Rigid polyester polyols

Sometimes, this polyester is modified with oleic acid in order to improve its compatibility with blowing agents. The chemistry for the synthesis of rigid polyester polyols is absolutely the same as the chemistry for the synthesis of polyester polyols used in elastic PU, described in detail in the Chapter 8. 

Generally, these residues from DMT fabrication are difficult to transport and are used on-site to be transformed into aromatic polyester polyols by transglycolysis [4]. Excellent rigid polyester polyols are obtained from pure DMT (reaction 16.1). 

In this section, several methods for rigid polyester polyols synthesis, of minor industrial importance at this moment, but which present a real potential for developing new polyol structures will be presented. 

A synthetic method for rigid polyester polyols, by the propoxylation of compounds having both hydroxyl and carboxyl groups was developed [33, 34]. 

Propoxylation of organic hydroxy acids such as citric acid (16.12) [34] or propoxylation of the mixture between polyols and polyacids (for example sorbitol and adipic acid, reaction 16.13) give rise to interesting rigid polyester polyols [34]. 

The most important structures of rigid polyester polyols presented in this chapter (Chapter 4.4) are the low functionality aromatic polyester polyols with terephthalic or phthalic structures, used for PU/PIR rigid foams. 

Miscellaneous chemicals are used to modify the final properties of rigid polyurethane foams. Eor example, halogenated materials are used for flammabihty reduction, diols may be added for toughness or flexibiUty, and terephthalate-based polyester polyols may be used for decreased flammabiUty and smoke generation. Measurements of flammabihty and smoke characteristics are made with laboratory tests and do not necessarily reflect the effects of foams in actual fire situations. 

The avadabihty of PMDI also led to the development of polyurethane-modified isocyanurate (PUIR) foams by 1967. The PUIR foams have superior thermal stabiUty and combustibiUty characteristics, which extend the use temperature of insulation foams well above 150°C. The PUIR foams are used in pipe, vessel, and solar panel insulation glass-fiber-reinforced PUIR roofing panels having superior dimensional stabiUty have also been developed. More recently, inexpensive polyester polyols based on residues obtained in the production of dimethyl terephthalate (DMT) have been used in the formulation of rigid polyurethane and PUIR foams. 

Polyester Polyols. Initially polyester polyols were the preferred raw materials for polyurethanes, but in the 1990s the less expensive polyether polyols dominate the polyurethane market. Inexpensive aromatic polyester polyols have been introduced for rigid foam appHcations. These are obtained from residues of terephthaHc acid production or by transesterification of dimethyl terephthalate (DMT) or poly(ethylene terephthalate) (PET) scrap with glycols. 

Over 4 billion PETP bottles will be available for colleetion across Europe in 1999. PUR Products has introduced technology into the UK which involves glycolysis of postconsumer PETP into materials for the manufacture of rigid urethane foams for building insulation. This application offers a substantial new market for aromatic polyester polyols derived from glycolised PETP recyclate. PUR(PRODUCTS)LTD. 

The aromatic polyols resulting from the reaction can be mixed with commercial polyols, blowing agents, surfactants, catalysts, and polymeric isocyanates to produce a rigid polyurethane foam. n compared w control foams produced from commercially available polyester polyols, the foams produced from reclaimed materials were found to have essentially the same properties. 

The dimensional stability of low density, water blown rigid PU foams for pour-in-place thermal insulation applications was improved by the use of a phthalic anhydride based polyester polyol containing a dispersed cell opening agent. The foam systems obtained allowed some of the carbon dioxide to be released through the cell windows immediately after filling of the cavity, and to be rapidly replaced by air. Studies were made of the flowability, density, open cell content, dimensional stability, mechanical properties, thermal conductivity and adhesion (particularly to flame treated PE) of these foams. These properties were examined in comparison with those of HCFC-141b blown foams. 21 refs. 

Much work has been done on the incorporation of castor oil into polyurethane formulations, including flexible foams [64], rigid foams [65], and elastomers [66]. Castor oil derivatives have also been investigated, by the isolation of methyl ricinoleate from castor oil, in a fashion similar to that used for the preparation of biodiesel. The methyl ricinoleate is then transesterified to a synthetic triol, and the chain simultaneously extended by homo-polymerization to provide polyols of 1,000, 000 molecular weight. Polyurethane elastomers were then prepared by reaction with MDl. It was determined that lower hardness and tensile/elongation properties could be related to the formation of cyclization products that are common to polyester polyols, or could be due to monomer dehydration, which is a known side reaction of ricinoleic acid [67]. Both side reactions limit the growth of polyol molecular weight. 

The most important segments of polyester polyol applications are those of polyurethane elastomers (43% of global polyester polyols consumption), flexible foams (15-18%), coatings, adhesives, rigid foams, synthetic leather, and sealants. 

Mannich polyols, aromatic polyester polyols, novolak-based polyols) lead, by the reaction with crude MDI, to very rigid polyurethane structures [2] (see Chapter 15). 

The most important oligo-polyols for rigid polyurethanes are polyether polyols and aromatic polyester polyols [1-4, 6]. The aromatic polyether polyols, based on condensates of aromatic compounds with aldehydes, become very important polyols, especially after the introduction of new blowing agents (see Chapter 21). 

After this general presentation of oligo-polyols for rigid polyurethanes, each group of polyols will be presented in detail in the next few chapters, in order of importance, the most important being the group of polyether polyols, followed by the polyester polyols. 

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