4.3. Isodimorphism in P(3HB-co-3HV) copolymers
Semicrystalline random copolymers can on rare occasions be isodimorphic in nature, where by two or morecomonomer units can exist in the crystal unit structureof the other monomer units in the copolymer. As a resultthere is approximately the same high degree of crystallinityacross the compositional range, with little resulting dis-ruption to the crystal unit dimensions. There is usuallypseudoeutectic melting behavior and a structural transi-tion occurs near the pseudoeutectic composition [190,191].P(3HB-co-3HV) is one such isodimorphic copolymer. Arelatively high crystallinity (>50%) has generally beenobserved across the entire range of HV content (0–95 mol%)in P(3HB-co-3HV) (by XRD); when the materials have beencarefully fractionated and allowed time to fully developtheir crystallinity [192] there is evidence of a minimum atthe pseudoeutectic (Fig. 4).