Patent Publication Number: US-3875109-A

Title: Compositions resistant to burning

Description:
United States Patent 1 Bridgland et al.  
 [ Apr. l, 1975 COMPOSITIONS RESISTANT TO BURNING [75] lnventors: Brian Edward Bridg&#39;land; Derek James Rowland Massy; Bernard Peter Stark, all of Cambridge, England [73] Assignee: Ciba-Geigy AG, Basel, Switzerland [22] Filed: Aug. 30, 1973 [21] Appl. No.: 392,919  
 [30] Foreign Application Priority Data Sept. 1, 1972 United Kingdom 40652/72 [52] U.S. Cl... 260/45.7 R, 260/2.5 AJ, 260/2.5 BB, 260/37 R, 260/42.l7, 260/42.18, 260/45.75  
 N, 260/45.85 R, 260/45.95 R  
 [51] Int. Cl C08d 7/10 [58] Field of Search. 260/45.7 R, 45.85 R, 45.75 N, 260/45.95 R, 2.5 A], 2.5 BB  
 [56] References Cited UNITED STATES PATENTS 3,651,174 3/1972 Bialous 260/45.7 R  
 Primary Examiner-Melvyn l. Marquis Attorney, Agent, 0&#34; FirmJoseph G. Kolodny; Edward McC. Roberts; Prabodh I. Almaula [57] ABSTRACT Compositions suitable for use as moulding resins, floor-covering compositions, casting, dipping, sealing, impregnating and filling resins, adhesives and foams comprise (i) an unsaturated ester of the general formula R (cantuan?) ococu=cucoon where a is an integer of at least 1, b is an integer of at least 2 and at most 6,  
 each alkylene group contains a chain of at least 2 and at most 6 carbon atoms between consecutive oxygen atoms,  
 R represents or the monovalent residue of an alcohol after removal of an -OH group,  
 (ii) a polymercaptan having, per average molecule, at least two mercaptan groups, the sum of the number of the indicated ethylenic bonds in the unsaturated ester (i) and the number of the mercaptan groups in the polymercaptan (ii) being more than 4, and  
 (iii) a salt or hydroxide of an alkali metal.  
 These compositions cure, optionally in the presence of a Bronstead base as accelerator, to give products which are resistant to burning.  
 1.4.: Claims, No Drawings COMPOSITIONS RESISTANT TO BURNING This invention relates to certain curable mixtures of polyenes and polymercaptans which yield cured products showing a high resistance to burning.  
  We have found that by incorporating relatively small amounts of a salt or the hydroxide of an alkali metal in compositions obtained by curing certain polyenes, having at least two ethylenic double bonds each a to a carbonyloxy group, with polymercaptans, materials with increased resistance to burning are obtained: further, even when the products can be ignited, they emit little smoke. Resistance to burning and emission of little or no smoke are obviously desirable features of plastics materials to be used in shops, factories, homes, and other places where fire hazards exist.  
  The present invention provides compositions which cure to form products resistant to burning, comprising i. an unsaturated ester of the general formula where a is an integer of at least 1,  
 b is an integer of at least 2 and at most 6,  
 R denotes the radical of valency b remaining after removal of b alcoholic hydroxyl groups from a polyhydric alcohol or after removal of b phenolic hydroxyl groups from a polyhydric phenol, or the acyl radical remaining after removal of b OH groups from a compound having at least b carboxyl groups,  
 each alkylene group contains a chain of at least 2 and at most 6 carbon atoms between consecutive oxygen atoms,  
 R represents -H or the monovalent residue of an alcohol after removal of an -OH group,  
  ii. a polymercaptan having, per average molecule, at least two mercaptan groups, the sum of the number of the indicated ethylenic double bonds in the unsaturated ester (i) and the number of the mercaptan groups in the polymercaptan (ii) being more than 4, perferably from 5 to 8, and  
 iii. a salt or hydroxide of an alkali metal.  
  Another aspect of this invention provides products obtained by curing the aforesaid curable compositions.  
  A further aspect provides a process for forming a product resistant to burning, which comprises curing a polymercaptan having, per average molecule, at least two mercaptan groups, with an unsaturated ester of formula l, the sum of the mercaptan groups in the polymercaptan and the indicated ethylenic double bonds of the said ester being more than 4, and preferably from 5 to 8, in the presence of an effective amount of a salt or the hydroxide of an alkali metal. Curing includes allowing to cure. 1  
  Desirably, the polymercaptan has an average molecular weight of at most 10,000 and contains up to 6 mercaptan groups&#39;per average molecule. Preferably at least one of the unsaturated ester and the polymercaptan has an average molecular weight in the range 1,000 to The preferred unsaturated esters (i) have an average molecular weight in the range 400 to 10,000. Further preferred are those of formula I in which R represents an aliphatic radical containing from 3 to 60 carbon (0,- alkylene) OCCH=CHC00R atoms, especially a saturated hydrocarbon radical of not more than -6 carbon atoms, or a radical of one of i the formulae groups. Preferably the alkylene units are C H R preferably, represents hydrogen, but it may also be, for example, an alkyl group of l to 6 carbon atoms, such as an n-butyl group, or a group of formula 0R where &#39;--Cli fll CH2 where I R represents -l-l or a group of formula R represents a monovalent alkyl group of l to 16 carbon atoms, especially an n-butyl group, an alkenyl group of 2 to l6 carbon atoms (such as an allyl group), an aliphatic acyl group of -2 to 16 carbon atoms (such as the acyl residue of a tertiary monocarboxylic acid of 9 to 11 carbon atoms), or a phenyl group, which may be substituted by-one or two alkyl groups, each of l to 9 carbon atoms, or by chlorine (such as phenyl, pcresyl, or p-chlorophenyl), and  
  R represents -H, an alkyl or alkenyl group of l to 6 carbon atoms, or a group of formula Compounds of formula I where R denotes hydrogen are obtainable by reaction of the alcohol of formula VI with maleic anhydride. The resultant poly( hydrogen maleate) may then be esterified in a conventional manner with an alcohol HOR, or treated with a glycidyl ether or a glycidyl ester of formula O CH CllCll OR VII to yield the ester of formula 5 (O-alkylene) OCOCH=CHCOOCH CLCH 0R VIII and the secondary hydroxyl group so formed may, if desired, be esterified.  
  A wide range of polymercaptans is suitable for incorporation in the composition of this invention.  
  One class, which is preferred because of the ready availability of many of its members, comprises esters of &#39;monomercaptancarboxylic acids with polyhydric alcohols and of monomercaptanmonohydric alcohols with polycarbo&#39;xylic acids.  
 Further preferred such esters are of the formula where R represents an aliphatic or araliphatic hydrocarbon radical of at least 2 and at most 60 carbon atoms, which may contain not more than one ether oxygen atom,  
  R represents a hydrocarbon radical, which may contain not more than one carbonyloxy group, and is preferably from 1 to 4 carbon atoms,  
 d is an integer of from 2 to 6,  
  e is zero or a positive integer of at most 3, such that (d e) is at most 6, and  
 fand g each represent zero or 1, but are not the same.  
  Yet further preferred among such polymercaptans are those which are also of the formula R9 (ocoR sH where R is an aliphatic hydrocarbon radical of from 2 to 10 carbon atoms,  
 R denotes Cl-l (CH or where j is an integer of from 1 to 6,  
 k and m are each zero or 1 but are not the same,  
  R represents a divalent organic radical, linked through a carbon atom or atoms thereof to the indicated O or CO- units,  
  R represents a divalent organic radical, linked through a carbon atom or carbon atoms thereof to the indicated SH group and O- or CO units, and  
  R represents an organic radical which must contain at least one SH group whenj is l.  
  Preferably R denotes, when k is zero, a saturated aliphatic hydrocarbon chain of 2 to 250 carbon atoms, which may be substituted by methyl groups and by SH groups, and which may be interrupted by ether oxygen atoms and by carbonyloxy groups; when k is l, R preferably denotes a. a saturated aliphatic hydrocarbon group of 2 to 10 carbon atoms, which may bear an SH group,  
  b. a cycloaliphatic-aliphatic hydrocarbon group of 5 to 34 carbon atoms, which may contain ethylenic unsaturation, or  
  c. a mononuclear arylene hydrocarbon group of 6 to 12 carbon atoms.  
  When k is zero, R preferably denotes a saturated aliphatic hydrocarbon group of 1 to 3 carbon atoms, which may bear a carboxyl group, and when k is 1, R preferably denotes a saturated aliphatic hydrocarbon group of 2 to 4 carbon atoms which may be substituted by a hydroxyl group or by a chlorine atom.  
 R preferably denotes a. an aliphatic or cycloaliphatic-aliphatic hydrocarbon group of 2 to 51 carbon atoms, which may bear at least one SH group,  
  b. a mononuclear or dinuclear arylene or arylenealiphatic hydrocarbon group of 6 to 15 carbon atoms,  
  0. a chain of4 to 250 carbon atoms interrupted by at least one ether oxygen atom and optionally substituted by at least one SH group, or  
  d. a chain of 6 to 750 carbon atoms interrupted by at least one carbonyloxy group, optionally interrupted by ether oxygen atoms and optionally substituted by at least one SH group.  
  These esters are described in United Kingdom Patent specifications Nos. 1,31 1,090 and 1,315,820.  
  Also suitable are esters and ethers of the general formula R XII v/ (O--a1kylerte) 0 (CO)PR where alkylene&#34; has the meanings previously assigned,  
  11 is a positive integer such that the average molecular weight of the compound is at least 400, but preferably at most 10,000,  
 p is zero or 1,  
  q is zero or a positive integer such that (q r) is at most 6, 4  
 r is an integer of from 2 to 6,  
  R represents the radical of a polyhydric alcohol after removal of (q r) alcoholic hydroxy groups, and  
  R represents an aliphatic radical containing at least one mercaptan group.  
  Preferred amongst the compounds of formula XII are the esters of formula alkylene&#34; q, n, and r have the meanings previously assigned,  
  R stands for an aliphatic hydrocarbon radical of from 2 to 6 carbon atoms, and  
 u is l or 2.  
  These esters and ethers are described in United Kingdom Patent specification No. 1,278,934.  
  Yet other suitable polymercaptans are mercaptanterminated polysulphides of the general formula as R17 o (cuo (R SS a (O)V(CHO)W(RI?)XSH xv 1 R18 where each R&#34; denotes an alkylene hydrocarbon group containing from 2 to 4 carbon atoms,  
 R denotes H, CH or C H y is an integer which has an average value of at least l, and is preferably such that the average molecular Weight of the polymercaptan is at most 10,000, and either v is zero, in which case w and x are each also zero,  
 v is 1, in which case w is zero or 1 and x is l.  
  The preferred polymercaptans of formula XV are those where R denotes hydrogen and v and w are each 1, y being such that the molecular weight of the polysulphide is from 500 to 8,000.  
  These polysulphides are described in, inter alia, United Kingdom Patent specification No. 1,316,579.  
  Another class of polymercaptans comprises mercaptan-terminated po1y(butadienes) which are of the general formula Z represents CN, COOH, CONI-I COOR C I-l or OCOR where R is an alkyl group of one to eight carbon atoms,  
 b is an integer of at least one,  
 0 is zero or a positive integer, and  
  d is an integer such that the average number molecular weight of the polymercaptan is at least 500, but preferably not more than 10,000.  
  Preferably the polymercaptans of formula XVI and XVII are also of the formula us ama on cncH 1 tca cro. 1 a mucm L 81 HS T tcu cn l sir Fa cu xrx where Further suitable polymercaptans include tris(2- f is either zero, in which case e, i 1, r it is l, i hydroxyethyl) isocyanurate trithioglycollate, pentahi h case i an integer f f 2 to d erythritol tetrakis(3-mercaptopropionate), l,2-bis(2- g, is an integer such that the average molecular mercaptoethoxylethane, the tfisflhioglycollate) Of a weight of the polymercaptan is at least 1,250 and at 5 glycerolpropylene Oxide adducll of average molecular weight 600, i.e., of formula XXI where I1, is an integer of average value 2.9, and mercaptan-terminated polyesters made by reaction of poly(oxypropylene) glycol of average molecular weight 1025 (3 moles), thiomalic l0 acid (2 moles), and thioglycollic acid (2 moles); or  
 trimerised linoleic acid (1 mole), poly(oxyethylene) glycol of average molecular weight 300 (3 moles), and  
  thioglycollic acid (3 moles).  
 I Usually, the polymercaptan is employed in a quantity r sufficient to supply from 0.8 to 1.2 mercaptan groups HS (-Cm2Ch0)c CHZCHSH per OCOCH=CHCOOR group of the unsaturated ester (i).  
  Particularly suitable polyenes are the tris(hydrogen maleates) of a poly(oxyethylene)triol or a poly(oxypropylene)triol, or the bis(hydrogen maleates) of a poly(oxyethylene) glycol or of a poly(oxypropylene) glycol. Preferably the polyene contains, per kilogram, from 0.2 to 8.0 gram-equiv. of the group most 5,000.  
  These polymercaptans are described in United Kingdom Patent specification No. 1,315,124.  
  Yet other suitable polymercaptans comprise those of the general formula where each R and c have the meanings previously assigned.  
  Still other suitable polymercaptans are the poly(mer- 2O captocarboxylates) especially the trithioglycollates, the tris(Z-mercaptopropionates), and the tris(3-mercaptopropionates), of tris(2-hydroxyethyl) isocyanurate or of tris(2-hydroxypropyl) isocyanurate. O CHCOOH Examples of specific suitable polymercaptans include XXIV penmerythmol tetraklsuhloglyconme) dlpemaenh Specific examples of suitable polyenes include those of thritol hexakis( 3-mercaptopropion ate 1,1,1- trimethylolpropane tris(thioglycollate), glycerol tris(- thioglycollate), the tris(thioglycollates) of a glycerolpropylene oxide adduct of average molecular weight CH the formula 700 or 4,000, i.e., of formula I 2 3 CH CH CH) 1 OCOCH CHCOOH 3 XXV CH 1 2 i 3 2 cu CH CH) 1 ococu su m where L 3 k, is an integer of average value 16.7 or 22.5,  
 where I1, is an integer of average value 3.5 or 22.5, the tris(- 2-hydroxy-3-mercaptopropyl) ether of formula l c11 on CH (ocu cm lococa C1-IO0OCH2CHCH2O(CH2)3CH3 q] 3- CH2 CH2 I l XXVI where where j is an integer of average value 2.5, a mercaptanterminated polyester made by the reaction of glycerol (1 mole), adipic acid (4 moles), butane-1,4-diol (4 moles), and thioglycollic acid (3 moles), and the polyj sulphide of average formula n, is an integer of average value 22.5, and q, is an integer of value 2.7. Other suitable polyenes include tris(hydrogen maleates) of formula XXV where k, is an integer of average value 2.9 or 8.1, a partial maleate ester of formula XXVI where n, is an integer of average value 22.5 and HS (C2HOCH2OC2HSS)23 C2H4OCH2OC2H4SH q, is an integer of average value 1.8, and those of the XXI&#34; formula 3 l C OCH2CHOC0CH=CHCOOH XXVII I 2. 3  
 (OCH CH OCOCH=CHCOOH XXV&#39;III 2 2 p g 2 CH2 where p, is an integer of average value 12.2,  
 CH I 2 CH (IIH CH CH) lOCOCH CHCOO(CH GB xxIx where k, is an integer of average value 22.5.  
  Usually the composition contains at least 0.04 percent, but preferably not more than percent and especially from 0.1 to 2 percent, by weight of the salt or hydroxide of an alkali metal calculated on the combined weight of the polyene and the polymercaptan. Sodium and potassium are the preferred metals. In most cases the salt is one of a weak acid, i.e., one having an acid strength, -log K, of at least 5, but sodium nitrate which is presumably converted into sodium nitrite under burning conditions has also proved effective. Examples of particularly suitable hydroxides and salts are sodium hydroxide, borax (Na B O sodium carbonate. sodium acetate, sodium sulphide, sodium dithionite (Na S O sodium bicarbonate, sodium tartrate, sodium silicate, sodium fumarate, sodium maleate, potassium hydroxide, potassium carbonate, and potassium bicarbonate.  
  While curing may take place at room temperature, it can, if desired, be made more rapid by heating the composition, usually at from to 180C, temperatures in the range to 150C being the more convenient in practice; the composition is generally heated for from 5 to 20 minutes, depending on the curing temperature employed. Usually the conditions of time and temperature employed in curing have little effect on the fireresistant properties.  
  Advantageously an accelerator for the reaction between the unsaturated ester and the polymercaptan is also incorporated, and preferably this accelerator is an organic or inorganic Bronsted base. Examples of suitable bases are primary, secondary, and tertiary amines, such as triethylamine, triethylenediamine,- N,N- dimethylaniline, and N-benzyldimethylamine, lower alkanolamines (e.g., mono-, di-, and tri-ethanolamine), lower alkylenepolyamines (e.g., ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, propane-1,2-diamine, propane l ,3- diamine, hexamethylenediamine and 2,2,4- and 2,3,3-  
 trimethylhexamethylenediamine) also quaternary ammonium bases such as tetramethylammonium hydroxide, and water-soluble inorganic hydroxides (especially sodium hydroxide) and inorganic salts such as triso- 5 dium phosphate, sodium carbonate, sodium bicarbonate, sodium pyrophosphate, and sodium acetate. In many cases where an alkali metal hydroxide or a sufficiently basic salt (such as potassium carbonate, sodium carbonate, sodium bicarbonate, and sodium acetate) is employed as the agent imparting increased resistance to burning, curing-takes place sufficiently rapidly without the need to add another Bronsted base as accelerator. The accelerator may also be a freeradical catalyst, such as an organic or inorganic peroxide or a persalt, specific examples being benzoyl peroxide, tert.butyl hydroperoxide, di-isopropyl peroxydicarbonate, and ammonium persulphate.  
  The compositions may contain colouring matter, conventional flame retardants, and difficultly combustible flame-resistant fibrous reinforcing materials such as glass fibres, asbestos fibres, and metal wires. We have found however that, surprisingly, many inorganic particulate fillers do not enhance the flame-retardant effect; indeed, calcium carbonate and china clay decrease the resistance to burning. Particularly if the polyene and/or the polymercaptan has a poly(oxyalkylene) chain the compositions may also contain substances which stabilise the cured product against adverse effects of light. Suitable stabilisers include compounds having at least one phenolic hydroxyl group and at least one alkyl or alkoxy group of l to 8 carbon atoms in the same benzene ring, especially compounds having 1 to 4 benzene rings, at least one of which bears a phenolic hydroxyl group ortho to such an alkyl or alkoxy group. Specific examples of suitable stabilisers include l, l-bis( 3,5-di-tert.butyl-2-hydroxyphenyl )butane, l ,1-bis( 3-tert.butyl-2-hydroxyphenyl)butane, l,- l-bis( 2-te rt.butyl-4-hydroxy-6-methylphenyl )butane bis(3-tert.butyl-2-hydroxy-5-ethylphenyl)methane, bis- (3-tert.butyl-4-hydroxy-6-methylphenyl)sulphide, octadecyl 3-(3,5-di-tert.butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(3-( 3,5-di-tert.butyl-4- hydroxyphenyl)propionate) and the nickel complex of the formula Usually, about 0.1 to 5 percent by weight of the stabiliser, calculated on the weight of the poly(oxyalkylene)-containin g polymercaptan and/or polyene, is employed.  
  The unsaturated ester and the polymercaptan, which are liquids or fusible or soluble solids, can, as already indicated, be cured in the presence of a salt or a hydroxide of an alkali metal to yield insoluble, infusible, cross-linked structures which are resistant to burning; curing may be accompanied if desired by shaping to form mouldings such as castings or to form coatings and adhesive bonds. The compositions of this invention are therefore useful as moulding resins, floor-covering I -be utilised in the form of foams.  
  The following Examples illustrate the invention. All parts and percentages are by-weight unless otherwise indicated and temperatures are in degrees Celsius.  
  The unsaturated esters and polymercaptans employed were obtained in the following manner.  
  Polyol I&#34; is a polyoxypropylenetriol (a glycerolpropylene oxide adduct) of average molecular weight 600. Polyols II and III, are similar, but have average molecular weights of 4,000 and 1,500 respectively.  
  Polythiol A denotes pentaerythritol tetrathioglycollate.  
  Polythiol B denotes 1,1,l-trimethylolpropane trithioglycollate.  
  Polythiol C denotes the trithioglycollate of Polyol II and is of formula XXI, where h, is an integer of average value 22.5.  
  Polythiol D is the trithioglycollate of tris(2- hydroxyethyl) isocyanurate.  
 Polythiol E is 1,2-bis(2-mercaptoethoxy)ethane.  
 PolythiolF is pentaerythrito] tetrakis(3-mercaptopropionate).  
 Polythiol G is a polyester, made in the following way:-v  
  A mixture of glycerol (1 mole), adipic acid (4 moles), butane-1,4-diol (4 moles) thioglycollic acid (3 moles), toluene-p-sulphonic acid (3 g), and perchloroethylene (350 ml) was heated under reflux in an atmosphere of nitrogen. Water formed during the reaction was removedas itsazeotrope with perchloroethylene. The mixture was cooled and washed with water, the organic layer was separated, and the solvent was evaporated off to leave Polythiol G having a thiol content of 2.35 equiv./kg.  
  Polythiol H, also a polyester, was made similarly, from 3 moles. of a poly(oxypropylene) glycol of average molecular weightv 1025, 2 moles of thiomalic acid, and 2 moles. of thioglycollic acid. Its thiol content was 1.15 equiv./kg.  
 Polythiol J is dipentaerythritol hexakis(3-mercapto- &#39;propionate).  
  Polythiol K is a polyester made in the same way as Polythiol G but from trimerised linoleic acid (1 mole.), poly(oxyethylene)glycol of average molecular weight 300 (3 moles), and thioglycollic acid (3 moles).  
  Polythiol L is glycerol trithioglycollate.  
 POLYENE I A mixture of Polyol II (200 g), maleic anhydride, (14.7 g), and N-benzyldimethylamine (2 g) was stirred at 120 for 100 minutes. The product is substantially the tris(hydrogen maleate), of formula XXV, where k is an integer of average value 22.5.  
 POLYENE II This was prepared in the same way as Polyene I using, however, Polyol III: Polyene II can also be represented by formula XXV, k, then denoting an integer of average value 8.1.  
 POLYENE III 2,2-bis(4-hydroxyphenyl)propane (1 14 g) was heated with propylene oxide (30.5 g) to reflux temperature (61), a 40 percent aqueous caustic soda solution (0.57 g) was added, and the reaction was allowed to continue for 50 minutes, during which time the temperature increased to 66. More 40 percent caustic soda solution (0.57 g) was added and the mixture was heated to reflux for a further 2 hours, the temperature rising to Propylene oxide (30.5 g) was added, and refluxing was continued for a further 4 hours, during which time the temperature increased to 140. The solution was cooled to 100 and maleic anhydride (98 g) and N-benzyldimethylamine (2.75 g) were added and the mixture was heated at for 100 minutes to afford Polyolefin III, which is substantially of formula XXVII.  
 POLYENE IV To 541.5 g of Polyene I was added 32.7 g of n-butyl glycidyl ether of epoxy content 7.1 equiv./kg, i.e., 0.6 molar proportion, and the mixture was heated at 120C for 100 minutes, by which time the epoxy content of the product was zero.  
  Polyene IV is substantially of the formula XXVI where n, is an integer of average value 22.5 and q, is an integer of average value 1.8.  
 POLYENE V This was prepared in the same way as Polyene I using, however, Polyol I: Polyene V can be represented by formula XXV, where k denotes an integer of average value 2.8.  
 POLYENE VI A poly(oxyethylene) glycol of average molecular weight 600 (300 g), maleic anhydride (98 g), and triethylamine (6 g) were mixed and heated for 2 hours at 80C. The product had an acid value of 2.48 equiv./kg (theoretical 2.48 equiv./kg) and is substantially of formula XXVIII where p is an integer of average value 12.2.  
 POLYENE VII A mixture of Polyene I (430 g), n-butanol (111 g), toluene-p-sulphonic acid (5.5 g), and toluene (400 g) was heated under reflux and water formed during the reaction was removed continuously as its azeotrope with toluene. The mixture was then evaporated on a rotary&#39; evaporator. The product isthe tri n-butyl ester of Polyene I, i.e., is of the. formula XXIX.  
 EXAMPLE I Polyene I (14 parts) and Polythiol A (1 part) were mixed at about 20 and the additive (as shown in Table I) was stirred in, the mixture (which contains 1 SH group equivalent per ethylenic double bond) then being poured quickly into a demountablebrass mould which had been coated internally with a silicone release agent. After being cured (this usually taking only a few minutes at room temperature,.although in some cases the compositions were also subjected to a post-cure heating period) the sample was removed from the mould as a casting 12.7 X 1.27 X 0.63 cm.  
  The samples were tested for flammability by the procedure laid down in ASTM D635. In this test, lines are marked 2.5 cm. from each end of the casting. The sample is then clamped at one end and mounted, at 45 to the horizontal, over a fine wire gauze, and a blue bunsen burner flame 2.5 cm high is applied to one end for 30 seconds. If the sample does not burn after the bunsen burner has been removed, the sample is then subjected to the flame for a further 30 seconds. Should the sample not continue to burn after this treatment, it is considered non-burning by this test -a. If combustion occurs but is extinguished before reaching the mark 2.5  
  Table I shown the results obtained using compositions containing the various additives: Experiments Nos. 1 to 8 are for purposes of comparison, the remaining Experiments illustrate the invention.  
 cm from the further end the sample 15 self- EXAMPLE 2 extinguishing -c and the length burned from the initial mark is recorded. If the burning continues to the fur- The procedure of Example 1 was repeated, using, {her mark, the Sample 15 deemed to be g y thls however, nonstoichiometric proportions of the reaclest and the rate of bummg 15 recorded! tants: 17 and 11.2 parts of Polyene I were used per part of Polythiol A with, respectively, 0.055 and 0.065 part TABLE 1 Additive Results No. Designation /1 of ASTM D635 ASTM D 2863 composn. Cure Class remarks &#34;/1 l 20 b 6.8 cm/min 2 120/ b 6.3 cm/min min 3 DETA 0.066 b 4.3 crn/min 4 DETA&#39; 0.066 120/ b 4.0 cm/min 15 min 5 NH, OH&#39; 0.066 20 b 2.8 cm/min 6 Ba(OH) 0.066 20 b 4.3 cm/min 7 Al(OH);i&#39; 0.066 20 b 5.6 cm/min 8 ARCH) 0.33 20 b 5.3 cm/min 9 NaOH 0.066 20 a nonbuming 10 Na B O;.10H. O 1.32 20 21 nonbuming l 1 NaOH 0.066 l50/ a nonbuming 1.5 min l2 NJ CQ, 0.5 20 a nonbuming 23 1 3 Na- ,CO;, 1 .0 20 a nonbuming l4 Na CO; 2.3 20 a nonburnin g I5 Na CO 4.5 20 21 nonbuming 27 16 Na C 0;, 6. 5 20 a nonbuming 29 17 Na CQ, 8.5 20 a nonbuming 33 18 Na acetate 0.066 20 11 nonbuming l9 Na s 0.066 20 :1 nonbuming 20 Na- ,S O.,.2H O 0.066 20 21 nonbuming 21 NaHCO 0.066 20 a nonbuming 22 Na tartrate dihydrate 0.066 20 a nonbuming 23 NaNOf 1.32 20 a nonbuming 24 NaNQ,&#34; 0.67 20 a nonbuming 25 LLCO 0.066 20 C 0.8 cm burnt 26 KOH 0.066 20 c 0.9 cm burnt 22 Notes: added as an aqueous 1% solution/suspension 2 an aqueous 20% solution an aqueous 10% solution an aqueous 5% suspension Replicates of certain samples were also tested according to the procedure of ASTM D2863. The results from this test give the relative ignition ranking of materials. The sample is burned in a measured mixture of 45 oxygen and nitrogen in which the percentage of oxygen of sodium hydroxide (added as a 1 percent aqueous solution). The first of the compositions was also postcured by heating at 150 for 15 minutes. Both cured products were rated a non-burning by the ASTM D 635 test.  
 EXAMPLE 3 The procedure of Example 1 was repeated, using other combinations of polyene and polymercaptan. The samples were all cured at 20; the results obtained are shown in Table 11.  
 TABLE 11 No Polyene Polythiol Additive Results No. Parts Desig- Parts Designation 71 of ASTM D635 nation comp. Class remarks 29 l 1 C 1 NaOH&#34; 0.36 a nonbuming 30 11 5.86 A 1 NaOH 0.15 a nonbuming 31 11 5.86 A l Na CO, 3.64 a nonbuming &#39;32 111 I 2.5 A 1 NaOH&#34; 0.285 a nonbuming 33 l 1 K 1 NaOH 0.312 a. nonbuming 34 11 3.67 D 1 NaOH&#34; 0.214 a nonbuming 35 1 15.7 E l NaOH 0.30 a nonbuming 36 11 4.5 F 1 NaOH 0.545 a nonbuming 37 V 1 G 1.37 NaOH 0.55 a nonbuming 38 11 l H 1 5 NaOH 6.8 a nonbuming 39 l 14 J l NaOH 0.13 a nonbuming 40 l 12 B l NaOH 0.15 a nonbuming TABLE II Continued No. Polyene Polythiol Additive Results No. Parts Desig- Parts Designation 71 of ASTM D635 nation com p. Class re marks 4] VII 7 A l NaOH 1 84 a nonburnihg 4 VI 4 A l NaOH 0.l3 a nonburning 43 IV l4 A NaOH 0.13 c 0.6 cm burnt 44 l l i L l KZCOH 0.2 &#39;a nonburning We claim: 1. A composition which cures to form a product resistant to burning, comprising 8(3) i. an unsaturated ester having an average molecular 7 8 R weight of 250 to 10,000, of the general formula l (emf g P sd (1 1 where R (o-alkylene)aococH=cHcooR b R represents an aliphatic or araliphatic hydrocarbon radical of 2 to 60 carbon atoms, or an aliphatic or araliphatic hydrocarbon radical of at least 2 and at h most 60 carbon atoms which contains one ether oxw ere a is an integer of at least 1,  
 b is an integer 2 to 6,  
 R denotes the radical, of 3 to 60 carbon atoms, of valency b remaining after removal of b alcoholic hydroxyl groups from a polyhydric alcohol or after removal ofb phenolic hydroxyl groups from a polyhydric phenol. or the acyl radical remaining after removal of b OH groups from a compound having at least b carboxyl groups,  
 each alkylene group contains a chain of 2 to 6 carbon atoms between consecutive oxygen atoms,  
 R represents H or the monovalent residue of an alcohol after removal of an OH group,  
 ii. a polymercaptan having an average molecular weight of at most 10,000 and containing, per average molecule, two to 6 mercaptan groups, the sum of the number of the indicated ethylenic double bonds in the unsaturated ester (i) and the number of the mercaptan groups in the polymercaptan (ii) being more than 4 and at most 8, and  
 iii. 0.04 to 10 percent by weight ofa salt or hydroxide of an alkali metal, calculated on the combined weight of the said polymercaptan and unsaturated ester.  
  2. A composition according to claim 1, in which the said salt is of an acid having an acid strength, -log K of at least 5, or is sodium nitrate.  
  3. A composition according to claim I, in which the polyene contains from 0.2 to 8.0 gram-equiv. of the group of formula -CH=CHCOOH per kilogram.  
  4. A composition according to claim 1, in which the polymercaptan supplies from 0.8 to 1.2 mercaptan groups per -CH=CHCOOH group of the polyene.  
  5. A composition according to claim 1, in which the polymercaptan is an ester of a monomercaptancarboxylic acid with a polyhydric alcohol or of a monomercaptanmonohydric alcohol with a polycarboxylic acid.  
  6. A composition according to claim 5, in which the polymercaptan is of the formula ygen atom, R represents a hydrocarbon radical, or a hydrocarbon radical which contains one carbonyloxy group, d is an integer of from 2 to 6, e is zero or a positive integer of at most 3, such that (d e) is at most 6, and fand g each represent zero or 1, but are not the same. 7. A composition according to claim 5, in which the polymercaptan is a polyester of formula where j is an integer of from 1 to 6,  
 k and m are each zero or 1 but are not the same,  
 R represents a divalent organic radical, linked through a carbon atom or carbon atoms thereof to the indicated O- or CO units,  
 R represents a divalent organic radical, linked through a carbon atom or carbon atoms thereof to the indicated SH group and --O- or CO- units, and  
  R represents an organic radical, which must contain at least one SH group whenj is I, linked through a carbon atom or carbon atoms thereof to the indicated O- or CO- units.  
 8. A composition according to claim 1, in which the polymercaptan is an ether of the general formula Ruiw-alkylend 01!] q where each alkylene group contains a chain of 2 to 6 carbon atoms between consecutive oxygen atoms, n is a positive integer such that the average molecular weight of the polymercaptan is at least 400, p is zero or 1,  
  17 18 q is zero or a positive integer such that (q r) is at of one to eight carbon atom most 6, b is an integer of at least one, r is an integer of from 2 to 6, c is zero or a positive integer, and R represents the radical of a polyhydric al h l a a, is an integer such that the average number molecuafter removal of (q r) alcoholic hydroxyl groups, 5 lat weight of the polymercaptan is at least 500. and 11. A composition according to claim 1, in which the R represents an aliphatic radical containing at least p ym p s of h f rmula one mercaptan group.  
  9. A composition according to claim 1, in which the polymercaptan is of the formula us(ca 0110) on CHSH 17 17 ,17 1 2 2 as R (o) (cao) n ss i. (o) (czio) a Su where each R represents H or CH;, and Y c is an integer of l to 4.  
  12. A composition according to claim 1, in which the where V polymercaptan is a poly(monomercaptancarboxylate) R denotes an alkylene hydrocarbon group contain- 0f y y y isocyanaurate of Of 0- ing from 2 to 4 carb atom 20 hydroxypropyl) isocyanurate. R denotes H, -CH &#39;r C H 13. A composition according to claim 1, which cony is an integer which has an average value of at least tains a Bfonsled base as accelerator- 1, and eith v i zero, i hi h case w d are 14. A process for forming a product resistant to burneach also zero, or v is l, in which case w is zero or hlg which comprises Curing a polymercaptan having an 1 and x is l. g a average molecular weight of at most 10,000 and con- 10. A composition according to claim 1, in which the mining, P average molecule, at least tWO and at mOSt polymercaptan is a mercaptan-terminated poly(butadi- 6 mercaptan g p with an unsaturated ester having ene) of the formula an average molecular weight of at least 250 and at most 19 10,000, of the. general formula H R 19 v i l, R  
  l l 1 I l R O-allzylene OCCCH=CElCOOR as +011 7 c c-cH l( 01 .6 1 SH a v b Z where d1 a is an integer of at least 1, a b is an integer of 2 to 6, or t I R denotes the radical, of 3 to 60 carbon atoms, of valency b, remaining after removal of b alcoholic hy- 40 droxyl groups from a polyhydric alcohol or after removal of b phenolic hydroxyl groups from a polyl hydric phenol, or the acyl radical remaining after the removal of b OH groups from a compound havc\ CH2 2 t SH ing at least b carboxyl groups, 19 each alkylene group contains a chain of 2 to 6 car- 0 z a bon atoms between consecutive oxygen atoms, l R represents H or the monovalent residue of an 3 alcohol after removal of an OH group, thesum of b and the number of mercaptan groups in the polymercaptan being more than 4 and at most 8, in the presence&#39;of at least 0.04 percent and at most 10 lz R19 represents H or CH percent by weight, calculated on the combined 3 weight of the said polymercaptan and unsaturated Z represents CN, COOl-l, CONH COOR&#34;,  
  6 5, or CCORH, where R20 is an a y g p ester, of a salt (1r hZdl&#39;gXld: 0: an alkali metal.