Technology for Polyester Polyols Fabrication

In the second stage of the polyesterification reaction the pressure is decreased to 400-200 Pa. In this second stage the polyesterification catalyst can be added, such as p-toluene sulfonic acid, stannous octoate, titanium, lead or manganese compounds. Carrier gas or inert solvents, which give azeotropes with water (for example, xylene) may be used, to help the water elimination as much as possible. 

The evolution of the polyesterification reaction is monitored by measuring the quantity of water distilled and by the determination of acid number, hydroxyl number and viscosity. 

Finally, the resulting polyester polyol is filtered and sometimes stabilised with acid scavengers, such as epoxies or carbodiimides (reactions 8.25 and 8.26). 

Transesterification reactions between dialkyl esters of dicarboxylic acids and glycols are made using similar equipment. 

The composition and structure of the polyester polyols lead to polyurethanes with distinct properties. These polyester-based polyurethanes have specific applications, as shown in Table 8.5. 

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