The multiple endothermic peaks without observable recrystallization phenomenon of isomorphous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] with the middle HV content of 19.4 mol% and 28.7 mol% were confirmed by differential scanning calorimetry (DSC), and the evolutions of crystal structure and lamellar morphology in the heating and melting process were tracked by in situ synchrotron wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) techniques. The emergence of asymmetric features of both the diffraction peaks and scattering curves indicates the coexistence of different lamellar crystals with varied unit cell parameters. Based on the in situ WAXD and SAXS measurements, we calculated the evolutions of the unit cell parameters a and b as well as the long period and lamellar thickness upon heating. The comparative analysis of WAXD and SAXS data confirms that the multiple endothermic peaks of P(HB-co-19.4%HV) and P(HB-co-28.7%HV) result from the melting of different lamellae rather than the melting/recrystallization. The thinner, unstable uniform lamellae with HV counits total inclusion melt first and the thicker, stable sandwich lamellae with HV counits partial inclusion melt last. In addition, the large second melting peak in P(HB-co-19.4%HV), differing from that of samples with HV content of 28.7 mol% and 36.2 mol%, is due to the unique state of HV content leading to a transition of sandwich lamellae to uniform lamellae. The present study establishes the relationship between the different lamellae structure and multiple melting behaviors of isomorphous copolymer.

的多个吸热峰不同晶聚观察到的再结晶现象（3-羟基丁酸酯共-3-羟基戊酸酯）[P（HB-共-HV）]为19.4摩尔％和28.7摩尔％的中间HV含量通过差示扫描证实通过原位同步加速器广角X射线衍射（WAXD）和小角度X射线散射（SAXS）技术跟踪热分析法（DSC）以及加热和熔化过程中晶体结构和层状形态的演变。衍射峰和散射曲线的不对称特征的出现表明具有不同晶胞参数的不同层状晶体共存。基于原位通过WAXD和SAXS测量，我们计算了晶胞参数a和b的演变以及加热时的长周期和层状厚度。对WAXD和SAXS数据的比较分析证实，P（HB- co -19.4％HV）和P（HB- co -28.7％HV）的多个吸热峰是不同薄片的熔融而不是熔融/重结晶导致的。首先是带有HV共基的总夹杂物的较薄的，不稳定的均匀薄层首先熔化，最后带有带有HV共基的部分夹杂物的较厚的，稳定的夹心薄层最后的熔化。此外，P（HB- co-19.4％HV）与HV含量分别为28.7 mol％和36.2 mol％的样品不同，这是由于HV含量的独特状态导致夹心薄片转变为均匀薄片。本研究建立了不同的片状结构与同构共聚物的多重熔融行为之间的关系。