GB2033413A

GB2033413A - Phenol/aldehyde condensates; polyurethane foams

Info

Publication number: GB2033413A
Application number: GB7935488A
Authority: GB
Original assignee: Baxenden Chemicals Ltd
Current assignee: Lanxess Urethanes UK Ltd
Priority date: 1978-10-13
Filing date: 1979-10-12
Publication date: 1980-05-21

Abstract

Phenol/aldehyde condensates are prepared by reacting a phenol with an aliphatic aldehyde under non-aqueous conditions in the presence of an aliphatic polyol. The condensates are used as polyol component to react with isocyanates to form polyurethane or poly-isocyanurate foams.

Description

SPECIFICATION Improvements relating to polyurethanes This invention restates to improved polyurethane foams and is particularly concerned with foams obtained by reacting isocyanates with phenol/aldehyde reaction products.

The preparation of foamed plastic materials by reacting a di- or poly-functional isocyanate with an active hydrogen containing compound forms the basis of a well established industry and, when the active hydrogen compound is a hydroxy compound, it is possible to obtain polyurethane foams. The hydroxy compound may be a simple di- or poly-hydric alcohol, polyether alcohol or polyester alcohol.

One type of hydroxy compound that is readily available but has rarely been considered as a candidate hydroxy reactant for the production of polyurethane foams is the condensation product obtained by reaction between a phenol and an aldehyde. These reaction products fall into two categories depending upon whether the condensation between the phenol and the aldehyde is carried out under acid or under basic conditions. When such reaction products are to be used as hydroxy components in the production of rigid polyurethane foams, it is preferable that the reaction product be one of relatively low molecular weight. Traditionally, the reaction is carried out in aqueous medium and reaction tends to be exothermic and leads to the production of cross-linked novolak resins when the reaction is carried out under acidic conditions or resoles when the reaction is carried out under basic conditions.When such novolak or resole reaction products of high molecular weight are used as the hydroxy component in a foaming reaction with an isocyanate, it is found that irregular foams are formed and that, from the industrial point of view, a satisfactory polyurethane foam cannot easily be produced.

We have now found that it is possible to react a phenol with an aldehyde under non-aqueous conditions in the presence of a modifying polyol to give a reaction product containing both phenolic and alcoholic hydroxy groups which can subsequently be reacted with isocyanates to give satisfactory polyurethane or polyisocyanurate foams.

Accordingly, the present invention provides a process for producing a phenol/aldehyde condensate which comprises reacting the phenol with an aliphatic aidehyde under non-aqueous conditions in the presence of an aliphatic polyol.

In the most simple case, when the phenolic reactant is phenol itself and when the aldehyde is formaldehyde and the aliphatic polyol is ethylene glycol, the resole resins formed are etherified under acid conditions by the glycol to give a reaction product including residues having the structure

The reaction product therefore includes both phenolic and alcoholic hydroxy groups, as well as aliphatic ether groups, and each aromatic residue will frequently be substituted by one or more further aliphatic substituents including one or more ether linkages and terminating either in an alcoholic hydroxy group or linking to a further aromatic residue.

In accordance with the present reaction any phenolic compound can be used although it is preferred that the phenolic compound dontain a single aromatic ring system and a single phenolic hydroxy group. Consequently, phenol itself is the preferred phenolic reactant although substituted phenols may be used including cresols, xylenols, other alkyl substituted phenols such as tertiary butyl phenol, halogeno substituted phenols such as chloro phenols, chloro cresols etc., or 4,4'-thiodiphenol.

Of these various phenols, phenol itself and chlorophenol are preferred reactants.

The aliphatic aldehyde used as a reactant in the process of the present invention is preferably formaldehyde itself which may be used as such or in the form of an oligomer, e.g. paraformaldehyde.

Alternatively, use may be made of one of the higher aldehydes, such as propionaldehyde etc.

The properties of the eventual polyurethane foam are influenced by the nature of the aliphatic polyol used to modify the reaction between the phenol and the aldehyde. Thus, it is preferred to use an a-o-alkanediol containing from two to ten atoms in the chain linking the two hydroxy groups. The diol can be an alkane diol e.g. ethylene glycol, propane-i ,3-diol or butane-l ,4-diol but use of diols in which the carbon chain is interrupted by ether oxygen atoms, e.g. low molecular weight polymers of ethylene oxide or propylene oxide based on three to five alkylene oxide units is preferred.

In a variant of the process, use may be made of modifying compounds having from one to eight hydroxy groups such as ethanol, butanol, glycerol, TMP, pentaerythritol, sorbitol or sucrose. This variant can be adopted in cases where it is desired to increase or reduce the active hydrogen content of the phenol/aldehyde reaction product.

In a further variant, the phenol may be reacted with the aldehyde in the presence of an aromatic alcohol such as benzyl alcohol.

In order to produce a reaction product which will give rise to a satisfactory foam in subsequent reaction with an isocyanate, it is preferred that the phenol be reacted with the aldehyde in the presence of the modifying alcohol under non-aqueous conditions. Since water is formed as a by-product in the reaction when the modifying alcohol reacts with the hydroxy methyl groups introduced as a result of the reaction between the aldehyde and the phenol, it is important that this water of reaction be removed as far as possible or low density foams will result.To achieve this, it is desirable to carry out the condensation reaction at a temperature above 1 000C. It is desirable to reduce the pH of the reaction mixture to below 6 by introducing an acid such as maleic acid and then to heat the reaction mixture at a temperature above 1 000C until a desired number of hydroxymethyl substituents on the aromatic ring have been etherified. From the practical point of view, a reaction product suitable for use as the hydroxy component in the polyurethane foaming reaction is produced in two to five hours at temperatures in the region of 110 to 1 500C.

When the reaction is carried out under acidic conditions the initial reaction between the phenol and the aldehyde proceeds along lines similar to those occurring in the production of novolak resins.

However, it is preferable to avoid using inorganic acids since their presence in the subsequent foaming reaction with the isocyanate is undesirable. The use of acid catalysts throughout gives rise to a more linear reaction product which makes a more satisfactory hydroxy reactant for the production of polyisocyanurate foams.

It is also possible to carry out the reaction between the phenol and aldehyde in the presence of the modifying alcohol under base catalysed conditions when the initial reaction between the phenol and aldehyde proceeds along the conventional route in the production of resoles. For example the reaction can be carried out, still under non-aqueous conditions, in the presence of alkali metal compounds such as sodium or potassium hydroxide or sodium or potassium carbonate or in the presence of ammonia or in the presence of organic amines. When the reaction is carried out under basic conditions, it is preferred to use a reaction mixture having a pH of about 7 to 8.

It is also possible to combine both alkaline and acid conditions by carrying out the reaction between the phenol and formaldehyde initially under basic conditions and then to neutralise the reaction mixture with organic acid and add additional organic acid to reduce the pH to 4 to 6 when the etherìfication of the hydroxy methyl groups formed in the earlier resole reaction proceeds at a taster rate and a more cross-linked reaction product is obtained. Such cross-linked reaction products are more satisfactory hydroxy components for use in the production of polyurethane foams.

While it is possible to control the degree of cross-linking of the phenol/aldehyde reaction product by controlling the pH of the environment during reaction, it is also possible to control this by appropriate selection of reagents. For example, if use is made of an ortho or para-blocked phenol, e.g. parachlorophenol, the reaction product will be substantially linear.

The use of solvent as a diluent is not usually necessary in the production of the phenol/aldehyde reaction products in accordance with the invention. However an aromatic hydrocarbon solvent may be added to assist in the removal of water of reaction.

Once the modified phenol/aldehyde reaction product has been obtained in accordance with the present invention, this reaction product can be used as the hydroxy reactant in a reaction with an isocyanate to produce a polyurethane or polyisocyanurate foam. The reaction of the hydroxy compound of the invention with the isocyanate can be carried out using any of the isocyanates conventionally used in the polyurethane and polyisocyanurate foam industry and under the reaction conditions conventionally used in that industry.

Thus, the isocyanate will normally be an aromatic polyisocyanate such as 4,4'diisocyanatodiphenylmethane either as a pure compound, or, more usually, as a crude mixture or alternatively, may be toluene diisocyanate (TDI) which again, is normally available as a mixture of isomers.

A further aspect of the present invention therefore comprises a process for the preparation of a foam material which comprises reacting an aromatic di- or polyisocyanate with a phenol/aldehyde reaction product obtained by a process according to the present invention.

Foams of the present invention may be prepared under conventional isocyanate/hydroxy reaction conditions. Thus, the reaction mixture may include a catalyst, for example an aliphatic amine, particularly an aliphatic tertiary amine such as triethylamine or dimethylcyclohexylamine or an alkanolamine such as dimethylaminoethanol which is a preferred catalyst. Use may also be made of tin catalyst, for example an alkylated tin ester of a higher carboxylic acid, e.g. an acid containing from 8 to 1 8 carbon atoms, e.g. lauric or stearic acid, the alkyl group preferably containing 1 to 6 carbon atoms and, in this category, dibutyl tin dilaurate is preferred.

The foam forming reaction of the present invention will normally be carried out by reacting an isocyanate component comprising normally only the isocyanate with a resin component comprising the phenol/aldehyde reaction product according to the invention together with the catalyst and any other ancillary reactants or reaction assisters. The exact proportions of the resin component and the isocyanate component may be varied and will normally depend upon the chemical structure of the isocyanate component and the hydroxy component. It is convenient to be able to use approximately equal amounts by weight of the isocyanate component and the resin component so that use may be made of one of the commercially available foaming machines or spraying machines which are designed to be used with approximately equal amounts of the two types of reactants.

The amount of catalyst to be used with the foaming reaction may be varied and again will depend upon its chemical nature and the nature of the various reactants but normally will be in the region of 0.5 to 10% by weight of the hydroxy component.

It is frequently desirable to enhance the fire resistant properties of polyurethane and polyisocyanurate foams by incorporating in the reaction mixture a fire retardant such as one of the phosphate esters which have already become established as fire retardants in the polyurethane foam industry. The ester conventionally used is tris-(monochloropropyl)phosphate although other trishaloalkylphosphates such as tris-(chloroethyl)phosphate, tris-(dichloropropyl)phosphate or tris (dibromopropyl)phosphate may also be used. The amount of phosphate ester to be used will depend upon the nature of the isocyanate and hydroxy component to be used and the final phosphate ester concentration desired in the finished foam but will normally be in the region of 10% to 1 50% by weight of the hydroxy component.

Of course, the fire resistant properties of the foams obtained in the present invention can be influenced by the nature of the reactants used and, where the phenol/aldehyde reaction product is based upon chlorophenol, the fire resistant properties of the resulting foam may be adequate for certain purposes.

In addition to the catalyst and fire retardant, the resin component used in the foaming reaction of the present invention may also include surface active agents, e g. polyoxyalkylene polydimethylsiloxane copolymers which can act as a surfactant to modify the pore structure of the foam.

In addition to the hydroxy component obtained in accordance with the present invention, the foaming reaction mixture may also include further active hydrogen compounds such as glycerol or urea which can act as modifying and/or cross-linking reagents.

The following Examples are given to further illustrate the invention.

EXAMPLE 1 Into a flask fitted with a stirrer, thermometer, vigreux column and distillation head, phenol (225.6 g, 2.4 M), paraformaldehyde (124.6 g, 4.03 M) and diethylene glycol (249.4 g, 2.35 M) were introduced and heated to 1 350C in the presence of 0.35 g KOH. The viscosity of the mixture was followed and, when it reached 3.5 poise as 250C, 1.2 g maleic anhydride was added. The temperature of the mixture was maintained at 1 350C and the water of reaction was removed by fractional distillation. After a further period of two hours, the viscosity of the reaction product was found to be 2.0 poise at 500C and 45 ml of water of reaction had been collected.The reaction mixture was then cooled to give 500 grams of a resin, designated resin 1, which was a phenol/formaldehyde resole in which some of the hydroxy methyl groups were etherified with diethylene glycol. This reaction product included both phenolic and alcoholic hydroxy groups.

EXAMPLE 2 The procedure described in Example 1 was repeated reacting 2.82 kg (30 M) phenol, 1.855 kg (60 M) paraformaldehyde and 3.18 kg (30 M) diethylene glycol in the presence of 20 g maleic anhydride.

600 ml of water was collected. 6.5 kg of a resin, designated resin 2, were recovered which contained both phenolic and alcoholic hydroxy groups.

EXAMPLE 3 The procedure described in Example 1 was repeated using 1 88 g (2 M) phenol, 93 g (3 M) paraformaldehyde, 106 g (1 M) diethylene glycol and 92 g (1 M) glycerol. These reactants were heated at 1 400C in the presence of 2 g fumaric acid and after 40 ml water were collected, a resin 3 was recovered containing both phenolic and alcoholic hydroxy groups.

EXAMPLE 4 Polyurethane Foam A resin component was prepared containing the following Resin 1 28 parts by weight Tris-(chloropropyl)phosphate (TCPP) 11.5 parts by weight Polyoxyalkylenepo lydimethylsiloxane block copolymer (L5340) (ex Union Carbide) 0.55 parts by weight Dimethylaminoethanol (DMAE) 0.165 parts by weight Dibutyl tin dilaurate (DBTL) 0.033 parts by weight Freon 11 (fluorocarbon refrigerant) R.1 1 14.3 parts by weight 55 parts of the above resin component and 45 parts of the undistilled polymeric diisocyanatodiphenylmethane were then rapidly mixed together with vigorous agitation at room temperature. After 35 seconds the foam began to rise and was fully risen and tack free in approximately 2 minutes.The resulting foam was rigid and non-friable with K factor of 0.090 Btu in ft~2 F~lhr~1.

EXAMPLE 5 A resin component was prepared containing the following materials Resin 1 19.4 parts by weight TCPP 6.4 parts by weight Potassium acetate in dipropyleneglycol (1:4 parts by weight) 2.4 parts by weight 2,4,6, tris(dimethylaminomethyl)phenol (amine catalyst Anchor Chemicals) (K54) 0.24 parts by weight L5340 0.4 parts by weight Freon 11 11.2 parts by weight 40 parts of this resin component was mixed with an isocyanate component comprising 60 parts by weight of undistilled polymeric diisocyanatodiphenylmethane at room temperature. After a creaming time of 14 seconds, the foam began to rise to give, after 32 seconds, a tack free polyisocyanurate containing foam having a density of 1.84 pounds/cubic foot with a K factor 0.101 Btu in ft~20F~hr~1.

When the procedure described above was repeated using resin 2 in place of resin 1 , the cream time was 6 seconds and a tack free polyisocyanurate foam was obtained in 1 7 seconds of density 1.85 Ib/cu. ft.

EXAMPLE 6 A resin component was prepared having the following composition Resin 3 26 parts by weight TCPP 10 parts by weight L5340 0.5 parts by weight DBTL 0.03 parts by weight DMAE 0.25 parts by weight Freon 11 13.35 parts by weight 50 parts of the resin component was mixed with 50 parts by weight of isocyanate component comprising diisocyanatodiphenylmethane at room temperature. After a creaming time of 25 seconds the foam began to rise to give a tack free polyurethane foam in 1 minute 25 seconds. The foam had a density of 1.73 pound per cubic foot and a K factor of 0.148 Btu in ft~20F~'hr~1.

EXAMPLE 7 The procedure described in Example 1 was repeated replacing the phenol by the following substituted phenols and using the diethylene glycol (DEG) and paraformaldehyde in the following proportions

Mols Mols Resin Phenolic Phenolic Diethylene Mols No. Compound Compound Glycol Paraformaldehyde 4 t-butyl 2 1.96 3.84 phenol 5 orcresol 2 2 4 6 mcresol 2 2 4 7 zchloro- 2 2 4 phenol Resins 4 to 6 were reacted by the procedures described in Examples 4 and 5 to give polyurethane foams and polyisocyanurate foams. Resin 7 was reacted by the procedure described in Example 5 to give a polyisocyanurate foam.

EXAMPLE 8 The procedure described in Example 2 was repeated replacing the phenol by the following substituted phenolic compounds and using the diethylene glycol and paraformaldehyde in the following proportions

s Molts Mols Resin Phenolic Phenolic Diethylene Mol No. Compound Compound Glycol Paraformaldehyde 8 Cresylicacid 2 2 4 9 oCresol 2 2 4 10 pCresoi 2 2 4 11 pChloro- 2 2 4 phenol 12 4,4'-Thiodi- 2 2 4 phenol Resins 8 to 11 were reacted by the procedure described in Example 5 to give isocyanurate foams. Resin 12 was reacted by the procedure described in Example 4 to give a polyurethane foam. It was found that resins 7 and 11 gave rise to foams of superior fire resistant properties.

The procedure described in Example 2 was also repeated replacing the diethylene glycol by monoethylene glycol to give a resin 1 3 which was reacted by the procedure described in Example 5 to give an isocyanurate foam. This was found to be a more friable foam than the one obtained in Example 5.

Claims

1. A process for producing a phenol/aldehyde condensate which comprises reacting a phenol with an aliphatic aldehyde under non-aqueous conditions in the presence of an aliphatic polyol.

2. A process according to claim 1 wherein the phenol is phenol itself or a chlorophenol.

3. A process according to claim 1 or 2 wherein the aldehyde is formaldehyde.

4. A process according to any one of the preceding claims wherein the polyol is an alkane diol in which the alkane chain is optionally interrupted by at least one ether oxygen.

5. A process according to claim 4 wherein the polyol is diethylene glycol.

6. A process according to any one of the preceding claims wherein the polyol is partly replaced by a hydroxy compound having 1 or 3 to 8 hydroxy groups.

7. A process according to any one of the preceding claims wherein the reaction is carried out at above 1000C.

8. A process according to any one of the preceding claims wherein the reaction is carried out at a pH below 6 using an organic acid to control pH.

9. A process according to any one of claims 1 to 7 wherein the reaction is carried out at a pH of 7 to 8.

10. A process according to any one of the preceding claims wherein the reaction is carried out first under basic conditions and then at a pH of 4 to 6.

11. A process according to claim 1 substantially as hereinbefore described with reference to any one of Examples 1 to 3.

12. A phenol/aldehyde condensate obtained by a process according to any one of the preceding claims.

1 3. A process for the preparation of a foam material which comprises reacting an aromatic di- or poly-isocyanate with a phenol/aldehyde condensate according to claim 12.

14. A process according to claim 1 3 wherein the isocyanate is 4,4'-di-isocyanatodiphenylmethane.

15. A process according to claim 1 3 or 1 4 wherein the reaction is carried out in the presence of an aliphatic amine catalyst.

1 6. A process according to claim 1 5 wherein the reaction is carried out in the presence of a foam modifier which is a polyoxyalkylene polydimethylsiloxane.

1 7. A process according to claim 1 3 substantially as hereinbefore described with reference to any one of Examples 4 to 8.

1 8. A foam obtained by a process according to any one of the preceding claims.