Manufacture of block polyester polyols, and polyurethanes derived therefrom

A method for the manufacture of polyester polyols comprising:

• (a) feeding to a reactor (i) at least one aliphatic dicarboxylic acid having 4 to 10 carbon atoms, or ester thereof, (ii) up to one mole, per mole of acid, of at least one secondary dihydric alcohol having 4 to 8 carbon atoms, and (iii) 0.05 to 0.65 moles, per mole of acid, of at least one primary trihydric alcohol having 4 to 14 carbon atoms, the range of the molecular weights of said acid, dihydric alcohol and trihydric alcohol being not more than 100;
• (b) heating the mixture obtained in (a) in said reactor in the substantial absence of oxygen and removing water formed in the resultant esterification reaction;
• (c) when the amount of water removed from the reaction mixture of (b) is at least 95% of the stoichiometric amount for the formation of the polyol, cooling the resultant reaction mixture to a temperature of less than 140.degree. C. and adding 0.15 to 0.35 moles, per mole of acid, of at least one N-phenyl dialkanolamine and 0.10 to 0.70 moles, per mole of acid, of at least one primary trihydric alcohol having 4 to 14 carbon atoms such that the total amount of secondary dihydric alcohol, trihydric alcohol and dialkanolamine is greater than the amount of acid on a molar basis, the range of the molecular weights of said alkanolamine and trihydric alcohol and of said acid, dihydric alcohol and trihydric alcohol of (a) being not more than 100;
• and
• (d) further heating the reaction mixture and removing water to obtain a polyester polyol, said polyol having a hydroxyl number of less than 650, an acid value of less than 3.5 and a hydroxyl functionality of at least 2.0.