Sucrose-polyether polyol

Mannich polyols are aromatic polyols, which confer excellent physico-mechanical, thermal and fire proofing properties to rigid PU foams. Mannich polyols, especially those based on p-nonyl phenol, have a very good compatibility with pentanes used as blowing agents (for example sucrose polyether polyols have a poor compatibility with pentanes, giving emulsions at normal concentrations for foaming, but not real solutions). 

Mix sucrose polyether polyol, foaming agent, catalyst, cross-linking agent, foam stabilizer, and frame retardant as white material, its appearance was bright yellow viscous liquid. 

Polyether polyol (Sucrose based, OH No. 360) Blowing agent, (CFC-11)... 

The most important low molecular weight polyols used as starters for polyether polyols destined for rigid PU foams synthesis are glycerol, trimethylolpropane (TMP), triethanolamine, pentaerythritol, dipentaerythritol, a-methyl glucoside, xylitol, sorbitol and sucrose [1-27]. The main properties of these starter polyols, which are of interest for polyurethane chemistry, are presented in Table 13.1. 

A very interesting catalyst used in the synthesis of polyether polyols for rigid PU foams is urea [41]. Sucrose poly ether polyols obtained in the presence of urea as catalyst have a very light colour [41]. Unfortunately with urea it is possible to obtain lower molecular weight polyether polyols, with an hydroxyl number (OH ) higher than 500 mg KOH/g. 

Reactors used for the synthesis of rigid polyether polyols need an internal stirrer, because frequently high melting point polyols (such as pentaerythritol or sucrose) are used as starters and the initial reaction mass is a suspension of solid polyols in liquid. 

Unfortunately, it is a difference between a starter, such as nonylphenol, or a fatty alcohol, which have only one type of hydroxyl group and polyols. Some polyols used as starters for rigid polyether polyols have in the same molecule various types of hydroxyl groups (for example, primary hydroxyls and secondary hydroxyls) which do not have equivalent reactivities in the alkoxylation reactions. For example, sorbitol has two primary hydroxyls and four secondary hydroxyls, sucrose has three primary hydroxyls and five secondary hydroxyls. In both polyols, the secondary hydroxyls have different substituents and they are not totally equivalent. TMP, pentaeriythritol and dipentaerythritol have only one type of equivalent primary hydroxyl group. Thus, the initiation reaction (reaction of PO with hydroxyl groups of starter) is in fact the sum of the reactions of PO with each type of hydroxyl group of the starter ... 

Many important polyols used as starters for synthesis of rigid polyether polyols are solid in the conditions used for PO (or/and EO) poly addition, having a melting point higher than 130 °C. Such polyols are sucrose (mp = 179-180 °C), pentaerythritol (mp = 253 °C), dipentaerythritol (mp = 222 °C), a-methyl glucoside (mp = 164-165 °C) and other polyols. As mentioned previously, the main technical problem is to react a solid polyol with a gaseous monomer. This problem was solved by several practical solutions ... 

One of the most popular technologies for synthesis of sucrose derived polyether polyols is based on the propoxylation of a mixture of sucrose - water (mixture very rich in sucrose). It is well known that water is the best solvent for substances having hydroxyl groups such as carbohydrates and polyols. Water is the best solvent for sucrose, one part of water is able to solubilise four parts of sucrose, at 100 °C. 

The representative examples are the synthesis of sucrose-based polyether polyols with a low melting point. Sucrose is well solvated by low molecular weight polyols such as glycerol, diethylene glycol, dipropylene glycol, triethanolamine and sorbitol. At the... 

Figure 13.8 Flow chart for sucrose-water technology for polyether polyol fabrication...

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. 

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. 

Table 13.5 shows the characteristics of some rigid polyether polyols, based on sucrose... 

Table 13.5 The characteristics of some sucrose - glycerol based rigid polyether polyols for rigid PU foams (structures I, II and III) ...

Table 13.6 The characteristics of a representative sucrose-triethanolamine-based rigid polyether polyol for rigid PU foams (structure I) ...

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. 

Unfortunately when KOH is used as catalyst, a suspension of sucrose in polyether polyol cannot be propoxylated totally, a substantial part of sucrose always remains unreacted. Sometimes, a very unpleasant phenomenon appears during propoxylation of solid sucrose suspended in a liquid polyether polyol, in the presence of KOH as catalyst. An aggregation of solid particles of sucrose into big particles takes place, which makes stirring impossible. This proves that polyether is a modest agent for sucrose solvation. 

Polyether polyol based on sucrose-glycerol mixture... 

Utilisation of sucrose as a starter polyol for rigid polyether polyols is extremely advantageous from the economic point of view. Sucrose is in fact a renewable raw material, commercialised on a large scale and available in a high purity form. The cycloaliphatic structure and the high functionality lead to high performance rigid polyether polyols. 

By solubilisation of propoxylated bisphenol A with the structure 15.28, in a sucrose-based polyether polyol for rigid foams, an homogeneous mixture is obtained [29]. The viscosities of these mixtures increase with the content of propoxylated bisphenol A. From these mixtures rigid PU foams were obtained. Due to the aromaticity introduced by the propoxylated bisphenol A, the physico-mechanical properties of the resulting rigid PU foams were superior to the rigid PU foams made with the sucrose-based poly ether polyol alone [29]. 

Sucrose, the most important starter for rigid polyether polyols is produced exclusively by extraction from naturally resources (Figure 17.1) [1]. 

The carbohydrate content of polyether polyols derived from a-methyl glucoside is much higher than the carbohydrate content of sucrose-based polyether polyols at the same viscosities. Thus, at a viscosity of 10000 mPa-s at 25 °C, sucrose polyols have a... 

Polyether polyols are prepared commercially by the base-catalyzed addition of alkylene oxides such as propylene, ethylene, and butylene oxide to di- or polyfunctional alcohols. Since, for most applications, it is desirable to have hydrophobic urethane compositions, propylene oxide is usually used alone or in combination with small amounts (generally less than 10%) of ethylene oxide. The alcohols used in the manufacture of polyethers include glycols (e.g., propylene glycol) for diols, glycerol, trimethylolpropane, and 1,2,6-hexanetri o 1 for triols, pentaerythritol and a-methyl glucoside for tetrols, sorbitol for hexitols, and sucrose for octols. The base-catalyzed addition of... 

Preparation of polyether polyols dispersions with high solids content and low viscosity from sucrose and propylene oxide with triethanolamine and tributylamine initiation [93],... 

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