Novel compositions comprising structural isomers of 1,4-cyclohexanedimethanol dibenzoate and polymer compositions containing same

This invention relates to novel mixtures containing two structural isomers of 1,4-cyclohexanedimethanol dibenzoate in controlled portions. More particularly this invention relates to a method for preparing these isomeric mixtures and the use of these mixtures to impart desirable properties to a variety of polymer compositions including but not limited to hot melt adhesives.

The dibenzoate of 1,4-cyclohexanedimethanol, hereinafter referred to as CHDM, exists in two isomeric forms. One of these is a trans form that can be represented by the formula

The second is a cis form that can be represented by the formula

It has been found that the cyclohexane ring in both of these isomers is in the “chair” form to avoid steric interactions between the bulky methylbenzoate groups.

One commercial process for preparing 1,4-cyclohexanedimethanol, the starting material for preparing the dibenzoate, involves hydrogenation of 1,4-cyclohexanedicarboxylic acid or an ester of this acid to the corresponding dialcohol. The isomeric distribution in the resultant mixture of cis and trans isomers is determined by the starting materials and hydrogenation catalyst. U.S. Pat. No. 6,919,489, which issued to Orth et al. uses a Raney nickel catalyst doped with rhenium to obtain CHDM with a cis to trans ratio of 0.7 or less from the dimethyl ester of the corresponding dicarboxylic acid having a cis to trans ratio of 1.2 to 2.1.

Other patents disclosing the ability to control the cis to trans ratio of CHDM by adjusting the conditions or molar ratio of hydrogen to a dialkyl ester of 1,4-cyclohexanedicarboxylic acid include U.S. Pat. Nos. 5,395,986 and 5,395,987.

Methods for separating the cis- and trans-stereoisomers of CHDM are reported in the literature. Malachowski et al (Ber. 1938, 71, 159 accomplish this by reducing diethyl hexahydroterephthalate with sodium and alcohol. From either the cis- or trans-hexahydro ester a stereoisomeric mixture of the corresponding alcohol was obtained. The cis- and trans esters in the mixture were separated by conversion to the corresponding benzoates followed by fractional crystallization and hydrolysis.

The present invention is based on the discovery of a method for separating a commercially available version of CHDM dibenzoate containing about 70 weight percent of the trans isomer and about 30 weight percent of the cis isomer into fractions containing up to 100 percent by weight of either isomer. Mixtures containing from 1 to 66 weight percent or from 72 to 99 weight percent of the trans isomer have not been reported in the literature and are therefore considered novel compositions.

The present inventors have discovered that the properties imparted to polymer compositions, particularly hot melt adhesives, by the present benzoate ester mixtures will vary considerably depending upon the relative concentrations of trans and cis isomers in the mixture.

U.S. Pat. No. 5,026,756 to William D. Arendt discloses that the distinguishing feature of the compound referred to in the patent as the dibenzoate of 1,4-cyclohexanedimethanol (hereinafter CHDMDB) relative to other esters of benzoic acid is the existence of a well-defined freezing point. When heated above their melting points and then allowed to cool to below this temperature most other dibenzoates will typically remain liquid at temperatures substantially below their melting points, a phenomenon referred to as “supercooling”.

The ability to reproducibly solidify makes the isomers of CHDMDB uniquely suitable for use in hot melt adhesives. The aforementioned Arendt patent contains the curve produced when a sample of CHDMDB is heated in a differential scanning calorimeter. The curve is described as bimodal, with melting points at “about 80 and 123° C.” The higher melting point is more sharply defined.

The CHDMDB described in the aforementioned Arendt patent is prepared from a commercially available product containing about 68 weight percent of the trans isomer and about 32 weight percent of the cis-isomer of CHDM.

The present invention is based on the discovery that when a mixture of CHDMDB isomers referred to in the aforementioned Arendt patent is heated above its melting point and then gradually cooled, a partial solidification in the form of a crystalline material occurs at a temperature of about 100° C. Analysis of this crystalline material by gas chromatography reveals that it is a mixture typically containing more than 90 weight percent of the trans isomer. The remainder of the molten material solidifies below about 70° C. to a non-crystalline material containing approximately equal weights of the trans and cis isomers.