Tunable properties and degradability of polyester network based on Tulipalin A and (ε-caprolactone with dynamic crosslinking

Abstract

The newly developed cross-linked materials in this study combine the advantages of aliphatic polyesters with their biocompatibility and ability to hydrolyze with thermal reprocessing without flow due to dynamic bonds and crosslinking. A contribution to sustainability in the plastics industry is the use of Tulipalin A (methylene butyrolactone) as a bifunctional monomer available from renewable resources. Dynamic polyester networks based on the transalkylation between trialkylsulfonium and thioether groups were prepared via the crosslinking of a copolyester of ε-caprolactone (CL) with α-methylene-γ-butyrolactone (MBL) (P(CL-co-MBL)) by either 1,5-pentanedithiol (PDT) or pentaerythritol tetrakis(3-mercaptopropionate) (PETK). The alkyl-sulfonium salts of the corresponding polyester networks were synthesized using butyl‑p-bromobenzenesulfonate (butyl‑brosylate) at either 5 or 10 mol% relative to thioether groups. The thermal properties of the obtained materials were determined using the DSC and TGA analyses showing thermal stability up to 200 °C for dynamic networks. Well-developed crosslinking in polyester networks were proved by frequency independent storage moduli, which led over loss moduli as determined by rheology. Alkylated networks kept these properties at 150 °C only if they were made of pre-polymers containing < 10 mol% of MBL in copolyester. Selected alkylated and healed samples kept Young's modulus of 100 – 150 MPa, while its strain at break slightly decreased due to the partial degradation of polyester chains in network. The dynamicity of the PDT or PETK crosslinked networks with 5 mol% MBL content was proved by stress relaxation experiments in temperature range 150–200 °C. Furthermore, the self-healing capability of these materials has been proved through creep recovery experiments over 10 cycles. Alkylated networks showed slightly better stability in alkaline media, but acid hydrolysis was faster for networks with higher MBL content, independent of the degree of alkylation, and was faster than for pure PCL. Finally, the obtained materials can be considered as non-cytotoxic towards 3T3 fibroblast, and with limited antibacterial properties.