Abstract
This work explores for the first time the enzymatic synthesis of poly(butylene-co-ε-caprolactone) (PBSCL) copolyesters in bulk using commercially available monomers (dimethyl succinate (DMS), 1,4-butanediol (BD), and ε-caprolactone (CL)). A preliminary kinetic study was carried out which demonstrated the higher reactivity of DMS over CL in the condensation/ring opening polymerization reaction, catalyzed by Candida antarctica lipase B. PBSCL copolyesters were obtained with high molecular weights and a random microstructure, as determined by 13C NMR. They were thermally stable up to 300 °C, with thermal stability increasing with the content of CL in the copolyester. All of them were semicrystalline, with melting temperatures and enthalpies decreasing up to the eutectic point observed at intermediate compositions, and glass transition temperatures decreasing with the content of CL in the copolyester. The use of CALB provided copolyesters free from toxic metallic catalyst, which is very useful if the polymer is intended to be used for biomedical applications.
Highlights
Aliphatic polyesters have been recognized as environmentally friendly polymers
We succeeded in synthesizing poly(butylene succinate-coε-caprolactone) (PBSCL) copolyesters, as well as poly(butylene succinate) (PBS) and PCL homopolymers, for the entire range of compositions proposed (70/30, 50/50, and 30/70), using the immobilized enzyme Candida antarctica lipase B
Such temperatures are not applicable for enzymatic synthesis, as they would lead to enzyme denaturalization
Summary
Aliphatic polyesters have been recognized as environmentally friendly polymers They present biodegradable properties and a great biocompatibility, which places them in a privileged position among bio-based polymers [1]. PBS is a biodegradable and bio-based polyester obtained by melt polycondensation of dimethyl succinate (DMS) or succinic acid (SA) and 1,4butanediol (BD) It is a semicrystalline polymer with mechanical properties comparable to isotactic poly(propylene). PCL is obtained by ring opening polymerization of ε-caprolactone (CL) This semicrystalline polyester has a melting point of 65 ◦C and a glass transition temperature of −60 ◦C. Copolymerization presents a great solution to overcome these limitations [8,15,16,17] It offers a wider range of possible combinations of properties, the exact balance of which can be tuned through the copolymer composition. These polyesters and copolyesters are usually produced using metallic and organometallic catalysts such as titanium (IV) isopropoxide (TIP), aluminum alkoxides, and tin octoate, which are difficult to remove from the final polymer, making the material too toxic for use in the biomedical field [18,19,20]
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