How the Aliphatic Glycol Chain Length Determines the Pseudoeutectic Composition in Biodegradable Isodimorphic poly(alkylene succinate-ran-caprolactone) Random Copolyesters

We synthesize four series of novel biodegradable poly(alkylene succinate-ran-caprolactone) random copolyesters using a two-step ring-opening/transesterification and polycondensation process with ϵ-caprolactone (PCL) as a common comonomer. The second comonomers are succinic acid derivatives, with variations in the number of methylene groups (n _CH2) in the glycol segment, n _CH2 = 2, 4, 8, and 12. The obtained copolyesters were poly(ethylene succinate-ran-PCL) (ES _xCL _y), poly(butylene succinate-ran-PCL) (BS _xCL _y), poly(octamethylene succinate-ran-PCL) (OS _xCL _y), and poly(dodecylene succinate-ran-PCL) (DS _xCL _y). We discovered a new mixed isodimorphic/comonomer exclusion crystallization in ES _xCL _y copolymers. The BS _xCL _y, OS _xCL _y, and DS _xCL _y copolymers display isodimorphic behavior. Our findings revealed a significant variation in the pseudoeutectic point position, from mixed isodimorphism/comonomer exclusion crystallization to isodimorphism with pseudoeutectic point variation from 54% to up to 90%. Moreover, we established a link between the melting temperature depression slope variation and the comonomer inclusion/exclusion balance, providing valuable insights into the complex topic of isodimorphic random copolymers.