Polyester polyols synthesis

The third type of reaction for polyester polyols synthesis is the ring opening polymerisation of cyclic esters, such as -caprolactone (reaction 8.4) or cyclic carbonates, such as ethylene glycol carbonate, propylene glycol carbonate, neopentyl glycol carbonate, etc., (reaction 8.5) initiated by diols (or polyols) and catalysed by specific catalysts [7, 16]. 

Table 8.1 The most important diols and triols used for polyester polyol synthesis ...

The intensive research done in the last few years proved that the hydrophobicity of the glycol or of the dicarboxylic acid used for polyester polyol synthesis is one of the most important parameters to improve the hydrolysis resistance of polyester-based PU. 

Figure 8.3 Installation for polyester polyols synthesis. 1) polyesterification reactor 2) separation column 3) induction elements for heating 4) condenser 5) vessel for condensed water 6) vacuum pump 7) filter...

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. 

All these products sebacic acid, 1,10-decanediol and 1,12-hydroxystearyl alcohol are interesting raw materials for polyester polyol synthesis. 

Synthesis MDI prepolymer with 1000 MW polyester polyol, NCO/OH = 2.0, chain-extended with 1,4-butandiol, acid number of polyester 0.6. 

Hie most representative member of this class of polyesters is the low-molar-mass (M 1000-3000) hydroxy-terminated aliphatic poly(2,2/-oxydiethylene adipate) obtained by esterification between adipic acid and diethylene glycol. This oligomer is used as a macromonomer in the synthesis of polyurethane elastomers and flexible foams by reaction with diisocyanates (see Chapter 5). Hydroxy-terminated poly(f -caprolactonc) and copolyesters of various diols or polyols and diacids, such as o-phthalic acid or hydroxy acids, broaden the range of properties and applications of polyester polyols. 

Polyester polyols have an intrinsic defect they are liable to hydrolyse under high humidity/temperature conditions. To prevent the hydrolysis of polyester-based polyurethanes a worldwide research effort, led to the synthesis of polyester polyols with improved hydrolysis resistance [1, 6-8, 12, 13]. 

The hydrolysis susceptibility of a polyester or a polyester-based PU depends on the concentration of ester bonds, on the polyester polyol acidity, on the hydrophobicity of the glycol or dicarboxylic acid used for polyester synthesis, and on the steric hindrance around the ester groups. Low concentration of the ester bonds, low polyester acidity, high comonomer hydrophobicity and high steric hindrance around the ester groups confer hydrolysis resistance to the polyester-based PU. 

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. 

Polyester polyols with equivalent weight of 167, functionality of 2 OH groups/mol, hydroxyl number of 310-350 mg KOH/g and viscosity of 1,300-3,000 mPa-s at 25 °C, are used in thermal insulation of appliances. The initial ratio between DEG and PET used in synthesis, followed by the utilisation of one of the previously mentioned procedures avoids solidification (section 16.2, a-e), and means that a large range of aromatic polyester polyols, having various hydroxyl numbers, functionalities and aromaticity can be obtained. 

Other Methods for the Synthesis of Polyester Polyols for Rigid Foams... 

In addition to the possible reuse of BHET in the preparation of fresh PET polymer, two other processes have been proposed starting from the PET glycolysis products preparation of unsaturated polyesters20-27 and synthesis of polyester polyols.28-32 The latter can be used in the formulation of polyurethanes and polyisocyanurate foams26-30 (see Figure 2.1). 

CO purity, 234 derivatives, 232 dimethyl carbonate, 252 membrane material of construction, 92 nonphosgene chemistry, 252-254 phosgene chemistry, 232-234 Scheiten-Baumann synthesis, 232, 233 transesterification, 233, 253, 254 Polyester fiber, 129, 132, 205 Polyester polyols, 229 Polyether polyols, 147, 148, 229 Polyethylene, 132, 183, 266 Polymerization ... 

Through the synthesis of poly(urethane-imide) films and their carbonization, carbon films were obtained whose macropore structure could be controlled by changing the molecular structure of polyurethane prepolymer [164-166]. Poly(urethane-imide) films were prepared by blending poly(amide acid), which was synthesized from pyromellitic dianhydride (PMDA) and 4,4 -oxydianiline (ODA), and phenol-terminated polyurethane pjrejwlymers, which were synthesized through the reaction of polyester polyol with either hexamethylene diisocyanate (HDI), tolylene-2,4-diisocyanate (TDI) or 4,4 -diphenyknethane-diisocyanate (MDI). The reaction schemes of two components, poly(imide) (PI) and poly(urethane) (PU), are shown in Fig. 46a). 

Uses Flexibilizer in metal decorative, automotive primers and topcoats, oveq)rint varnishes, aerospace coatings, and prepolymer synthesis Features Highest reactivity exc. adhesion to substrates fast cure Prr rerties Gardner < 1 color It. straw liq. sol. in alcohols, esters, ketones, xylene partly sol. in min. spirits low m.w. sp.gr. 1.12 dens. 9.3 Ib/gal vise. 10,000 cps acid no. 0.1 hyd. no. 230 100% act. polyester polyol 0.02% moisture K-Flex UD-320 [King Ind.]... 

Guelcher SA, Patel V, Gallagher K, Connolly S, Didier JE, Doctor J, et al. Synthesis and biocompatibility of polyurethane foam scaffolds from lysine diisocyanate and polyester polyols. Tissue Eng 2006 12(5) 1247-59. 

One of the recent advancements and interests in alkyd resin technology is hyperbranched alkyd resins, which, due to their unique highly branched polymer architecture, have low viscosities at higher MWs. An important characteristic of these alkyds is rapid drying. Generally they are prepared by reacting hyperbranched polyester polyols with fatty acids. The main limitation of such alkyds, however, is higher cost, due to the need for unique, more expensive raw materials in their synthesis. 

Montero de Espinosa L, Meier MAR, Ronda JC, Galia M, Cddiz V. 2010. Phosphorus-Containing Renewable Polyester-Polyols via ADMET Polymerization Synthesis, Functionalization, and Radical CrossUnking. J Polym Sci Part A Polym Chem 48 1649-1660. 

Caillol, S., Desroches, M., Boutevin, G., Loubat, C., Auvergne, R., Boutevin, B., 2012. Synthesis of new polyester polyols from epoxidized vegetable oils and biobased acids. Eur. J. Lipid Sci. Technol. 114, 1447-1459. 

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