Reactions of p-Butyrolactone with Alkali Metal Supramolecular Complexes

REACTIONS OF P-BUTYROLACTONE WITH ALKALI METAL SUPRAMOLECULAR COMPLEXES 

Three types of initiators have been used for initiation of p-butyrolactone polymerization. 

The preparation of the first one was based on discoveries of Dye and Edwards concerning the dissolution of alkali metals potassium or sodium in an aprotic solvent, such as THE, containing a macrocyclic organic ligand e.g. 18-crown-6 or cryptand [2.2.2]. The specific procedure enables the preparation of an unique alkali metal supramolecular complex forming in THE solution alkali metal ion pairs, e.g. K /L/K (where L = 18-crown-6 or 15-crown-5). 

Such alkali metal ion pairs are capable of two electron transfer from the potassium anion towards a suitable substrate, e.g. p-butyrolactone with formation of a respective carbanion. The strong tendency to two electrons transfer is due to the unusual oxidation state of potassium anion bearing on its outer s orbital a labile electron doublet shielded from the positive potassium nucleus by inner orbitals. Using 5 -enantiometr of P-butyrolactone as a monomer and potassium supramolecular complex as catalyst, enolate carbanion is formed as the first reactive intermediate which induces polymerization, yielding poly-(R)-3-hydroxybutanoate. The resulting biomimetic polyester has the structure similar to native PHB produced in nature, except for acetoxy-end-groups, which are formed instead of the hydroxyl ones typical for natural PHB. 

HBANa = ((R) 3-hydroxybutanoic acid sodium salt/15 rown-5) compiex 

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