Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
• • 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
  • C08F2/38—Polymerisation using regulators, e.g. chain terminating agents, e.g. telomerisation
• • 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
  • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
  • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
  • C08F20/10—Esters
  • C08F20/12—Esters of monohydric alcohols or phenols
  • C08F20/16—Esters of monohydric alcohols or phenols of phenols or of alcohols containing two or more carbon atoms
  • C08F20/18—Esters of monohydric alcohols or phenols of phenols or of alcohols containing two or more carbon atoms with acrylic or methacrylic acids

Definitions

• the invention relates to a process for preparing polyacrylates by means of free radical polymerization, using natural or non-natural amino acids containing thiol and/or hydroxyl groups as non-toxic and non-volatile chain-transfer regulators for regulating the molar masses and molar mass distribution, allowing the solvent used in the polymerization, following its removal, to be reused for further polymerizations in the case of a drying operation or in the case of the preparation of a polyacrylate hotmelt, without a change in the molar masses and molar mass distribution of the polyacrylates as the number of recycling steps goes up.
• PSAs pressure sensitive adhesives
• hotmelt processes with solvent-free coating technology for preparing PSAs are of growing significance, since the environmental strictures are becoming ever greater and the prices of solvents are also rising.
• Hotmelt processes are already state of the art for SIS adhesives.
• acrylate PSAs are still processed largely from solution.
• an excessive average molecular weight continues to present problems, since, although it is essential for high shear strength, it causes a sharp rise in the flow viscosity, and so acrylate hotmelts with an average molecular weight of >1 000 000 g/mol are difficult to process from the melt.
• low molecular weight acrylate hotmelts have already been successfully implemented as hotmelt PSAs (BASF AG, e.g. UV 203 AC Resins).
• benzophenone derivatives or acetophenone derivatives are incorporated as an acrylated photoinitiator into the acrylate polymer chain and are then crosslinked with UV radiation [U.S. Pat. No. 5,073,611].
• the achievable shear strength for systems of this kind is still not satisfactory, although, as a result of the low average molecular weight ( ⁇ 250 000 g/mol), the flow viscosity is relatively low.
• the regulators used are generally thiols, alcohols or halides, such as carbon tetrabromide, for example [cf., for example, H.-G. Elias, “Makromoleküle”, Hüthig & Wepf Verlag Basel, 5th edition, 1990].
• halide regulators as described in U.S. Pat. No. 7,034,085 B2, for example, is decreasing persistently on environmental grounds.
• Thiols and alcohols are suitable as regulators and, depending on concentration, greatly reduce the average molecular weight of the polymer. Often, however, they have the disadvantage of being volatile and are therefore located in the distillate following the removal of the solvent mixture. This results in the disadvantages that reusing the solvent mixture removed by distillation for further polymerizations leads to an accumulation of the compound with chain-transfer regulator activity, and hence that a reproducible molar mass distribution is not ensured as the recycling rate goes up.
• US 20070299226 A1 describes various chain transfer regulators based on a thiol functionality. They do remain partly in the polymer, but have the disadvantage that they are partly toxic and, on account of their strong and unpleasant odour, are not suitable when the polymer is used for a product, such as a pressure-sensitive adhesive tape, for example, with which points of contact in everyday use are frequent. Moreover, the same specification describes polyfunctional thiols for use as regulators, but such thiols may even lead to crosslinking of the polymer and hence to high melt viscosities, thereby making it no longer possible to carry out processing from the melt.
• the mercapto-functionalized photoinitiators that are described in EP 1 311 554 B1 likewise result in crosslinking or make it necessary to ensure that the polymer prior to processing is not exposed to light or any other electromagnetic radiation, since otherwise there may be crosslinking.
• polyacrylate compositions having sufficiently high average molecular weights that they can be used, for example, as pressure sensitive adhesives.
• the solvent mixture or solvent used in preparing the polyacrylates ought preferably to be able to be reused without purification steps following distillative removal; and the capacity for the polyacrylate to be processed in a hotmelt operation ought to be ensured.
• the invention relates accordingly to a reaction solution, especially for free-radical polymerization, comprising one or more solvents and one or more monomers, at least 50% by weight of the solvents being organic solvents, and at least 70% by weight of the monomers being acrylic and/or methacrylic esters, the reaction solution additionally being admixed with at least one amino acid.
• the amino acids used may be natural or non-natural amino acids.
• the weight fraction of organic solvents when water is present in the solvent mixture employed is at least 50% by weight, advantageously at least 90% by weight.
• reaction solution it is very advantageous for the reaction solution to be a homogeneous solution.
• the amino acid or acids serve as polymerization regulators in the free-radical polymerization.
• Regulators, polymerization regulators or regulator substances are identified synonymously in the context of this specification as compounds having high transfer constants, which are used in free-radical polymerizations in order to limit the degree of polymerization of the macromolecules that form. They do not destroy the radical functionalities that are capable of propagation, but instead take over these functionalities from the ends of the growing macromolecules, in order then themselves to initiate the propagation of a new chain. In this way, for each radical produced in the system, two or more relatively short polymer chains are formed instead of one long one. Since the regulator substance does not destroy the radicals, there is also no change in the overall polymerization rate (see R ⁇ MPP online 2009, document code RD-18-00666).
• the at least one amino acid has at least one sulphanyl group (also referred to below as thiol groups or —SH group), at least one selanyl group (also referred to below as —SeH group) and/or a hydroxyl group (also referred to below as —OH group).
• the aforementioned groups in the amino acid are terminal.
• the reaction solution comprises at least one acrylic- or methacrylic-based monomer, a monomer mixture comprising at least 70% by weight of an acrylic or methacrylic ester, or, preferably, a monomer mixture comprising at least 70% by weight of acrylic and/or methacrylic esters.
• acrylic esters and methacrylic esters are also referred to collectively as acrylic monomers.
• the acrylic monomers are selected at least partly, preferably completely, from the group of the monomers encompassing compounds of the general formula
• R 1 H or CH 3
• R 2 H or an unbranched or branched, aliphatic, alicyclic or aromatic, unsubstituted or substituted hydrocarbon radical having 1 to 20 carbon atoms.
• the alcohol residue of acrylic acid monomers very preferably has no C ⁇ C double bonds.
• the monomers can be polymerized via a free radical polymerization, with the at least one natural or non-natural amino acid containing at least one thiol and/or hydroxy group acting as polymerization regulator.
• the invention further provides polyacrylates obtainable from a reaction solution as described above, particularly by free-radical polymerization of the monomers present therein.
• a process for preparing a polyacrylate from such a reaction solution by free-radical polymerization is possible to use one or more typical initiators, the initiators selected being more particularly those which do not enter into any unwanted secondary reactions with the amino acids.
• the procedure is preferably such that the solvent is removed from the polymerization product.
• the residual solvent fraction is to be lowered to a fraction of not more than 5%, more particularly not more than 2%, especially not more than 0.5%, by weight, based on the mixture that remains following removal of the solvent (polymerization product, residual solvent, amino acids, possibly further constituents). It is preferred to aim for a solvent-free system.
• the polymerization product is processed further from the melt (known as a “hotmelt”).
• the solvent removed is supplied to a recycling operation.
• the solvent used for preparing the reaction solution may be taken wholly or partly from a recycling operation.
• the solvent is wholly or partly circulated—that is, following a polymerization, some or all of the solvent removed is used for preparing a reaction solution for a further polymerization.
• the amino acid or, where the reaction solution had two or more amino acids added to it, the amino acids, remain in the polymerization product when the solvent is removed. This may be accomplished more particularly through precipitation in the form of a solid. It is therefore particularly preferred for there to no longer be any amino acid radicals present (or, if any at all, in a negligible amount) in the solvent removed, particularly in the solvent supplied to the recycling operation.
• the monomer mixture is preferably selected such that plasticizing monomers in particular, and also monomers with functional groups that are capable of entering into reactions, especially addition reactions and/or substitution reactions, and also, optionally, further copolymerizable comonomers, more particularly hardening monomers are chosen.
• the nature of the polyacrylate to be prepared (more particularly PSA; however, also possible for use as heat-sealing compound, non-tacky viscoelastic material, and the like) may be influenced more particularly by varying the glass transition temperature of the polymer through different weight fractions of the individual monomers.
• Amorphous or partly crystalline systems are characterized by the conversion of the more or less hard amorphous or partly crystalline phase into a softer (rubber-like to viscous) phase.
• thawing or “freezing” on cooling
• the transition from the melting point T m also “melting temperature”; actually defined only for purely crystalline systems; “polymer crystals”
• the glass transition point T g also “glass transition temperature”
• the glass transition temperature can be reported as a dynamic temperature or as a static temperature.
• Figures for dynamic glass transition temperatures are based on the determination by means of dynamic mechanical analysis (DMA) at low frequencies (temperature sweep; measurement frequency: 10 rad/s; temperature range: ⁇ 40° C. to max. 130° C.; heating rate: 2.5° C./min; Rheometric Scientific RDA III; parallel-plate arrangement, sample thickness 1 mm: sample diameter 25 mm: pre-tensioning with a load of 3N; sample stress for all measurements 2500 Pa), while those for the static glass transition temperature and for the melting points relate to determination by means of differential scanning calorimetry (DSC) in accordance with DIN 53765:1994-03.
• DMA dynamic mechanical analysis
• the quantitative composition of the monomer mixture is advantageously selected such that the desired T g for the polymer results in accordance with an equation (E1) in analogy to the Fox equation (cf. T. G. Fox, Bull. Am. Phys. Soc. 1 (1956) 123).
• n represents the serial number of the monomers used
• w n the mass fraction of the respective monomer n (% by weight)
• T g,n the respective static glass transition temperature of the homopolymer of each of the monomers n, in K (kelvins).
• the fractions of the corresponding components are preferably selected such that the polymerization product exhibits more particularly a dynamic glass transition temperature ⁇ 15° C. (DMA).
• DMA dynamic glass transition temperature
• acrylic and methacrylic esters with hydrocarbon radicals comprising 4 to 14 C atoms, preferably 4 to 9 C atoms.
• monomers of this kind are n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, n-amyl acrylate, n-hexyl acrylate, hexyl methacrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, isobutyl acrylate, isooctyl acrylate, isooctyl methacrylate, and their branched isomers, such as 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate, for example.
• monomers with functional groups it is preferred to use those selected from the following listing of functionalities: carboxyl, sulphonic acid or phosphonic acid groups, phenols, thiols or amines.
• monomers are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aconitic acid, dimethylacrylic acid, ⁇ -acryloyloxypropionic acid, trichloroacrylic acid, vinylacetic acid, vinylphosphonic acid, itaconic acid, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate.
• Monomers identified by way of example are as follows: methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate, benzyl acrylate, benzyl methacrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl acrylate, phenyl methacrylate, isobornyl acrylate, isobornyl methacrylate, t-butylphenyl acrylate, t-butylphenyl methacrylate, dodecyl methacrylate, isodecyl acrylate, lauryl acrylate, n-undecyl acrylate, stearyl acrylate, tridecyl acrylate, behenyl acrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, phenoxyethyl acrylate, phenoxyethy
• Macromonomers such as 2-polystyrene-ethyl methacrylate (molecular weight M w from 4000 to 13 000 g/mol), poly(methyl methacrylate)ethyl methacrylate (M w from 2000 to 8000 g/mol).
• the monomers may advantageously also be selected such that they contain functional groups which support subsequent radiation crosslinking (by electron beams, UV, for example).
• Suitable copolymerizable photoinitiators are, for example, benzoin acrylate and acrylate-functionalized benzophenone derivatives; monomers which support crosslinking by electron beams are, for example, tetrahydrofurfuryl acrylate, N-tert-butylacrylamide, and allyl acrylate, this list not being conclusive.
• Free-radical initiators that can be used for the free radical polymerization are all typical initiators known for such purpose in respect of acrylates.
• the production of C-centred radicals is described in Houben Weyl, Methoden der Organischen Chemie , Vol. E 19a, pp. 60-147. These methods can be employed in analogy.
• radical sources are peroxides, hydroperoxides and azo compounds
• typical free-radical initiators include potassium peroxodisulphate, dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-tert-butyl peroxide, azodiisobutyronitrile, cyclohexylsulphonyl acetyl peroxide, diisopropyl percarbonate, tert-butyl peroctoate and benzpinacol.
• the initiators are added in two or more stages, and so the conversion is raised to above 90%.
• the residual monomer content remaining in the polymer may in this way be lowered to below 10% by weight; a low residual monomer content considerably enhances the properties of the polyacrylate with respect to its further processing in a hotmelt operation.
• the initiators used to initiate the polymerization are preferably selected such that they have a low tendency to form side chains in the polymers; their grafting activity is preferably below a value of ⁇ 5 at the temperature of the reaction mixture when the initiator is added.
• the initiators may advantageously be added before or at the beginning of the polymerization to the monomer solution, and it is possible for the mixture to be topped up with initiators during the polymerization.
• the initiators are preferably used in the reaction solution in a fraction of 0.001% to 1% by weight, more preferably of 0.025% to 0.1% by weight, based on the monomer mixture.
• the absolute grafting activity is defined as the number of chemical side-chain formations per 100 mol units of decomposed initiator. In analogy to van Drumpt and Oosterwijk [ Journal of Polymer Science, Polymer Chemistry Edition 1976, 14 1495-1511], a value for this number can be specified by determining the dimers in a defined solution of the initiator; see also DE 43 40 297 A1:
• High ⁇ values for the grafting activity denote a high tendency on the part of the initiator to form side chains during the polymerization, whereas small ⁇ values result in preferentially linear polymers.
• sequence of the process is as follows:
• Preferred initiators having a low ⁇ value are those whose free radicals cause no or very infrequent abstraction of hydrogen on the polymer chains, on account of their low energy content.
• azo initiators such as azoisobutyrodinitrile or derivatives thereof, an example being 2,2-azobis(2-methylbutyronitrile) (Vazo® 67, DuPont).
• Initiators having a high tendency to form side chains produce high grafting yields even at relatively low temperatures.
• Particular preference here is given to using bis(4-tert-butylcyclohexyl) peroxydicarbonate (Perkadox® 16, Akzo Chemie), dibenzoyl peroxide or the like.
• the polymerization can be carried out in the presence of an organic solvent or in the presence of water, or in mixtures of organic solvents and/or water.
• Solvents used for the polymerization may be all solvents that are suitable or used typically for free-radical polymerizations, with acetone, ethyl acetate, benzine, toluene or any desired mixtures of these solvents being particularly appropriate.
• the solvent or solvent mixture is present within the reaction solution in customary quantity ranges; advantageously it is present at 20% to 99% by weight, based on the reaction solution; very preferably, however, as little as solvent as possible is used.
• the polyacrylates prepared, especially adhesive polyacrylates, have an average molecular weight of between 250 000 and 1 000 000 g/mol, the average molecular weight being measured by SEC or GPC (for measurement see experimental section).
• the (co)polymers prepared generally possess the same or slightly narrower molecular weight distributions as the polymerizations carried out analogously with conventional regulators.
• the polydispersity may be lowered to a value of less than 6.
• the flow viscosity of the polyacrylate especially of the PSA
• the polyacrylate is much simpler to process as a hotmelt (lower temperature needed for melting, higher throughput for the concentration procedure).
• polymerization regulators comprising natural or non-natural ⁇ -amino acids containing thiol, selanyl and/or hydroxyl groups, advantageously compounds of the following general structural formula
• R 1 , R 2 and R 3 are selected independently of one another.
• R 1 is preferably selected from the group (i), encompassing
• R 2 and R 3 are preferably selected from group (i) above or from group (ii), encompassing:
• acyl radicals more particularly alkanoyl radicals, and cycloalkanecarbonyl radicals and arenecarbonyl radicals (—C(O)—R′′), alkoxycarbonyl radicals (—C(O)—O—R′′), carbamoyl radicals (—C(O)—NR′R′′), and sulphonyl radicals (—SO 2 R′), where R′ and R′′ are radicals from group i) that are selected independently of one another;
• X is selected more particularly to be oxygen (O), sulphur (S) or selenium (Se).
• n in the FIGURE indicates the length of the hydrocarbon chain; n is a natural number including zero, and particularly 0 ⁇ n ⁇ 18.
• the ⁇ -amino acids have a stereogenic centre (labelled by the star * in the FIGURE) and are therefore chiral.
• the chain-transfer regulators are used as the optically cure substance in the (D) or (L) configuration or are employed in the form of a racemic mixture.
• regulators it is additionally possible to use ⁇ -amino acids, aromatic amino acids and other non-natural amino acids familiar to the skilled person.
• the natural or non-natural amino acids containing thiol, sulphanyl and/or hydroxyl groups are used with a weight fraction of 0.001% to 5%, more particularly of 0.005% to 0.25%.
• the polyacrylates prepared by the inventive process as PSAs are optimized optionally by blending with at least one resin.
• Tackifying resins for addition include, without exception, all tackifier resins that are already known and are described in the literature. Representatives that may be cited include the pinene and indene resins, rosins, their disproportionated, hydrogenated, polymerized and esterified derivatives and salts, the aliphatic and aromatic hydrocarbon resins, terpene resins and terpene-phenol resins, and also C5, C9 and other hydrocarbon resins. Any desired combinations of these and further resins may be used in order to adjust the properties of the resultant adhesive in accordance with requirements.
• one or more plasticizers are metered into the PSA, examples being low molecular mass polyacrylates, phthalates, whale oil plasticizers (water-soluble plasticizers) or plasticizing resins.
• phosphates/polyphosphates are used for acrylate hotmelts.
• the acrylate hotmelts may additionally be blended with one or more additives such as ageing inhibitors, light stabilizers, ozone protectants, fatty acids, resins, nucleating agents, expandants, compounding agents and/or accelerants.
• additives such as ageing inhibitors, light stabilizers, ozone protectants, fatty acids, resins, nucleating agents, expandants, compounding agents and/or accelerants.
• fillers such as fibres, carbon black, zinc oxide, titanium dioxide, solid or hollow glass (micro)spheres, microspheres made of other materials, silica, silicates and chalk.
• the polyacrylate is applied as a layer preferably from solution to a support or to a carrier material.
• the polyacrylates prepared as described above are concentrated to give a polyacrylate composition whose solvent content is ⁇ 5% by weight, more particularly ⁇ 2% by weight. This operation takes place preferably in a concentrating extruder.
• the polyacrylate composition is applied as a hotmelt composition, in the form of a layer, to a support or to a carrier material.
• the invention therefore further provides adhesive tapes coated on one or both sides with adhesive.
• the solvent or solvent mixture is used again in the polymerization, and the polymers thus prepared, even after a very high recycling rate of the solvent or solvent mixture, exhibit no change in molar masses or in molar mass distribution.
• carrier materials for adhesive tapes, for example, to use the materials that are customary and familiar to the skilled person, such as films (polyester, PET, PE, PP, BOPP, PVC), nonwovens, foams, woven fabrics and woven sheets, and also release paper (glassine, HDPE, LDPE). This list is not conclusive.
• crosslinking may advantageously be induced thermally or by means of high-energy radiation, in the latter case more particularly by electron beams or, following addition of suitable photoinitiators, by ultraviolet radiation.
• Preferred radiation-crosslinking substances according to the inventive process include, for example, difunctional or polyfunctional acrylates or difunctional or polyfunctional urethane acrylates, difunctional or polyfunctional isocyanates or difunctional or polyfunctional epoxides. Very advantageously it is likewise possible to use metal chelate compounds. However, use may also be made here of any other difunctional or polyfunctional compounds that are familiar to the skilled person and are capable of crosslinking polyacrylates.
• Suitable photoinitiators include preferably Norrish type I and type II cleavers, with some possible examples of both classes being benzophenone derivatives, acetophenone derivatives, benzyl derivatives, benzoin derivatives, hydroxyalkylphenone derivatives, phenyl cyclohexyl ketone derivatives, anthraquinone derivatives, thioxanthone derivatives, triazine derivatives or fluorenone derivatives, this list making no claim to completeness.
• polyacrylate PSA prepared as described, for an adhesive tape, in which case the polyacrylate PSA may be applied to one or both sides of a carrier.
• a 20 mm wide strip of an acrylate PSA applied as a layer to polyester was applied to steel plates.
• the PSA strip was pressed onto the substrate twice using a 2 kg weight.
• the adhesive tape was then immediately pulled from the substrate at 300 mm/min and at an angle of 180°.
• the steel plates were washed twice with acetone and once with isopropanol. The results are reported in N/cm and are averaged from three measurements. All measurements were conducted at room temperature.
• a 13 mm wide strip of the adhesive tape was applied to a smooth steel surface which had been cleaned three times with acetone and once with isopropanol.
• the application area was 20 mm ⁇ 13 mm (length ⁇ width).
• the adhesive tape was then pressed onto the steel support four times under an applied pressure of 2 kg.
• a 1 kg weight was affixed to the adhesive tape, at room temperature a 1 kg or 2 kg weight.
• the holding powers measured are reported in minutes and correspond to the average from three measurements.
• the residual monomer content was determined analytically by liquid extraction of the PSAs used, followed by capillary gas chromatography.
• the measurements were carried out using the Dynamic Stress Rheometer instrument from Rheometrics.
• the frequency range from 0.1 to 100 rad/s was scanned at 25° C.
• the temperature sweep was measured 10 rad/s in a temperature range from ⁇ 25° C. to 130° C. All experiments were conducted with the parallel plate arrangement.
• the average molecular weight M w and the polydispersity PD were determined by the following techniques: the eluent used was THF containing 0.1% by volume trifluoroacetic acid. Measurement was carried out at 25° C. The preliminary column used was PSS-SDV, 5 ⁇ m, 10 3 ⁇ (10 2 nm), ID 8.0 mm ⁇ 50 mm. Separation was effected using the columns PSS-SDV, 5 ⁇ m, 10 3 and also 10 5 and 10 6 , each with ID 8.0 mm ⁇ 300 mm. The sample concentration was 4 g/l, the flow rate 1.0 ml per minute. Measurement was made against PMMA standards.
• the K value is a measure of the average size of molecules of high polymers. It is measured by preparing one percent strength (1 g/100 ml) toluenic polymer solutions and determining their kinematic viscosities with the aid of a VOGEL-OSSAG viscometer. Following standardization to the viscosity of toluene, the relative viscosity is obtained, and the K value can be calculated from this FIGURE by the method of FIKENTSCHER ( Polymer 1967, 8, 381 ff.)
• a 2 l glass reactor conventional for free-radical polymerizations was charged with 4 g of acrylic acid, 4 g of maleic anhydride, 32 g of N-tert-butylacrylamide, 180 g of 2-ethylhexyl acrylate, 180 g of n-butyl acrylate, 150 g of acetone and
• a 2 l glass reactor conventional for free-radical polymerizations was charged with 4 g of acrylic acid, 4 g of maleic anhydride, 32 g of N-tert-butylacrylamide, 180 g of 2-ethylhexyl acrylate, 180 g of n-butyl acrylate and 150 g of acetone/isopropanol (97:3). After nitrogen gas had been passed through the reactor for 45 minutes, with stirring, the reactor was heated to 58° C., and then 0.2 g of azoisobutyronitrile (AIBN) was added.
• AIBN azoisobutyronitrile
• a 2 l glass reactor conventional for free-radical polymerizations was charged with 4 g of acrylic acid, 4 g of maleic anhydride, 32 g of N-tert-butylacrylamide, 180 g of 2-ethylhexyl acrylate, 180 g of n-butyl acrylate and 150 g of acetone. After nitrogen gas had been passed through the reactor for 45 minutes, with stirring, the reactor was heated to 58° C., and then 0.2 g of azoisobutyronitrile (AIBN) was added.
• AIBN azoisobutyronitrile
• Vazo® 52 DuPont
• Vazo® 52 DuPont
• 2 h 0.6 g Vazo® 52 After 4 h, the batch underwent gelling and the polymerization was discontinued.
• a 2 l glass reactor conventional for free-radical polymerizations was charged with 4 g of acrylic acid, 4 g of maleic anhydride, 32 g of N-tert-butylacrylamide, 180 g of 2-ethylhexyl acrylate, 180 g of n-butyl acrylate, 150 g of acetone and
• a 2 l glass reactor conventional for free-radical polymerizations was charged with 4 g of acrylic acid, 4 g of maleic anhydride, 32 g of N-tert-butylacrylamide, 180 g of 2-ethylhexyl acrylate, 180 g of n-butyl acrylate, 150 g of acetone and
• P n is the degree of polymerization
• P n,0 is the degree of polymerization of the unregulated reaction
• [regulator] is the concentration of the chain-transfer regulator
• [monomer] is the monomer concentration
• C tr is the chain-transfer constant.
• Table 1 shows that a polymerization in pure solvent (Example 3) is attended by problems. Achieving a high conversion requires a relatively large quantity of initiator, in which case the batch has undergone gelling after a reaction time of just 4 h, and it is necessary to discontinue the polymerization.
• the polymerizations of Examples 1, 2, 4 and 5 show that regulators prevent the gelling whilst still enabling high conversions of >98% to be achieved, through initiation in two or more stages and with two or more initiators.
• alcohols, such as isopropanol are of only limited suitability, since the latter regulator cannot be incorporated into the PSA and hence remains in the solvent.
• Thiols are incorporated into the polymer during the polymerization process and do not adversely affect the concentration process.
• the achievable average molecular weight and the molecular weight distribution (dispersity) are critically important for the technical adhesive properties.
• Examples 1a-c show that amino acids containing thiol groups, such as N-acetyl-(L)-cysteine, are the most efficient regulators and therefore achieve the lowest polydispersity for the polyacrylate PSA in question.
• such amino acids are not toxic, thereby removing any controversy from operation with such compounds and from the residual presence of trace amounts in the polyacrylate material.
• the tetrafunctional thiol PETMP causes high crosslinking of the polymer, which would likewise give rise to disadvantages in the concentration process.
• the polymers investigated are prepared conventionally via a free radical polymerization in solution.
• fresh solvent is used for the first polymerization of the respective base polymers P1 to P4.
• all further polymerizations are carried out with the solvent or solvent mixture recovered by method 1.
• a reactor conventional for free-radical polymerizations was charged with 27 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate, 3 kg of methyl acrylate, 3 kg of acrylic acid and 66 kg of acetone/isopropanol (95:5). After nitrogen gas had been passed through the reactor for 45 minutes, with stirring, the reactor was heated to 58° C. and 50 g of AIBN were added. Thereafter the external heating bath was heated to 75° C. and the reaction was carried out constantly at this external temperature. After 1 h a further 50 g of AIBN were added, and after 4 h dilution took place with 20 kg of acetone/isopropanol mixture.
• a reactor conventional for free-radical polymerizations was charged with 27 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate, 3 kg of methyl acrylate, 3 kg of acrylic acid, 50 g of N-acetyl-(L)-cysteine and 66 kg of acetone. After nitrogen gas had been passed through the reactor for 45 minutes, with stirring, the reactor was heated to 58° C. and 50 g of AIBN were added. Thereafter the external heating bath was heated to 75° C. and the reaction was carried out constantly at this external temperature. After 1 h a further 50 g of AIBN were added, and after 4 h dilution took place with 20 kg of acetone.
• a reactor conventional for free-radical polymerizations was charged with 27 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate, 3 kg of methyl acrylate, 3 kg of acrylic acid, 55 g of rac-N-acetylcysteine methyl ester and 66 kg of acetone.
• nitrogen gas had been passed through the reactor for 45 minutes, with stirring, the reactor was heated to 58° C. and 50 g of AIBN were added. Thereafter the external heating bath was heated to 75° C. and the reaction was carried out constantly at this external temperature. After 1 h a further 50 g of AIBN were added, and after 4 h dilution took place with 20 kg of acetone.
• a reactor conventional for free-radical polymerizations was charged with 27 kg of 2-ethylhexyl acrylate, 67 kg of n-butyl acrylate, 3 kg of methyl acrylate, 3 kg of acrylic acid, 62 g of dodecanethiol and 66 kg of acetone. After nitrogen gas had been passed through the reactor for 45 minutes, with stirring, the reactor was heated to 58° C. and 50 g of AIBN were added. Thereafter the external heating bath was heated to 75° C. and the reaction was carried out constantly at this external temperature. After 1 h a further 50 g of AIBN were added, and after 4 h dilution took place with 20 kg of acetone.
• the acrylate copolymers (base polymers P1 to P4) are very largely freed from the solvent (residual solvent content ⁇ 0.3% by weight; cf. the individual examples) by means of a single-screw extruder (concentrating extruder, BERSTORFF GmbH, Germany).
• the solvent is condensed and used again without further purification for the polymerization of P1 to P4, with a check being made by determination of the K value, using test method F, after each polymerization, in order to ensure that PSAs having the same properties are prepared.
• the screw speed was 150 rpm, the motor current 15 A, and a throughput of 58.0 kg liquid/h was realized.
• a vacuum was applied at three different domes. The reduced pressures were, respectively, between 20 mbar and 300 mbar.
• the exit temperature of the concentrated hotmelt is approximately 115° C.
• the solids content after this concentration step was 99.8%.
• WELDING Engineers Orlando, USA
• Model 30 MM DWD screw diameter 30 mm
• screw 1 length 1258 mm
• the rotary speed was 451 rpm, the motor current 42 A, and a throughput of 30.1 kg/h was realized.
• the temperatures in zones 1 and 2 were each 105° C.
• the melt temperature in zone 1 was 117° C.
• the composition temperature on exit (zone 3 ) was 100° C.
• the acrylate hotmelt PSA prepared by methods 1-2 were melted in a feeder extruder (single-screw conveying extruder from TROESTER GmbH & Co KG, Germany) and using this extruder were conveyed as a polymer melt into a twin-screw extruder 1 . 3 (cf. FIG. 1) (LEISTRITZ, Germany, ref. LSM 30/34).
• the assembly is heated electrically from the outside and is air-cooled via a number of fans, and is designed such that, with the effective distribution of the crosslinker Polypox R16 (pentaerythritol polyglycidyl ether, CAS No.: 3126-63-4, tetrafunctional epoxide from UPPC AG, Germany) and of the accelerant Polypox H205 (polyoxypropylenediamine, CAS No.: 9046-10-0, amine hardener from UPPC AG, Germany) in the polymer matrix, there is at the same time a short residence time ensured for the adhesive in the extruder.
• crosslinker Polypox R16 penentaerythritol polyglycidyl ether, CAS No.: 3126-63-4, tetrafunctional epoxide from UPPC AG, Germany
• the accelerant Polypox H205 polyoxypropylenediamine, CAS No.: 9046-10-0, amine harden
• the mixing shafts of the twin-screw extruder were arranged in such a way that conveying elements are in alternation with mixing elements.
• the addition of the respective crosslinkers and accelerants is made with suitable metering equipment, where appropriate at two or more locations (cf. FIG. 1: metering locations 1 . 1 and 1 . 2 ) and, where appropriate, with the use of metering assistants into the unpressurized conveying zones of the twin-screw extruder.
• coating takes place in accordance with FIG. 1 onto a carrier material in web form onto the coating roll (BW).
• BW coating roll
• the time between metered addition of the crosslinker-accelerant system and the shaping or coating procedure is termed the processing life.
• This processing life indicates the period within which the adhesive, blended with the crosslinker or crosslinker-accelerant system, can be coated with the visually good appearance (gel-free, speck-free). Coating takes place with web speeds between 1 m/min and 20 m/min; the doctor roll (RW) of the 2-roll applicator is not driven.
• the base polymers P1-P4 are polymerized in accordance with the polymerization process described, and are concentrated using method 1 (solids content 99.8%), and a sample of the non-crosslinked polymer is analysed for its K value, in order to show that there are no residues in the solvent recyclate that have a molar mass regulator function. Subsequently, using method 2, the compositions were blended with Dertophene® T110 resin, and these resin-modified acrylate hotmelts were then compounded continuously by method 3 with the crosslinker-accelerant system.
• the processing life of the completed compound formulation was more than 10 minutes at an average adhesive temperature of 125° C. after leaving the LEISTRITZ twin-screw extruder. Coating takes place on a 2-roll applicator as per FIG. 1, with roll surface temperatures of 100° C. in each case and at a coat weight of 110 g/m 2 onto 23 ⁇ m PET film.
• Examples B1 to B4 were carried out a total of ten times, the polymerization being carried out in each case using the solvent recovered by distillation, by method 1, in order to demonstrate that there are no residues of the regulator in the solvent anymore. After each concentration of the polymer, the K values were determined by test method F (K1 to K10 for each respective polymerization mixture). For technical adhesive testing of Examples 1 to 4, test methods A and B were carried out.
• Table 2 demonstrates that reusing the solvent distillate consisting of acetone and isopropanol (Example 1) is attended by problems.
• the isopropanol acts as a chain-transfer regulator, but because of its lower vapour pressure as compared with acetone it is depleted with each distillation cycle, hence leading, in the polymerization carried out with the solvent recyclate, following distillation, to increases in the molar masses and hence in the K value. This would mean that following each distillation it will be necessary to check the proportion of isopropanol to acetone and, where necessary, re-adjust it once more, in order to continue to obtain polymers with the same molar mass distribution.
• Examples 2 and 3 demonstrate that amino acids which are solids are suitable regulators and that even after multiple re-use of the solvent recyclate there is no change in K value, within the bounds of measurement accuracy.
• the regulator concept of the invention for improving the recycling of solvent for the polymerization has therefore been proven.
• Table 3 shows the bond strengths to steel and also the holding powers for the first mixture in each case.
• composition regulated using isopropanol gave the highest shear strength as compared with the other polymerization regulators, which, however, are not substantially poorer. In general it was possible to show that similar technical adhesive properties were achievable with all the regulators.
• Example 1.10 shows very clearly the advantage of the inventive regulator system.
• Example 1.10 shows very clearly the advantage of the inventive regulator system.
• Example 4.10 there is a very significant change in the technical adhesive properties as compared with those of Example 1.1.
• the other regulators produced samples with reproducible technical adhesive data; in Example 4.10 there is a slight fall in the shear strength, owing to the reduction in molar mass, and the viscosity as well is lower as compared to the compositions regulated with amino acids.

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• 2009
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