540 Chemie und zugeordnete Wissenschaften
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This paper is directed to the development of a new type of branched aromatic polyester polyols (APP) based on PET wastes designed to produce high quality polyurethanes (PUR). To this end, a modifi ed transesterification of PET by a glycol mixture was used and simultaneously small amounts of triols were incorporated into the reaction mixture. By this method, a series of branched APP’s with hydroxyl numbers in the range of 260 to 380 mg KOH/g and hydroxyl functionalities between 2.00 and 2.30 was received. The viscosity of the products increased slowly with the functionality in the range of 2.03 to 2.12 and sharper beyond this value. An optimum of properties was found in each series of APP with hydroxyl numbers of 260, 320, and 380 mg KOH/g, resp. with respect of viscosity, long term stability and hydroxyl functionality. APP with a higher hydroxyl functionality are useful to produce cast polyurethane resins, those with lower hydroxyl numbers for coatings, e. g. of leather.