Polyester, hydrolysis 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. 

During their synthesis esters and polyesters can be modified by the following side reactions alcoholysis, aridolysis, ester interchange, hydrolysis. 

Acid anhydride-diol reaction, 65 Acid anhydride-epoxy reaction, 85 Acid binders, 155, 157 Acid catalysis, of PET, 548-549 Acid-catalyzed hydrolysis of nylon-6, 567-568 of nylon-6,6, 568 Acid chloride, poly(p-benzamide) synthesis from, 188-189 Acid chloride-alcohol reaction, 75-77 Acid chloride-alkali metal diphenol salt interfacial reactions, 77 Acid chloride polymerization, of polyamides, 155-157 Acid chloride-terminated polyesters, reaction with hydroxy-terminated polyethers, 89 Acid-etch tests, 245 Acid number, 94 Acidolysis, 74 of nylon-6,6, 568... 

The future direction of polyester R D efforts is likely to involve further progress in polyester synthesis given the wide range of potential monomer combinations, new blending technology and the use of advanced functional additives such as nanoclay reinforcements, reactive impact modifiers, anti-hydrolysis agents and chain extenders. 

The conventional synthesis of aliphatic polyesters based on adipic acid and a range of diols, such as 1,4-butanediol or 1,6-hexanediol, involves a high-temperature esterification reaction typically at 240-260 °C and an organometallic catalyst such as stannous octano-ate. The use of enzyme catalysis results in a much lower reaction temperature, but also the possibility of removing the esterification catalyst, giving the polyester significantly improved hydrolysis resistance. 

Hydrolysis of Copolyamide-esters (CPAEs) by Lipase (jj,). CPAEs were synthesized by the amide-ester interchange reaction between polyamide and polyester. The length of the polyamide blocks was measured after hydrolysis of ester bonds in CPAE by alkali at 30 C. The infrared spectra after hydrolyzing ester bonds on CPAEs showed that the ester bonds were almost completely removed. The molecular weight distribution of polyamide blocks was examined by GPC (Table II). The following samples were used CPAE-1 (reaction time for synthesis, 1 hr) and CPAE-2 (reaction time, U hr) composed of nylon 6 and PCL at a 50/50 molar ratio, CPAE-3 (reaction time, 1 hr) and CPAE-U (reaction time,... 

Multifunctional initiators made up of metal alkoxides rather than alcohols have been less used for the synthesis of star-shaped polyesters than have the tin (II) bis-(2-ethylhexanoate)/alcohol system. Nevertheless, Kricheldorf initiated the polymerization of sCL using a spiro-cyclic tin(IV) aUcoxide to obtain a tin-containing height-shaped polyester whose final hydrolysis resulted in the formation of a star-shaped polyester (Fig. 35) [25, 159-161]. 

Lipases are enzymes that catalyze the in vivo hydrolysis of lipids such as triacylglycerols. Lipases are not used in biological systems for ester synthesis, presumably because the large amounts of water present preclude ester formation due to the law of mass action which favors hydrolysis. A different pathway (using the coenzyme A thioester of a carboxylic acid and the enzyme synthase [Blei and Odian, 2000]) is present in biological systems for ester formation. However, lipases do catalyze the in vitro esterification reaction and have been used to synthesize polyesters. The reaction between alcohols and carboxylic acids occurs in organic solvents where the absence of water favors esterification. However, water is a by-product and must be removed efficiently to maximize conversions and molecular weights. 

Hydrolases in Polymer Chemistry Part III Synthesis and Limited Surface Hydrolysis of Polyesters and Other Polymers... 

Polyesters, polyamides and other poly-condensation polymers can be chemically recycled simply by reversing their synthesis process by raising the process temperature, using traditional processes such as hydrolysis, ammonolysis, acidolysis, transesterification, etc. Bayer and other interested suppliers pioneered such processes that are beyond the scope of this book. Such processes can also be used for adjusting the MW required in one application (e.g. PET-bottles) to that needed in a different market (e.g. polyester fibres). 

Lipase Transesterification and direct esterification (inch polyester synthesis) Ring-opening polymerization of 8-caprolactone Hydrolysis alcoholysis acetylation Higher stability of enzyme greater activity catalyst recyclable sometimes higher enantio- and regio-selectivity compared with VOCs... 

In the case of polyester synthesis from divinyl esters, hydrolysis of the vinyl end group partly took place, resulting in the limitation of the polymer growth.201 A mathematical model showing the kinetics of the polymerization predicts the product composition. On the basis of these data, a batch-stirred reactor was designed to minimize temperature and mass-transfer effects.202 The efficient enzymatic production of polyesters was achieved using this reactor poly(l,4-butylene adipate) with Mn 2 x 104 was synthesized in 1 h at 60 °C. 

Addition of low-molecular monoepoxides at the beginning and at the end of PETP synthesis allows to increase PETP hydrolysis resistance, thereby to improve physico-chemical properties of the fibre, to obtain polyester fibre with high degree of polymerization, to increase greatly thermal stability of polyester fibres. 

Among enzymes, lipases proved to be the most efficient for the in vitro polyester synthesis. Lipases or triacylglycerol acylhydrolases are water-soluble enzymes that catalyze the hydrolysis of ester bonds in water-insoluble, lipid substrates, and therefore comprise a subclass of the esterases. 

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. 

The synthesis of dimeric fatty acids is based on the reaction between a fatty acid with one double bond (oleic acid) and a fatty acid with two double bonds (linoleic acid) or three double bonds (linolenic acid), at higher temperatures in the presence of solid acidic catalysts (for example montmorillonite acidic treated clays). Dimerised fatty acids (C36) and trimerised fatty acids (C54) are formed. The dimer acid is separated from the trimeric acid by high vacuum distillation. By using fatty dimeric acids and dimeric alcohols in the synthesis of polyesters and of polyester polyurethanes, products are obtained with an exceptional resistance to hydrolysis, noncrystalline polymers with a very flexible structure and an excellent resistance to heat and oxygen (Chapter 12.5). Utilisation of hydrophobic dicarboxylic acids, such as sebacic acid and azelaic acid in polyesterification reactions leads to hydrolysis resistant polyurethanes. 

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