US 10,619,000 B2  82  81  TABLE 10-continued  Example 5  INDUSTRIAL APPLICABILITY  <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.  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  Amount of malic  Stress at break of  acid in raw material Molecular weight of polyurethane [Mwl polyurethane [MPal  Comparative  Example 4  succinic acid  [ppm)  5,000  MDI: 1.00  equivalent  375,000  MDI: 1.01  equivalents  (Gelated)  MDI: 1.00  equivalent  14.4 