Blowing Agents and Their Use in Preparations of Polyester Foams

(1) Field of the Invention

This invention relates to quaternary ammonium borohydrides, their preparation and use in the preparation of polyester foams.

(2) Discussion of Prior Art

Some quaternary ammonium borohydrides are known and are used as reducing agents in organic reactions. In particular tetra-alkyl ammonium borohydrides are disclosed generally by B. D. James et al in "Progress In Inorganic Chemistry", Vol. 11, Interscience Publishers, 1970, pages 170-171. There is also disclosed in the same publication N,N'-dimethyl and N-methyl-N-ethyl piperidinium borohydride. Certain tetra-alkyl ammonium borohydrides are also disclosed in "Boron, Metallo-Boron Compounds and Borones", by Roy M. Adams, Interscience Publishers, pages 457-60.

It has now been discovered that quaternary ammonium borohydrides are useful in foaming compositions for foaming unsaturated polyester compositions. This is due to the characteristics that these compounds are extremely reactive with hydroxyl groups to release hydrogen in quantities suitable for foaming.

During research concerning foaming of polyester compositions, attempts were made to find liquid foaming compositions which might be used in conventional spray-mix apparatus in conjunction with polyester compositions. This research led to the discovery of new quaternary ammonium borohydrides useful in foaming compositions.

Accordingly, in one aspect the invention provides a quaternary ammonium borohydride which is liquid or a low melting solid easily liquified at ambient temperatures with small amounts of solvents or addition of impurity and is of the formula: ##STR2## where R.sup.1, R.sup.2 and R.sup.3 may be the same or different and each is selected from alkyl, alkenyl, cycloalkyl, aryl, alkaryl and aralkyl groups and R.sup.4 is selected from alkyl or alkenyl groups having from 1 to 30 carbon atoms with the proviso that R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are not all alkyl or that R.sup.1, R.sup.2 or R.sup.3 is not benzyl when the remainder of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are all methyl or ethyl.

Suitable low melting solid borohydrides are those which have a melting point of less than 60.degree. C., preferably less than 30.degree. C. In use, the melting point of such solid borohydrides can be depressed by the addition of impurity or by employing a mixture of borohydrides.

Another aspect of the invention provides a quaternary ammonium borohydride of the formula: ##STR3## in which R.sup.1 and R.sup.2 are methyl groups, R.sup.3 is a benzyl group and R.sup.4 is an alkyl or alkenyl group having 6 to 20 carbon atoms.

One method of preparing the novel compounds of the invention comprises mixing alkaline aqueous solutions of a borohydride salt and a quaternary ammonium salt corresponding to the desired quaternary ammonium borohydride, extracting the resulting quaternary ammonium borohydride with an organic solvent, and evaporating the solvent.

Another method of preparing the novel compounds according to the invention comprises adding, as reactants, a finely divided solid borohydride salt to an organic solution of a quaternary ammonium salt corresponding to the desired quaternary ammonium borohydride, and permitting the reactants to react to form quaternary ammonium borohydride in solution and precipitate by-product.

However, it is believed that these methods are novel of themselves and can also be employed for preparing known quaternary ammonium borohydrides. Accordingly, a further aspect of the invention provides a method of preparation of a compound which is a liquid or low melting solid at ambient temperatures and has the formula: ##STR4## in which R.sup.1, R.sup.2 and R.sup.3 may be the same or different and each is selected from alkyl, alkenyl, cycloalkyl, aryl, alkaryl and aralkyl groups and R.sup.4 is selected from alkyl or alkenyl groups having from 1 to 30 carbon atoms, which method comprises:

Mixing alkaline aqueous solutions of a borohydride salt, and a quaternary ammonium salt corresponding to the desired quaternary amine borohydride, extracting the resulting quaternary amine borohydride with an organic solvent, and evaporating the solvent; or

adding, as reactants, a finely divided solid borohydride salt to an organic solution of a quaternary ammonium salt corresponding to the desired quaternary amine borohydride, and permitting the reactants to reach to form quaternary amine borohydride in solution and precipitate by-product.

Polyester resin composition which may be foamed using quaternary ammonium borohydrides are the thermosetting polyesterification or condensation products of polyhydric alcohols with polycarboxylic acids at least one of which is ethylenically unsaturated. In practice, these polyester resins are used in admixture ith copolymerizable ethylenically unsaturated monomers. Preferred resins are of medium to high reactivity, i.e. those where molar ratio of ethylenically unsaturated polycarboxylic acid to other polycarboxylic acid is equal or greater than one.

In order to simultaneously foam and crosslink the polyester composition by the process of this invention, the polyester component is catalyzed with peroxide, hydroperoxide or perester. The catalysts useful in this invention are the peroxides which are used conventionally as curing agents for unsaturated polyester compositions. The particularly suitable ones are those which give acceptable pot life i.e. at least 8 hours when incorporated into the resin composition, i.e. benzoyl peroxide especially with admixture of cumyl hydroperoxide, tert. butyl hydroperoxide or tert. butyl perbenzoate.

In order to promote a better cure of the foamed product obtained by the process of the invention, a promoter can be included in the system. The promoter may be, for example, a tertiary amine which is stable with the borohydride. Preferred amines are dimethyl aniline and diethyl aniline and their mixtures. Due to the chemistry of the unsaturated polyester resin and the foaming system, this amine promoter has to be incorporated in the foaming component.

The resin composition can also contain hydroxyl bearing compounds such as organic acids, alcohols, glycols and polyglycols or their mixtures to act as activators for promoting the decomposition of the borohydride. Also addition of suitable surfactant is helpful in establishing a fine, uniform cell structure. This can be of anionic, cationic or nonionic nature. The preferred surfactant is of a silicon type. Fillers, additives such as fire retardants, dyes, thixotropic agents, waxes, etc. and reinforcement to modify properties and cost can also be incorporated into the resin composition.

The unsaturated polyester resin composition, and the liquid foaming agent are eminently suitable for use with conventional spray up equipment (supplied by Venus, Binks, Glasscraft, etc.). The foaming, gelling and cross-linking proceed on emergence of the mix from the head of the spraying equipment. Application of heat is unnecessary, the crosslinking reaction is exothermic. Using spray up equipment, the two components can advantageously be mixed in a ratio of polyester resin to foaming agent of 100 to 0.5 to 100:12 by volume in the spray up equipment.

In another embodiment of the invention, the polyester component suitably promoted is mixed in separate but successive steps with the foaming agent and curing catalyst. The promoter can be a transition metal salt such as a cobalt salt (e.g. naphthenate, octoate etc.) optionally in combination with a tertiary amine (e.g. dimethyl aniline, diethyl aniline or mixtures thereof). Alternatively, the amine may be incorporated in the foaming agent. The curing agent is a liquid peroxide or peroxidehydroperoxide, such as methyl ethyl ketone peroxide.

The three components can be mixed in small volumes by mechanical agitator or preferably using a modified 3 stream spray upon equipment. The foaming, gelling and cross-linking proceed on emergence of the mix from the head of the spraying equipment. The three components are advantageously mixed in a ratio of polyester resin to foaming agent to peroxide of 100:0.5-10:0.5-5 by volume, preferably 100:2-6:1-3.

The following preparative Examples are given for the purpose of illustrating the invention.

Quaternary ammonium borohydrides were prepared from the following quaternary ammonium salts:

The methods employed were as follows:

(a) From aqueous solutions of the starting quaternary ammonium salt

Sodium borohydride (1.05 mole) as 15% by weight solution in water at pH 12 was added to a solution of the quaternary ammonium chloride (1 mole) in water at pH 12. After agitation for two minutes, the mixture was extracted with methylene chloride, the organic layer separated and solvent removed (reduced pressure evaporation) to give the quaternary ammonium borohydride.

(b) From non-aqueous solutions of the starting quaternary ammonium salt

Powdered sodium borohydride (1.1 mole) was added to a solution in isopropanol of the quaternary ammonium salt (1 mole) and optionally aromatic amines (e.g. dimethyl aniline and diethyl aniline at 15% by weight in total) and the mixture was stirred for 1 hour. After filtration to remove the precipitated sodium salt, a solution of the quaternary ammonium borohydride was obtained. This solution may be used as a foaming composition in the preparation of foamed polyester resins.

In each case, the borohydride was obtained as a clear liquid. The identity of the product obtained was verified by infrared spectrum, nitrogen content and hydrogen content, with the results conforming generally with those expected from theoretical considerations.

Thus, for dimethyl benzyl ammonium borohydride (obtained from Alkaquat 451), quantitative elemental analysis of the product obtained indicated 4.1% nitrogen which agrees well with the calculated value of 4.14%.

The hydrogen content of the borohydrides, was ascertained by determination of the volume of hydrogen evolved when the salt was treated with dilute acid, since theoretically 4 moles of hydrogen are produced per mole of borohydride. For the dimethyl benzyl ammonium borohydride obtained as described above, it was calculated that 1 gram should produce 265 ml of hydrogen at standard temperature and pressure. Experimentally it was found that 1 gram of the Alkaquat based borohydride reaction product produced 259 ml of hydrogen, (not normalized to STP), thus indicating that substantially complete formation of the borohydride had been achieved in the reaction of the chloride with NaBH.sub.4.

Moreover, the infrared spectrum for the Alkaquat based borohydride showed clearly the B-H stretch and bend bands at 2200-2400 cm.sup.-1 and 1120 cm.sup.-1 for the sodium borohydride molecule and at 2130-2280 cm.sup.-1 and 1080 cm.sup.-1 for the quaternary ammonium salt.

These Examples illustrate use of the quaternary ammonium borohydrides in preparation of low density foams with filled and unfilled resin formulations. In these Examples, the following materials were used:

Resin 1: Unsaturated polyester resin based on propylene glycol, isophthalic acid and maleic anhydride of 3:1 maleic:isophthalic molar ratio.

Resin 2: Unsaturated polyester resin based on propylene and diethylene glycols, isophthalic acid and maleic anhydride or 1:1 acid:anhydride ratio.

Resin 3: Unsaturated polyester resin based on propylene and diethylene glycols, adipic, phthalic and maleic anhydride of 3.3:1 acids to maleic anhydride molar ratio.

Resin 4: Unsaturated polyester resin based on propylene and diethylene glycols, phthalic and maleic anhydride of 2:1 phthalic to maleic anhydride ratio.

Resin 5: Unsaturated polyester resin based on propylene glycol, phthalic and maleic anhydrides with 1:1 phthalic to maleic ratio.

Surfactant: (preferred) DC193, Dow Corning--a silicone glycol copolymer.

Thixotropic agent: Aerosil 200, Degussa--fumed silicon dioxide.

The components A and B were prepared according to the formulations detailed in the Table. Mixing and spraying was carried out using standard processing equipment, i.e. Venus H.I.S. System.

The components were mixed in spray equipment in a ratio of A to B of from 100:3 to 100:11 by volume to give foams which gelled within 10-20 sec. and cured within 5 minutes. The densities obtained for individual foams are shown in Table I.

These examples illustrate the use of a foaming agent in combination with cobalt-methyl ethyl ketone peroxide cure. Suitably formulated resin component (50 g) as shown in Table II was mixed with the peroxide and then with the foaming agent in a paper cup and the foam allowed to gel and cure. The gel time and the maximum cure temperature were recorded. The results are shown in Table II, with percentages being by weight based on the resin, unless otherwise indicated.

This example illustrates the use of the foaming agent in a three component system when using spray up equipment, namely a suitably modified three stream Venus spray gun. The resin component, formulated as shown in Table II with a surfactant, thixotropic agent, activator and promoters and filled with calcium carbonate and glass bubbles was spray mixed with the foaming agent and the curing agent at 3% and 2% by volume respectively. The foam produced gelled within 2 minutes and cured within 10 minutes to five fine celled foam of 0.72 g/cc density.