By contrast, none of the other comonomer units foundin PHA have demonstrated any degree of co-crystallization.Mitomo and Doi [195] found that there was no change inlattice parameters in P(3HB-co-4HB) with increasing 4HBcontent, implying that there was no inclusion of 4HB inthe 3HB crystal, and Iawata et al. [204] also demonstratedthat the second monomer units for P(3HB-co-6HHx) andP(3HB-co-4HB) copolymers are largely found on the crys-tal surfaces (and also that these surfaces are irregular withloose loop chain foldings). Xie et al. [216] likewise foundthat HHx is excluded from the HB crystal (at 7.2% HHx),and high-resolution solid-state13C NMR of composition-ally fractionated bacterial P(3HB-co-3HP) [217] showedthat co-crystallization did not occur in the P(3HB-co-3HP)system. From the lineshape analyzes of the 3HB methyl car-bon peak it was also shown that the presence of minor 3HPcomonomer units significantly suppressed the crystalliza-tion of a 3HB-rich semicrystalline copolyester; there was acorrelation between HB block length and the crystallizabil-ity of the copolymers.