Polyols transesterification with

PET wastes, proved to be an excellent raw material for low cost aromatic polyester polyols. By transesterification with DEG and (or) propylene glycol or dipropyleneglycol (DPG), liquid, low viscosity and low functionality aromatic polyester polyols were obtained. Due to the low cost, DEG is the preferred glycol for transesterification (reaction 16.3) [4, 6-8, 12]. 

The polyols that can be used for transesterification with castor oil are glycerol, trimethylolpropane, pentaerythritol, sorbitol, and sucrose. The catalysts of the reaction between castor oil and various polyols are alkali alcoholates, such as sodium methoxide or potassium methoxide. Thus, by the reaction of one mol of castor oil with two mols of glycerol, a mixture of mono, di and triglycerides of ricinoleic acid, having a much higher hydroxyl number than the initial castor oil, of around 420-430 mg KOH/g (reaction 17.5) is obtained. 

The 3-(ferf-butyl)-4-hydroxyphenyl motif can likewise be incorporated in extended polyol assemblies. For example, Hostanox 03 ethane-1,2-diyl-bis(3,3-bis(3-(tert-butyl)-4-hydroxyphenyl)butanoate), a product of Clariant, is preferentially used as an antioxidant for plastics with high resistance against hydrolysis. It can be produced on a large scale by the reaction of p-tert-h xXy phenol with methyl acetoacetate in the presence of an alkyl mercaptan and final transesterification with ethylene glycol catalyzed by Bu2SnO (Scheme 2.72) [42]. 

Ttirtin O, Kayaman-Apohan N, Kahraman MV, Mencelolu Y, Giingor A. 2008. Nonisocyanate based polyurethane/silica nanocomposites and their coating performance. J Sol-Gel Sci Technol 47(3) 290-299. Valero MF, Pulido JE, Ramirez A, Cheng Z. 2008. Polyurethanes synthesized of polyols obtained from castor oil modified by transesterification with pentaerythritol. Quim Nova 31 2076-2082. 

Recently, new poly(ether ester) polyols were synthesized by epoxidation, followed by hydroxylation and transesterification with 1,3-propanediol and 1,2-propanediol (Kong et al., 2011,2012) (Fig. 3.3). This reaction has the peculiarity of yielding polyols which do not contain the glycerol backbone. The hydroxyl number of these polyols ranges from 270 to 320mgKOH/g. 

Highly cross-linked polyol polytitanates can be prepared by reaction of a tetraaLkyl titanate with a polyol, such as pentaerythritol, followed by removal of the by-product alcohol (77). The isolated soHds are high activity catalysts suitable for use in the preparation of plasticizers by esterification and/or transesterification reactions. The insoluble nature of these complexes faciUtates their... 

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. 

Fatty Acid Esters and Fatty Alcohols Fatty acid esters are obtained by transesterification of triglycerides (vegetable oils) or by esterification of fatty acid with alcohol or polyols. Fatty alcohols are obtained by hydrogenation of esters on metal catalysts. Fatty acid esters and fatty alcohols are useful platform molecules to prepare surfactants, emulsifier, lubricants and polymers. 

Incorporation of the tetrahydrofuran ring into condensation polymers has been accomplished (79USP4180646) by transesterification of orthoester (43) with polyols to prepare poly (orthoesters) (44 Scheme 11). This polymerization reaction has been extended to a wide variety of other orthoester and orthocarbonate starting materials. The product polymers are reported to be excellent biodegradable matrices for drug delivery. 

PU was fully formed before initiation of the acrylic. In the present system, polyol concentration decreases as delay time increases. It is well-established (16) that organotin compounds are transesterification catalysts. Thus, it is suggested that, in the presence of the tin catalyst and during irradiation, transesterification between BMA and one or more of the OH groups in the polyols may lead to the formation of PU chains terminated with methacrylate moieties to provide grafting sites for BMA polymerization. 

Dimethyl terephthalate for the production of polyethylene terephthalate) is produced by the cobalt salt-catalyzed oxidation of p-xylene with oxygen (reaction 1.15).209 In this free radical process, some biphenyl derivatives are formed. In addition, triesters are formed from any trimethylbenzenes in the feed. Thus, the still bottoms contain several compounds, which are all methyl esters. Hercules found that transesterification of this mixture with ethylene glycol led to a mixture of polyols that could be used with isocyanates to form rigid polyurethanes. For the price, the Terate product was hard to beat. 

The direct polyesterification reaction of diacids with glycols is the most important industrial synthetic route to polyester polyols. The second most important synthetic route is the transesterification reaction between dimethyl esters of dicarboxylic or dibasic acids (dimethyl adipate, dimethyl terephthalate, dimethyl carbonate or even polyethylene terephthalate) and glycols (reaction 8.2) [1, 3-8]. 

The bottom residues from DMT fabrication are benzyl and methyl esters of dicarboxylic and tricarboxylic acids with biphenyl or triphenyl structures together with DMT [4, 6. By the transesterification reactions of these complex ester residues with diethyleneglycol (DEG), aromatic polyester polyols with a functionality in the range 22-23 OH groups/mol are obtained. 

The process of PET glycolysis with DEG has several disadvantages the reaction products are viscous liquids with a tendency to solidification or even to be solid at room temperature, the reproducibility of the characteristics of the resulting polyester polyols are difficult to realise (poor consistency) and the products of transesterification are not compatible with the blowing agents (pentanes or hydrofluorocarbons) [4, 6]. 

Thus, glycerol, the most important starter for the synthesis of polyether polyols for flexible PU foams and for polyether for rigid foams is produced by the hydrolysis of natural triglycerides (esters of glycerol with fatty acids with C6 to C22 carbon atoms), from vegetable or animal resources (reaction 17.1) [1]. Large quantities of glycerol appear in bio-diesel production, by transesterification of natural oils with methanol. 

By the transesterification of castor oil with polyols with high functionality and high hydroxyl number [29], or by transamidation with poly amines or alkanolamines [29] new polyols are obtained which are of real use in the fabrication of rigid PU foams with good physico-mechanical properties. These polyols are made without PO. 

The transesterification between castor oil and various polyols is an equilibrium reaction of all the hydroxyl group species from the reaction system with the ester groups. Because no reaction component is removed, the reaction time is in fact the time needed to establish the reaction equilibrium (around 1-2 hours at 90-120 °C). 

Figure 17.7 Structure of polyols resulting from transesterification of castor oil with...

The scission of urethane groups is explained by the following two consecutive reactions (20.13 and 20.14). The first reaction is the addition of alkylene oxide to the active hydrogen of urethane groups (20.13). The resulting hydroxyalkyl urethane, by an intramolecular transesterification, leads to the splitting of the urethane bonds of PU, the PU network is destroyed with the formation of an oxazolidone and a polyether polyol. 

Transesterification of polyols results in castor oil polyols with lower or higher functionality. Oxidation of castor oil, by blowing air or oxygen through the oil, results in polymerization that yields products with increased viscosity, specific gravity, and saponification value of the oil. The bodied oils have been reported to be more useful in urethane coatings than the untreated castor oil (10). 

This deblocking reaction is accelerated by certain catalysts and by the presence of a polyol which can compete with the caprolactam for the NCO group via a transesterification type reaction. The blocking of the isocyanate group allows lEM-containing polymers to be formulated with polyols to give room temperature-stable formulations which deblock and cross-link at higher temperatures. 

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