IE42438B1

IE42438B1 - Stabilized curable compositions

Info

Publication number: IE42438B1
Application number: IE153075A
Authority: IE
Original assignee: Loctite Ltd
Priority date: 1975-07-09
Filing date: 1975-07-09
Publication date: 1980-08-13
Also published as: JPS6131122B2; AU512819B2; GB1547481A; FR2362188B1; FR2362188A1; IE42438L; AU1562176A; DE2631007A1; JPS5210393A; CA1077190A

Abstract

Stabilized, curable compositions formed from known free radical-polymerizable monomers (e.g., acrylates, styrene, etc.), and free radical initiators (e.g., peroxides, hydroperoxides, ultraviolet-sensitive compounds) by dissolving therein compounds containing the combination of allyl lower alkoxyl and hydroxyl groups. All the groups may be present in one molecule, or the allyl group may occur in a separate molecule. Concentration of each compound may be in the range of about 0.01 to about 5 percent by weight of the total composition.

Description

This invention relates to curable compositions and, in general, curing compositions of the type wherein cure is initiated by means of peroxy compounds such as peroxides or hydroperoxides or by means of ultraviolet irradiation, and takes place by virtue of free radical polymerisation. Such compounds typically contain vinyl unsaturation.

It is desirable that compositions of the kind indicated shall be stable in storage for extended periods. Many of these compositions are anaerobic, i.e. undergo cure when deprived of access to oxygen, but can be caused to cure by other means. It is desirable that such anaerobic compositions be preserved from curing when stored in an oxygen-poor environment, in order to undergo cure later, when required, by the use of said other means.

Certain types of compounds are well known as inhibitors of premature polymerisation for such compounds. Typically, these inhibitors are quinone- or hydroquinone-type compounds and their derivatives. Free radical scavengers of various types have also been used with some success.

None of these known inhibitors has proven fully satisfactory for all uses, however, especially in connection with acrylate and urethane-acrylate monomers such as those specifically described herein. Inhibitor systems capable of imparting significantly improved stabiiity to free radical curing compositions would thus have great utility.

The present invention relates to inhibitors which provide advantageous and unexpected improvement in stability. Accordingly, the present invention provides a stabilised, curable composition comprising: a) a free radical-polymerisable monomer; b) a peroxy or photo-sensitive initiator; and c) an inhibitor which contains alkoxyphenol and allyl groups, which allyl groups may be present as substituents on the alkoxyphenol groups, or as an allyl compound in admixture with an alkoxyphenol compound, the inhibitor system being dissolved in the monomer.

The initiator and the inhibitor should each be present in the composition in an effective amount, i.e. there should be a sufficient amount of initiator present in the composition to effect polymerization of the monomer when standard polymerization techniques are used; and there should be enough inhibitor present to prevent premature polymerization or gellation of the composition prior to using these polymerization techniques.

Preferred monomers are those prepared by reacting at a temperature from 10°C to 175°C: (i) an organic polyisocyanate, and (ii) an acrylate ester containing a hydroxy or amino group in the non-acrylate portion thereof, the ester being used in sufficient amount to react with substantially all of the isocyanate groups of the polyisocyanate.

Other preferred monomers formula are those having the wherein R3 represents a hydrogen atom, an alkyl group of 5 1-4 carbons, a hydroxyalkyl group of 1-4 carbon atoms, or a group of the formula II —-CH2-0 — C—· C=CH2 ; H1 R1 is a hydrogen or a halogen atom or an alkyl group 2 of 1-4 carbon atoms; R is a hydrogen atom, a hydroxy 10 group or a group of the formula m is an integer equal to at least 1; n is an integer equal to at least 1; and p is 0 or 1. - 5 The invention also provides a method of stabilising a curable composition comprising a free radicalpolymerisable monomer and an effective amount (as hereinbefore defined), for initiation of a peroxy or photosensitive initiator, comprising dissolving in the monomer an effective amount (as hereinbefore defined), for stabilisation of the composition of an inhibitor which is an allyl alkoxy phenol or the combination of an allyl compound with an alkoxy phenol.

Photo-initiated compositions are especially benefited since, by using increased levels of the inhibitor systems, improved stability is obtained without sacrifice of desirable cure properties.

With curable compositions which are inherently anaerobic in nature, the present inhibitor systems can effectively suppress the anaerobic cure characteristics, thereby allowing these desirable monomer compositions to be used in oxygen-starved applications, such as the adhesive layer on tightly-wound tapes or in oxygenimpermeable containers such as aerosol cans.

When a single compound is used as the inhibitor, preferred compounds are of the formula where R is an alkyl group having 1 to 4 carbon atoms, preferably methyl. A particularly preferred compound has the formula δ s 4 a ο ,OCH CH2=CH-CH2OH When, on the other hand, a pair of compounds is used, one member of the pair is a phenol substituted by an alkoxy group; the other member of the pair contains the allyl group CH2=CH-CH2 in the molecule.

A preferred combination is a mixture of an allyl compound containing an inorganic group, more preferably, a triallyl phosphate, or of diallyl phthalate, with a compound of the formula HO 0-R where R is an alkyl group having 1 to 4 carbon atoms, preferably methyl, more preferably hydroquinone monomethyl ether of the formula HOOCH. - 7 It Is believed that In those oases where a pair of added compounds Is present, the members of tho pair have a mutual synergistic effect. More generally defined, the alkoxy group may be an alkoxyl of one to four carbon atoms. It will be understood that the group may also be substituted, provided only that the substituent does not interfere substantially with the effectiveness of the over-all compound.

While in the preferred compounds the alkoxy group is in the ortho position relative to the hydroxyl group, it may optionally also occur in the meta or para position. Similarly, when all three required groups occur in the same molecule, the allyl group need not necessarily be in the para position relative to the hydroxyl group, although that position is preferred. In either case, the aromatic group may be further substituted, provided only that the substituent does not interfere substantially with the effectiveness of the inhibitor system.

When a separate allyl compound is used, it may be either completely organic or it may contain an inorganic group, the latter being preferred. However, reducing-type compounds, such as allyl phosphites and sulphites, should preferably be avoided.

Representative useful compounds include, in addition to those already mentioned, triallyl orthoformate, triallyl phosphate, 2-allyl phenol, 2-allyl-6methyl phenol, and 2-allyl-4-methyl phenol.

It is necessary that the inhibitor system be soluble in the monomeric composition in the concentrations used. When the inhibitor system comprises a single compound, its concentration should preferably be in the range of 0.01 percent to 5 percent by weight of the total curable composition. Preferably, its concentration will be 0.02 percent to 2 percent, and more preferably 0.025 to 0.5 percent by weight of the total curable composition. 038 - 8 When the inhibitor comprises two compounds, the concentration of each of them may be in the range of 0.01 percent to 5 percent by weight of the total curable composition. Preferably, the concentration of the allyl compound is in the range of 0.1 percent to 4 percent, and more preferably 1 to 2 percent. Preferably, the concentration of the alkoxy phenol is 0.1 to 3 percent, and more preferably 0.2 to 0.4 percent by weight of the total curable composition. The ratio of the allyl compound to the alkoxy phenol compound may vary over a rather wide range, typically from 0.1:1 to 10:1, respectively, preferably 1:1 to 5:1, respectively. For those curable compositions which are anaerobic in nature, it has been observed that the anaerobic cure characteristics become progressively more inhibited the closer the ratio comes to 1:1.

Because of the large number of curable monomeric compounds which may be stabilised by the present invention, it is not practical to specify concentration ranges for the stabilisers and ratios of compounds in more than general terms. Ip any given case, appropriate concentrations and/or ratios may be readily determined by simple experimentation.

As has been stated, the threshold requirement is that the inhibitor system be soluble in the monomeric composition. This, of course, may be easily ascertained. Effectiveness as a stabiliser against premature polymerisation may be easily determined by storing a small quantity of curable composition containing the inhibitor system at room temperature, or at an elevated temperature if an accelerated test is desired, and observing the length of time elapsed before the composition begins to gel, i.e., cure or polymerise. While the selection of test temperature is basically a matter of convenience, it has been found that 82°C is a particularly useful temperature for acrylate and methacrylate adhesive/sealant 43438 - 9 compositions formulated with hydroperoxy initiators.

In such systems, a no-gel period of one hour or more at 82°C indicates a probable shelf-life of one year or more at room temperature. Other temperatures at which thermal stability is customarily measured include 65°C, 55°C and 37°C.

As haq been mentioned, the present inhibitor systems are effective in stabilising a wide variety of monomeric, curable compositions. Thus, a useful stabilising effect will be observed with curable compositions based upon vinyl monomers such as styrene, butadiene and vinyl chloride, vinylidene chloride, acrylate/methacrylate-type monomers such as methylmethacrylate, ethyleneglycol diacrylate, bisphenol-Λ dimethacrylate and hydroxypropyl methacrylate, such as those taught in United States Patent No. 2,895,950. Included among the latter types are the urethane-acrylates/ methacrylates, such as those taught in United States Patent No. 3,425,988, those disclosed in Patent Specification No. 39134, as well as those taught in British Patent Specification Nos. 1,531,351 and 1,545,061 and U.S. Patent No. 4,018,851.

Monomers of the preceding types are curable by free radical polymerisation using any of numerous wellknown initiators as a source of free radicals. Among such initiators there may be mentioned peroxides such as hydrogen peroxide and organic peroxides such as benzoyl peroxide and methyIethyl ketone peroxide; azo-compounds such as 2,2'-azobis(isobutyronitrile); organic hydroperoxides such as cumene hydroperoxide, t-butyl hydroperoxide and methyIethyl ketone hydroperoxide; peresters which hydrolyse to peroxy compounds, such as t-butyl perbenzoate and t-butyl peracetate, and photo-sensitive compounds such as benzophenone and the benzoin ethers.

As will be appreciated, the concentration of such initiators in any given curable system will be a matter -ίο-. of choice and well within the skill of the art to determine. As a general rule, the initiator concentration will be in the range from 0.1 percent to 10 percent by weight of the total curable composition. As to the photo5 sensitive (i.e., ultraviolet-sensitive) types of initiator systems, it is a particular advantage of the present inhibitors that they may optionally be used in substantially increased concentration without significantly Interfering with the UV-initiated cure properties.

Thus, the inhibitor system concentration may be increased by 4 to 5-fold, or more, over the lowest commercially useful level, thereby obtaining an outstandingly stable composition but yet without destroying its cure speed. In selecting photo-initiators, a degree of care Should be exercised to avoid creating an interactive initiatorcombination which could impair the effectiveness of either. Thus, for example, the combination of ben2oin ethers with the monoethyl ether of hydroquinone should preferably be avoided since these have been found to interact.

The curable stabilised compositions of this invention may be modified by inclusion of any Of numerous known additives such as polymerisation accelerators (e.g., amides, imides and amines), diluents, viscosity regulators and plasticisers, dyes provided only that such additives do not significantly interfere with the effectiveness of the present inhibitor systems.

The following examples illustrate the present invention.

Example 1 This example shows how the thermal stability of a styrene-based composition of the prior art (1) compares with that of two similar compositions (2), (3) according to the invention.

I - 11 42438 (1) Styrene Benzoyl peroxide (2) Styrene Benzoyl peroxide Triallyl phosphate Hydroquinone monomethyl ether (3) Styrene Benzoyl peroxide Triallyl phosphate Hydroquinone monomethyl ether Thermal stability Parts by (hours) Weight 95.0 55°C 65°C 5.0 93.8 5.0 19 6 1.0 0.2 92.6 5.0 76 19 2.0 0.4 140 27 Composition (1) would normally also contain a conventional hydroquinone-type polymerisation inhibitor which can be omitted from (2) and (3). All three compositions were readily polymerisable by techniques standard in styrene technology.

Example 2.

This example shows how the thermal stability of a polyethyleneglycol dimethacrylate-based composition of the prior art (4) compares with that of a similar composition (5) according to the invention. 4243 (4) (5) Polyethylene glycol dimethacrylate 95.2 94.0 parts by weight Saccharin 0.4 0.4 parts by weight Cumene Hydroperoxide 4.0 4.0 parts by weight N,N-dimethyl-p-toluidine 0.4 0.4 parts by weight Hydroquinone monomethyl ether (M.E.H.Q.) Nil 0.2 parts by weight Triallyl phosphate Nil 1.0 parts by weight Thermal stability at 82°C. (minutes) 30 72 These compositions are inherently anaerobic in nature, i.e., rapid cure is achieved only in the absence of oxygen. In order to test their anaerobic cure characteristics, a few drops of each composition were applied to the threads of mating black oxide nuts and bolts, the nuts and bolts were assembled (thereby excluding oxygen), and cure was allowed to proceed. Both compositions developed satisfactory cured properties; however, it was found that the cure speed of composition (5), while commercially usable, was slower than that of composition (4) of the prior art. (Appropriate tests for anaerobic cure properties are well described in the literature, e.g., United States Patents 2,895,950 and 3,043,820).

Example 3 This example shows how the thermal stability of a trimethylol propane trimethacrylate-based composition of the prior art (6) compares with that of a similar composition (7) according to the invention. - 13 42138 (6) (7) Trimethylol propane trimethacrylate 95.0 93.8 parts by weight Benzoyl peroxide 5.0 5.0 parts by weight 5 Triallyl phosphate Nil 1.0 parts by weight M.E.H.Q. Nil 0.2 parts by weight Thermal Stability i at 55°C <8 hours >24 hours 65°C <1 hour >4 hours 10 82°C 50 minutes >100 minutes It was found that compositions (2), (3), (5) and (7) could be packed safely in high density polyethylene containers almost completely full, whereas the prior art compositions (1), (4) and (6) had to be packed in partly filled low density polyethylene containers if premature polymerisation due to oxygen exclusion were to be avoided.

Example 4 This example relates to a typical ultraviolet light initiable curing composition of the prior art (8) and a similar composition according to the invention (9). In both, a representative monomer A (in the conventional sense which includes oligomers) is used having the formula cii2=c(ch3)coo(ch2) 3oconh C(CH3)2 43438 This monomer A may be Obtained by reacting 1 mole (120 g) of hydrogenated Bis- phenoltA (i.e., 4,4'-dicyclohexanolyl dimethyl methane) with two moles (174 g) of toluene 2,4-diisocyanate, and reacting the product with 2 moles (144 g) of 3-hydroxypropyl methacrylate.

Monomer A Benzophenone Acrylic Acid Triallyl phosphate M.E.H.Q. (8) 93.0 .0 2.0 Nil Nil (9) 91.0 parts by weight .0 parts by weight 2.0 parts by Weight 1.0 parts by weight 1.0 parts by weight Composition (8) polymerises either on deprivation of oxygen or on irradiation by ultra-violet light of suitable intensity, whereas composition (9) polymerises only on irradiation, the anaerobic polymerisation tendency having been substantially suppressed.

Thus the new composition (9) can be applied to tapes which are afterwards coiled into rolls for use. This would not be possible for composition (8) unless expensive extra precautions were taken.

Claims

1. A stabilised, curable composition comprising: a) a free radical-polymerisable monomer? b) a peroxy or photo-sensitive initiator; and 5 c) an inhibitor which contains alkoxyphenol and allyl groups, which allyl groups may be present as substituents on the alkoxyphenol groups or as an allyl compound in admixture with an alkoxyphenol compound, the inhibitor system 10 being dissolved in the monomer.

2. A composition as claimed in Claim 1 wherein the monomer is a vinyl compound.

3. A composition as claimed in Claim 1 wherein the monomer is an acrylate ester. 15

4. A composition as claimed in Claim 1 wherein the monomer is a methacrylate ester.

5. A composition as claimed in Claim 3 or 4 wherein the monomer has the formula - 16 3 wherein R represents a hydrogen atom, an alkyl group of 1-4 carbon atoms, a hydroxyalkyl group of 1-4 carbon atoms, or a group of the formula -CH 2 — 0—C— C=CH 2 ; 5 R 3 is a hydrogen or a halogen atom or an alkyl group of 1-4 carbon atoms; R is a hydrogen atom, a hydroxy group or a group of the formula O m is an integer equal to at least 1, n is an integer 10 equal to at least 1; and p is 0 or 1.

6. A composition as claimed in Claim 1 wherein the monomer is a urethane acrylate adduct.

7. A composition as claimed in Claim 6 wherein 15 the monomer is an adduct of bisphenol-A or hydrogenated bisphenol-A and an aromatic polyisocyanate, the adduct being capped with a hydroxyalkyl methacrylate.

8. A composition as claimed in Claim 6 or 7 wherein the monomer is a polymerisable monomer prepared 20 by reacting at a temperature from 10°C to 175°Cs (i) an organic polyisocyanate; and (ii) an acrylate ester containing a hydroxy or amino group in the non acrylate portion thereof, the ester being used in sufficient amount to react with substantially all of the isocyanate 25 groups of the polyisocyanate.

9. A composition as claimed in any of Claims 1 to 8 wherein the initiator is an organic peroxide.

10. A composition as claimed in any of Claims 1 to 8 wherein the initiator is an organic hydroperoxide

11. A composition as claimed in any of Claims 1 to 8 wherein the initiator is a perester.

12. A composition as claimed in any of Claims 1 to 11 wherein the inhibitor is a mixture of an allyl compound containing at least one inorganic group and a compound of the formula where R is an alkyl group having 1 to 4 carbon atoms.

13. A composition as claimed in Claim 12 wherein R is methyl.

14. A combination as claimed in Claim 13 wherein the inhibitor is a mixture of hydroquinone monomethyl ether and triallyl phosphate.

15. A composition as claimed in any of Claims 1 to 11 wherein the inhibitor is a compound having the formula 0-R OH - 18 wherein R is an alkyl group having 1 to 4 carbon atoms.

16. A composition as claimed in Claim 15 wherein R is methyl.

17. A composition as claimed in Claim 16 wherein 5 the inhibitor is 4-allyl-2-methoxy-phenol.

18. A stabilised curable composition according to Claim 1 substantially as herein described with reference to any of the Examples.

19. A method of stabilising a curable composition 10 comprising a free radical-polymerisable monomer and an effective amount for initiation of a peroxy or photosensitive initiator, which method comprises dissolving in the monomer an effective amount for stabilisation of the composition of an inhibitor system selected from the group 15 consisting of an allyl alkoxyl hydroquinone, and the combination of an allyl compound with an alkoxyl hydroquinone.

20. A method as claimed in Claim 19 wherein the monomer is as defined in any of Claims 2 to 8.

21. A method as claimed in Claim 19 .or 20 wherein 20 the initiator is as defined in any of Claims 9 to 11.

22. A method as claimed in any of Claims 19 to 21 wherein the inhibitor is as defined in any of Claims 12 to