Catalysts for polyesterol synthesis

A process of producing a polyesterol, the process comprising:

• catalyzing a reaction with a compound of formula I
• R1-CH2—S—S—CH2—R2 (I),
• wherein R1 is selected from the group consisting of Ar1 and —(CH2)x—COOH,
• wherein
• x is 0, 1, 2 or 3;
• and R2 is selected from the group consisting
• of Ar2 and —(CH2)y—COOH, wherein y is 0, 1, 2 or 3,
• wherein Ar1 and Ar2 are substituted or unsubstituted phenyl;
• wherein said reaction is a reaction of at least one di-carboxylic acid with at least one diol or polyol;
• and
• wherein an amount of the compound of formula I in a reaction mixture is between 1 to 104 ppm.