The molecular weight distribution of carefully prepared thermostabilized poly(ethylene terephthalate) was determined immediately after polycondensation in vacuo (P̄n = 121) and after the melt was stirred at 280°C for 5.5 hr under nitrogen (P̄n = 123). The fractionation was carried out by successive precipitation in liquid phases. The samples were separated into 25 fractions including refractionation. The Flory distribution was observed in all samples.
ZUSAMMENFASSUNG:Mit Kaliumcarbonat als Aktivator werden aus Hochamylosestarke (HAS) rnit iiberschiissigem Acetanhydrid bei Reaktionszeiten von 1-2 h in hohen Ausbeuten Produkte mit hohen Durchschnittssubstitutionsgraden (DS) erhalten.In N-Methyl-2-pyrrolidon konnen HAS mit stochiometrischen Mengen Acetanhydrid und rnit nichtfliichtigen starken organischen Basen wie 4-Dimethylaminopyridin oder 1 ,4-Diazabicyclo[2.2.2]octan als Katalysatoren in Reaktionszeiten von weniger als 1 h und in hohen Ausbeuten zu Acetaten mit DS < 2 umgesetzt werden.
SUMMARY:Acetylation of high-amylose starch to products of high average degree of substitution (DS) with yield of > 90% proceeds in 1 -2 h using potassium carbonate as activating agent. Acetylstarches of DS < 2 are available by acetylation with stoichiometric amounts of acetic anhydride in N-methyl-2-pyrrolidone applying organic catalysts as 4-dimethylaminopyridine and 1,4-diazabicyclo[2.2.2]octane, respectively. Reaction times of 1 h and less are sufficient to receive the desired acetates in high yield.
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