the transfer agent, located at one of the chain ends of the surface-active block polymer, is rendered inert, by any appropriate means, with respect to the said subsequent radical polymerization relating to the preparation of the latex proper. It is possible for the nature of the polymerization reaction medium (for example, pH conditions, nature of the constituents of the reaction medium, monomers to be polymerized) to be sufficient per se to inactivate the transfer agent. It is recommended to mask the active chemical functional groups of the said agent by means of a suitable chemical masking agent or to destroy the transfer agent by a hydrolysis or oxidation reaction by metal catalysis or by the use of primary radicals. In the case of xanthate as transfer agent, it is recommended to render it inert, if necessary, by treatment of the copolymer formed by means of a heat treatment, for example in the temperature range 80 to 180° C., in the presence of an alcoholamine, such as triethanolamine.
The ethylenically unsaturated monomers which can be employed to prepare the latex will now be described.
Mention may very particularly be made, among suitable monomers, of those corresponding to the following formula:
Xd and X′d, which are identical or different, represent: H, an alkyl group or a halogen,
Vd and V′d, which are identical or different, represent H, a halogen or an R, OR, OCOR, NHCOH, OH, NH2, NHR, N(R)2, (R)2N+O−, NHCOR, CO2H, CO2R, CN, CONH2, CONHR or CONR2 group, in which R, which are identical or different, are chosen from alkyl, aryl, aralkyl, alkaryl, alkene or organosilyl groups which are optionally perfluorinated and which are optionally substituted by one or more carboxyl, epoxy, hydroxyl, alkoxy, amino, halogen or sulphonic groups,
t has the value 0 or 1.
According to a specific embodiment of the invention, the monomers employed are preferably hydrophobic monomers.
Mention may in particular be made, as illustration of hydrophobic monomers, of styrene or its derivatives, butadiene, chloroprene, (meth)acrylic esters, vinyl esters and vinyl nitriles.
The term “(meth)acrylic esters” denotes esters of acrylic acid and of methacrylic acid with hydrogenated or fluorinated C1-C12 alcohols, preferably C1-C8 alcohols.
The vinyl nitriles include more particularly those having from 3 to 12 carbon atoms, such as, in particular, acrylonitrile and methacrylonitrile.
It should be noted that styrene can be replaced, in all or in part, by derivatives, such as α-methylstyrene or vinyltoluene.
The other ethylenically unsaturated monomers, which can be used alone or as mixtures, or which can be copolymerized with the above monomers, are in particular:
carboxylic acid vinyl esters,
unsaturated ethylenic monomers comprising a secondary, tertiary or quaternary amino group or a heterocyclic group comprising nitrogen. It is likewise possible to use zwitterionic monomers, such as, for example, sulphopropyl(dimethyl)aminopropyl acrylate.
It should be noted that it is possible to employ hydrophilic monomers, such as, for example,
unsaturated ethylenic mono- and dicarboxylic acids,
monoalkyl esters of the dicarboxylic acids of the type mentioned with alkanols preferably having 1 to 4 carbon atoms and their N-substituted derivatives, amides of unsaturated carboxylic acids,
ethylenic monomers comprising a sulphonic acid group and its alkali metal or ammonium salts,
amides of unsaturated carboxylic acids, such as acrylamide, methacrylamide, N-methylol-acrylamide or N-methylolmethacrylamide, or N-acrylamides.
It should be noted that all the monomers which have been mentioned in the context of the definition of the surface-active block copolymer can be used for the preparation of the latex. Reference may thus be made to this part of the description.
Use is preferably made, as ethylenically unsaturated monomer, of at least one monomer chosen from styrene or its derivatives, butadiene, chloroprene, (meth)acrylic esters, vinyl esters and vinyl nitriles.
The polymerization reaction according to the invention takes place in the presence of a radical polymerization initiator. The latter can be chosen from the initiators conventionally used in radical polymerization. It can, for example, be one of the following initiators:
hydrogen peroxides, such as: tert-butyl hydroperoxide, cumene hydroperoxide, t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl peroxyoctoate, t-butyl peroxyneodecanoate, t-butyl peroxyisobutyrate, lauroyl peroxide, t-amyl peroxypivalate, t-butyl peroxypivalate, dicumyl peroxide, benzoyl peroxide, potassium persulphate or ammonium persulphate,
azo compounds, such as: 2,2′-azobis-(isobutyronitrile), 2,2′-azobis(2-butanenitrile), 4,4′-azobis(4-pentanoic acid), 1,1′-azobis(cyclohexane-carbonitrile), 2-(t-butylazo)-2-cyanopropane, 2,2′-azobis[2-methyl-N-(1,1)-bis(hydroxymethyl)-2-hydroxyethyl]propionamide, 2,2′-azobis(2-methyl-N-hydroxyethyl]propionamide, 2,2′-azobis(N,N′-dimethyleneisobutyramidine) dichloride, 2,2′-azobis(2-amidinopropane) dichloride, 2,2′-azobis (N,N′-dimethyleneisobutyramide), 2,2′-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide), 2,2′-azobis(2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide), 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] or 2,2′-azobis(isobutyramide) dihydrate,
redox systems comprising combinations such as:
mixtures of hydrogen peroxide, alkyl peroxide, peresters, percarbonates and the like and of any from iron salts, titanous salts, zinc formaldehyde-sulphoxylate or sodium formaldehydesulphoxylate, and reducing sugars,
alkali metal or ammonium persulphates, perborates or perchlorates, in combination with an alkali metal bisulphite, such as sodium metabisulphite, and reducing sugars,
alkali metal persulphates, in combination with an arylphosphinic acid, such as benzenephosphonic acid, and other similar substances, and reducing sugars.
The polymerization reaction takes place conventionally and a nonionic or anionic surfactant chosen from alkoxylated mono-, di- or trialkylphenols, alkoxylated mono-, di- or tristyrylphenols, alkoxylated fatty alcohols and alkali metal or ammonium salts of C8-C12 alkyl sulphates, fatty alcohol alkoxylated and sulphated hemiesters, C12-C18 alkyl sulphonate esters, and the like, can be added to the polymerization medium.
The polymerization temperature, by way of illustration, is between 50 and 120° C., more particularly between 70 and 90° C.
Thus, an embodiment of the latex polymerization process according to the invention comprises the following stages:
a) a stable aqueous preemulsion comprising the starting ethylenically unsaturated monomers and the surface-active block copolymer is prepared using, for example, from 2 to 3 parts of monomers per 1 part by weight of water,
b) a reaction mixture comprising a conventional surfactant as defined above, an initiator and water is introduced into a radical polymerization reactor and from 1 to 10, preferably from 3 to 7, % by weight of preemulsion prepared in stage a) is added to the said mixture,
c) the reaction mixture obtained at the end of stage b) is heated to a temperature of between 40 to 90°c, preferably between 60 and 80° C., for the purpose of generating a seed formed of latex particles in dispersion in the water,
d) the preemulsion obtained in stage a) is added with an additional amount of initiator via two separate inlets of the reactor to obtain the latex, and
e) optionally, the latex obtained in stage d) is heated at a temperature of between 40 and 90° C., preferably between 60 and 80° C.
It is generally recommended to use an effective amount of block copolymer so as to obtain the desired surfactant effect within the polymerization medium, which generally corresponds to using from 0.5 to 5, preferably from 1 to 4, % by weight of surface-active block copolymer with respect to the total weight of water employed during the polymerization of the latex. It is also recommended to use from 1 to 8, preferably from 2 to 5, % by weight of copolymer with respect to the total weight of the monomers employed during the polymerization of the latex.
Another subject-matter of the present invention is composed of redispersible powders capable of being obtained by drying the latex prepared by the process of the invention. The drying of the latex can be carried out in a way known per se. Thus, drying can be carried out at low temperature or, preferably, by atomization. It can be carried out in any known device, such as, for example, an atomization tower which combines a spraying carried out via a nozzle or a turbine with a stream of hot gas. The inlet temperature of the hot gas (generally air) at the column top is preferably between 100 and 115° C. and the outlet temperature is preferably between 55 and 65° C. According to an advantageous embodiment of the present invention, the drying is carried out in the presence of a drying additive. Conventional dispersing agents can be employed. Mention may be made, for example, of polyphenols, salts of glutamic acid, polyvinyl alcohol, polyvinylpyrrolidone or cellulose derivatives. It should be noted that a nonionic or anionic surfactant can also be used. In a particularly advantageous way, the content of drying additive is less than or equal to 5% by weight with respect to the polymer.
The latices prepared by the process of the present invention generally exhibit:
good resistance to Ca++ ions at a concentration in water of greater than 0.25%,
a contact angle and a surface tension which can be adjusted,
good stability towards shearing,
good resistance to moisture after formation of the film,
a high thickening capability, and
little or no tendency towards whiting.
The latices and redispersible powders which form the subject-matter of the present invention can be employed in the conventional fields of use, such as in the field of building materials, paints, paper or adhesives, including pressure-sensitive adhesives, inter alia.
Thus, the present invention likewise has as subject-matter formulations, intended for applications in the field of building materials, comprising the latex or the redispersible powders prepared by the process of the invention.
It also relates to formulations, intended for applications in the field of paints, comprising the latex or the redispersible powders.
Finally, it relates to formulations, intended for applications in the field of adhesives and pressure-sensitive adhesives, comprising the latex or the redispersible powders.
Concrete but nonlimiting examples of the invention will now be presented. In the examples which follow:
Mn represents the number-average molecular mass Mn of the polymers; Mn is expressed in polystyrene equivalents (g/mol),
Mw represents the weight-average molecular mass (g/mol),
Mw/Mn represents the polydispersity index.
the polymers, before hydrolysis, are analysed by chromatography (GPC) with THF as elution solvent.