Crystallization Control and Melt Memory in <scp>PHPM</scp> ‐ <scp> PCL _x </scp> Copolymers Tuned by <scp> <i>ε</i> ‐CL </scp> Content

ABSTRACT Previous studies on the crystallization control behavior of biodegradable poly (methyl 3‐hydroxypropanoate) (PHPM) copolymers have been limited. In this study, a series of random copolymers of poly (3‐hydroxypropyl methyl ether) (PHPM‐PCL x ) containing 10–80 wt% polycaprolactone (PCL) were synthesized by introducing ε‐ caprolactone ( ε‐ CL) through transesterification reactions. The numerical suffix in the sample names denotes the PCL content. For example, the x value in PHPM‐PCL x denotes the PCL mass percentage based on PHPM. The structure and crystallization behavior of the copolymers were systematically investigated. Analysis of crystallization behavior revealed a distinct compositional threshold at 20% ε‐ CL: below this value, the PHPM crystalline phase dominates, while above it, the PCL crystallinity prevails. At 40% ε ‐CL content, the PHPM crystal lattice structure is disrupted, causing the material to transition into an amorphous state. Self‐nucleation (SN) experiments confirmed the melt memory effect and the existence of self‐nucleation domains. Within the self‐nucleation domain, the self‐nucleation density increases, and the crystallization temperature T c rises as the self‐crystallization temperature T s decreases. Successive self‐nucleation and annealing (SSA) further confirmed the microcrystalline separation phenomenon in the copolymer due to different methyl sequence lengths. The PHPM‐rich component exhibited triple melting peaks, while the PCL‐rich component only showed the PCL crystalline phase melting peak. This study demonstrates that molecular design can effectively regulate the crystallization behavior of biodegradable polyesters, providing important insights for tailoring material properties for specific applications.