Anti-hydrolysis additives

Hydrolysis during melt processing can be suppressed significantly by the addition of such anti-hydrolysis additives. This enables the IV to be maintained across 

Stabaxol KE 7646 is a grade claimed for maintaining the intrinsic viscosity of recycled PET during melt processing. Such additives expand the possibilities for applications of recycled PET resin into new fields. 

Polycarbodiimides are also used as additives to provide long-term hydrolytic stability to polyester components in service in moist and humid environments (e.g. glass-filled PET in dishwasher applications). 

Heitz et al. [35] (BASF) describe the use of polycarbodiimide as an additive to produce hydrolysis-resistant PBT. Further patents describe glass-fiber-reinforced mixtures of PBT with an aromatic polycarbodiimide having improved impact strength [36], and mixtures of PBT with an aromatic polycarbodiimide having improved melt strength and intrinsic viscosity [37], 

Stabaxol P is used normally as a hydrolysis stabilizer in non-food polyester applications. One of the main applications is the stabilization of monofilament. An additional advantage of Stabaxol P is that it also works as a viscosity modifier. Stabaxol P has no FDA approval, and this means that it can be used only for technical applications. 

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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 hydroboration of unsymmetrical alkenes thus gives monoalkylboranes (addition of H—BH2), dialkylboranes (addition of H—BHR), or trialkylboranes (addition of H—BR2), which are typical anti-Markovnikov products. Therefore, the reaction sequence hydrobora-tion/oxidation/hydrolysis brings about the anti-Markovnikov addition of H20 to unsymmetrically substituted alkenes. 

Addition of carbon monoxide and water to an alkene, i.e. hydrocarboxylation, is catalyzed by a variety of transition metal complexes, including [Ni(CO)4], [Co2(CO)s] and [HaPtClg]. Unfortunately this reaction usually leads to mixtures of products due to both metal-catalyzed alkene isomerization and the occurrence of Irath Markownikov and anti-Markownikov addition of the metal hydride intermediate to the alkene. The commercially available zirconium hydride [(C5Hs)2Zr(H)Cl] can be used as a stoichiometric reagent for conversion of alkenes to carboxylic acids under mild conditions (equation 23). In this case the reaction with linear alkenes gives exclusively terminal alkyl complexes even if the alkene double bond is internal. Insertion of CO followed by oxidative hydrolysis then leads to linear carboxylic acids in very good yield. 

Polyester TPU can also be protected by carbodiimide-based anti-hydrolysis agents that act as acid interceptors. Service life can be doubled or even quadrupled by such an additive, Table 5.101. Outdoor weathering in central European climate has shown that polyester TPU surfaces are not attacked for up to five years, even without hydrolysis protection. Special hydrolysis protection is required under constant contact with moisture, especially at elevated temperature and/or in tropical climates [673]. 

R)- and (,S )-1.1,2-Triphenyl-l,2-ethancdiol which are reliable and useful chiral auxiliary groups (see Section 1.3.4.2.2.3.) also perform ami-sclcctive aldol additions with remarkable induced stereoselectivity72. The (/7)-diastercomer, readily available from (7 )-methyl mandelate (2-hy-droxy-2-phcnylaeetate) and phenylmagnesium bromide in a 71 % yield, is esterified to give the chiral propanoate which is converted into the O-silyl protected ester by deprotonation, silylation, and subsequent hydrolysis. When the protected ester is deprotonated with lithium cyclohexyliso-propylamide, transmetalated by the addition of dichloro(dicyclopentadienyl)zirconium, and finally reacted with aldehydes, predominantly twm -diastereomers 15 result. For different aldehydes, the ratio of 15 to the total amount of the syn-diastereomers is between 88 12 and 98 2 while the chemical yields are 71 -90%. Furthermore, high induced stereoselectivity is obtained the diastereomeric ratios of ami-15/anti-16 arc between 95 5 and >98 2. 

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