GB1571487A - Process for preparing a resin - Google Patents

Description

(54) PROCESS FOR PREPARING A RESIN (71) We, ALBRIGHT & WILSON LIMITED, a British Company of Albright and Wilson House, Hagley Road West, Oldbury, Warley, West Midlands, England, formerly of P.O. Box 3, Oldbury, Warley, West Midlands, England do hereby declare the invention, for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to a process for preparing a resin capable of being cured to a thermoset polymer.

In our British Patent No. 1,150,203, we describe the reaction of (I) an aralkyl ether of the general formula R'-(CH2OR)8 and/or an aralkyl halide of the general formula R"HCH2X)a, wherein R' is a divalent or trivalent aromatic hydrocarbon or hydrocarbonoxy-hydrocarbon radical, R" is a divalent or a trivalent aromatic hydrocarbon radical, R' and R" optionally containing inert substituents in the aromatic nucleus, R is an alkyl radical containing up to 6 carbon atoms, X is chlorine, bromine or iodine and a has a value of 2 or 3, with a molar excess of (2) a phenolic compound our a phenolic compound and a compound containing aromatic nuclei. The product is a curable resin I having at least some repeating units of formula

where ArX is R' or R" and ArOH represents the phenolic compound, and is terminated by the ArOH groups.

In the Specification of our British Patent Application No. 43345/74, (Serial No.

1,528,748), we describe the production of the resin by a similar procedure but with replacement of the ether or halide by an aralkyl ester of formula R'HCH2OYR,)a where R' and a are as defined above, R1 is an alkyl group of 1 to 6 carbon atoms or aryl group of 6-13 carbon atoms and Y is a carbonyl or sulphonyl group.

We have now found a new class of resins having both phenolic and carboxyl and/or carboxylate groups, which have at least one carboxylic repeat unit of formula

and optionally at least one repeat phenolic unit of formula

the resin having terminal units containing phenolic groups, where ArX is a divalent or trivalent aromatic hydrocarbon or aromatic hydrocarbon-oxy-aromatic hydrocarbon group, each of which may have at least one inert substituent, HOAr(CH2)bCOOR2 I is a divalent radical derived from a molecule of formula HO AR(CH2)bCOOR2, which is an aromatic phenolic carboxylic acid or ester thereof, by removal of 2 nuclear hydrogen atoms, ArOH I is a divalent radical derived from a molecule of formula ArOH, which is a phenol which does not contain a COOR2 group, by removal of 2 nuclear hydrogen atoms, R2 is a hydrogen atom or alkyl group of 1-6 carbon atoms, a is 2 or 3 and b is 0 or 1, the molar proportion of phenol of formula ArOH to the total phenol and phenolic carboxylic acid or ester being O50V0.

Preferably the resin has at least one carboxylic repeat unit of formula II and is terminated with groups derived from a phenol carboxylate of formula HOAr(CH2)bCOOR2.

The present invention also provides a process for preparing a curable resin containing phenolic hydroxyl and carboxylic acid and/or ester groups, which process comprises reacting an aralkylene compound of formula ArX(CH2D)a, wherein ArX and a are defined above and D represents a group of formula OR, X, or OYR, where R, X, Y or R, are defined above, with (i) a molar excess of an aromatic phenolic carboxylic compound of formula Ar(OH)d(CH2)b(COOR2)c where d is an integer of 1--3, b is 0 or 1, c is an integer of 1--3, subject to the proviso that when b is 1, c is 1, R2 is hydrogen or an alkyl group of 1-6 carbon atoms, and Ar is the residue of an aromatic hydrocarbyl nucleus, e.g. of 6, 10 or 12 carbon atoms, which may be substituted with at least one halogen, nitro, alkyl or alkoxy each of 1--4 carbon atoms, phenyl or substituted phenyl group, in which the substituent in the phenyl group is at least one hydroxyl carboxylic group of formula COOR2, halogen, nitro or alkyl or alkoxy group each of 1--4 carbon atoms, with the proviso that the phenolic carboxylic compound contains no substituent in the nucleus in at least 1 and preferably in at least 2 positions ortho or para to a hydroxyl group, (ii) (less preferred), with a molar excess of a mixture of the aromatic phenolic carboxylic compound and up to 50 mole percent (based on the total amount of phenolic containing compound) of a carboxyl free phenol of formula Ar(OH)e where Ar is as defined above and e is an integer of 1--3.

The phenolic carboxyl compound has carboxyl groups, or carboxylate ester groups or a mixture of both. Preferably in the carboxyl compound b is 0, d is 1, 2 or 3, c is 1 or 2, Ar is a residue of a benzene nucleus, which may be substituted by at least one alkyl or alkoxy group of 14 carbon atoms e.g. methyl, methoxy or ethoxy, phenyl or phenyl substituted by at least one hydroxyl or carboxyl group of formula COOR2. Especially preferred are carboxyl compounds in which d is 1, 2 or 3, b is 0, c is 1 and either no other substituent in the nucleus, one of the above mentioned preferred substituents or two alkoxy groups. Examples of the carboxyl compound are salicylic, m- and p- hydroxy-benzoic acid, gallic and syringic acids, and their corresponding methyl and ethyl esters, especially methyl salicylate. When b in the carboxyl group or ester therefrom is 1, preferably d is 1 or 2 and Ar is a benzene ring. Examples of such compounds are hydroxy phenyl acetic acid and dihydroxyphenylacetic acid and their esters. Mixtures of the carboxylic acids and their esters may be used. When the aralkylene ether is reacted, an alkanol is liberated as by-product and this may esterify some of the carboxylic acids thus producing a resin based on carboxylic acid and ester compounds.

The aromatic phenolic carboxyl compound may be mixed with up to 50 mole %, preferably up to 20 mole 0/, e.g. 1--10 mole Vo of a phenol for formula Ar(OH)e wherein e is 1-3, preferably 1 or 2, and Ar is as defined above, but does not contain a carboxyl group of formula COOR2. Subject to the need for no substitution in at least 2 of the ortho and para positions to a hydroxyl group or groups, the substituents in the aromatic nucleus (apart from hydroxyl) may each be alkyl of 1 to 8 carbon atoms, e.g. methyl, ethyl, isopropyl, tert. butyl or tert. octyl, halogen e.g. chlorine, nitro, phenyl, hydroxy phenyl, hydroxyphenyl alkyl e.g.

hydroxy phenyl-methylene, -ethylene and -isopropylidene. Preferably the phenolic compounds contain only one aromatic ring and have 1 or 2 hydroxyl groups and no other substituent or only 1 alkyl substituent. Examples of the phenolic compounds are phenol, p-cresol, m-cresol, resorcinol, catechol, 4-methyl catechol, isopropyl catechol, diphenylol propane (bis 2,2-(4-hydroxy phenol)propane), diphenylolethane, monoalkyl phenols for example p-ethylphenol, p-tert. butyl phenol and p-tert. octyl phenol, m- and p-phenyl phenol, pyrogallol and phloroglucinol.

In the general formula ArX represents any divalent or trivalent aromatic hydrocarbyl or aromatic hydrocarbyloxy aromatic hydrocarbyl radical, for example the m- or p-phenylene radical, a diphenylene radical, a diphenylene oxide radical e.g. a bis (p-phenylene) oxide radical, a 2,6-napthylene radical or a 1,3,5phenylene tri radical. The ArX group contains no phenolic hydroxyl group.

Thus both mono nuclear, and fused and unfused poly nuclear radicals may be represented by ArX, the mononuclear radicals are preferred especially m- and pphenylene. If desired the ArX radical may contain at least one substituent which is a phenyl group, alkyl group of 1--4 carbon atoms e.g. a methyl group or a halogem atom, attached to the aromatic nucleus the substituent or substituents being inert under the conditions of the reaction. The presence of chlorine or fluorine atoms in some or all of the available positions in the aromatic nucleus is advantageous in that it leads to improved flame resistance in the resulting polymeric products.

Examples of such substituted aralkylene compounds, which may be employed according to this invention, are 2,3,5,6-tetrachloro- 1 ,4-di(methoxymethyl)benzene and its corresponding l,4-di(chloromethyl) and l,4-di(acetoxymethyl analogues).

The group D in the aralkyl compound of formula ArX(CH2D)a is preferably of formula OR, where R is methyl or ethyl, X, where X is chlorine, OYR1 where, especially when Y is a carbonyl group, R, is preferably an unsubstituted alkyl radical of 1 to 4 carbon atoms, especially a methyl radical, and especially when Y is a sulphonyl group, R, is preferably a mononuclear aryl group e.g. of 6-8 carbon atoms for example a phenyl, tolyl, xylyl or halophenyl e.g. bromophenyl group. The preferred aralkylene compounds are those in which a has a value 2, particularly pxylylene glycol dimethyl ether, p-xylylene dichloride, p-xylylene a,'-diacetate, pxylylene ct,a'-di-benzene sulphonate and p-xylylene a,a'-di-p-toluene sulphonate.

The aralkyl, phenolic carboxyl and phenolic compounds are preferably at least 90 pure but technical grade materials may be used. Thus the p-xylylene glycol dimethyl ether may be the technical product having 65-90% of the desired compound, 0.1-5% of p-methylbenzyl methylether, 0.1-10% p-tolualdehyde dimethyl acetal and 5-35% p-methoxymethyl benzaldehyde dimethyl acetal; the proportion of acetal includes any amount of the corresponding free aldehyde present.

The reaction to form the resin is carried out with one mole of aralkylene compound and a molar excess of the phenolic carboxyl compound or mixture thereof with the phenolic compound. Preferably a total of at least 1.3 moles of all the compounds containing phenolic groups per mole of aralkylene compound are used, especially 1.3 to 3 moles. When the molecular proportion falls below the specified 1.3:1 ratio and approaches 1:1 the reaction mixture exhibits an increased tendency to gel prematurely. Polymeric products having the highest softening points are obtained when the ratio is at the low end of the specified range. When a is 2 the phenolic carboxyl compound is preferably employed in a ratio of 1.3:1 to 2:1, e.g. 1.3 to 1 to 1.7 to 1, especially 1.4 to 1.6:1. When a in the aralkyl compound is 3, the ratio is preferably 2:1 to 3:1 e.g. 2.5:1 to 3:1.

The reaction between the compounds containing phenolic groups, the phenolic compound (if present) and the aralkylene compound involves condensation of the -CH2D side chain groups in the aralkylene compound with nuclear hydrogen atoms in the phenols with the elimination of the corresponding compound of formula HD, that is alcohols, hydrogen halides, carboxylic or sulphonic acids. Preferably the process of an invention is carried out in the presence of a catalyst for this reaction for example certain ball clays or a Friedel Crafts type catalyst for example stannic chloride, zinc chloride or ferric chloride.

Other catalysts are dialkyl sulphates where the alkyl group has 1-6 carbon atoms e.g. dimethy, diethyl and dipropyl sulphates. Diethyl sulphate is the preferred catalyst. The quantity of catalyst is not critical and from 0.01-1% by weight (based on the total weight of the reactants) has been found to be sufficient for most purposes, especially 0.02-0.5%, although up to 3% or more may be used if desired.

The catalyst may be added as such or as a solution or dispersion in a compatibilizing solvent, for example methyl alcohol.

The reactants can be dissolved in a suitable high boiling inert organic solvent e.g. an aromatic compound with a deactivated ring such as chlorobenzene or nitrobenzene or in the case of the compounds, where D is of formula OOCR, an alkane carboxylic acid e.g. of 2 to 7 carbon atoms such as acetic acid. Where D is an alkoxy group, the reaction is preferably carried out in the absence of a solvent; where D is a halogen atom, the reaction is preferably performed in the solvent, especially in large scale production, the solvent acting as a diluent to moderate the exotherm reaction.

The reaction to prepare the resin is generally carried out by heating the reactants together at a suitable temperature usually at least 1000C e.g. 131700C, conveniently until the by-product compound of formula HD is liberated. The byproduct alcohols, hydrogen halides and carboxylic acids are preferably distilled out of the reaction mixture; the by-product alcohols and carboxylic acid may be recycled for preparation of the aralkylene compounds. The reaction time depends on such variables as the nature of the reactants, the type and quantity of catalyst and the reaction temperature, but is usually 5 min to 24 hr, especially 30 min to 5 hr. The reaction is preferably continued until the liberation of by-product compound is substantially complete. At the end of the reaction the volatile byproducts (if any remain) and solvent (if any) may be evaporated by heating under vacuum e.g. 1--50 mm Hg usually at the reaction temperature. The evaporation also removes any unreacted volatile phenolic compound, so it is desirable that the reaction be substantially complete before the evaporation is started. In view of the tendency of the resins to self cure on prolonged heating at high temperature, the evaporation to remove volatile compounds should be as short as possible, e.g. less than 5 mins.

In the case of the sulphonic acid by-product the residual by-product acid can be removed from the crude resin product by filtration from a solution of the crude resin in a solvent for example a dialkyl ketone of 3-7 carbon atoms e.g. methyl ethyl ketone in which the acid is insoluble.

The aralkyl compounds may be prepared by the following routes; the aralkyl halides by side chain halogenation of the corresponding hydrocarbons, the aralkyl ethers by alkoxylation of the halides, and the carboxylate and sulphonate esters from the halides by reaction with an alkali metal carboxylate or sulphonate e.g. as described in British Patent Specification No. 1,410,474 and the Specification of British Patent Application No. 43345/74. (Serial No. 1,528,748).

When the resins are prepared by reacting the aralkyl compounds with the aromatic phenolic carboxyl compounds, the resins II are believed to be of nominal structure

where Ar, ArX, R2 a and b are as defined above and n is an integer of 1--5, usually 2 or 3. The resins are a mixture of compounds with different values of n; preferably the average value of n is about 2. When the resins are prepared by reacting the aralkyl compounds with the mixture of aromatic phenolic carboxyl compounds and phenolic compounds, the resins contain at least one unit of formula

and at least one unit of formula

terminated by ArOH and/or Ar(OH)(CH2)bCOOR2 groups. It is to be understood that the resin product may be a mixture of resins, some of which II contain phenolic groups derived from the carboxyl compound only, others of which I contain phenolic groups derived from the phenolic compound only and the remainder of which contain phenolic groups from both types of compound.

The present invention also comprises mixtures of said carboxylic resin II and said phenolic resin I in weight proportions of 1-99:99-1, e.g. 1-10:99-90. These mixtures may be useful in having a greater adhesion to aminosilane treated fibrous reinforcement, e.g. glasscloth fabric mats than the resin I above.

In the resins, all the groups R2 in the carboxyl group COOR2 may be hydrogen, or all may be alkyl of 1-6 carbon atoms, or both hydrogen and alkyl groups for R2 may be present, the resins being described hereafter for convenience as acid resins, ester resins and acid/ester resins respectively. These resins are interconvertible.

Treatment of the ester or acid ester resins with dilute aqueous acid or base hydrolyses the ester groups to give the acid resins. Similarly esterification of the acid or acid/ester resins with alkanols of 1-6 carbon atoms in the presence of an acid catalyst gives the ester resins.

The resins may be cured to thermoset products in a variety of ways. The acid/ester and ester resins are self curable, the action of heat alone e.g. at 175 250"C, preferably 190--2500C being sufficient to give a cured product; cure times of 10 mins to 8 hrs. at 2500C to 1900C respectively are suitable e.g. 1 hr at 2000C.

Alternatively a curing agent may be used; for example all these classes of resin may be cured by heating with 8-20% by weight (based on the weight of resin) of hexamine. Alternatively, the curing agent may be an epoxide with at least 2 epoxide groups per molecule, preferably with at least one of the epoxide groups and preferably both of them fused to a cycloaliphatic ring, the proportion of total equivalents of phenolic hydroxyl and acid groups (if present) to epoxide groups in the epoxide being in the range 2:1 to 1:2 e.g. 1.2:1 to 1:1.2 especially 1:1. Further the curing agent may be an isocyanate with at least two NCO groups per molecule, the product being a cured foam; an amount of isocyanate to give total equivalents of hydroxyl and acid groups (if present) to isocyanate groups of 2:1 to 1:2 is preferable.

Alternatively the curing agent may be a saturated aliphatic alcohol with 2 to 4 hydroxyl groups and 2-6 carbon atoms or an ethylenically unsaturated alcohol with 1 to 4 hydroxyl groups and 3-6 carbon atoms. Examples of the alcohols are ethylene and propylene glycols, butane 1 ,4-diol, glycerol, penta-erythritol, trimethylol-methane and -ethane, allyl alcohol and methallyl alcohol. The unsaturated alcohols react with the carboxyl groups to give unsaturated esters which can be cured by peroxide catalysis alone or with an ethylenically unsaturated monomer for example styrene. The amount of alcohol is usually in a proportion of equivalents of the total carboxyl and carboxyl ester groups to equivalents of alcohol groups of 2:1 to 1:2 preferably 1.2:1 to 1:1.2.

Thus the resins with or without curing agent may be dissolved in an organic solvent to give a solution useful as a coating liquid or an impregnant for fibrous reinforcements, e.g. fabric mats for making laminates. The resins with or without curing agent may be mixed with fillers and reinforcements, e.g. asbestos or glass fibres, and then moulded to give moulded articles. The cured products usually have high strength especially at high temperatures.

The invention is illustrated in the following Examples in which the technical grade cY,a'-dimethoxy-p-xylene contained 75.20/, of ,a'-dimethoxy-p-xylene, 4.20/, of p-methylbenzyl methyl ether, 3.3 /a p-tolualdehyde, 4.9% p-tolualdehyde dimethyl acetal, 6.5% of p-methoxymethylbenzaldehyde dimethyl acetal and 2.8% p-methoxy methyl benzaldehyde.

Example 1 Salicylic acid (3 moles, 414 g.) and technical a,a'-dimethoxy-p-xylene (2 moles, 332 g.) were weighed into a reaction flask which was fitted with a thermometer and stirrer and set for distillation via a condenser. Diethyl sulphate (1.5 mls.) was added to the stirred reactants and the mixture was heated. When the temperature reached 1 380C, methanol began to distil out of the mixture and this continued while the temperature was gradually raised to 1600C. At this point the distillation finished and the product was cooled to 1400C and then poured into an aluminium tray to solidify. The distillate had a strong smell of methyl salicylate.

The resin produced had a softening point of 91"C.

Example 2 Example 1 was repeated, using p-hydroxybenzoic acid (1.5 moles, 207 g.) technical ,a'-dimethoxy-p-xy1ene (1 mole, 166 g.) and 1 ml. of diethyl sulphate.

The product had a softening point of 136"C. Heating of the product for 1 hour at 200"C gave a hard infusible cured material.

Claims (21)

WHAT WE CLAIM IS:

1. A curable resin having at least one carboxylic repeat unit of formula

and optionally at least one repeat phenolic unit of formula

the resin having terminal units containing phenolic groups, where ArX is a divalent or trivalent aromatic hydrocarbon or aromatic hydrocarbon-oxy-aromatic hydrocarbon group, each of which may have at least one inert substituent, HOAr(CH2)bCOOR2 I is a divalent radical derived from a molecule of formula HO Ar(CH2)bCOOR2 which is an aromatic phenolic carboxylic acid or ester thereof, by removal of 2 nuclear hydrogen atoms, ArOH I is a divalent radical from a molecule of formula ArOH, which is a phenol which does not contain a COOR2 group, by removal of 2 nuclear hydrogen atoms, R2 is a hydrogen atom or alkyl group of 1-6 carbon atoms, a is 2 or 3 and b is 0 or 1, the molar proportion of phenol of formula ArOH to the total phenol and phenolic carboxylic acid or ester being 0--50.

2. A curable resin having at least one repeat unit of

and terminated with groups derived from a phenol carboxylate of formula HOAr(CH2)bCOOR2, -wherein ArX is a divalent or trivalent aromatic hydrocarbon or aromatic-hydrocarbon-oxy aromatic group, each of which may have at least one inert substituent, HOAr(CH2)bCOOR2 is a divalent radical derived from a molecule of formula HO Ar(CH2)bCOOR2 which is an aromatic phenolic carboxylic acid or ester thereof, by removal of 2 nuclear hydrogen atoms, R2 is a hydrogen atom or alkyl group of 1-6 carbon atoms, a is 2 or 3 and b is 0 or 1.

3. A resin according to Claim 1 or 2wherein Ar represents a benzene nucleus.

4. A resin according to any one of Claims 1 -3 wherein b is 0.

5. A resin according to any one of Claims 1-4 wherein the phenolic carboxylic acid or ester is salicylic acid or p-hydroxybenzoic acid or an alkyl ester thereof.

6. A resin according to any one of Claims 1-5 wherein a is 2.

7. A resin according to Claim 2 wherein ArX is a phenylene group and the HOAr(CH2)bCOOR2 group is derived from salicyclic or p-hydroxybenzoic acid or an alkyl ester thereof.

8. A process for the preparation of a curable resin containing phenolic hydroxyl and carboxylic acid and/or ester groups, which process comprises reacting an aralkylene compound of formula ArX(CH2D)a, wherein ArX and a are as defined in Claim 1, and D represents a group of formula OR, X, or OYR1 where R is an alkyl radical of 1-6 carbon atoms, X is chlorine, bromine, or iodine, Y is a carbonyl or sulphonyl group and R1 is an alkyl group of 1 to 6 carbon atoms or aryl group of 6-13 carbon atoms, with (i) a molar excess of an aromatic phenolic carboxylic compound of formula Ar(OH)d(CH2)b(COOR2)c where d is an integer of 1--3, b is 0 or 1, c is an integer of 1--3, subject to the proviso that when b is 1, c is 1, R2 is hydrogen or an alkyl group of 1-6 carbon atoms, and Ar is the residue of an aromatic hydrocarbyl nucleus, which may be substituted with at least one halogen, nitro, alkyl or alkoxy group each of 1 > carbon atoms, phenyl or substituted phenyl groups, in which the substituent in the phenyl group is at least one hydroxyl, carboxylic group of formula COOR2, halogen, nitro or alkyl or alkoxy group each of 1A carbon atoms, with the proviso that the phenolic carboxylic compound contains no substituent in the nucleus in at least 1 position ortho or para to a hydroxyl group, or (ii) with a molar excess of a mixture of the aromatic phenolic carboxylic compound and up to 50 mole percent (based on the total amount of phenolic containing compound) of a carboxyl free phenol of formula Ar(OH)e where Ar is as defined above and e is an integer of 1--3.

9. A process according to Claim 8 wherein the aralkylene compound is reacted with the aromatic phenolic carboxylic compound in the presence of a Friedel Crafts catalyst or a dialkyl sulphate with 1-6 carbon atoms in each alkyl group.

10. A process according to Claim 9 wherein ArX is a phenylene group.

11. A process according to Claim 9 or 10 wherein the aralkylene compound is of formula ArX(CH2D)2 where D is of formula OR.

12. A process according to any one of Claims 9-11 1 wherein a is 2 and the resin is prepared by reacting 1.3-2.0 molar proportions of the aromatic phenolic carboxylic compound with one molar proportion of the aralkylene compound.

13. A process according to any one of Claims 9-12 wherein b is 0.

14. A process according to any one of Claims 9-13 wherein the Ar group is a benzene nucleus.

15. A process according to any one of Claims 9-14 wherein the carboxylic compound is salicyclic or p-hydroxybenzoic acid or an alkyl ester thereof.

16. A process for preparing a curable resin substantially as described in Example 1 or 2.

17. A curable resin prepared by a process according to Claim 8.

18. A curable resin prepared by a process according to Claim 9.

19. A resin composition comprising a carboxylic resin according to Claim 2 or 18 and a phenolic curable resin having at least one repeating unit of formula

where ArX and ArOH are as defined in Claim 1, and is terminated by the ArOH groups.

20. A cured product obtained by heating a curable resin according to Claim 18.

21. A cured product obtained by heating a curable resin according to any one of claims 17-19 with hexamine.