Oligomerization of Lactones

Abstract

Preparation of oligomers of β-propiolactone (β-PL) and e-caprolactone (e-CL) having reactive functional groups such as hydroxyl, carboxyl and acid chloride groups have been studied. In order to clarify the pattern of bond fission of the lactones, reactions of β-PLwith ethanol, acetic acid and acetyl chloride were carried out with or without catalysts. The investigation of the reaction products revealed that β-PL cleaved exclusively at alkyl oxygen bond in the absence of catalyst and in general at acyl-oxygen bond in the presence of acid or base catalysts. In the reaction of β-PL and ethanol with sodium ethoxide as catlayst, ethyl acrylate was produced as byproduct, and when this reaction was carried out at higher temperature (50°C), polymerization of β-PL was induced even in the presence of a large excess of ethanol. The reaction of β-PL and acetic acid with sulfuric acid as catalyst afforded a small amount of acrylic acid besides the main product, β-acetoxypropionic acid. Reaction of e-CL and ethanol in the presence of acid or base catalysts gave, as a sole product, e-hydroxy ethyl hexanoate, indicating the exclusive acyl-oxygen bond fission of e-CL. This reaction, however, did not take place at all without catalyst. Based on these results, several oligomers of β-PL and e-CL having reactive functional groups such as hydroxyl, carboxyl and acid chloride groups were prepared by the reaction of β-PL or e-CL with various difunctional compounds (ethylene glycol, ethanolamine, ethylenediamine, succinic acid, succinyl chloride, terephthalic acid and terephthalyl chloride). These oligomers were characterized by end group analysis, infrared spectrum and molecular weight determination. Molecular weight of these oligomers ranged from 135 to 1800. In the reaction of β-PL and ethanolamine, the first molecule of β-PL was added to the amino group of ethanolamine, and further addition of β-PL took place not at the hydroxyl group of ethanolamine unit but at the hydroxyl group of β-PL unit formed by the addition of β-PL to the amino group of ethanolamine. Polycondensation of some oligomers having hydroxyl end groups with terephthalyl chloride was attempted in tetrachloroethane or anisole in the presence of magnesium powder at 140 to 160°C. The polymers obtained were white or light yellow and powdery or gummy materials which showed reduced viscosity of about 0.2. These polymers were confirmed by infrared spectra to have aromatic ester bond together with aliphatic ester or amide bonds in the polymer chain.