*Article* **Development of Biodegradable Polyesters: Study of Variations in Their Morphological and Thermal Properties through Changes in Composition of Alkyl-Substituted (**ε**-DL) and Non-Substituted (**ε**-CL, EB, L-LA) Monomers**

**Felipe Robles-González , Teresa Rodríguez-Hernández , Antonio S. Ledezma-Pérez, Ramón Díaz de León , Marco A. De Jesús-Téllez \* and Héctor Ricardo López-González \***

> Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna Hermosillo 140, Saltillo 25294, Coahuila, Mexico **\*** Correspondence<EMAIL_ADDRESS>(M.A.D.J.-T<EMAIL_ADDRESS>(H.R.L.-G.)

**Citation:** Robles-González, F.; Rodríguez-Hernández, T.; Ledezma-Pérez, A.S.; Díaz de León, R.; De Jesús-Téllez, M.A.; López-González, H.R. Development of Biodegradable Polyesters: Study of Variations in Their Morphological and Thermal Properties through Changes in Composition of Alkyl-Substituted (ε-DL) and Non-Substituted (ε-CL, EB, L-LA) Monomers. *Polymers* **2022**, *14*, 4278. https://doi.org/10.3390/ polym14204278

Academic Editor: Edina Rusen

Received: 16 September 2022 Accepted: 7 October 2022 Published: 12 October 2022

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**Abstract:** Three series of polyesters based on monomer combinations of *ε*-caprolactone (*ε*-CL), ethylene brassylate (EB), and L-Lactide (LLA) with the alkyl substituted lactone *ε*-decalactone (*ε*-DL) were synthesized at different molar ratios. Copolymers were obtained via ring opening polymerization (ROP) employing TBD (1,5,7-triazabicyclo-[4.4.0]-dec-5-ene), an organic catalyst which can be handled under normal conditions, avoiding the use of glove box equipment. The molar monomer composition of resulting copolymers differed from theoretical values due to lower *ε*-DL reactivity; their *Mn* and *Mw* values were up to 14 kDa and 22.8 kDa, respectively, and distributions were (*Ո*) ≤ 2.57. The thermal stability of these materials suffered due to variations in their *ε*-DL molar content. Thermal transitions such as melting (*Tm*) and crystallization (*Tc*) showed a decreasing tendency as *ε*-DL molar content increased, while glass transition (*Tg*) exhibited minor changes. It is worth mentioning that changes in monomer composition in these polyesters have a strong impact on their thermal performance, as well as in their crystallization degree. Consequently, variations in their chemical structure may have an effect on hydrolyic degradation rates. It should be noted that, in future research, some of these copolymers will be exposed to hydrolytic degradation experiments, including characterizations of their mechanical properties, to determine their adequacy in potential use in the development of soft medical devices.

**Keywords:** ROP; biodegradable polyesters; TBD; organic catalyst