Fractionation and thermal characteristics of biosynthesized polyhydoxyalkanoates bearing aromatic groups as side chains

Abstract

Two polyhydroxyalkanoate (PHA) copolymers, poly(3-hydroxybutyrate-co-3-hydroxy-3-phenylpropioate) [P(3HB-co-3H3PhP)] and poly(3-hydroxybutyrate-co-3-hydroxy-4-phenylbutyrate) [P(3HB-co-3H4PhB)], both bearing aromatic side chains, were biosynthesized by recombinant Ralstonia eutropha fed with a respective precursor for the aromatic unit. As bacterial PHA copolymers generally exhibit broad comonomer compositional distribution, the as-biosynthesized samples, P(3HB-co-18 mol% 3H3PhP) and P(3HB-co-11 mol% 3H4PhB), were fractionated into several fractions with narrow comonomer compositional distribution using a chloroform/n-hexane mixed solvent. When the fractionated samples were aged under ambient conditions, the P(3HB-co-3H3PhP) fraction with 12 mol% 3H3PhP exhibited a melting temperature (Tm) of 132–148 °C, whereas the fractions with 15–21 mol% 3H3PhP did not exhibit melting behavior. As for P(3HB-co-3H4PhB), all fractions with a range of 4–15 mol% 3H4PhB exhibited Tm in the range 105–151 °C. The glass transition temperature (Tg) of these copolymers increased with increasing aromatic unit content, and the highest Tg of 20 °C was observed for the fraction with 21 mol% 3H3PhP. On the basis of the results presented here, the effects of aromatic comonomers on the thermal properties of the resulting copolymers are discussed. Two polyhydroxyalkanoate copolymers, poly(3-hydroxybutyrate-co-3-hydroxy-3-phenylpropioate) [P(3HB-co-3H3PhP)] and poly(3-hydroxybutyrate-co-3-hydroxy-4-phenylbutyrate) [P(3HB-co-3H4PhB)] were biosynthesized. The as-biosynthesized polymers were fractionated into several fractions with narrow comonomer compositional distribution using a chloroform/n-hexane mixed solvent. Using these fractions, the effects of aromatic comonomers on the thermal properties were investigated.