Solid polyols

Figure 5. Weighted concentration of effective strands versus bake temperature for a typical high solids polyol crosslinked with hexamethoxymethylmelamine. The ratio of methoxy to hydroxy groups is given by "R". For the dashed lines, the extent of methoxy self-condensation is assumed to be zero. The solid lines use the self-condensation data of T. Nakamichi, Prog. Org. Coat., 14, 23 (1986).

While nitric acid is a good solvent for many organic substrates, sulfuric acid is not, and its presence often reduces the solubility of polyols in the mixed acid, leading to heterogeneous suspensions. This is the case for many solid polyols, particularly sugars which form heterogeneous pastey masses on addition to mixed acid. This has meant, for some substrates, nitric acid is... 

We were supported in our thesis by the work of Huddelston et al In order to achieve phase separation, they employed a salting out principle with good success. We employed a polyalcohol backbone and achieved phase separation by reacting the terminal alcohol groups with isocyanates. This was done after the addition of crosslinking chenficals yielded a solid polyol, which, as we will show in subsequent chapters, has the extractive properties we sought. Additional processing techniques allowed us to build an open-cell structure that permitted the flow of fluids and extracted the pollutants. 

Care must be taken when melting any solid polyols not to overheat the drum. This can cause an explosive drum rupture. 

Several solid polyols can be used as direct compression diluents, usually after some physical modification. Most such polyols can be obtained from natural sources, but are usually manufactured by hydrogenation of the parent sugar molecule. Some properties of polyols, together with comparative data for lactose and sucrose, are shown in Table 6. 

Normally a 70/30 to 50/50 blend of a 4500-6500 EO-capped polyether triol with a polymer polyol is used, together with an 80 20 blend of TDI (80/20 isomer ratio) and polymeric MDI. Recently, higher-solids-content graft polyols, e.g., 30-50% solid polyols, have become available in the market. 

This area is expected to see further growth for RIM, part of which will come at the expense of cast systems (4). Many new formulations with inproved properties will become possible through the use of "HOT RIM" equipment which will allow low melting solid isocyanate MDI prepolymers to be used along with low melting solid polyols in the "B" side. 

The oligo-polyol s viscosity is determined using a Brookfield viscosimeter. The Standard Test Method for oligo-polyol viscosity determination is ASTM D4878 [37]. There are two test methods, A and B, applicable for viscosities between 0.01 to 1000 Pa-s, at 25 °C, or for solid polyols (such as polytetrahydrofuran), at 50 °C. Test method A is indicated for oligo-polyols of very high viscosities. 

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. 

In order to decrease the total reaction time, a small reactor, with a stirrer, is linked to the polymerisation reactor, for the preparation of the initial starters - catalyst mixture. In this reactor, there are 1-3 polyols used as starters, the catalyst (KOH, NaOH or a tertiary amine) and sometimes, for solid polyols, an initial liquid medium (for example a part of an intermediary or final polyether polyol called heel , or an inert solvent). Generally, in the synthesis of polyether polyols for rigid foams it is preferred to avoid the utilisation of inert solvents, which need recycling and a more complicated installation. 

The second group of polyols, which are solid at the temperature conditions of PO polymerisation lead to very serious technological problems how is it possible to efficiently react a solid polyol with a gaseous monomer (PO boiling point (bp) is 33.6 °C and the EO boiling point is 10.8 °C). This problem was solved in various ways and is discussed in detail in section 13.2.4. 

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 ... 

In all the previous variants for propoxylation of solid polyols one thing is very important the second substance added must solvate the solid polyol well. The reaction between gaseous monomer and solid polyol takes place at the surface, and partially, with the solvated polyol. Liquid adducts of PO to the solid polyol are formed. These adducts are solubilised into the liquid reaction medium and, step-by-step, all the solid is transformed in liquid polyether polyols. If the liquid reaction medium does not solvate the surface of the solid polyol well, a large quantity of unreacted polyol remains at the end of the propoxylation reaction. 

Of course, in some variants, the solid polyols are partially solubilised, for example in water, in glycerol or in DMF. In these situations the reaction takes place without problems in the liquid phase and, at the same time at the well solvated surface of the high melting... 

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. 

Of course the polyether polyol having terminal hydroxyl groups is not inert in propoxylation reactions. It was observed experimentally that, due to the presence of primary hydroxyl groups in all solid polyols, PO reacts preferentially with the solid polyol and not with the polyether which generally has only secondary hydroxyl groups. On the other hand, the superior reactivity of short chains, as compared with long chains, is another element which makes PO react preferentially with the solid polyol. For example, in the presence of amines used as catalysts, the polyether reacts with only 10-15% of the total PO used for synthesis. 

The polyoxyalkylation of polyhydroxy compounds is usually carried out using basic catalysts in high-pressure reactors. The starting polyols are in most cases solids and are reacted with either ethylene or propylene oxide with or without a solvent (e.g., water, xylene, DMSO), under about 100 psig pressure at temperatures ranging from 100°C to 150°C. In most cases the reaction is run under anhydrous conditions. When water is used, a low-molecular-weight polyoxyalkylene derivative is observed and this is used again as the solvent for subsequent polyoxyalkylation reactions of the solid polyol. 

Tertiary amine catalysts are suggested for the addition of alkylene oxides under anhydrous conditions to alkali sensitive, solid polyol initiators such as sucrose (11, 12). It has been claimed that the use of a triaTlcylamine catalyst containing two or three carbon atoms in the alkyl group limits the addition to only one hydroxypropyl group on each of the hydroxyl groups of the initiator (] ),... 

When uncatalyzed, primary alcohol groups react with isocyanates two or three times as fast as secondary alcohol groups, whereas the presence of catalysts, particularly metal catalysts, cause an even greater spread in reactivity between primary and secondary alcohol groups (20-22). Recently Knodel ( ) reported the use of mixtures of ethylene oxide and propylene oxide in the preparation of polyether polyols from solid polyol initiators such as sucrose in the presence of trimethyl- or triethylamine as catalysts. This process was said to reduce the preparation time for the polyether polyols by as much as 67 percent, and the viscosity of the resulting polyether polyol was lower than in conventional processes using propylene oxide as the sole alkylene oxide. 

Uniplex 260 is a solid polyol benzoate modifier for a wide range of polymers. Considered as a very safe plasticizer. 

Properties Pale yel. solid, polyol odor sol. in water, aliphatic ketones, alcohols, glycol ethers, esters, aromatic hydrocarbons si. sol. in aliphatic hydrocarbons sp.gr. 1.08 (70 C) vapor pressure < 0.1 mm Hg acid no. 0.1-0.3 hyd. no. 73.4-81.4 flash pt. (PMCC) > 300 F Toxicology Not expected to cause skin or eye irritation Precaution Incompat. with strong oxidizing materials Hazardous decomp, prods. Thermal decomp, may produce CO ... 

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