CA2198814A1 - Reduction of benzene formation in dibenzoyl peroxide formulations - Google Patents

Abstract

The present invention generally relates to a method for reducing the rate and amount of free benzene formation in BPO formulations. The method comprises adding at least one free-radical scavenger to said formulations in an amount effective to reduce the rate of BPO
decomposition. The invention also relates to BPO formulations having reduced decomposition rates and improved stability which contain an effective amount of at least one free-radical scavenger added thereto.

Description

~ 2 ~8 8 ~ 4 REDUCTION OF BENZENE FORMATION lN DIBENZOYL PEROXIDE FORMULATIONS

Field of the Invention The present invention generally relates to a method for the reduction of free ben_ene fo,."~lion in diacyl peroxide formulations.

5 Background ofthe Invention Dibenzoyl peroxide ('BPO') is com~only used as a free-radical initiator for the synthesis of various types of polymers, graft copolymers and interpenetrating nelwo.k~ that are applied in the m~nuf~ctllre of industrial and co~cumer products, and as curing agents and cross-linking agents in polymer industries. Recently, however, it has been discovered that BPO
10 formulations such as pastes, emulsions and suspensions based on organic p!~ctiri7ers, whether in the presence or absence of water, show continuously increasing levels offree benzene throughout their useful lifetime. This free benzene is formed due to the slow decon~position of the BPO over time.

Bull. Envir. Contam. Toxicol. (1994) 53: 747-752 provides a det~iled dicc~1ssion ofthe formation of benzene by hardeners co~ g BPO and phth~t~tec and concludes that BPO and phth~l~te co~ in;l~g hardeners may be a potential source of exposure to consumers as well as for industry workers.

Because of the known carcinogenic properties of benzene, ~ ;",;~ on of its formation is highly desilab'e Accordingly, it is an object ofthe invention to ,llin~nl;7e the decomposition of BPO formulations over time, thus reducing the rate and amount of free benzene formation.

It is also an object of the present invention to provide BPO forrnulations having a sllb~ ;o11y lower rate offree be.~el e formation. These and other objects are realized by the invention h~ ler de~,i~d.

Sl)mm~ory of the Invention S The present invention generally relates to a method for reducing the rate of free bel~ne formation in BPO form~lotion~ The method generally co."p,ises adding at least one free-radical scavenger to said form~ tionc in an amount effective to reduce the rate of BPO decomposition.

The invention also relates to BPO formulations having reduced decomposition rates which contain an effective amount of at least one free-radical scavenger added thereto.

Detailed Description of the Invention The present invention broadly relates to a method for re~uci~ the rate and amount of diacyl peroxide deco",position which comprises adding to said composition at least one free radical scavenger in an amount effective to reduce the rate of diacyl peroxide decomposition.
The method ofthe present invention also minimi7es the gene~alion of ha~rdous by-products which are formed by the decomposition of diacyl peroxides. The invention also relates to a diacyl peroxide composition having improved stability and reduced decomposition rate which has added thereto, an effective amount of at least one free radical scavenger.

In another embodiment, the invention relates to a method for red~lcin~ the rate of free benzene and/or ben_ene derivative formation in BPO formulations based on organic p!~tiçi7ers, such as pastes, emulsions, suspensions, dispersions and the like. More particularly, the present inventors have discovered that through the addition of select free-radical scavengers, the rate and amount of free benzel-e formation can be significantly reduced in BPO formulations without any direct loss in reactivity or adverse affects on the formulations themselves.

Dibe~ l peroxides within the context of the present invention shaU mean any diacyl peroxide which, upon deco.~.l,osition, generates free benzene or ben7~n~ derivatives. Diacyl peroxides ofthis type generally co,-esl)ond to those ofthe general formula:

O O

R C--O--O--C R
~Lere~n each R group may be the same or dilrci,~nl and is s~lected from subst;h~tGd or 10 ~ln~b~ te~ aryl, arallcyl, alkyl, alkaryl, and the like, with the proviso that at least one of said R
groups cGIll~ins a benzyl moiety. ~lerh,~d peroxides are dibenzoyl peroxide, 2,4-dichloro, ortho-and para-methyl derivatives of dil~enzoyl peroxide. Dibenzoyl peroxide is the p,ere"ed peroxide to be ernployed in accordance with the present invention.

Any free-radical scavenger capable of reacting with the free-radical species in the BPO
forrnulation can suitably be employed in the present invention. The normal deco"~position pathway of BPO is the initial formation of benzoyloxy radicals followed by either decarboxylation with formation of the phenyl radical and hence benzene, and/or the attack of the benzoyloxy or phenyl radical on the BPO, sometimes referred to as induced decomposition, res~llting in 20 additional decomposition of the BPO. Without wishing to be bound to any particular theory of operation, it is believed that the free-radical scavenger reacts and/or traps the benzoyloxy radicals or phenyl radicals that are formed during the decomposition of the BPO, which prevents the formation of benzene by el;l--ln~ing the precursors. The tlapping of precursor radicals also slows in-luc~ d~...position of the BPO, which results in a formulation with superior stability over 25 time.

~ ere-,ed free-radical scavengers include but are not limited to cil~n~ ale esters, fumarate esters, maleate esters, natural fatty acids, oligomeric phosphonates, phenol derivatives, Z ~ ~ 8 8 ~ 4 thiobi~phen~!ics~ phosphites~ polythiodipropiorlates, thioesters, propionate esters, qUinon~s~
vitamin compounds, l,i&z,net~ione derivatives, and the like. Specific e,.a ~'es of free-radical scavengers which are employable in the context ofthe present invention include but are not limited to:
1,2-bis(3,5-di-t-butyl-4-hydroxyhydrocinn~rnoyl)hydrazine (eg, Irganox~) MD1024,Ir~,an~A is a registered tradernark of Ciba-Geigy Inc.), octa~ecyl 3,5~i-t-butyl-4-hydro~l.ydloc~ n-~te (eg. Irganox~3) 1076), tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydroc: ~na~.ale)] ~~.e~ -e (eg. I.g~o.,~3 1010), dibutyl furnarate, dioctyl filmarate, dibutyl m~le~te, dibutyl and dioctyl m~leate, linoleic acid and oleic acid, styrene phosphonic acid c?lrium bis[monoethyl(3,5-di-t-butyl-4-hydroxybenzyl) phosphonate] (eg. Irganox(E~
1425), benzoic acid, n-nonyl phenol ("NNP"), 2,6-di-t-butyl-4-methylphenol ("BHT"), trisnonylphenylphosphite ("TNPP"), t-butyl catechol ~"TBC"), triethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-ethylphenyl) propionate] (eg., Irganox~
245), pyrrolidones, vitamin A (all-trans-retinol), vitamin C (ascorbic acid), vitamin E (2,5,7,8-tetramethyl-2-(4',8',12'-trimethyltridecyl)-6-chrc,~,anol, DL~-tocophelol], 1,3,5-tris(3,5-di-t-butyl4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (eg., Irganoxt~) 3114), hydroquinone ('~HQ"), Z ~ ~ ~ 8 ~ 4 toluhydroquinone ("THQ"), p-ben~quinone ("pBQ"), mono-t-butylhydroquinone ("MTBHQ") 2,5~i-t-butylhydro~u;none ("DTBHQ"), hydroquinone mono,l-~L~l ether ("HQMME"), and the like.

The most p.ef~"ed free-radica~ scavengers are BHT, Vitamin E, Irganox~1010, Irg~l~JA~1425 and NNP. BHT is especially prefel,ed.

In order to realize the objectives of the present invention, at least one free-radical scavenger is added to the BPO formulation in an arnount effective to u cr~ase the stability of said formulation. Obviously, the amount of free-radical scavenger required is a function of the type of scavenger to be employed and the amount of BPO in the formulation. Most BPO form~ tion~
generally contain from about 3~/O to about 85% by weight BPO, more typically, from about 25%
to about 60% BPO. Regardless ofthe BPO conce.l~ ion, it is well within the abilities of one of ordina,y skill in the art to determine, without undue experiment~tion, the amount of free-radical scavenger required to decrease the decomposition rate of the BPO, thereby increasing the stability of said formulation and reducing the rate and amount of free benzene formation.

An effective amount of free-radical scavenger is, in most cases, in the range of between about 0.001% by weight to about 10% by weight based on the diacyl peroxide formulation. More ple~,ably, an effective amount of the free-radical scavengers is in the range of 0.01 - 5%. In a most pr~fe.,ed embodiment the free-radical scavenger con~ ises from about 0.1-3% by weight of formulation.

In a pre~e,led embodiment, the invention contemplates a BPO formulation having asubst~nti~lly reduced rate of free benzene formation wherein said formulation comprises BPO, and at least one free-radical scavenger in an amount effective to reduce the rate of BPO
s 8 ~ ~

d~col,lposilion in said formulation. The BPO formulation can be in the form of a paste, emulsion, sUspenn;on~ gel and the l;ke. The types and ~rnounts offree-radical scavengers are the same as l.~einl~fo.e described.

In another embodiment~ the invention cont~mpl?t~s a BPO formulation having a s~ t~ y reduced rate of free ben~ e formation ~I,ere~n said form~lqtion col~l;ses 3-60 wt% BPO, and 0.001-10 wt%, p~crelably 0.1 to Swt% of at least one free-radical scavenger in an nollnt effective to reduce the rate of BPO decomposition in said forrnulation.
In a third pre~,led embo~iment~ the invention contempl~tes BPO form~ tion with reduced benzene formation which comprises:

3-60 wt% BPO
10-30 wt% water 0.5-95 wt% plasticizers 0-10 wt% surfactant 0-10 wt% rheologicial additive O S wt% pi~rnents 0.01-5 wt% scavenger An optimum formulation preferably comprises:
25-60 wt% BPO
5-50 wt% water 5.5-50 wt% plasticizers 0-10 wt% surfactant 0-10 wt% rheological additive 0-5 wt% pigm~nt~
0. 1-3wt% scavenger The invention will now be illustrated by the following nonl;..~;t;i~ examples.

Example I - Paste Prepalation A kneader w. s cl~ar~ed with BPO (BPO 75% in water) isodecyl be~71)at~" water, and zinc ~te~dte. After 10 minlJte~ of mixing, polyrneric thickener, Carbopol~ 690 (Ca,bopol~ is a registered trademark of B.F. Goodrich Inc.) was added . nd mixed for an additior~ol 20 n.;..~es S Finally, nonionic surfactant, Tergitol~) XD, was added and the mixture w. s blended for 30 minl~tes (Tergitol~) is a registered trademark ofthe Union Carbide Co"~,alion). A smooth, uniform paste was produced.

Test Method Des~,l iplions:
Akzo Nobel Test Method 220ASSAY.l Assay dete",~ ion was conducted on 0.5 g samples for BPO paste and 1.0 g for resin anchor catalyst formulations. All samples were run in duplicate.

The sample was added to a 250ml flask, followed by the addition of 25 ml of acetone. 0. 5 ml of 10% hydrochloric acid and 3 ml of potassium iodide were then added, and the flask was swirled to mix the ingredients. The inside wall of the flask was washed down with acetone. After stan~ling one minute, the rnixture was titrated with O.IN sodium thiosulfate. Assay was dete-""ned by the following calculation:
% peroxide assay = (A x N x F) . sample weight in grams wherein, A = Volume of the thiosulfate used, N = Normality of the thiosulfate F= 12.11 forBPO

Akzo Nobel Internal Method Of Analysis AR/88. I HPLC
Ren7ene dete--,-il alion was conducte~ on prepared pre-weighed 0.5 g s~mrl~s sealed in 20 ml he~dspace vials. All samples were run in duplicate.

~ 2 ~

5 m~ of hexane was added by syringe through the septa. The sample was ~t~te~ andallowed to stand for 10-15 minutes Another S ml of hexane was then added. An empty syringe was used to allow the air to escape from the vial. The sample was ultrasonicated for appro~--dtely S minutes to extract the b~n7~ ne, with aliquots of appro~in~lely 3 ml wi~ l aw 5 for analysis.

In the reverse phase liquid ch~o--lolography analysis, the following conditions/procedures were used:

10 ~ 20 ul injection with WISP A/S
~ 15 cm x 4 mm ODS column ~ Wat205nm ~ Time 0 minute~ I mVmin 70/30 acetonitrile/water with 0.05m acetic acid ~ 4 minute gradient over 2 min~ltes to 100% acetontrile at 2 ml/min, held for 5 min.~tes, then 15 reversed to original conditions over 2 min~ltes and held for a total run time of 20 min~ltes ~ The ,l,;n;".al detection limit for the instrument was 0.5 ppm benzene. Due to dilution and interfering peaks present in the sample chlo"latograms, the minim~l q~l~ntifi~le amount was 20 ppm.

Employing the following test methods, a 55% BPO paste was plep~d in accordance with the present invention and tested for pe~-.nance of benzene reducing additives.
Pel~olnlance was measured against a neat paste prepared in the same manner, except that no free radical scavenger was added.

Samples were stored for two weeks at 50~C to accelerate BPO decomposition. This is inten~led to simUl~te typical ~ee benzene forrnation at ambient temperatures over the useful life of the paste product. Both free benzene and assay loss were monitored. A neat paste sample "~ ined at 20~C served as the control for all subsequent comparisons. The bel~el-c level of 2 ~ ~ ~ 8 ~ ~

this control ,~ ed fairly eol ~AI~1 during testing in the range of 400ppm. The data is Sl~ na.iZOd in Table 1, below:

Table 1 - P~l~ nce of Benzene P~ed~cing Additives in 55% BPO Paste Benzene content (ppm) Assay (%BPO) Increase % change % change Ne~ paste 2653 663% -3.1%
Dibutyl fi~T~ate 1442 361% -12.6%
Dicc~yl film~rate 1317 329% -1.1%

Styrene phosphonic acid 1351 338% 0.5%
Linoleic acid 2312 578% -6.8%
Benzoic acid 1013 253% -5.1%
kganox 245 1734 434% -3.5%
~ganox 1010 332 83% 0.0%

~ganox ~DD 1024 375 94% -0.9%
~ganox 1076 1924 481% 2.2%
~ganox 1425 251 63% 0.0%
~nox 3114 650 163% -2.6%
BHrr 267 67% -1.8%
~P 454 113% -3.4%

~fi~aunin E 817 204% -5.4%
Dibutyl n~eate 1835 459% -0.5%
Dio~yl m~lP~te 1223 306% -2.5%
Oleic acid 3094 774% -4.5%

Benzene % change was c~lc -l~ted by the following formula:
[(ending benzene content - starting benzene content) . starting benzene content] x 100 5 Assay % change for the BPO was c~lr,~ ted in accordance with the following formula:
[(ending BPO content - starting BPO content) . starting BPO content] x 100 The data indicate that the rate of free benzene formation in the formulations cont~initlg the free-radical scavengers in accordance with the present invention is, in most situations, 10 dramatically lower than in the formulations co.~ no scavenger. Furthermore, the stability of the formulations of the present invention, as demonstrated by the % assay loss of BPO was markedly improved over compositions which lacked free-radical scavengers in accordance with the present invention.

For example, over the two week period at 50~C, the neat paste increased in benzene content by 2653 ppm. This is equivalent to a 663% increase over the room temperature control paste, and is indicative of the degree of benzene formation expected over the paste's useful lifetime. The assay of the neat paste decreased by I . 8% over the same two week period.

The paste sample cont~ininE the free radical scavenger BHT increased in benzene content by only 267 ppm, which is equivalent to a 67% increase over the room temperature control paste.
In addition, the assay of the BHT-co.~t ~ i l-g paste decreased by only 3.1%. Similar results were observed for other pastes cont~ining free radical scavenger in accordance with the present invention.
Resin Anchor System To demonstrate the effect of the addition of free-radical scavenger on cure behavior, a resin anchor system was tested with the additives listed in Table 2. The formulation consisted of ~ ~ 8 ~ 9 an unsaturated polyester resin/ralcrlm carbonate ~A" comronent and a BPO/calcium czlbon~e ~B~ co.npol c.,l to which 0.1% of additive was added.

A Haake Rheocord 90 rheometer with delta blades at 60 rpm was used for cure 5 dele~ n~l;o~ The "A" componenl was added to the mixing bowl at ambient teln~.al lre cond;~;ons After 30 seconds, the 'IB" col-lpontllt was injected into the bowl with a syringe, and cure response was oblaincd by measuring torque as a function of time. The data is tabulated in Tables 2 and 3, below.

10 Table 2 - Pc.rolll,ance of Benzene Re~çin~. Additives in Resin Anchor "B" Colllpon~

Additive Assay loss, % BPO change Benzene level, ppm a~er x weeks ~ 50~C a~er x weeks (~1 50~C

None -23 -30 15 181 230 Table 3 - Cure Perfolll.dnce of Benzene Redllcing Additives in Resin Anchor System AdditiveTime to maximum torque, sec Maximum torque, m-g None 48 3325 ~ 2 ~8 ~ ~ ~

The data in Table 2 clearly indicate a reduction of benzene formation and an improvernent in stability ofthe BPO formul~tiQn without any app~ 'e loss in pe~ ,l&nc~. The systern in Table 3 Co~ JIiSil~ BHT was similar in cure res~eG to the control h&r~eller which cQ.~ d no additive. NNP did, however, adversely effect cure r~spoll.Q~, although b~n~ ~e rçduction was 5 favorable. Thus, it is clear that end use applic~tionQ- are an important conQidçration in dete."~"~.ng the type and amount of additive to be employed.

Claims (26)

1. A method for reducing the rate and amount of hazardous by-product formation in diacyl peroxide formulations which generate hazardous by-products upon decomposition which comprises adding to said formulations at least one free-radical scavenger in an amount effective to reduce the rate of diacyl peroxide decomposition in said formulation.

2. The method of claim 1 wherein said diacyl peroxide is of the general formula:

wherein each R group may be the same or different and is selected from a substituted or unsubstituted aryl and aralkyl, alkyl or alkaryl group which generates hazardous by-products upon decomposition.

3. The method of claim 1 wherein said diacyl peroxide is dibenzoyl peroxide, or an ortho-, para-methyl or 2,4-dichloro derivative of dibenzoyl peroxide.

4. The method of claim 1 wherein said diacyl peroxide is dibenzoyl peroxide.

5. The method of claim 1 wherein said free-radical scavenger is selected from the group consisting of cinnamate esters, maleate esters, phenolic derivatives, triazinetrone derivatives, propionic esters, fumerate esters, oligomeric phosphonates, thiobisphenolics, phosphites, polythiodipropionates, thioesters, natural fatty acids, quinones, vitamin compounds and mixtures thereof.

6. The method of claim 5 wherein said free-radical scavenger is selected from the group consisting of 1,2-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamoyl)hydrazine, octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate, tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]
methane, dibutyl fumerate, dioctyl fumarate, dibutyl maleate dioctyl maleate, linoleic acid, oleic acid, styrene phosphonic acid, calcium bis[monoethyl(3,5-di-t-butyl-4-hydroxybenzyl) phosphonate], benzoic acid, n-nonyl phenol, 2,6-di-t-butyl4-methylphenol, triethylene glycol bis[3,3-t-butyl-4-hydroxy-5-ethylphenyl)propionate], trisnonylphenylphosphite, t-butyl catechol, pyrrolidones, hydroquinone, toluhydroquinone, p-benzoquinone, mono-t-butylhydroquinone, 2,5-di-t-butylhydroquinone, hydroquinone monomethyl ether, Vitamin A, Vitamin C, Vitamin E, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and mixtures thereof.

7. The method of claim 1 wherein said effective amount of free-radical scavengers is in the range of from about 0.001% - about 10% by weight based on the total weight of the diacyl peroxide formulation.

8. The method of claim 7 wherein said effective amount of free-radical scavenger is in the range of from about 0.01 -5% by weight based on the total weight of the diacyl peroxide formulation.

9. The method of claim 8 wherein said effective amount of free-radical scavenger is in the range of from about 0.1 -3% by weight based on the total weight of the diacyl peroxide formulation

10. The method of claim 1 wherein said diacyl peroxide formulation is a paste, emulsion, suspension or gel.

11. A diacyl peroxide formulation with improved stability and reduced hazardous by-product formation which comprises at least one diacyl peroxide which generates hazardous by-products upon decomposition, and at least one free-radical scavenger in an amount effective to reduce the rate of diacyl peroxide decomposition in said formulation.

12. The formulation of Claim 11 wherein said diacyl peroxide is of the general formula:

wherein each R group may be the same or different and is selected from a substituted or unsubstituted aryl and aralkyl, alkyl or alkaryl group which generates free benzene upon decomposition.

13. The formulation of claim 12 wherein said diacyl peroxide is dibenzoyl peroxide or an ortho-, para-methyl or 2,4-dichloro derivative of dibenzoyl peroxide.

14. The formulation of claim 13 wherein said diacyl peroxide is dibenzoyl peroxide.

15. The diacyl peroxide formulation of claim 11 wherein said formulation is a paste, emulsion, suspension or gel.

16. The formulation of claim 11 which additionally comprises water and plasticizer.

17. The formulation of claim 16 which additionally comprises an emulsifier, rheological additive and optionally, pigment.

18. The formulation of claim 11 wherein said free-radical scavenger is selected from the group consisting of cinnamate esters, maleate esters, phenolic derivatives, triazinetrone derivatives, propionic esters, fumerate esters, thiobisphenolics, phosphites, polythiodipropionates, thioesters, oligomeric phosphonates, natural fatty acids, quinones, Vitamin compounds and mixtures thereof.

19. The formulation of claim 18 wherein said free-radical scavenger is selected from the group consisting of 1,2-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamoyl)hydrazine, octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate, tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]
methane, dibutyl fumerate, dioctyl fumarate, dibutyl maleate, dioctyl maleate, linoleic acid, oleic acid, styrene phosphonis acid, calcium bis[monoethyl(3,5-di-t-butyl-4-hydroxybenzyl) phosphonate], benzoic acid, n-nonyl phenol, 2,6-di-t-butyl-4-methylphenol, triethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-ethylphenyl)propionate], trisnonylphenylphosphite, t-butyl catechol, pyrrolidones, hydroquinone, toluhydroquinone, p-benzoquinone, mono-t-butylhydroquinone, 2,5-di-t-butylhydroquinone, hydroquinone monomethyl ether, Vitamin A, Vitamin C, Vitamin E, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and mixtures thereof.

20. The formulation of claim 11 wherein an effective amount of free-radical scavenger is in the range of from about 0.001% - about 10% by weight based on the total weight of the diacyl peroxide formulation.

21. The formulation of claim 20 wherein said effective amount of free-radical scavenger is in the range of from about 0.01 - 5% by weight based on the total weight of the benzoyl peroxide formulation.

22. The formulation of claim 20 wherein said effective amount of free-radical scavenger is in the range of from about 0.1 - 3% by weight based on the total weight of the benzoyl peroxide formulation

23. A dibenzoyl peroxide formulation having reduced free benzene formation which comprises benzoyl peroxide and at least one free-radical scavenger in an amount to reduce the rate of benzoyl peroxide decomposition.

24. The formulation of Claim 23 which comprises 3-60 wt% of dibezoyl peroxide and 0.001 to 10 wt% free radical scavenger.

25. The formulation of Claim 23 wherein said free-radical scavenger is selected from the group consisting of BHT, IrganoxR1010, IrganoxR1425, Vitamin E, NNP and mixtures thereof.

26. The formulation of Claim 23 which comprises 25 - 55% dibenzoyl peroxide and 0.1 - 3%
by weight of a free-radical scavenger selected from the group consisting of BHT, IrganoxR1010, IrganoxR1425, Vitamin E, NNP and mixtures thereof.