GB2102825A - Polymer-modified polyols - Google Patents

Abstract

Dispersions of poly-addition product in a polyol are obtained by reacting pure 4,4' or 2,4' MDI or mixtures thereof with an olamine in the presence of a polyol. The olamine is preferably a trialkanolamine and the polyol is preferably a polyoxyalkylene polyol. The dispersions are particularly useful for preparing paring harder highly resilient flexible polyurethane foams for cushioning applications.

Description

SPECIFICATION Polymer-modified polyols This specification describes an invention which relates to polymer-modified polyols useful in polyurethane manufacture.

According to one aspect of the invention there is provided a polymer-modified polyol comprising a polyol and the reaction product substantially pure diphenylmethane diisocyanate and an olamine in which the olamine has reacted at least predominantly polyfunctionally with the isocyanate.

Other aspects of the invention include a method of forming the polymer-modified polyol, its use in the manufacture of polyurethane products, especially polyurethane foam, and the polyurethane products so obtained.

By the term "polymer-modified polyol" is meant a polyol containing additional polymeric material.

Such polymer-modified polyols are described in, for example, British Patent 1453258. These are dispersions of polyureas and poiyhydrazo-dicarbonamides in polyethers obtained by reacting polyisocyanates with primary and secondary amines, hydrazines or hydrazides in polyethers. The polymer-modified polyol of the present invention is generally a dispersion but may be a solution of a poly-addition product of pure diphenlymethane diisocyanate (hereinafter called pure MDI) and an olamine in a polyol.

The polyol used in the invention may be any of the polyols used in the manufacture of polyurethanes or mixtures thereof. These polyols contain two or more hydroxyl groups. They are well known to polyurethane technologists and are documented in the relevant literature. Normally the polyol will be a polymeric polyol such as a polyether, polythioether, polyester, polyesteramide, polyacetal or polycarbonate or a mixture thereof. Of particular interest, however, are polyether polyols having a molecular weight of from 200 to 10,000 such as are described in British Patent No. 1482213. Suitably they are polyoxyalkylene polyols obtained by reacting an alkylene oxide or mixture of alkylene oxides with an active hydrogen-containing initiator. Ethylene oxide-tipped polyoxypropylene polyols are especially useful for the manufacture of high resilience flexible polyurethane foams.Other poly(oxypropyleneoxyethylene)polyols in the form of random or block copolymers are also useful.

Pure MDI is obtained by distilling crude diphenymethane diisocyanate (hereinaftercalled crude MDI) which is made by phosgenating a mixture of polyamines obtained by the acid condensation of aniline and formaldehyde. Crude MDI is a mixture of a diphenylmethane diisocyanates and polymethylene polyphenyl polyisocyanates of higher functionality and when distilled, the distillate consists largely of diphenylmethane-4,4'diisocyanate and smaller amounts of the 2,4'-isomer and sometimes traces of the 2,2'-isomer. By further refining procedures, it is possible to obtain isomer mixtures having different compositions or, if desired, to separate the isomers as individual compounds. These various forms of pure MDI and their methods of preparation are well known to polyurethane technologists and are documented in the relevant literature.

In this specification pure MDI means dipheny Imethane diisocyanate which is substantially free from polymethylene polyphenyl polyisocyanates. It may comprises a single isomer of diphenylmethane diisocyanate or a mixture of isomers.

Of particular interest are pure MDI containing 70 to 100%, especially 80%, by weight of the 4,4'-isomer and from 0 to 30%, especially 20%, by weight of the 2,4'-isomer, and the pure 4,4' and 2,4'-isomers themselves.

By the term "olamine" is meant an organic compound having one or more hydroxyl groups and also one or more primary, secondary or tertiary amine groups. Having two or more active hydrogen atoms the olamine can react polyfunctionaly with pure MDI to form a poly-addition product. Where the olamine is a primary or secondary amine it has hydroxyl and amine groups with active hydrogen atoms which may be reactive towards the isocyanate groups of the pure MDI. Where it is a tertiary amine it has two or more hydroxyl groups with active hydrogen atoms all of which may be reactive towards the isocyanate groups of the pure MDI. In each case all or some of the reactive hydrogen atoms may, in fact, react with isocyanate groups.

Suitably the olamine is an alkanolamine which may carry substituents such as halogen atoms. The alkanolamine may be a primary, secondary or tertiary alkanolamine, such as a monolkanolamine or a dialkanolamine either of which may carry an N-alkyl substituent in which the alkyl group conveniently contains 1 to 4 carbon atoms. Preferably it is a trialkanolamine, such as tri-isopropanolamine and especially triethanolamine.

Thus in a preferred aspect of the invention there is provided a polymer-modified polyol comprising a polyol and the reaction product of substantially pure MDI and a trialkanolamine.

Trialkanolamines which may be used include substantialy pure trialkanolamine, for example, 98% by weight of pure triethanolamine which contains about 2% by weight of diethanolamine and trace amounts of monoethanolamine; commercial grades of trialkanolamines, for example, a commercial grade of triethanolamine which contains 83 to 85% by weight of triethanolamine, about 15% by weight of diethanolamine and 1 to 2% of monoethanolamine; and commercial grades which have oxyalkylated to reduce the di- and mono-alkanolamine content, for example a commercial grade of triethanolamine which has been treated with an alkylene oxide, such as ethylene oxide, a butylene oxide or epichlorohydrin and especially propylene oxide, until the combined mono- and di-alkanolamine content, expressed as dialkanolamine, has been reduced to less than 5%, preferably 2% or less, by weight of the treated material. Oxyalkylated trialkanolamines of this type are described in British Patent No. 1140867.

According to another aspect of the invention there is provided a method of forming a polymer-modified polyol in which substantially pure MDI is reacted with an olamine in the presence of a polyol, the olamine reacting at least predominantly polyfunctionally with the MDI. In another preferred aspect of the invention there is provided a method of forming a polymer-modified polyol in which substantially pure MDI is reacted with a trialkanolamine in the presence of a polyol.

In carrying out the method of the invention, the substantially pure MDI and olamine are mixed together in a molar ratio of about 0.5:1.0 to 1.5:1, preferably 0.8:1.0 to 1.1:1.0 and especially 1.0:1.0, in the presence of the polyol. The molecular weight and viscosity of the poly-addition product so formed may be varied by adjusting the ratio of pure MDI and olamine. Generally, the higher the proportion of pure MDI used, the higher is the molecular weight and viscosity of the product.

The molecular weight of the the poly-additon product may be varied by introducing monofunctionally reactive compounds to act as chain terminators. Such compounds are described in British Patent No. 1453258 and include monofunctional isocyanates, amines and N-dialkylalkanolamines.

They may usefully be used in amounts of up to 25 mol % of the olamine.

The reaction may be catalysed by a catalyst of the type and in an amount conventionally used for the formation of polyurethanes, for example, an organometallic compound such as stannous octoate and dibutyl tin dilaurate or an amine such as triethylene diamine.

The concentration of the poly-additon product in the polyol may vary within wide limits but for most purposes it will be between 1 and 35% by weight, usually from 3 to 30% by weight, of the polyol. The reaction is exothermic. Generally, the higherthe concentration of the poly-addition product to be formed, the greater is the exotherm.

The polymer-modified polyol of the invention may be formed by a batch process in which one of the olamine and pure MDI reactants is dissolved or dispersed in the polyol followed by the addition, with agitation, of the other reactant. Where a dispersion is formed, it will normally have a finer particle size if the reactants are mixed more efficiently. The viscosity of the product will also tend to be lower. Alternatively, the polymer-modified polyol may be formed by a continuous in-line blending process. in this process the olamine, pure MDI and polyol are pumped at controlled rates and may be mixed simultaneously or one reactant may be mixed firstly with the polyol followed by addition and mixing of the other reactant.

Normally it will be sufficient to add the components at room temperature allowing the temperature to rise to up to 1 50 C through the exothermic reaction and heat generated by high shear mixing, if used.

The polymer-modified polyols of the invention are useful in the manufacture of polyurethane products, especially polyurethane foams.

Polyurethane products are made by reacting a polyisocyanate with a polyol. A blowing agent is added to produce a foamed product. The polymermodified polyol of the invention may be used as the polyol component to produce flexible, elastomeric, semi-rigid and rigid foams. The nature of the foam will depend on the particular polyol chosen in preparing the polymer-modified polyol and also on the polyisocyanate and other ingredients conventionally used in the manufacture of polyurethane foams. They may be selected in known manner to produce the type of foam desired.

Polyisocyanates whic may be used in making polyurethane prdducts include aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates. Such isocyanates are well known to polyurethane technologists and are documented in the relevent literature (see, for example, British Patent No. 1453258). Of particular interest are the aromatic polyisocyanates, for example tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI) which are commerically available in substantially pure and crude forms.More particularly these include 2,4 and 2,6-tolylene diisocyanates and mixtures thereof; the pure MDI used in preparing the polymer-modified polyol; mixtures of MDI with polyphenyl polymethane polyisocyanates made by phosgenating a mixture of polyamines which is obtained by condensing aniline with formaldehyde (generally referred to as crude or polymeric MDI); and mixtures of TDI and MDI, pure or crude, for example, a mixture containing 60% by weight of TDI and 40% by weight of MDI. There may also be used diisocyanates which have been modified in known manner to introduce a significant isocyanurate, carbodiimide, uretonimine, biuret or allophanate content.Other polyisocyanates which may be used include isocyanate-ended prepolymers, for example, reaction products of a diisocyanate with a deficiency of one or more low molecularweight polyols such as trimethylol propane, dipropylene glycol or tripropylene glycol.

The polymer-modified polyols of the invention are of particular value in making highly resilient flexible foams for cushioning and similar application. These types of foams and their method of manufacture are well-known in the polyurethane foam industry. Such foams made from the polymer-modified polyols of the invention have advantages in respect of increased hardness and shrinkage properties. For foams of this type the polymer-modified polyol is usefully prepared from polyoxyalkylene polyols, especially ethylene oxide-tipped polyoxypropylene polyols, and reacted with TDl, pure or crude MDI, or mixtures of TDI or a TDI prepolymer and pure or crude MDI.

The polymer-modified polyols of the invention may be used directly they are made, or stored. If they are made by a continuous in-line blending process an intermediate storage vessel between the blending unit and polyurethane mixing head may be used, if necessary, to allow reaction between the pure MDI and olamine to be completed where this is slow.

Polymer-modified polyol dispersions have good storage stability and can be stored before use.

Other conventional ingredients may be used in making the polyurethanes. These include catalysts, for example, tertiary amines and organic tin compounds, surfactants, cross linking or chain lengthen ing agents, for example, low molecular weight diols, triols and diamines, flame proofing agents, for example, halogenated alkyll phosphates, fillers and pigments. Blowing agents used for forming polyurethane foams include water, which reacts with the polyisocyanate to form carbon dioxide, and inert low boiling liquids such as halogenated hydrocarbons, examples of which are trichlorofluoromethane and dichlorodifluoromethane. Foam stabilisers, for example polysiloxane-polyalkylene oxide block copolymers, may be used to stabilise or regulate the cells of the foam.

The amount of these minor ingredients and blowing agents used will depend on the nature of the product required and may be varied within limits well known to a polyurethane foam technologist. In the case of high resilient water blown flexible foams, it is appropriate to use from 1.0 to 5.5%, preferably from 1.5 to 4.0%, by weight of water based on the weight of the total polyol component. An inert low boiling liquid may be used as an additional blowing agent, if it is desired to reduce the foam density.

In general, the composition of the foam-forming reaction mixture should be such that the ratio of isocyanate groups to active hydrogen atoms is within the range of 0.7:1 to 1.2:1, preferably 0.8:1 to 1.1:1.

One shot, prepolymer or quasi-prepolymer methods may be employed as may be appropriate for the particular type of polyurethane being made.

The components of the polyurethane forming reaction mixture may be mixed together in any convenient manner, for example by using any of the mixing equipment described in the prior art for the purpose. If desired, some of the individual components may be pre-blended so as to reduce the number of component streams requiring to be brought together in the final mixing step. It is often convenient to have a two-stream system whereby one stream comprises a polyisocyanate or prepolymer and the second stream comprises all the other components of the reaction mixture.

Claims (4)

1. A polymer-modified polyol comprising a polyol and the reaction product of substantially pure diphenylmethane diisocyanate and an olamine in which the olamine has reacted at least predominantly polyfunctionaly with the isocyanate.

2. A polymer-modified polyol comprising a polyol and the reaction product of substantially pure MDI and a trialkanolamine.

3. A method of forming a polymer-modified polyol in which substantially pure MDI is reacted with an olamine in the presence of a polyol, the olamine reacting at least predominantly polyfunctionally with the MDI.

4. A method of forming a polymer-modified polyol in which substantially pure MDI is reacted with a trialkanolamine in the presence of a polyol.