Synthesis and Properties of Alternating Copolymers of 3-Hydroxybutyrate and Lactate Units with Different Stereocompositions

Alternating copolymers of (R)-3-hydroxybutyrate ((R)-3HB) and lactate (2-hydroxypropionate: 2HP) units were synthesized by polycondensation reaction of preprepared dimeric monomers, (R)-3HB-(R)-2HP and (R)-3HB-(S)-2HP, in the presence of condensation agent. On the basis of the NMR analyses, it was confirmed that the obtained copolymers had an alternating sequence of (R)-3HB and 2HP units. In contrast to random copolymers of (R)-3HB and 2HP units, the repeating sequence of alternately connected (R)-3HB and 2HP units formed crystalline region. The copolymer with alternating sequence of (R)-3HB and (S)-2HP units had a melting temperature at 83 degrees C. On the other hands, the melting temperature of copolymer of (R)-3HB and (R)-2HP units was quite higher than those of the corresponding homopolymers (around 180 degrees C) and reached to 233 degrees C. When the alternating copolymers were prepared from a mixture of stereoisomeric dimers, both the melting temperature and crystallinity varied in the wide ranges depending on the composition of stereoisomeric dimers.