No abstract

Comonomer compositional distribution of bacterially synthesized poly(3‐hydroxybutyric acid‐co‐3‐hydroxypropionic acid) [P(3HB‐co‐3HP)] was investigated via solvent/non‐solvent fractionation techniques. The result indicates the presence of extremely broad comonomer compositional distribution in the original bacterial product. Furthermore, utilizing compositionally fractionated bacterial copolyesters with much narrower comonomer compositional distributions, the 3HP comonomer content‐dependence of their thermal and crystallization behavior was studied by means of differential scanning calorimeter (DSC) and polarized optical microscopy and the results compared with those of unfractionated copolyesters. It was revealed that the physical features of the fractionated copolyester P(3HB‐co‐3HP)s strongly depends on the 3HP comonomer content. In addition, to clarify the effect of the compositional distribution on the properties of the unfractionated copolyester, the miscibility between bacterial poly(3‐hydroxybutyric acid) [P(3HB)] and two fractionated P(3HB‐co‐3HP) samples with 11.3 and 14.9% 3HP was investigated for blends obtained by solvent casting techniques. The evidence of thermal analysis and spherulitic growth rates imply miscibility of the P(3HB)/3HB‐rich P(3HB‐co‐3HP) binary blends. © 1999 Society of Chemical Industry

Bacterially synthesized poly(3-hydroxybutyrate-co-3-hydroxypropionate) [P(3HB-co-3HP)] samples were compositionally fractionated using solvent/nonsolvent fractionation techniques. Binary blends between these compositionally fractionated P(3HB-co-3HP) samples, with much narrower comonomer compositional distribution, were prepared, and their thermal and crystallization behavior were studied using differential scanning calorimeter (DSC) and polarized optical microscopy. It was found that, in the amorphous phase of these blends, the miscibility mainly depends on the difference of 3HP contents (or 3HB contents) between the two components of the blend. When the difference of 3HP content between two copolyesters is less than 30-40 mol %, they become miscible in the amorphous phase. The type of crystal lattice, miscibility, and difference of the spherulite growth rate between the two components of the blend appear to be the important factors controlling the crystalline phase behavior. The results are compared with those of unfractionated P(3HB-co-3HP)s and the effects of comonomer composition and its distribution on the properties of unfractionated copolymers are discussed.