Process for producing polyester polyols having secondary OH end groups

1. A process for producing a polyester polyol comprising secondary hydroxyl end groups which comprises reacting a polyester comprising carboxyl end groups with an epoxide of formula (1):

wherein R1 represents an alkyl or an aryl and the reaction is carried out in the presence of a catalyst comprising:

(A) amines of formula (2):

wherein:

R2 and R3 represent, independently of one another, hydrogen, alkyl or aryl; or

R2 and R3 form, jointly with the N atom carrying them, an aliphatic, unsaturated or aromatic heterocyclic compound;

n represents an integer from 1 to 10;

R4 represents hydrogen, alkyl or aryl; or R4 represents —(CH 2 ) x —N(R41)(R42), wherein

R41 and R42 represent, independently of one another, hydrogen, alkyl or aryl; or

R41 and R42 form, jointly with the N atom carrying them, an aliphatic, unsaturated or aromatic heterocyclic compound;

x represents an integer from 1 to 10;

(B) amines of formula (3):

wherein

R5 represents hydrogen, alkyl or aryl;

R6 and R7 represent, independently of one another, hydrogen, alkyl or aryl;

m and o represent, independently of one another, an integer from 1 to 10; and/or:

(C) diazabicyclo[2.2.2]octane, diazabicyclo[5.4.0]undec-7-ene, dialkylbenzylamine, dimethylpiperazine, 2,2′-dimorpholinyldiethyl ether and/or pyridine,

wherein the polyester comprising carboxyl end groups exhibits an acid value of from ≧25 mg KOH/g to ≦400 mg KOH/g and a hydroxyl value of ≦5 mg KOH/g and wherein the polyester comprising carboxyl end groups is produced by ≧1.03 mol to ≦1.90 mol carboxyl groups or carboxyl-group equivalents of an acid component being employed per mol hydroxyl groups of an alcohol, and wherein the molar proportion of secondary hydroxyl groups amounts to ≧50 mol % to ≦100 mol %.

2. The process according to claim 1 , wherein the polyester comprising carboxyl end groups is produced immediately before the reaction with the epoxide of formula (1).

3. The process according to claim 1 , wherein the polyester comprising carboxyl end groups is obtained from

the reaction of ethylene glycol, diethylene glycol, the higher homologues thereof, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, 2-methylpropanedio1-1,3, neopentyl glycol, 3-methylpentanedio1-1,5, glycerin, pentaerythritol and/or 1,1,1-trimethylolpropane

with

succinic acid, fumaric acid, maleic acid, maleic acid anhydride, glutaric acid, adipic acid, sebacic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, phthalic acid, phthalic acid anhydride, isophthalic acid, terephthalic acid, pyromellitic acid, trimellitic acid and/or caprolactone.

4. The process according to claim 1 , wherein in the epoxide of formula (1) R1 represents methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, cyclohexyl or phenyl.

5. The process according to claim 1 , wherein in the amine of formula (2), R2 and R3 represent methyl, R4 represents hydrogen and n is 2; or

alternatively R2 and R3 represent methyl, R4 represents —(CH2)2—N(CH3)2 and n is 2.

6. The process according to claim 1 , wherein in the amine of formula (3) R5 represents methyl, R6 and R7 represent hydrogen, m is 2 and o is 2.

7. The process according to claim 1 , wherein the reaction with the epoxide of formula (1) takes place at a temperature of from ≧70° C. to ≦150° C.