The cyclization of low molecular weight polyethylene glycol (PEG) via its mono-tosylated intermediate is known for many years. We improved this basic reaction to minimize the quantities of linear precursor and higher molecular weight condensation products in the raw products. For the optimization of the reaction conditions it is essential to know the kinetics of the cycle formation and the condensation reactions leading to chain extended by-products. Therefore, the reaction kinetics was simulated using known compositions of reaction products to quantify the rate constants. As a result, the cyclization reaction of PEG with molecular weights up to 100,000 g/mol yielded raw products with the unimeric cycle as the main component. For the removal of residual linear mother compound and chain-extended PEG, a process was developed which comprises the quantitative oxidation of alcoholic chain ends to carboxyl groups and their subsequent removal with the help of a basic ion exchange resin (see Figure 1). Smaller quantities of larger cycles were removed by classical fractionation using chloroform/heptane as solvent/non-solvent pair. The efficient cleaning processes allowed carrying out the ring closure reaction at relatively high concentrations and so increasing sample quantities. As a result, cyclic polyethylene glycol was obtained in high structural purity in quantities of several grams. In order to monitor the oxidation reaction and to prove the absence of linear chains a <sup>1</sup>H-NMR characterization technique was developed, which is extremely sensitive up to high molecular weights.

Multi-Gram scale synthesis of high molecular weight cyclic polyethylene glycol

255th National Meeting (2018)

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