Functionality sucrose-polyol mixtures

Figure 13.9 shows the equivalent functionalities of different sucrose - polyol mixtures as a function of the gravimetric ratio of sucrose/second polyol. Figure 13.9 shows that, except... 

By propoxylation of this mixture of sucrose - water, in anionic catalysis (KOH or NaOFI), propylene oxide (or EO) react not only with the hydroxyl groups of sucrose but react with water too, which is not an inert compound in this reaction (see Chapter 4). The reaction of PO with water causes diols (propyleglycol, dipropyleneglycol, etc.) to be formed, which decrease markedly the functionality of the resulting sucrose polyol. In order to minimise as much as possible, the diol formation, the propoxylation reaction of the sucrose - water mixture is divided into two steps ... 

The advantage of these types of processes direct propoxylation of a mixture of high melting point polyol with a low melting point polyol, is the perfect control of the final functionality in the resulting polyether (function of the ratio of sucrose/second polyol), and the simplicity of the process with only one propoxylation step, without intermediate distillations. 

The mixtures of sucrose - triethanolamine, usually of 1-1.5/1 (sucrose/triethanolamine) [9] are very stirrable mixtures, at the propoxylation temperature, and are frequently used in practice. Triethanolamine can be replaced by diethanolamine, monoethanolamine and even by ammonia [59]. The triol is formed in situ by the reaction of ammonia or primary or secondary ethanolamines with PO. The polyols based on sucrose - triethanolamine (Table 13.6) are frequently used to make rigid PU foams for thermoinsulation of freezers. The mixtures of sucrose - sorbitol lead easily to high functionality polyols, sorbitol having an excellent solvating capability for solid sucrose. 

DEG is a very interesting copolyol for making sucrose-based rigid polyether polyols. Due to the high polarity of ethylene oxide units, DEG-sucrose mixtures [51] show an excellent stirrability of the initial reaction mass, but only for medium functionalities of around 4-5 OH groups/mol. 

Polyether polyols for rigid PU foams or intermediate polyether polyols (with a higher hydroxyl number than the final polyether) proved to be excellent reaction media for the propoxylation of solid polyols, especially to obtain very high functionality polyols. These polyether polyols, used as a liquid reaction medium, are called heel . For example, at the PO polymerisation temperature (110-120 °C) a mixture of 60% sucrose and 40% sucrose-based polyether polyol is a perfectly stirrable mixture. 

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