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<Production 2 of Polyester Polyol> 

In a one-liter four-necked flask installed with a thermom- eter, an induction stirrer, a condenser-equipped oil-water separator, and a dropping funnel, 170 g (1.5 moles) of succinic acid having a content of malic acid of 0.2 ppm (prepared by purifying succinic acid as produced by the fermentation method), 110 g (1.8 moles) of ethylene glycol as a polyhydric alcohol, and 80 g (0.9 moles) of 1,4- butanediol were charged. Thereafter, operations of pressure reduction to 30 Torr and pressure return with nitrogen were repeated several times, thereby substituting the inside of the reactor with nitrogen. 

The temperature was increased to 145° C. while stirring the reaction mixture, and stirring was kept at that tempera› ture for 30 minutes. At that time, since formed water started to come out, the removal of water formed from the con- denser was started. Thereafter, the temperature was increased to 190° C. over about one hour. After the tem› perature increase, 0.35 mL of a tetraisopropoxy titanium (TPT) 5 wt/vol % toluene solution was added. The pressure of the reactor was reduced from ordinary pressure to 20 Torr over about 2 hours, thereby removing a prescribed amount of the excessive dial together with water. Thereafter, when it was confirmed that the acid number became not more than 1.0 KOH-mg/g, the reaction was completed. 

After completion of the reaction, the temperature was decreased to 160° C., and a hydroxyl number of the contents in the flask was measured. For the purpose of obtaining a polyester polyol having a number average molecular weight of 2,000, in the case where the hydroxyl number is large than 56.0, the removal of the dial was further carried out; whereas in the case where the hydroxyl number is smaller than 56.0, the raw material polyhydric alcohol was added so as to correspond to the hydroxyl number of 56.0, and superheat› ing was carried out with stirring at 190° C. for an arbitrary period of time to achieve a depolymerization reaction, thereby regulating the hydroxyl number to about 56.0. As a result, a polyester polyol having a hydroxyl number of 55.8 (hydroxyl number-calculated molecular weight: 2,011) was produced. 

A polyurethane was produced in the above-described production method of Polyurethane Production 2, except for using 58.8 g of the foregoing polyester polyol as a raw material, 2.63 g of 1,4-butanediol as a chain extender, and 14.8 g (1.00 equivalent to the active hydrogen) of diphe› nylmethane diisocyanate (MDI) and using DMF as a sol› vent. At that time, the water content was 0.029 g (0.0016 moles) in total in the polyester polyol and the solvent. The resulting polyurethane revealed target results such that a weight average molecular weight was 198,000, and a molecular weight distribution Mw/Mn was 2.0. Also, an abnormal increase of the molecular weight was not observed, and excellent production stability was revealed. 

## Example 5 

From the foregoing results, as shown in the present Comparative Examples, it has been noted that in the case of producing a polyester polyol using, as a raw material, a dicarboxylic acid having a content of an organic acid having a pKa value of not more than 3. 7 of more than 1,000 ppm and producing a polyurethane using this polyester polyol, since the produced polyester polyol and polyurethane have a crosslinking structure, gelation and abnormal molecular weight increase occur at the time of polyisocyanate reaction due to the crosslinking structure, and hence, control of the reaction is difficult. Furthermore, it has been noted that physical properties of the resulting polyurethane are rigid and low in elongation. 

In addition, as shown in the present Comparative Examples, it has been noted that in the case of producing a polyester polyol using a dicarboxylic acid having a content of an organic acid having a pKa value of not more than 3.7 of O ppm (less than a detection limit) and producing a polyurethane using this polyester polyol, molecular weights of the produced polyester polyol and polyurethane do not sufficiently increase, and the mechanical strength of the resulting polyurethane is lowered. 

On the other hand, as shown in the present Examples, it has been noted that in the case of producing a polyester polyol using, as a raw material, a dicarboxylic acid having a content of an organic acid having a pKa value of not more than 3.7 of more than O ppm and not more than 1,000 ppm and producing a polyurethane using this polyester polyol, since a crosslinking structure appropriately relies upon the produced polyester polyol and polyurethane, not only the molecular weight or the like is easily controllable at the time of polyisocyanate reaction, but a polyurethane with suffi› cient mechanical strength is obtained. 

It has hitherto been considered that in a polyester polyol using, as a raw material, succinic acid as the dicarboxylic acid, the reaction control is difficult at the time of polyure› thane reaction, and physical properties of a polyurethane using it are rigid and low in elongation. However, by using certain specified succinic acid as a raw material, it has now been astonishingly noted that even when succinic acid is used as the raw material, the reaction control is possible, and furthermore, a polyurethane having sufficient mechanical strength can be produced. 

While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Incidentally, the present appli› cation is based on a Japanese patent application, filed Mar. 31, 2010 (Japanese Patent Application No. 2010-082393), the entire contents of which are incorporated therein and made hereof by reference. 

Since a biomass-resource-derived polyurethane using, as a raw material, a biomass-resource-derived polyester polyol according to the present invention is easily controllable in 

## INDUSTRIAL APPLICABILITY 

