Reactive esters of 2-cyanopenta-2,4-dienoic acid and the adhesives and polymers thereof

The present invention provides pure, storage stable, reactive esters of 2-cyanopenta-2,4-dienoic acid and the adhesives and polymers thereof. The monomers of the present invention have the formula: ##STR1## where R is alkyl, alkenyl, alkynyl, alkoxyalkyl, alkenyloxyalkyl, alkynyloxyalkyl, poly(oxyalkyl), aryl, cycloalkyl or a heterocyclyc radical. R may also be one of the foregoing moieties substituted with one or more of the other moieties; this includes the case of the substituent itself being substituted, and may also contain halogens. The reactive monomers of the present invention can be formulated into adhesives by incorporating certain modifiers and additives such as polymeric thickeners, viscocity regulators, plasticizers, thixotrophic agents, compatibilizers, adhesion promoters, pigments and colorants, fillers, deodorants and perfumes. They can also be used in composition with other monomers containing a reactive double bond such as for example cyanoacrylates.

This invention relates to reactive esters of 2-cyanopenta-2,4-dienoic acid
 and the adhesives and polymers thereof.
 Esters of the 2-cyanopenta-2,4-dienoic acid have been reported in the
 patent literature. The ethyl (U.S. Pat. No. 3,316,227), alkenyl and
 alkoxyalkyl (U.S. Pat. No. 3,554,990) esters have been particularly
 described. These monomers can polymerise under the influence of weak
 alkali and are suitable for adhesives. Their use as modifiers to
 cyanoacrylate adhesives (U.S. Pat. No. 4,425,471) and for the manufacture
 of photoresists (EP 0404 446 A2) has also been reported. All of the
 cyanopentadienoates reported in the literature were obtained and used in
 non-purified form, which renders them unstable for storage and does not
 reveal fully their inherent adhesive properties.
 The present invention provides pure, storage stable, reactive esters of
 2-cyanopenta-2,4-dienoic acid and the adhesives and polymers thereof. The
 monomers of the present invention have the formula:
 ##STR2##
 where R is alkyl, alkenyl, alkynyl, alkoxyalkyl, alkenyloxyalkyl,
 alkynyloxyalkyl, poly(oxyalkyl), acryl, cycloalkyl or a heterocyclyc
 radical. R may also be one of the foregoing moieties substituted with one
 or more of the other moieties; this includes the case of a substituent
 itself being substituted. R may also contain halogens.
 Specific examples of R are methyl, ethyl, allyl, methoxyethyl, ethoxyethyl.
 The reactive monomers of this invention are obtained by reacting acrolein
 with
EQU CHCH.sub.2 COOR
 where R is the same radical as described above. The reaction of acrolein
 with cyanoacetates is chemically consistent in nature to the reaction of
 acrolein with active methylene compound as described in U.S. Pat. No.
 3,316,227. All of the considerations derived in this reference hold true
 for the present reaction between acrolein and cyanoacetates.
 A distinctive feature of the reactive monomers of the present invention is
 that they are purified by one or more consecutive distillations under
 vacuum.
 A distinctive feature of the reactive monomers of the present invention is
 that they posses improved shelf-life in monomeric form compared to
 non-purified monomers.
 A distinctive feature of the reactive monomers of the present invention is
 that they have quicker setting time when used as adhesives, compared to
 non-purified monomers.
 A distinctive feature of the reactive monomers of the present invention is
 that they can polymerise to high molecular weight polymers via anionic,
 cationic or radical mechanism (FIG. 1) as well as via a combination of any
 of them.
 A distinctive feature of the reactive monomers of the present invention is
 their universal adhesion towards metals, plastics, rubbers, glass, wood,
 paper, live soft or bone tissue. Adhesive bond is formed within seconds to
 minutes at ambient temperature when the reactive monomers or their
 formulated adhesives are spread as a thin film between the substrates.
 A distinctive feature of the reactive monomers of the present invention is
 that their adhesive bonds have higher bond strength, higher temperature
 and moisture resistance, compared to non-purified monomers.
 A distinctive feature of the reactive monomers of the present invention is
 that the monomers and the adhesive bond and polymers thereof are free from
 impurities from the manufacturing process, compared to non-purified
 monomers.
 A distinctive feature of the reactive monomers of the present invention is
 that their purity makes them especially suitable for bonding soft or bone
 tissue, as well as for embolic and occluding agent, in medicine and
 surgery. An added advantage is that the resultant polymeric adhesive
 jointing layer is rubbery at body temperature.
 A distinctive feature of the reactive monomers of the present invention is
 that they are stabilised with anionic and free-radical polymerisation
 inhibitors. Anionic polymerisation inhibitors could be sulfur dioxide,
 hydrogen fluoride, phosphoric, phosphonic, sulfuric, sulphonic, carboxilic
 and organic sulfonic acids, sultones, boron trifluoride and its complexes,
 and phosphazenes for example. The free-radical polymerisation inhibitors
 are usually hydroquinone, p-methoxyphenol, t-butyl catehol, butylated
 hydroxytoluene or butylated hydroxyanisole, for example.
 The inhibitors are normally used in small amounts of from 0.00001 to 1% by
 weight of the monomer. The preferred quantities for the above mentioned
 inhibitors are: acidic gasses--from 0.0001% to 0.06%; acids--from 0.0001%
 to 0.01%; sultones--from 0.001% to 0.1%; boron trifluoride--from 0.0001%
 to 0.01%; phosphazenes--from 0.00001% to 0.001%; free-radical
 inhibitors--from 0.001% to 1%. The foregoing percentages are percentages
 by weight of the reactive monomer. It should be noted that the quantity of
 inhibitor will influence the onset of polymerisation of the monomers of
 the present invention and could be used as a means to control the setting
 time of the adhesives.
 The reactive monomers of the present invention may contain polymerisation
 initiators. They could be anionic polymerisation initiators like pyridine,
 aminopyridine, vinylpyridine, methoxyethylpyridine, piperidine, picoline,
 lutidine, N,N-dimethyl-p-toluidine, triphenylphosphine, triethylphosphine,
 tribenzylamine, triethylamine, benzyldimethylamine, diethylenetriamine,
 polyvinylpiridine, calixarenes, tertiary amine-SO.sub.3 complexes,
 polyethylene glycol, phenolformaldehyde resins, vinylimidazole,
 triethanolaminatotitanium, aminosilanes, phosphites, metal
 acetylacetonates, N-(oxydiethylene)benzothiazole-2-sulfenamide, bismuth
 dimethyldithiocarbonate, as well as alcohols, bases and hydroxyl or amine
 group containing compounds. They could be cationic polymerisation
 initiators. They could be free-radical polymerisation initiators such as
 methylethylketone peroxide, cyclohexyl peroxide, cumene hydroperoxide,
 dibenzoyl peroxide or redoxy systems for generating free-radicals.
 Compounds which generate radicals or ions under visible, ultraviolet or
 electron-beam irradiation could also be used to initiate polymerisation of
 the reactive monomers of the present invention. The various initiators
 could be used alone or in conjunction with each other.
 The reactive monomers of the present invention can be formulated into
 adhesives by incorporating certain modifiers and additives such as
 polymeric thickeners, viscosity regulators, plasticisers, thixotropic
 agents, compatibilisers, adhesion promoters, pigments and colourants,
 fillers, deodorants and perfums. They can also be used in composition with
 other monomers containing a reactive double bond, cyanoacrylates for
 example.
 Application of the reactive monomers of the present invention is in
 structural and industrial, as well as in medical and surgical adhesives,
 sealants and coatings.
 The above mentioned applications are only indicative and do not limit the
 scope of application of the reactive monomers of the present invention, as
 well as the applications of their adhesives and polymers.
 The invention is illustrated by the following examples:

EXAMPLE 1
 Catalyst is dispersed into a mixture of 0.5 g mole allyl cyanoacetate and
 solvent (see Table 1) and the temperature is reduced to 18.degree. C.
 Acrolein is then added dropwise while the mixture is cooled so that the
 reaction temperature does not exceed 20.degree. C. The molar ratio of
 acrolein to allyl cyanoacetate is 1.2:1.0. The type and quantity of
 catalyst and solvent is stated in Table 1. After the addition of acrolein
 is completed the reaction is continued at 20.degree. C. until the catalyst
 is dissolved and clear transparent solution is obtained. Extraction
 solvent (see Table 1) is added in the same amount by volume to the
 reaction mixture. Then two consecutive catalyst wash-out steps are
 performed by using 2N HCl (the volume ration of HCl solution to organic
 product solution being 1:2). When the mixture is left to settle two
 distinct layers are formed. The water layer is dropped out and the wash
 repeated. The organic layer can be further dried with inorganic or organic
 drying agents (see Table 1). In a separate step the organic layer is
 subjected to vacuum distillation with gradual increase of temperature and
 vacuum to remove the solvents and finally to distill the allyl
 2-cyanopenta-2,4-dienoate. To prevent spontaneous polymerisation of the
 product it was found that it is well stabilised with 1000 ppm of
 hydroquinone and 10 ppm of methanesulfonic acid, which are placed in the
 receiver. In the distillation pot it is also necessary to employ
 hydroquinone for prevention of radical polymerisation and a choice of
 acids, i.e. sulfuric, methanesulfonic, p-toluenesulfonic, tetraphosphoric
 etc. The allyl 2-cyanopenta-2,4-dienoate could easily be redistilled if
 the same precautions are taken. The results of 9 syntheses utilising
 various catalysts, solvents and drying agents are presented in Table 1.
 Allyl 2-cyanopenta-2,4-dienoate distills at 68.degree. C. at 0.25 mm Hg
 and has n.sub.D.sup.20 =1.5130. IR spectrum (FIG. 2) confirms the
 structure of allyl 2-cyanopenta-2,4-dienoate.
 EXAMPLE 2
 Synthetic procedures similar to those described in Example 1 but using
 methoxyethyl cyanoacetate and ethoxyethyl cyanoacetate were carried out.
 The reaction conditions and properties of the distilled methoxyethyl and
 ethoxyethyl 2-cyanopenta-2,4-dienoates are summarised in Table 2. FIG. 3
 and FIG. 4 show their IR spectra.
 EXAMPLE 3
 The purified by distillation monomers of allyl, methoxyethyl and
 ethoxyethyl 2-cyanopenta-2,4-dienoates were colourless liquids at room
 temperature with light pleasant odour. When a drop of them is placed
 between two fingers it polymerises in a matter of seconds to form an
 elastic bond. The same action and speed was displayed on various
 substrates--metals, plastics, rubbers, glass. The curing time depends on
 the level of stabilisers in the monomer. If no stabilisers are used the
 action is almost instant, however the product in a few hours polymerises
 in bulk. When bases, acids, amines, hydroxyl group containing compounds,
 water are added to stabilised, distilled cyanopentadienoate, they initiate
 polymerisation of the monomer, transforming it to a tough, resilient,
 rubber-like material.
 EXAMPLE 4
 Freshly distilled allyl 2-cyanopenta-2,4-dienoate containing 5 ppm of
 SO.sub.2 from the distillation process was used as base material. Samples
 with various content of hydroquinone and methanesulfonic acid were
 prepared, place in 5 cc.sup.3 bottles made of high density polyethylene
 and kept at room temperature. Stability was measured as the time interval
 before the onset of gelation. The results are presented in Table 3.
 EXAMPLE 5
 Adhesive bonds based on the reactive monomers of the present invention were
 prepared by placing a drop of monomer on one surface to which the other
 was manually pressed for 1 min. Adhesive strength was measured after 24
 hours and after ageing for 24 hours at various temperatures. The specimens
 had dimensions in accordance with ASTM D897, ASTM D1002 and ASTM D903 for
 tensile, shear and peel strength determinations respectively. The steel
 surfaces were roughened with extrafine sandpaper and degreased with
 methylene chloride. No chemical treatment of the surfaces was employed.
 The testing procedure followed the above mentioned standards. The obtained
 results are summarised in Table 4. Heating steel/steel joints bonded with
 allyl 2-cyanopenta-2,4-dienoate for 24 h at 200.degree. C. did not
 delaminate them and they sustained loads of 33 kg/cm.sup.2 and 20
 kg/cm.sup.2 in tensile and shear mode respectively. A value of 2.8 N/mm
 was obtained for 180.degree. peel test on steel strips bonded with allyl
 2-cyanopenta-2,4-dienoate.
 TABLE 1
 Reaction conditions of the allyl 2-cyanopenta-2,4-dienoate synthesis
 Yield of
 distilled
 allyl 2-
 Catalyst, wt Solvent, wt Drying agent,
 cyanopenta-2,4-
 % to allyl % to allyl Wash/extraction wt % to allyl dienoate (wt.
 % to
 No cyanoacetate cyanoacetate details cyanoacetate allyl
 cyanoacetate)
 1 zinc chloride, dioxane, 250 diethyl ether none 84
 64.8 solution; HCl
 2 zinc chloride, dioxane, 250 ethyl acetate none 72
 64.6 solution; HCl
 3 zinc chloride dioxane, 250 toluene solution; none 73
 64.8 HCI
 4 zinc chloride, dioxane, 250; C.sub.2 Cl.sub.3 F.sub.3 none
 60
 64.8 toluene, 50 solution; HCl
 5 zinc chloride C.sub.2 Cl.sub.3 F.sub.3, 340 none none
 36
 64.8
 6 zinc chloride, C.sub.2 Cl.sub.3 F.sub.3, 340 none
 MgSO.sub.4, 29 39
 64.8
 7 lithium dioxane, 250 HCl acetic 29
 salicylate, anhydride,
 6.5; salicylic 86
 acid, 6.5
 8 lithium dioxane, 250; HCl acetic 31
 salicylate, C.sub.2 Cl.sub.3 F.sub.3, 370 anhydride,
 6.5; salicylic 86
 acid, 6.5
 9 zinc chloride, tetrahydro- toluene; HCl none 57
 64.8 furan
 TABLE 2
 Reaction conditions and properties of methoxyethyl and
 ethoxyethyl 2-cyanopenta-2,4-dienoates
 Solvent,
 Yield of
 2-cyanopenta- Acrolein to cyano- Catalyst, % to % to
 distilled product Boiling point
 No 2,4-dienoate acetate(molar) cyanoacetate cyanoacetate
 Wash/extraction details (% to cyanoacetate) (.degree. C./mmHg)
 n.sup.20.sub.D
 1 methoxyethyl 1.2:1.0 zinc chloride, 56.6 dioxane, 217
 toluene solution extracted 50 80/0.35 1.5631
 twice
 with 2N HCl
 2 methoxyethyl 1.2:1.0 zinc chloride, 56.6 THF, 185 toluene
 solution extracted 69
 twice
 with 2N HCl
 3 ethoxyethyl 1.2:1.0 zinc chloride, 51.6 THF, 170 toluene
 solution extracted 61 80/0.3 1.4808
 twice
 with 2N HCl
 TABLE 3
 Stability of allyl 2-cyanopenta-2,4-dienoate
 Content of Content of methane Stability at room
 No hydroquinone (ppm) sulfonic acid (ppm) temperature (months)
 1 500 0 4
 2 500 5 5
 3 0 5 4
 4 1000 5 0
 5 1000 10 6
 6 0 10 4
 7 1000 0 more than 12
 TABLE 4
 Adhesive bond strength of joints bonded with alkoxyalkyl- and allyl
 2-cyanopenta-2,4-dienoates
 Adhesive bond strength
 2-cyanopenta- Mode of (kg/cm2) after 24 h at
 No 2,4-dienoate Substrates testing 20.degree. C. 100.degree. C.
 120.degree. C.
 1 allyl steel/steel tensile 68 80 75
 shear 39 62 67
 glass/steel tensile 47 78 78
 shear &gt;20* &gt;20* &gt;20*
 glass/glass tensile 36 71 69
 shear &gt;19* &gt;20* &gt;20*
 2 methoxyethyl steel/steel tensile 43 101 132
 shear 23 92 106
 glass/steel tensile 32 120 118
 shear &gt;20* &gt;20* &gt;20*
 3 ethoxyethyl steel/steel tensile 25 82 72
 shear 20 75 73
 glass/steel tensile 27 84 80
 shear &gt;20* &gt;20* &gt;20*
 *- glass substrate failure