The synthesis of lactic-acid-based telechelic prepolymers

We have studied how different catalysts and diols affect the properties of low-molecular-weight (M _w (GPC) <49800 g/mol) lactic-acid-based telechelic prepolymers. The catalysts and diols were tested separately in our previous studies. In this study, we used the best previously tested diols and catalysts together in order to prepare different types of telechelic prepolymers (for example, crystalline or amorphous). All condensation polymerizations were carried out in the melt, using different diols and different catalysts. The prepolymers were characterized by differential scanning calorimetry, gel permeation chromatography, titrimetric methods, and ¹³C nuclear magnetic resonance ( ¹³C-NMR). According to NMR, the resulting polymers contained less than 1 mol % of lactic acid monomer and less than 5.1 mol % of lactide. Dibutyltindilaurate, like tin(II)octoate, produced quite good molecular weights, but the resulting prepolymers contained exceptionally high amounts of D-lactic acid structures, and, therefore, these prepolymers were totally amorphous. Antimony(III)oxide produced a high-molecular-weight prepolymer when the diol used was aliphatic. Like DBTL, Sb ₂O ₃ produced amorphous prepolymers, which contained a lower amount of D-lactic acid structures than DBTL prepolymers. 1,8-dihydroxyanthraquinone produced a different kind of chain structure with Ti(IV)bu and Ti(IV)iso because one prepolymer had high crystallinity, and the other showed only a slight crystallinity. Sulphuric acid produced a very high-molecular-weight prepolymer with aliphatic 2-ethyl-1,3-hexanediol; and with aromatic diols, it produced quite good molecular weights, except with 1,8-dihydroxyanthraquinone. High-molecular-weight prepolymers produced with H ₂SO ₄ also showed high crystallinity; and, according to ¹³C-NMR, they did not contain lactide and D-lactic acid structures.