The present invention relates to hydroxyl-functionalized peroxides, their preparation, and their use to prepare improved co(polymer) resins to be applied in coating compositions, in particular those having a high solids/low VOC (Volatile Organic Compound) content.

Hydroxyl functionalization of acrylic resins for use in coating compositions has become very important, because European regulations require coating compositions to contain less solvent. Hence, there is a need for acrylic resins having reduced viscosity and molecular weight. A consequence of this lower molecular weight, however, is that the monomer commonly used to introduce the curable hydroxyl functionalities (hydroxyethylmethacrylate) is no longer present in each polymer chain. This reduces the extent of curing.

The present invention now solves this problem by providing a hydroxyl- functionalized peroxide which can be used in the preparation of acrylic resins, thereby allowing the introduction of hydroxyl functionalities in many polymer chains.

Several types of hydroxyl-functionalized peroxides are already known. For instance, JACS 68 (1946), p. 533 discloses hydroxyl-functionalized peroxides containing -OH groups in a secondary position. However, the use of these peroxides in the preparation of acrylic resins has been found to result in a significant increase in the resin's viscosity. Said increase in viscosity is presumed to be caused by crosslinking via dehydration resulting in ether groups, because secondary -OH groups seem to be sufficiently reactive at usual polymerization temperatures (about 16O ⁰ C).

Mono-functional primary hydroxyl-functionalized peroxides are known from e.g. JP 01 -138205A, JP 01 -31153A, and JP 01 -061453A. Said documents disclose peroxides of the formulae HO-CH ₂ -C(CHS) ₂ -O-O-C(CHS) ₂ -CH ₂ -CH ₃ and HO- CH ₂ -C(CHs) ₂ -O-O-C(CHs) ₃ .

Their use in the polymerization of acrylate monomers is known from JP 01 - 138205A. From US 3,959,244; US 2,605,291 ; SU 1212004; and SU 767095, a peroxide with the formula HO-CH ₂ -CH ₂ -O-O-C(CHs) ₃ is known.

It has now been found that peroxides containing two primary hydroxyl groups are able to provide low-viscosity acrylic resins with a high average number of terminal hydroxyl groups per chain.

Accordingly, the present invention relates to a hydroxyl-functionalized peroxide having the general formula (I):

HO-CH ₂ -R ¹ -O-O-R ² -CH ₂ -OH (I) wherein R ¹ and R ² are the same or different and selected from linear or branched alkyl groups containing 1-16 carbon atoms and aralkyl groups.

The present invention further relates to a process for preparing the hydroxyl- functionalized peroxide according to the invention. If R ¹ and R ² are equal and, hence, a symmetrical peroxide is desired, the process involves the reaction between a diol having the general formula HO-CH ₂ -R ¹ -OH or its chemical equivalent alkenyl-ol with hydrogen peroxide in the presence of an acidic catalyst and under stirring conditions.

When R ¹ and R ² are different and, hence, an asymmetrical peroxide is to be obtained, the process comprises the steps of: a) reacting an alkane diol having the general formula HO-CH ₂ -R ¹ -OH or its chemical equivalent alkenyl-ol with hydrogen peroxide in the presence of an acidic catalyst and under stirring conditions to obtain an alkyl- hydroperoxide of the formula HO-CH ₂ -R ¹ -OOH, and b) reacting said alkylhydroperoxide with a diol having the general formula HO-CH ₂ -R ² -OH or its chemical equivalent alkenyl-ol to obtain the hydroxyl- functionalized peroxide.

Evidently, the same results can be achieved with a process comprising the steps of: a) reacting an alkane diol having the general formula HO-CH ₂ -R ² -OH or its chemical equivalent alkenyl-ol with hydrogen peroxide in the presence of an acidic catalyst and under stirring conditions to obtain an alkyl- or aralkylhydroperoxide of the formula HO-CH ₂ -R ² -OOH, and b) reacting said alkyl- or aralkylhydroperoxide with an alkane diol having the general formula HO-CH ₂ -R ¹ -OH or its chemical equivalent alkenyl-ol to obtain the hydroxyl-functionalized peroxide.

The term "chemical equivalent alkenyl-ol of an alkane diol" refers to the dehydrated form of the alkane diol. For instance, the chemical equivalent alkenyl-ol of HO-CH ₂ -CH ₂ -C(CHs) ₂ -OH is HO-CH ₂ -CH ₂ -C(CHs)=CH ₂ and the chemical equivalent alkenyl-ol of HO-CH ₂ -C(CHs) ₂ -OH is HO-CH ₂ -C(CHs)=CH ₂ .

Moreover, the present invention relates to the use of a hydroxyl-functionalized peroxide as defined hereinbefore as a crosslinking agent, grafting agent, curing agent, polymer degradation agent, or initiator for polymerization reactions.

In the hydroxyl-functionalized peroxides according to the present invention, R ¹ and R ² are the same or different and selected from linear or branched alkyl groups containing 1 -16 carbon atoms and aralkyl groups.

R ¹ and R ² are preferably alkyl groups that contain at most 16 carbon atoms, preferably at most 10 carbon atoms, more preferably still at most 8 carbon atoms, and most preferably at most 6 carbon atoms. On the other hand, R ¹ and R ² contain at least 1 carbon atom, preferably at least 2 carbon atoms, most preferably at least 3 carbon atoms. According to a still more preferred embodiment of the present invention, R ¹ and R ² are alkyl groups containing 3-6 carbon atoms. Preferably, R ¹ and R ² are selected from CH ₂ -C(CHs) ₂ and C(CH ₃ ) ₂ . Most preferably, R ¹ is a CH ₂ -C(CH ₃ ) ₂ group. R ² also is most preferably a CH ₂ -C(CHs) ₂ group.

According to another preferred embodiment, R ¹ and/or R ² may be aralkyl groups containing at most 29 carbon atoms. More preferably, said aralkyl group contains at most 25 atoms, more preferably still at most 19 carbon atoms, and most preferably at most 16 carbon atoms. On the other hand, said aralkyl group preferably contains at least 8 carbon atoms. More preferably, said aralkyl group contains from 8 to 29 carbon atoms and still more preferably from 8 to 16 carbon atoms.

More preferably, if the hydroxyl-functionalized peroxide according to the present invention contains an aralkyl group, either R ¹ or R ² is an aralkyl group (but not both).

In the process for preparing the hydroxyl-functionalized peroxide of the present invention, an acidic catalyst is used. A variety of inorganic acids can be used as catalysts, although mineral acids such as sulphuric acid and perchloric acid and the like are preferred. Sulphuric acid is the most preferred catalyst. The acid- catalyzed reaction of alkane diol or alkenyl-ol with hydrogen peroxide is preferably carried out at temperatures in the range of from -20 to 100 ⁰ C, more preferably from -10 to 9O ⁰ C, more preferably still from -5 to 85 ⁰ C, and most preferably from 0 to 8O ⁰ C.

It will be appreciated that the hydroxyl-functionalized peroxides according to the present invention can be used for several types of chemical reactions:

- polymerization of monomers, such as production of polymers suitable for solvent-based coating applications, and

- modification of polymers such as crosslinking and/or degradation of polymers or grafting of polymers and curing of polymers. Therefore, the hydroxyl-functionalized peroxides of the present invention can be used as an initiator for polymerization reactions and as crosslinking agent, grafting agent, curing agent, and polymer degradation agent.

The present invention further provides a process for preparing a hydroxyl- functionalized acrylic resin for high-solids coating compositions, comprising heating a mixture of (meth)acrylate monomers in a suitable solvent, optionally one or more comonomer(s) and more preferably a styrene comonomer, and 0.5-12 wt% of a hydroxyl-functionalized peroxide according to the present invention, based on the total weight of monomers and comonomers in the reaction mixture. The hydroxyl-functionalized peroxide according to the present invention is used in an amount of at most 12 wt%, based on the total weight of the monomers and comonomers in the reaction mixture, and more preferably an amount of at most 10 wt%, based on the total weight of the monomers and comonomers in the reaction mixture. On the other hand, the amount of applied hydroxyl-functionalized peroxide according to the present invention is at least 0.5 wt% and more preferably at least 1 wt%, and most preferably at least 2 wt%, based on the total weight of monomers and comonomers in the reaction mixture. A still more preferred amount of applied peroxide according to the present invention is in the range of from 1 -10 wt%, more preferably 2 to 10 wt%, based on the total weight of monomers and comonomers in the reaction mixture.

It will be appreciated that other than low molecular weight, an important requirement of resins suitable for use in high-solids solvent-based coating compositions is that they must contain chemically active groups (usually with hydroxyl or carboxyl functionality) in order to undergo molecular weight build-up and network formation during the final crosslinking (curing) reaction where compounds such as melamine or isocyanates are used as the curing agents. Polymers suitable for use in high-solids coating formulations normally have a hydroxyl content of from about 2 to about 7 wt%. To prepare a polymer which has a hydroxyl content of about 2-7 wt%, a sufficient amount of a hydroxyl- functional comonomer, e.g. hydroxyalkyl acrylate or methacrylate, needs to be used (normally 20-40 wt% of the monomer composition). Specific examples of hydroxyalkyl acrylates and methacrylates that can be used to prepare polymers suitable for solvent based coating applications include but are not limited to: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2- hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 3-hydroxypropyl acrylate, 4- hydroxybutyl acrylate, and the like. Specific examples of alkyl acrylates and methacrylates that can be used to prepare polymers suitable for solvent based coating applications include methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, and the like.

Other monomers, such as styrene, para-methyl styrene, acrylic acid, methacrylic acid, vinyl acetate or vinylacetate versatic esters, can also be used in the preparation of polymers suitable for solvent based coating applications (i.e. for control of monomer costs and/or to obtain a balance of film properties). Chain transfer agents can be used, for example thiols, disulphides, or CCI ₄ .

Suitable comonomers for polymerization are olefinic or ethylenically unsaturated monomers, for example substituted or unsubstituted vinyl aromatic monomers, including styrene, α-methylstyrene, p-methylstyrene, and halogenated styrenes; divinylbenzene; ethylene; ethylenically unsaturated carboxylic acids and derivatives thereof such as (meth)acrylic acids, (meth)acrylic esters, acrylic acid, methoxyethyl acrylate, dimethylamino (meth)acrylate, isobutyl methacrylate, lauryl methacrylate, stearic methacrylate, allyl methacrylate, 2- hydroxypropyl (meth)acrylate, methacrylamide, butyl (meth)acrylate, 2- ethylhexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and glycidyl (meth)acrylate, methyl (meth)acrylate and ethyl (meth)acrylate; ethylenically unsaturated nitriles and amides such as acrylonitrile, methacrylonitrile, and acrylamide; substituted or unsubstituted ethylenically unsaturated monomers such as butadiene, isoprene, and chloroprene; vinyl esters such as vinyl acetate and vinyl propionate and vinyl ester of versatic acid; ethylenically unsaturated dicarboxylic acids and their derivatives including mono- and diesters, anhydrides and imides, such as maleic anhydride, citraconic anhydride, citraconic acid, itaconic acid, nadic anhydride, maleic acid, fumaric acid, aryl, alkyl and aralkyl citraconimides and maleimides; vinyl halides such as vinyl chloride and vinylidene chloride; vinyl ethers such as methylvinyl ether and n-butylvinyl ether; olefins such as ethylene isobutene and 4-methylpentene; allyl compounds such as (di)allyl esters, for example diallyl phthalates, (di)allyl carbonates, and triallyl (iso) cyanurate. A preferred monomer for use in the hydroxyl-functionalized acrylic resin is (meth)acrylic acid.

According to a preferred embodiment of the present invention, the prepared hydroxyl-functionalized acrylic resin has two terminal hydroxyl groups on at least 20% of its polymer chains, more preferably on at least 40% of its polymer chains, more preferably still on at least 60% of its polymer chains, and most preferably on at least 80% of its polymer chains. Such resins are unique in terms of the high number of polymer chains that have terminal hydroxyl groups. Hence, the present invention also relates to resins obtainable by the process according to the present invention.

Examples of solvents that are used to prepare resins suitable for solvent based coating compositions include: toluene, xylene, mesitylene, ethyl acetate, n-butyl acetate, acetone, methyl ethyl ketone, methyl n-amyl ketone, ethyl alcohol, benzyl alcohol, oxo-hexyl acetate, oxo-heptyl acetate, propylene glycol methyl ether acetate, mineral spirits and other aliphatic, cycloaliphatic and aromatic hydrocarbons, esters, ethers, ketones, and alcohols which are conventionally used. Commercially, the primary considerations in the selection of a suitable solvent are cost, toxicity, flammability, volatility, and chain-transfer activity. The process for preparing a hydroxyl-functionalized acrylic resin is usually carried out by blending the selected monomers with the peroxide according to the present invention and optionally a solvent and/or a chain-transfer agent, and heating the mixture to a temperature in the range of from 80 to 25O ⁰ C, preferably in the range of from 80 to 22O ⁰ C, and most preferably in the range of from 100 to 200 ⁰ C.

The polymerization time is usually in the range of from 0.1 to 20 hours, preferably in the range of from 0.5 to 15 hours, and most preferably in the range of from 1 to 10 hours.

The present invention also relates to a coating composition comprising a hydroxyl-functionalized acrylic resin composition as prepared by the process as defined hereinbefore. More in particular, such coating compositions are relatively high in solids content and low in VOC.

EXAMPLES

Example 1

Preparation of di-isopreneglycol peroxide (DIPGP)

To a stirred mixture of 462 g H ₂ O ₂ -70%, 416 g H ₂ SO ₄ -78%, and 516 g toluene were added 495 g isopreneglycol in 30 min, keeping the reaction temperature at 30 ⁰ C by cooling. The mixture was stirred for 90 min longer at 30°C followed by addition of 476 g of Na ₂ SO ₄ -I Oaq. After separation, the bottom phase was discarded. To the remains in the reactor were added 272 g Na ₂ SO ₄ -15% solution, 800 g water, and, slowly, 515 g NaOH-25% to reach pH 6.0 under stirring and applying cooling to keep the temperature at 25°C. After separation, the top phase was discarded and the remaining part in the reactor was extracted three times with 280 g portions of diethyl ether. After removal of the diethyl ether by distillation under vacuum, the resulting crude product was dissolved in 1 ,000 g water and under cooling 456 g of NaOH-25% solution were added, keeping the temperature below 26°C. The so obtained mixture was extracted three times with 80 g portions of diethyl ether. The combined diethyl ether phase was then washed with 80 g of saturated ammonium sulfate solution. To remove traces of isopreneglycol hydroperoxide the ether phase was washed with sodium sulphite solution in presence of sodium acetate solution to keep the pH at 4-6. After addition of 1.0 g of sodium bicarbonate, the diethyl ether phase was dried over MgSO ₄ .2aq. The diethyl ether was then removed by distillation under vacuum to yield 37.2 g of di-isopreneglycol peroxide with purity of 95.8% by GC (area/area).

Example 2

Preparation of an acrylic polyol polymer

To 100 g of butylacetate, heated at 160 ⁰ C and 2.3 bar pressure, was added a mixture of 56.7 g butylacrylate, 4.0 g methacrylic acid, 178.1 g methyl methacrylate, 115.6 g hydroxyethylmethacrylate, and 0.113 mole of DIPGP as prepared in Example 1 in 240 min, keeping the reaction temperature at 160 ⁰ C. The mixture was then cooled down to 125°C and post-cured by adding a solution of 0.00442 mole of tert-butylperoxy-3,5,5-trimethylhexanoate (obtained from AkzoNobel) dissolved in 9.4 g butylacetate in 30 min at 125°C. After an additional 60 min stirring at 125°C the polymer solution was cooled down, collected, and diluted with butylacetate to a concentration of 70.0% solids content.

Example 3 (Comparative Example)

Preparation of an acrylic polyol polymer

This Example was carried out in a similar manner to Example 2, except that now the following initiators were used instead of DIPGP: - di-tert-amyl peroxide (DTAP), a conventional radical initiator, - dihexyleneglycol peroxide (DHGP), a peroxide containing two secondary hydroxyl groups, and

- tert-butylhexyleneglycol peroxide (TBHGP), a peroxide containing one secondary hydroxyl group.

The various properties of the acrylic polyol polymers prepared in accordance with Examples 2 and 3 are shown in Table 1. From Table 1 it will be clear that the use of a novel hydroxyl-functionalized peroxide in accordance with the present invention, when compared with the use of a conventional hydroperoxide initiator, results in an acrylic polyol polymer having an increased hydroxyl- functionalization on the polymer chain, as is expressed by the higher hydroxyl value. Compared to peroxides with secondary hydroxyl groups, the hydroxyl- functionalized peroxide in accordance with the present invention results in polymers with a reduced molecular weight and a narrower molecular weight distribution. The higher molecular weights observed when using peroxides with secondary hydroxyl groups are probably due to crosslinking between ether bonds.

Table 1

a)

DIPGP di-isopreneglycolperoxide di-tert-Amylperoxide

DHGP TBHGP dihexyleneglycolperoxide tert-butylhexyleneglycol peroxide

a bi-modal molecular weight distribution was obtained with DHGP