title: Viscoelastic relaxations and thermal properties of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).
abstract: 3-Hydroxybutyrate-3-hydroxyvalerate (3HB-3HV) as well as 3-hydroxybutyrate-4-hydroxybutyrate (3HB-4HB) copolyesters have been investigated by differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical spectroscopy, over a wide range of compositions (0-95 mol% 3HV; 0-82 mol% 4HB). Both series of isolated copolyesters are partially crystalline at all compositions. Quenched samples show a glass transition that decreases linearly with increasing co-monomer molar fraction, more markedly when the co-monomer is 4HB. Above Tg, all copolyesters, rich in 3HB units, show a cold crystallization phenomenon followed by melting, while at the other end crystallization on heating is observed only in 3HB-3HV copolymers. The viscoelastic spectrum, strongly affected by thermal history, shows two relaxation regions: the glass transition, whose location depends on copolymer type and composition, and a secondary dispersion region at low temperatures (-130/-80 degrees C). The latter results from a water-related relaxation analogous to that of P(3HB) and, in 3HB-4HB copolymers, from another overlapping absorption peak centered at -130 degrees C, attributed to local motion of the methylene groups in the linear 4HB units.
authors.affiliation: Centro di Studio per la Fisica delle Macromolecole CNR, Universita di Bologna, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Scandola
authors.forename: G
authors.initials: G
authors.lastname: Ceccorulli
authors.forename: Y
authors.initials: Y
authors.lastname: Doi
mesh_terms: D002152:Calorimetry, Differential Scanning; D003460:Crystallization; D006885:Hydroxybutyrates / Q000737:chemistry*; D008970:Molecular Weight; D011091:Polyesters / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D013696:Temperature; D014631:Valerates / Q000737:chemistry*; D000094122:Polyhydroxybutyrates
chemical_list: D006885:Hydroxybutyrates; D011091:Polyesters; D011108:Polymers; D014631:Valerates; C052620:poly(3-hydroxybutyrate)-co-(3-hydroxyvalerate); D000094122:Polyhydroxybutyrates; C068056:poly(3-hydroxybutyrate-co-4-hydroxybutyrate)