SOLVENT-BORNE CROSSLINKABLE BLOCK COPOLYMERS OBTAINED USING RAFT

This invention relates to a process for obtaining a solvent-borne crosslinkable block copolymer and the use of such solvent-borne crosslinkable block copolymers.

For coatings, crosslinking is advantageous when certain properties are required, such as improved mechanical properties, resistance against solvents or stains or improved adhesion. It has been found that in the preparation of a film forming polymer for a coating composition using conventional free-radical polymerisation techniques there is a limited degree of control over the polymer chain composition and chain architecture. Very often the degree of chain growth control is insufficient to attain the desired final coating application properties. For example, the molecular weight of polymers produced via free-radical polymerisation is very difficult to control, and typically a significant amount of chains with high molecular weight are formed which may have a strong negative impact on the viscosity or the attainable solids level of the obtained polymer solution. It is therefore highly desirable to predict and control the molecular weight of film forming polymer solutions for use in coatings that require high solids content to reduce solvent emission during drying while at the same time maintaining a sufficiently low viscosity during application. Another drawback of polymers produced with conventional free radical polymerisation is that the incorporation of monomers with crosslink functionality in the polymer backbone is insufficiently controlled. This means that a non-homogeneous distribution of the crosslinkable monomers over the polymer chains is typically obtained, which results in ineffective intra-molecular (i.e. short) crosslinks. In addition, a large fraction of polymer chains may be formed that does not contain any crosslink functionality, which gives lower crosslink densities and poor final film properties. An increase in crosslink density can be attained through the use of higher levels of crosslinkable monomers as this increases the chance of each polymer chain having at least one crosslinkable monomer incorporated. However, the use of high levels of crosslinkable monomers to achieve good final application properties such as resistances is considered undesirable from an economical point of view and can be detrimental to the final properties.

Another problem often encountered, is that high levels of crosslinking monomers are needed to ensure that virtually all polymer chains become part of the ultimate polymer network. In addition, it may sometimes be desirable to have a

crosslinking functionality in only one segment of a polymer and to have a different monomer composition in another segment of the polymer, where often the second segment will have a specific functionality, such as for example water repellence or adhesion promotion. This will often be the case when the goal is to make compatibilisers, in which case the composition of each polymer segment in general will be quite different and different types of crosslink functionalities may be used in each segment.

Furthermore often a combination of good resistances and elasticity is desirable, for example when any resultant coatings are used on flexible or natural (wood, leather) substrates.

On substrates on which it may be difficult for coatings to adhere there is often a desire to apply coatings that combine good resistances with good adhesion. However, crosslinking will often have a negative effect on adhesion.

It would therefore be desirable to ensure that each polymer has some crosslinking functionality, and it would be especially preferred that each polymer has at least some crosslinkable groups at both polymer ends.

There is an increased scope of polymerisation methods available for adaptation to polymerisations to make solvent-borne polymers. In particular controlled radical polymerisation techniques such as nitroxide mediated radical polymerisation (NMP), atom transfer radical polymerisation (ATRP), and degenerative transfer techniques such as reversible addition-fragmentation chain transfer (RAFT) polymerisation have been investigated as means to control polymer chain composition and architecture.

DE 102004044087 discloses a functionalised polymer or contact adhesive containing functionalised polymer(s) with a high content of functional/crosslinkable monomer units and a special mol. wt. distribution in which the difference between peak mol. wt. and minimum mol. wt. is preferably less than 15000.

US 5371151 discloses a curable solvent-borne composition comprising a crosslinkable copolymer, wherein the copolymer is the free radical polymerization product of a mixture of monomers in the presence of a terminally unsaturated oligomeric chain transfer catalyst such as a chelate catalyst.

EP 1801 127 (Goodyear) describes amphiphillic block copolymers prepared by RAFT in aqueous media and without a polymeric surfactant.

US2004/0006151 discloses a pressure sensitive adhesive comprising a P(A/C)-P(B)-P(A/C) block copolymer, wherein P(B) is a polymer formed from

component B and component B comprises at least one monomer B1 , P(B) having a glass transition temperature not higher than O ⁰ C, P(A/C) represents a copolymer block of component A/C, which comprises at least two monomers A1 and C1 , P(A/C) having a glass transition temperature of 20 ⁰ C to 175 ⁰ C and C1 comprises at least one crosslinking-enabled functional group.

WO 01-77198 (Du Pont) discloses block copolymers prepared by RAFT in which one block must be insoluble to form a dispersion of micelles.

EP 1803754 (Cordis) describes block copolymers that may be prepared by RAFT, having hydrophilic, hydrophobic and biologically active blocks and are used to coat medical devices.

FR 2887888 (Biomerieux) discloses certain transfer agents for use in RAFT polymerization. Block copolymers are listed as one of the many types of polymer that can be prepared by using these agents.

We have surprisingly found that according to the present invention the reversible addition-fragmentation chain transfer (RAFT) polymerisation process provides a useful route for making solvent-borne crosslinkable block copolymers that contain a crosslinkable block next to at least a second, different, block. Such a process offers much better control over chain composition and chain architecture compared to for example chain transfer polymerisation. These block copolymers can provide polymer coating compositions with advantageous crosslinking properties. RAFT polymerisation in solution provides the possibility to fully control the polymer chain composition, in terms of molecular weight and functionality, and the chain architecture of the crosslinkable polymers. The controlled incorporation of crosslinkable monomers results in very efficient crosslinking, which allows the use lower amounts of the more expensive crosslink functional monomers while maintaining the desired application properties. By making an [A][B][C] type of block copolymer, with pre-defined crosslink functionality and molecular weight, solvent-borne polymer coating compositions having a high attainable solids level at sufficiently low viscosity level can be obtained. Such solvent borne crosslinkable polymer compositions have also shown to give the desired combination of coating application properties like for example good (outdoor) durability, good mechanical properties and good resistances against solvents or stains. Each of the blocks of the copolymers of the present invention are soluble in the organic solvents used in the process and no micelles are formed. According to the invention there is provided a process for obtaining a

- A -

solvent-borne crosslinkable block copolymer comprising at least blocks [A] _x [B] _y [C] _z , said block copolymer having an acid value < 20 mgKOH/g, where at least blocks [A][B][C] are obtained by a controlled radical polymerisation of at least one ethylenically unsaturated monomer via a reversible addition-fragmentation chain transfer (RAFT) mechanism in solution in the presence of a control agent and a source of free radicals; wherein blocks [A] and [C] may be the same or different and comprise: i) 15 to 100 mol%, preferably 25 to 100 mol%, of ethylenically unsaturated monomer units bearing crosslinking functional groups; ii) 0 to 85 mol%, preferably 0 to 75 mol %, of ethylenically unsaturated monomers units selected from Ci-i ₈ alkyl (preferably C _M2 alkyl) (meth)acrylate monomers and styrenic monomers; iii) 0 to 20 mol% of ethylenically unsaturated monomers units different from those from i) + ii); where i), ii) + iii) add up to 100%; and wherein block [B] comprises: i) 0 to 20 mol%, preferably 0 to 12 mol %, of ethylenically unsaturated monomer units bearing crosslinking functional groups; ii) 60 to 100 mol% of ethylenically unsaturated monomers units selected from C _M8 alkyl (preferably Ci _{- 12} alkyl) alkyl (meth)acrylate monomers and styrenic monomers; iii) 0 to 20 mol% of ethylenically unsaturated monomers units different from those from i) + ii); where i), ii) + iii) add up to 100%; and where [A] has an average degree of polymerisation x, where x is an integer from 3 to 40 (inclusive); where [B] has an average degree of polymerisation y, where y is an integer > 5, preferably > 10; where [C] has an average degree of polymerisation z, where z is an integer > 3; and where each of the blocks [A], [B] and [C] are solvent soluble. As used herein solvent soluble means that a polymer made solely from that block is completely soluble in an organic solvent such as at least one of those solvents preferred herein.

The average degree of polymerisation x (or y or z) is determined by the total molar amount of monomers in block [A] (or [B] or [C]) divided by the total molar amount of control (RAFT) agent.

The terms monomer, polymer, control agent, initiator, block are intended to cover the singular as well as the plural.

The term "comprising" as used herein will be understood to mean that the list following is non exhaustive and may or may not include any other additional suitable items, for example one or more further feature(s), component(s), ingredient(s) and/or substituent(s) as appropriate.

The term 'alkyl' or its equivalent (e.g. 'alk') as used herein may be readily replaced, where appropriate and unless the context clearly indicates otherwise, by terms encompassing any other hydrocarbo group such as those described herein (e.g. comprising double bonds, triple bonds, aromatic moieties (such as respectively alkenyl, alkynyl and/or aryl) and/or combinations thereof (e.g. aralkyl) as well as any multivalent hydrocarbo species linking two or more moieties (such as bivalent hydrocarbylene radicals e.g. alkylene).

The terms Optional substituent' and/or Optionally substituted' as used herein (unless followed by a list of other substituents) signifies the one or more of following groups (or substitution by these groups): carboxy, sulfo, sulfonyl, formyl, hydroxy, amino, imino, nitrilo, mercapto, cyano, nitro, methyl, methoxy and/or combinations thereof. These optional groups include all chemically possible combinations in the same moiety of a plurality (preferably two) of the aforementioned groups (e.g. amino and sulfonyl if directly attached to each other represent a sulfamoyl group). Preferred optional substituents comprise: carboxy, sulfo, hydroxy, amino, mercapto, cyano, methyl, halo, trihalomethyl and/or methoxy, more preferred being methyl, chloro, hydroxy and carboxy.

Any radical group or moiety mentioned herein (e.g. as a substituent) may be a multivalent or a monovalent radical unless otherwise stated or the context clearly indicates otherwise (e.g. a bivalent hydrocarbylene moiety linking two other moieties). However where indicated herein such monovalent or multivalent groups may still also comprise optional substituents. A group which comprises a chain of three or more atoms signifies a group in which the chain wholly or in part may be linear, branched and/or form a ring (including spiro and/or fused rings). The total number of certain atoms is specified for certain substituents for example a 'C _1-N moiety' signifies a moiety comprising from 1 to N carbon atoms. In any of the formulae herein if one or more substituents are not indicated as attached to any particular atom in a moiety (e.g. on a particular position along a chain and/or ring) the substituent may replace any H and/or may be located at any available position on the moiety which is chemically

suitable and/or effective in the applications described herein.

As used herein chemical terms (other than names for specifically identified compounds) which comprise features which are given in parentheses - such as (alkyl)acrylate, (meth)acrylate and/or (co)polymer denote that that part in parentheses is optional as the context dictates, so for example the term (meth)acrylate denotes both methacrylate and acrylate.

Certain moieties, species, groups, repeat units, compounds, oligomers, polymers, materials, mixtures, compositions and/or formulations which comprise and/or are used in some or all of the invention as described herein may (unless the context herein indicates otherwise) exist as one or more different forms such as any of those in the following non exhaustive list: stereoisomers (such as enantiomers (e.g. E and/or Z forms), diastereoisomers and/or geometric isomers); tautomers (e.g. keto and/or enol forms), conformers, salts, zwitterions, complexes (such as chelates, clathrates, crown compounds, cyptands / cryptades, inclusion compounds, intercalation compounds, interstitial compounds, ligand complexes, organometallic complexes, non stoichiometric complexes, π adducts, solvates and/or hydrates); isotopically substituted forms, polymeric configurations [such as homo or copolymers, random, graft and/or block polymers, linear and/or branched polymers (e.g. star and/or side branched), cross linked and/or networked polymers, polymers obtainable from di and/or tri valent repeat units, dendrimers, polymers of different tacticity (e.g. isotactic, syndiotactic or atactic polymers)]; polymorphs (such as interstitial forms, crystalline forms and/or amorphous forms), different phases, solid solutions; and/or combinations thereof and/or mixtures thereof where possible. The present invention comprises and/or uses all such forms which are effective in the applications described herein.

The values given herein for each of the parameters used to define the invention (such as integers x, y and z) when given as a range include the numbers at both ends of each range.

Preferably the crosslinkable block copolymer obtained by the process of the invention has an acid value < 15 and more preferably < 10 mg KOH per g of block copolymer.

Preferably integer x is from 3 to 25, more preferably from 3 to 15 Preferably integer y is from 10 to 80, more preferably from 10 to 50. Preferably integer z is from 3 to 40, more preferably from 3 to 25, most preferably from 3 to 15.

Preferably block [A] and block [C] have the same composition The crosslinkable block copolymer obtained from the process of the invention may contain low amounts of crosslinking monomers and yet the physical properties can still be dominated by the crosslinking monomers despite the low amounts.

A block copolymer is understood to be a copolymer comprising at least two successive sections of blocks of monomer units of different chemical constitutions. The block copolymers of the invention can therefore be multiblock (e.g. triblock) copolymers. Block copolymers may be linear, branched, star or comb like, and have structures like [A][B][C], [A][B][A], [A][B][A][B], [A][B][C][B] etc. Preferably the block copolymer is a linear triblock copolymer of structure [A][B][C], or in an alternative preferred embodiment a linear triblock copolymer of structure [A][B][A].

Furthermore any of the blocks in the block copolymer could be either a homopolymer, meaning only one type of monomer, or a copolymer, meaning more than one type of monomer. In case of a copolymer type of block the composition could be either random or gradient like, depending on the processing conditions used. A block with a gradient composition is understood to be a block having a continuously changing monomer composition along the block.

The term "controlled radical polymerisation" is to be understood as a specific radical polymerisation process, also denoted by the term of "living radical polymerisation", in which use is made of control agents, such that the polymer chains being formed are functionalised by end groups capable of being reactivated in the form of free radicals by virtue of reversible transfer or reversible termination reactions. Controlled radical polymerisation processes in which reversible deactivation of radicals proceeds by reversible transfer reactions include for example the process for radical polymerisation controlled by control agents, such as reversible transfer agents of the dithioester (R-S-C(=S)-R') type as described in WO98/01478 and WO99/35178, the process for radical polymerisation controlled by reversible transfer agents of trithiocarbonate (R-S-C(=S)-S-R') type as described in for example WO98/58974, the process for radical polymerisation controlled by reversible transfer agents of xanthate (R-S-C(=S)-OR') type as described in WO98/58974, WO00/75207 and WO01/42312, and the process for radical polymerisation controlled by reversible transfer agents of dithiocarbamate (R-S-C(=S)-NR ₁ R ₂ ) type as described for example in WO99/31144 and WO99/35177. Such controlled radical polymerisations are known in the art as

reversible addition-fragmentation chain transfer (RAFT) polymerisation (WO98/01478; Macromolecules 1998 31 , 5559-5562) or macromolecular design via interchange of xanthates (MADIX) polymerisation (WO98/58974; Macromolecular Symposia 2000 150, 23-32). "Addition-fragmentation" is a two-step chain transfer mechanism wherein a radical addition is followed by fragmentation to generate a new radical species.

When preparing a block copolymer in the presence of the control agent, the end of the growing block is provided with a specific functionality that controls the growth of the block by means of reversible free radical deactivation. The functionality at the end of the block is of such a nature that it can reactivate the growth of the block in a second and/or third stage of the polymerisation process with other ethylenically unsaturated monomers providing a covalent bond between for example a first, second and third block [A], [B] and [C] and with any further optional blocks.

Preferably the block copolymer is obtained from a controlled radical polymerisation process employing as a control agent, a reversible transfer agent. Reversible transfer agents may be one or more compounds selected from the group consisting of dithioesters, thioethers-thiones, trithiocarbonates , dithiocarbamates, xanthates and mixtures thereof.

Reversible transfer agents also include symmetrical transfer agents with two functional groups. An example is a dibenzyltrithiocarbonate such as

C ₆ H ₅ CH ₂ -S-C(=S)-S-CH ₂ C ₆ H ₅ .

Preferably the block copolymer is obtained from a controlled radical polymerisation process employing a control agent having a group with formula:

-S-C(=S)-. Preferably the block copolymer is obtained from a controlled radical polymerisation process employing xanthates and/or dibenzyltrithiocarbonate.

Preferably the block is obtained from a controlled radical polymerisation process employing a xanthate such as O-ethyl-S-(i-methoxycarbonyl) ethyl dithiocarbonate [ RSC(=S)-OC ₂ H ₅ where R = -CH(CH ₃ )-C(=O)-OCH ₃ ]. For clarity, control agents for use in RAFT do not include diphenylethylene, which although it is a control agent can not be used as a RAFT control agent, i.e. for a RAFT polymerization mechanism.

Control agents of the xanthate type have low transfer constants in the polymerization of styrenes and in particular methacrylate type monomers which may result in a higher polydispersibility and/or poor chain growth control of the resultant

polymers and may be considered as less effective RAFT control agents, although the actual mechanism involved is similar to the reversible-addition fragmentation chain transfer (RAFT) mechanism described in WO98/01478. Reversible transfer agents of the dithioester type like for example benzyl dithiobenzoate derivatives are generally considered as having a high transfer constant and being more effective RAFT control agents.

Transfer constants are described in WO98/01478. "Chain transfer constant" (C _tr ) means the ratio of the rate constant for chain transfer (k _tr ) to the rate constant for propagation (k _p ) at zero conversion of monomer and chain transfer agent (CTA). If chain transfer occurs by addition-fragmentation, the rate constant for chain transfer (k _tr ) is defined as follows: kt _r = k _add x [k _β / (k _-add + k _β )] where k _add is the rate constant for addition to the CTA and k _-add and k _β are the rate constants for fragmentation in reverse and forward directions respectively. In an embodiment of the invention the control agent preferably has a transfer constant C _tr = (k _add /k _p )[k _β /(k _-add +k _p )] of less than 50, more preferably less than 20 and most preferably below 10.

The process for radical polymerisation controlled by for example control agents of xanthate type may be carried out in bulk, in solution, in emulsion, in dispersion or in suspension. The RAFT polymerisation process, used in the present invention for obtaining block [A] [B] and [C], is performed in solution.

Solution polymerisation is a polymerisation process in which all the reaction components including the monomer(s), initiator and control agent are dissolved in a non-monomeric liquid solvent at the start of the reaction. By non-monomeric is meant a solvent that does not comprise monomers, in other words that won't react as part of the polymerisation. The solvent is also able to dissolve the polymer or copolymer that is being formed. The solvent is organic, and may be one solvent or mixtures of different organic solvents.

Preferred organic solvents include solvents selected from the group consisting of acetates such as ethyl acetate, butyl acetate; aromatic hydrocarbons such as toluene, xylenes; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone; butyl glycol; alcohols such as ethanol, iso-propanol; and mixtures thereof. Preferably non-aromatic solvents are used. Preferably the boiling point of the solvent is in the range of from 100° to 15O ⁰ C. Most preferably the organic solvent is selected from the group consisting of ethyl acetate and or butyl acetate.

Crosslinking functional groups are well known in the art and include groups which crosslink at ambient temperature (20 ± 3°C) or at elevated temperatures up to 185°C, preferably up to 160 ⁰ C by a number of mechanisms including but not limited to autoxidation, Schiff base crosslinking (for example the reaction of carbonyl functional groups with carbonyl reactive amine and/or hydrazine functional groups), silane condensation (for example the reaction of alkoxy silane or Si-OH groups in the presence of water) and melamine crosslinking. Other crosslinking mechanisms known in the art include those provided by the reaction of epoxy groups with amino, carboxylic acid or mercapto groups; the reaction of isocyanate groups with hydroxy or amine functional groups (for example block copolymers with hydroxy or amine (primary or secondary) functional groups are combined with polyisocyanates); the reaction of mercapto groups with ethylenically unsaturated groups such as fumarate and acryloyl groups, the reaction of masked epoxy groups with amino or mercapto groups, the reaction of isothiocyanates with amines, alcohols or hydrazines, the reaction of amines (for example ethylenediamine or multifunctional amine terminated polyalkylene oxides) with [beta]-diketo (for example acetoacetoxy or acetoamide) groups to form enamines.

By crosslinking by auto-oxidation is meant that crosslinking results from an oxidation occurring in the presence of air and usually involves a free radical mechanism and is preferably metal-catalysed resulting in covalent crosslinks. By Schiff base crosslinking is meant that crosslinking takes place by the reaction of a carbonyl functional group(s), where by a carbonyl functional group herein is meant an aldo or keto group and includes an enolic carbonyl group such as is found in an acetoacetyl group with a carbonyl-reactive amine and/or hydrazine (or blocked amine and/or blocked hydrazine) functional group. By silane condensation is meant the reaction of alkoxy silane or -SiOH groups in the presence of water, to give siloxane bonds by the elimination of water and/or alkanols (for example methanol) during the drying of the coating composition.

Examples of component i) comprise ethylenically unsaturated monomer units (preferably having at least 3 carbon atoms e.g. from 3 to 30 carbon atoms) bearing crosslinking functional groups such as hydroxyl, carboxyl, silane, anhydride, epoxy, acetoacetoxy, unsaturated fatty acid, (meth)acryloyl, (meth)allyl, acid amide, isocyanato, keto and or aldehyde functional groups, more preferably ethylenically unsaturated monomer units (optionally C _1-18 ethylenically unsaturated monomer(s)) bearing hydroxyl, carboxyl and or epoxy functional groups. Examples of monomer units bearing crosslinking functional groups include acetoacetoxyethyl

methacrylate, methylvinylketone, diacetone acrylamide, (meth)acroleine, maleic anhydride, glycidyl (meth)acrylate, alkoxysilane monomers such as gamma-methacryloxypropyltrimethoxysilane, (meth)acrylic acid, and hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and their modified analogues like Tone M-100 (Tone is a trademark of Union Carbide Corporation), and/or mixtures thereof.

Preferably the ethylenically unsaturated monomer units bearing crosslinking functional groups are selected from the group of glycidyl (meth)acrylate and hydroxyalkyl (meth)acrylates. Preferably block [A] comprises 50 to 100 mol% and more preferably

70 to 100 mol% of component i).

Preferably block [A] comprises > 1 , more preferably ≥ 3 and most preferably ≥ 5 of ethylenically unsaturated monomer units bearing crosslinking functional groups. Preferably block [B] comprises 0 to 10 mol%, more preferably 0 to

5 mol % and most preferably 0 mol% of component i).

Preferably block [B] comprises 0 to 10, more preferably 0 to 8 and most preferably 0 to 5 ethylenically unsaturated monomer units bearing crosslinking functional groups. Preferably block [C] comprises 50 to 100 mol% and more preferably

70 to 100 mol% of component i).

Examples of component ii); comprise alkyl (meth)acrylates (such as Ci- ₃ oalkyl (meth)acrylates) and/or styrenic monomers (such as C ₇ -i8Styrenic monomers), and include but are not limited to styrenic monomers such as styrene, α-methyl styrene, t-butyl styrene, chloromethyl styrene, vinyl toluene; and esters of acrylic acid and methacrylic acid of formula CH ₂ =CR ⁵ -COOR ⁴ wherein R ⁵ is H or methyl and R ⁴ is optionally substituted alkyl, cycloalkyl, aryl or (alkyl)aryl (such as optionally substituted C _1-18 alkyl, C ₃ - ₁₈ cycloalkyl, C ₃ - ₁₈ aryl or C ₄ - ₁₈ (alkyl)aryl) which are also known as acrylic monomers, which are also known as acrylic monomers, examples of which are methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate (all isomers), butyl (meth)acrylate (all isomers), 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyloxy methyl (meth)acrylate, benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 3,3,5-trimethyl-cyclohexyl (meth)acrylate, p-methylphenyl (meth)acrylate, 1-naphtyl (meth)acrylate,

3-phenyl-n-propyl (meth)acrylate; and hydrophobic acrylic monomers such as side-chain crystallisable monomers, examples of which are tetradecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate (= stearyl (meth)acrylate); and mixtures thereof. Preferably, the monomers are selected from styrene, and the group of Ci-i ₂ alkyl(meth)acrylate monomers such as methyl (meth)acrylate, ethyl

(meth)acrylate, propyl (meth)acrylate (all isomers), butyl (meth)acrylate (all isomers), 2-ethylhexyl (meth)acrylate, and isobornyl (meth)acrylate.

Examples of component iii) comprise diene monomers preferably C _2- i8 diene monomers such as 1 ,3-butadiene and isoprene; divinyl benzene; vinyl monomers preferably C ₂ - ₁ 8 vinyl monomers such as acrylonitrile, methacrylonitrile; vinyl halides preferably C _{2 -18} vinyl halides such as vinyl chloride; vinylidene halides preferably C _{2 -18} vinylidene halides such as vinylidene chloride; vinyl esters preferably C _2-18 vinyl esters such as vinyl acetate, vinyl propionate, vinyl laurate; vinyl esters of versatic acid such as VEOVA™ 9 and VEOVA™ 10 (VEOVA™ is a trademark of Resolution); heterocyclic vinyl compounds preferably C _{3 -18} vinyl heterocycles; alkyl esters of mono-olefinically unsaturated dicarboxylic acids, preferably C _{1 -18} alkyl esters such as di-n-butyl maleate and di-n-butyl fumarate; amides of unsaturated carboxylic acids preferably C _{1 -18} amides such as N-alkyl(meth)acrylamides that are different from those of components i) to ii). The Tg of a polymer herein stands for the glass transition temperature and is well known to be the temperature at which a polymer changes from a glassy, brittle state to a rubbery state. Tg values of polymers may be determined experimentally using techniques such as Differential Scanning Calorimetry (DSC) or calculated theoretically using the well-known Fox equation where the Tg (in Kelvin) of a copolymer having "n" copolymerised comonomers is given by the weight fractions "W" and the Tg values of the respective homopolymers (in Kelvin) of each comonomer type according to the equation

"1/Tg = W ₁ ZTg ₁ + W ₂ /Tg ₂ + W _n /Tg _n ".

The calculated Tg in Kelvin may be readily converted to ⁰ C. Preferably the calculated Tg of block [A] is < 20 ⁰ C, more preferably

< 10 ⁰ C and most preferably < 0 ⁰ C.

Preferably the calculated Tg of block [B] is > 5 ⁰ C, more preferably > 15 ⁰ C , most preferably > 2O ⁰ C, usefully > 30 ⁰ C and especially > 40 ⁰ C.

Preferably the calculated Tg of block [C] is < 20 ⁰ C, more preferably < 10 ⁰ C and most preferably < O ⁰ C.

Preferably the [A][B][C] block copolymer has a calculated overall Tg of > - 5°C, more preferably in the range of 0 to 80 ⁰ C and most preferably in the range of 5 to 50 ⁰ C.

High Tg is defined as a Tg > 20 ⁰ C. Low Tg is defined herein as a Tg < 20 ⁰ C. A high Tg block is preferred to facilitate fast initial drying. In an embodiment of the invention, the high Tg block preferably has a low percentage of ethylenically unsaturated monomer units bearing crosslinking functional groups such as hydroxyl functional groups. Preferably the ethylenically unsaturated monomer units bearing crosslinking functional groups such as hydroxyl functional groups are mainly concentrated in the relatively flexible low Tg block. This may assist the accessibility of the hydroxyl groups during drying and cure of the coating.

The weight average molecular weights (Mw) or number average molecular weights (Mn) of the block copolymer may be determined by using gel permeation chromatography (GPC) with THF as a solvent and polystyrene standards. Preferably the number average molecular weight (Mn) of the block copolymer is in the range of from 1 ,000 to 25,000 g/mol, more preferably 1 ,500 to 15,000 g/mol and especially 2,000 to 10,000 g/mol.

In an alternative embodiment of the invention conveniently the block copolymer of the invention has an Mn of 1 ,000 to 20,000 g/mol, more conveniently 1 ,500 to 10,000 g/mol and most conveniently 1 ,800 to 7,000 g/mol.

Preferably the number average molecular weight of block [A] is > 250, more preferably > 340 and most preferably > 650 g/mol.

Preferably the number average molecular weight of block [B] is 800 to 20,000 more preferably 1 ,000 to 12,000 and most preferably 1 ,200 to 7,500 g/mol. In an alternative embodiment of the invention conveniently the Mn of block [B] is 500 to 15,000 more conveniently 800 to 7,500 and most conveniently 1 ,000 to 5,000 g/mol.

Preferably the number average molecular weight of block [C] is > 250, more preferably > 340 and most preferably > 650 g/mol. Preferably the number average molecular weight of block [A] is

< 3,000 , more preferably < 2,500 and most preferably < 1 ,500 g/mol.

In an alternative embodiment of the invention conveniently the Mn of block [A] is < 2,500, more preferably < 1 ,500 and most preferably < 1 ,000 g/mol.

Preferably the number average molecular weight of block [C] is < 3,000, more preferably < 2,500 and most preferably < 1 ,500 g/mol.

In an alternative embodiment of the invention conveniently the Mn of block [C] is < 2,500, more preferably < 1 ,500 and most preferably < 1 ,000 g/mol.

In another embodiment of the invention there is provided a process for preparing a solvent-borne crosslinkable block copolymer according to the invention wherein said method comprises synthesis of the block copolymer in a solvent by means of a controlled radical polymerisation process of a first block [A] followed by the polymerisation of a second block [B] and a third block [C]. The order of preparation of [A], [B] and [C] can also be reversed. Furthermore blocks [A] and [C] may also be prepared simultaneously for example when a symmetrical control agent with two functional groups is employed.

Alternatively after preparation of the block copolymer the solvent is removed by a suitable method to get a dry powder. Thus in an embodiment of the invention there is provided a powder comprising in the range of from 100 to 45 wt% of the block copolymer prepared according to the process of the invention based on the wt% of total polymer present.

Furthermore the free radical polymerisation may be carried out as either a batch, semi-batch or a continuous process. When carried out in the batch mode, the reactor is typically charged with control agent and monomer. To the mixture is then added the desired amount of initiator. The mixture is then heated for the required reaction time. In a batch process, the reaction may be run under pressure to avoid monomer reflux.

Semi-batch operation typically involves the continuous or step-wise addition of monomer(s) (and/or other ingredients) during polymerization, and is often applied in copolymerisations to minimize copolymer composition drift in case monomer reactivities are very different. If the polymerisation is to be carried out as a semi-batch process, the reaction is typically carried out as follows: the reactor is charged with a polymerisation medium, typically an organic solvent, the control agent, and optionally (part of) the initiator. Into a separate vessel are placed the monomer(s) and optionally polymerisation medium and initiator. For safety reasons the initiator can also be added via another separate vessel. The polymerisation medium in the reactor is heated and stirred while the monomer(s) and initiator solutions are step-wise or gradually introduced. The rate of monomer and/or initiator addition is determined largely by the quantity of solution and/or the rate of polymerisation. When the additions are completed, heating may be continued for an additional half hour or more period of time with or without additional initiator to reduce unreacted monomer levels.

Furthermore, in the synthesis of the block copolymer the prepared first block can be purified from residual monomers and subsequently used for the polymerisation of a second monomer composition as a second block, or the second monomer composition can be polymerised directly after the preparation of the first block is completed. In this case at least 80 wt%, preferably at least 90 wt%, most preferred at least 95 wt% of the first block monomer composition is reacted before the second monomer composition is reacted. The second block can contain up to 20 wt% (preferably 10 wt% or less) of the first monomer composition.

In either type of process, the block copolymer may be isolated by stripping off the medium and unreacted monomer or by precipitation with a non-solvent. Alternatively, the block copolymer solution may be used as such, if appropriate to its application.

A free-radical polymerisation of ethylenically unsaturated monomers to prepare the block copolymer typically requires the use of a source of free radicals (i.e. an initiator) to initiate the polymerisation. Suitable free-radical-yielding initiators include organic peroxides, such as acyl peroxides including for example benzoyl peroxide; alkyl hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide; dialkyl peroxides such as di-t-butyl peroxide and di-tert-amyl peroxide; peroxy esters such as t-butyl perbenzoate and tert-amylperoxy 2-ethylhexyl carbonate; mixtures may also be used. The peroxy compounds are in some cases advantageously used in combination with suitable reducing agents (redox systems). Azo functional initiators such as for example 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2-methyl- butyronitrile) (AMBN) and 4,4'-azobis(4-cyanovaleric acid) may also be used. The selected initiator system preferably has the required solubility in the reaction medium and the appropriate half life time at the applied temperature of polymerisation. The amount of initiator or initiator system to use is conventional. Preferably the molar amount of initiator does not exceed the molar amount of control agent that is applied. A further amount of initiator may optionally be added at the end of the polymerisation process to assist the removal of any residual ethylenically unsaturated monomers.

The control agent may optionally be removed after the block copolymer preparation. Removal of the control agent is preferably performed via oxidation, aminolysis or radical induced reactions. Depending on the type of control agent that is used it can be preferred to remove the control agent prior to use of the composition of the invention. Whether the control agent is preferably removed is mostly

dependent on potential issues that may arise during synthesis or in particular during use of the composition regarding colour, odour and/or reactivity related to the presence of residual control agent (RAFT agent or derivative thereof in particular). The crosslinkability may be introduced by the use of a self-crosslinking monomer or, preferably, the composition comprising the crosslinkable block copolymer obtained by the process of the invention is combined with a separate crosslinking agent. This may provide either a self-crosslinking system (with a long pot life, triggered by for instance a change in temperature or pH or the evaporation of one of the ingredients in the overall system, like a solvent or water), or a two pack system. A separate crosslinking agent is preferably selected from group consisting of polyhydrazides (including dihydrazides such as adipic acid dihydrazide), polyisocyanates, carbodiimides, polyaziridines, epoxies, melamine resins and mixtures thereof. Usually the polyisocyanates are added shortly before application, lsocyanate crosslinking is most preferred when crosslinking is applied during the application process.

The block copolymer obtained by the process of the invention is particularly suitable for use in coating applications in which it may provide a key part of coating compositions or formulations. The block copolymer composition when applied as polymer solution can provide a coating composition or formulation with a higher attainable solids level at the required application viscosity, which results in faster drying and reduced solvent emission (lower VOC). In addition, the invention provides a route towards a more efficient use of crosslinking functional monomers and/or reduction of the amount of such costly monomers without compromising the desired application properties. The crosslinkable block copolymer may also provide excellent application properties in terms of for example mechanical properties, scratch resistance, (outdoor) durability, and resistances against solvents or stains, which makes the composition particularly suited for high performance coatings as in automotive clear coat and or base coat finishes and industrial maintenance finishes.

Such crosslinkable block copolymers may be used in coatings, including clearcoats and basecoat finishes or paints for automobiles and other vehicles or maintenance finishes for a wide variety of substrates. When the present compositions are used as automotive finishes, it is typical to apply a clearcoat over a basecoat where the basecoat or clearcoat or both may be an aqueous or solvent based composition. Alternatively the block copolymer obtained by the process of the

invention may be used in compositions suitable for applications where property changes like hardness, permeability and flow at a defined temperature can be beneficial i.e. in the fields of imaging, electronics, for example photoresists, engineering plastics, inks (especially for ink-jet devices), adhesives, dispersants, sealants and paints.

The composition may also contain conventional ingredients, some of which have been mentioned above; examples include pigments, dyes, emulsifiers, surfactants, plasticisers, thickeners, heat stabilisers, levelling agents, anti-cratering agents, fillers, sedimentation inhibitors, durability agents, corrosion and oxidation inhibitors, flow agents, sag control agents, metallic flakes, biocides, ultraviolet stabilizers (hindered amines and UV absorbers), antioxidants, drier salts, organic co-solvents, wetting agents and the like introduced at any stage of the production process or subsequently. It is possible to include an amount of antimony oxide in the emulsion to enhance the fire retardant properties. In an embodiment of the invention there is provided a use to coat a substrate with the solvent-borne crosslinkable block copolymer of the invention where the substrate is selected from the group consisting of wood, board, metals, stone, concrete, glass, cloth, leather, paper, carton, plastics, foam, fibrous materials (including hair and textiles) and the like. Compositions of the invention may be applied to a suitable substrate by any conventional method including brushing, dipping, flow coating, spraying, flexo printing, gravure printing any other method conventionally used in graphic arts or similar end uses .. The carrier medium is removed by natural drying or accelerated drying (by applying heat) to form a coating. Preferably a coating on a substrate comprising the solvent-borne block copolymer prepared according the invention which when dried is non-tacky.

Suitable organic co-solvents which may be added during the process or after the process during formulation steps are well known in the art and include xylene, toluene, methyl ethyl ketone, acetone, ethanol, isopropanol, ethyl acetate, butyl acetate, diethylene glycol, butyl glycol and 1-methyl-2-pyrrolidinone.

Preferably the solids content of the composition comprising the solvent-borne crosslinkable block copolymer is > 50 wt%, more preferably > 60 wt% and most preferably > 70 wt%. Especially preferred the solids of the composition comprising the solvent-borne crosslinkable block copolymer is > 75 wt%. Preferably the composition comprising the solvent-borne

crosslinkable block copolymer comprises < 10 wt%, more preferably < 5 wt% of water and most preferably < 0.5 wt% of water.

If desired the block copolymer obtained by the process of the invention can be used in combination with other polymer compositions which are not according to the invention.

Many other variations embodiments of the invention will be apparent to those skilled in the art and such variations are contemplated within the broad scope of the present invention.

Further aspects of the invention and preferred features thereof are given in the claims herein.

Examples

The present invention will now be described in detail with reference to the following non limiting examples which are by way of illustration only. In the examples, the following abbreviations and terms are specified:

DP average degree of polymerization

BA butyl acrylate

Sty styrene iBOA isobornyl acrylate

HEA 2-hydroxyethyl acrylate xanthate 1 = O-ethyl-S-(1-methoxycarbonyl)ethyl dithiocarbonate

(Rhodixan A1 , provided by Rhodia)

Example 1

This example illustrates the synthesis of a [A] _x -[B] _y -[C] _z triblock copolymer with a calculated overall Tg of 0 ⁰ C, where block [A] is based on BA and HEA with x = 8, block [B] is based on BA, Sty and iBOA with y = 18 and has a calculated Tg of 37°C, and block [C] is based on BA and HEA with z = 8.

Example 1a Block [A] 425 gram of butyl acetate and 192 gram (0.93 mol) of xanthate 1 were added to a 2L three-necked glass flask equipped with condenser cooler, temperature measuring probe and mechanical stirring device. The reaction mixture was degassed by purging with nitrogen at room temperature for 15 minutes while stirring. The temperature was raised to 80 ⁰ C and 10wt% of a monomer feed mixture of 475 gram (3.7 mol) of BA and 431 gram (3.7 mol) of HEA was added to the reaction

mixture. Then a mixture of 9.0 gram (approximately 0.05 mol) of 2,2'-azobis(2-methylbutanenitril) (Akzo Nobel) and 50 gram of butyl acetate was added. After 15 minutes at 80 ⁰ C the gradual addition was started of the remaining 90wt% of the BA / HEA mixture. The addition lasted 4 hours under a weak nitrogen stream and at a controlled temperature of 80 ⁰ C, after which the mixture was kept for an additional 3 hours at 80 ⁰ C. The reaction mixture was then cooled to 20 ⁰ C and a sample was withdrawn for further analysis. The conversion of BA as determined with gas chromatography was found to be 99.3%, and the conversion of HEA as determined with liquid chromatography was 99.6%. The solids level was experimentally determined at 68.5%. GPC analysis of the final product using THF as solvent and calibration on polystyrene standards resulted in the following values: Mn = 1010 g/mol, Mw = 1425 g/mol, PDI (= Mw/Mn) = 1.41.

Example 1 b Block [BI 272.0 gram of the block [A] reaction mixture, corresponding to approximately 0.16 mol of precursor block [A] based on a solids level of 68.5% and a theoretical molecular weight of 1200 g/mol, was added to a 2L three-necked glass flask equipped with condenser cooler, temperature measuring probe and mechanical stirring device. The reaction mixture was degassed by purging with nitrogen at room temperature for 15 minutes while stirring. The temperature was raised to 110°C and 10wt% of a monomer feed mixture consisting of 162.7 gram (1.56 mol) of Sty, 104.2 gram (0.81 mol) of BA, 103.8 gram (0.50 mol) of iBOA, and 160.0 gram of butyl acetate was added to the reaction mixture. After 10 minutes 10.4 gram (approximately 0.040 mol) of tert-amylperoxy 2-ethylhexyl carbonate (Trigonox 131 , Akzo Nobel) was added to the reaction mixture. Then after 10 minutes at 110 ⁰ C the gradual addition was started of the remaining 90wt% of the monomer feed mixture. The addition lasted approximately 4 hours under a weak nitrogen stream and at a controlled temperature of 110°C. A post reaction was then performed by keeping the reaction mixture for an additional 7.5 hours at 110 ⁰ C. An amount of 5.2 gram of tert-amylperoxy 2-ethylhexyl carbonate was added 2 and 4 hours after the start of the post reaction. The reaction mixture was then cooled to 20 ⁰ C and a sample was withdrawn for further analysis. The conversion of Sty, BA and iBOA as determined with gas chromatography were found to be 99.9%, 97.1 % and 96.8%, respectively. The theoretical final solids level was about 70%. GPC analysis using THF as solvent and calibration on polystyrene standards resulted in the following values: Mn = 3710 g/mol, Mw = 6500 g/mol, PDI = 1.75.

Example 1c Block [Cl

The reaction mixture of block [A]-[B] was heated to 1 10 ⁰ C under nitrogen atmosphere. Then a monomer feed mixture consisting of 81.6 gram (0.64 mol) of BA, 74.4 gram (0.64 mol) of HEA, and 68.0 gram of butyl acetate was gradually added to the reaction mixture over a period of 4 hours at a controlled temperature of 110 ⁰ C. At the end of the monomer feed the reaction mixture was kept for 2 hours at 110°C. A post reaction was then performed to react any residual monomer by keeping the reaction mixture for an additional 17.5 hours at 110 ⁰ C. Extra tert-amylperoxy 2-ethylhexyl carbonate was added 3 hours (2.0 gram) and 8.5 hours (1.0 gram) after the start of the post reaction. The reaction mixture was then cooled to 20 ⁰ C and a sample of the final product was withdrawn for further analysis. The conversion of Sty, BA, iBOA and HEA was determined at 100.0%, 97.7%, 99.1%, and 99.4%, respectively. The final solids level was experimentally determined at 70.8%. GPC analysis using THF as solvent and calibration on polystyrene standards resulted in the following values: Mn = 3935 g/mol, Mw = 7300 g/mol, PDI = 1.86.

Example 2

This example illustrates the synthesis of a [A] _x -[B] _y -[C] _z triblock copolymer with a calculated overall Tg of 24°C, where block [A] is based on BA and HEA with x = 8, block [B] is based on Sty and iBOA with y = 16 and has a calculated Tg of 97°C, and block [C] is based on BA and HEA with z = 8.

The preparation of Example 2 was performed using the same recipe and procedure as applied for Example 1 , but now the monomer reaction mixture for block [B] consisted of 162.7 gram (1.56 mol) of Sty, 208.0 gram (1.00 mol) of iBOA, and 160.0 gram of butyl acetate. At the end of the block [B] synthesis the conversion of Sty and iBOA was determined with gas chromatography at 99.9% and 97%, respectively. The theoretical final solids level was about 70%. GPC analysis using THF as solvent and calibration on polystyrene standards resulted in the following values: Mn = 3605 g/mol, Mw = 6325 g/mol, PDI = 1.75. Block [C] of Example 2 was prepared using the recipe and procedure as described for Example 1. Analysis of the final block copolymer product of Example 2 resulted in a conversion of Sty, BA, iBOA and HEA at 100.0%, 97.9%, 99.9%, and 99.5%, respectively. The final solids level was experimentally determined at 72.0%. GPC analysis using THF as solvent and calibration on polystyrene standards resulted in the following values: Mn = 3815 g/mol, Mw = 7215 g/mol, PDI = 1.89.

Comparative Example A

This comparative example illustrates the synthesis of a random copolymer based on BA, Sty, iBOA and HEA, with a calculated overall Tg of 0 ⁰ C via conventional free radical polymerization. 490.0 gram of butyl acetate was charged to a high pressure reactor equipped with temperature measuring probe and mechanical stirring device and heated under nitrogen atmosphere to 178°C. Then a mixture of 331.3 gram of Sty, 516.8 gram of BA, 212.0 gram of iBOA, 265.0 gram of HEA and 26.5 gram of cumene hydroperoxide was gradually pumped to the reaction mixture over a period of 3.5 hours at a controlled temperature of 178°C (reactor pressure around 4 bar). At the end of the feed the dosing pump was rinsed with 26.5 gram of butyl acetate and the reaction mixture was kept for 0.5 hours at 178°C. The reaction mixture was then cooled to 140 ⁰ C, and then 2.6 gram of di-tert-amyl-peroxide was added, followed by 20 gram butyl acetate. After 30 minutes at 140 ⁰ C a second shot of 2.6 gram of di-tert-amyl-peroxide and 20 gram of butyl acetate were subsequently added, and the mixture was kept for 1 hour at 140 ⁰ C. The reaction mixture was then cooled to 20 ⁰ C. Final free monomer levels were all (well) below 0.1 %. The final solids level was experimentally determined at 65.8%. GPC analysis using THF as solvent and calibration on polystyrene standards resulted in the following values: Mn = 3030 g/mol, Mw = 7040, PDI (=Mw/Mn) = 2.32.

The specifications for Examples 1 and 2 (block copolymers) and Comparative Example A (random copolymer) are given in Table 1.

Table 1

The Examples and Comparative Example were formulated into a clear-coat finish which utilises the crosslinking chemistry of an hydroxyl-functional acrylate/styrene copolymer and a polyisocyanate resin. The formulation recipes are given in Table 2. The preparation of the formulations was as follows. The Examples and Comparative Example were diluted with butyl acetate (BuAc) to a viscosity of 16 to 17 seconds #4 DIN Cup. Then a calculated amount (based on an NCO/OH molar ratio of 1/1 ) of a polyisocyanate resin (Tolonate HDT-LV, Bayer), diluted to 60% with butyl acetate to obtain a viscosity of 16 to 17 seconds #4 DIN Cup, was added while stirring. A 10wt% solution of dibutyltindilaurate (catalyst, Air Products) in butyl acetate was then added, followed by Byk 331 (10% in BuAc) defoamer.

Table 2

To determine the coating properties (hardness, MEK double rub resistance), the two-component formulations were cast onto glass plates at 150 micron wet and dried in an oven for 30 minutes at 50 ⁰ C. To determine the hardness of an air dried film (curing at ambient temperature) films were cast at 150 micron wet onto glass plates and dried at 20 (+/- 3) ⁰ C. Test results are given in Table 3.

Table 3

The test results given in Table 3 show that the use of the block copolymers of Example 1 and 2 in the two-component polyisocyanate formulation provide coatings with much higher MEK double rub resistance than the random copolymer of Comparative Example A, which is an indication of more efficient crosslinking and network formation.

Test descriptions Pot life / gel time

The pot life / gel time test is performed to determine the workability in terms of viscosity of the 2-component resin formulation after the two components have been mixed in 1 pot. Directly after mixing approximately 150 ml. of the components in

the right ratio at room temperature (20 +/- 3°C) and thorough homogenisation of the mixture, the approximate time interval is measured until the viscosity is doubled (from 17 seconds to 34 seconds #4 DIN cup) and until gelation has occurred.

Hardness (Konig) The Konig hardness was determined following DIN 53157 NEN5319 using Erichsen hardness measuring equipment. The values are given in seconds and the higher the value is the harder the coating is. Measurements were performed directly after the applied formulation was cured in an oven for 30 minutes at 50 ⁰ C, and 1 day and 7 days after cure (= Hardness cured). Also measurements were performed 1 day and 7 days after drying the coating at 20 (+/- 3) ⁰ C (= Hardness air dried).

Tackiness and dry to handle

The tackiness and "dry to handle" property is determined by curing the coatings in an oven for 30 minutes at 50 ⁰ C, where after the cured coated glass plates are taken out of the oven and a thumb is placed onto the coating. The tackiness of the cured coating is classified from 0 to 5, with 0 = non-tacky (good) and 5 = very tacky (poor). The "dry to handle" property is classified as "good" in case this does not leave a permanent visible thumb print on the coating.

MEK double rub resistance

The degree of crosslinking of the coating is determined by means of its resistance against wiping the coating surface with a wad of cotton wool which is wetted with a strong organic solvent like methyl ethyl ketone (MEK). The wad of cotton wool, soaked with MEK, is moved forward and backward with a pressure of about 2 kg over the coating over a length of about 10 cm and a cycle time of about 1 second. The cycles are repeated and counted until the coating is either ruptured or dissolved and the bare substrate becomes visible. One cycle equals one double rub (forward and backward). The MEK double rub test measurements were performed 7 days after cure in an oven for 30 minutes at 50 ⁰ C.