Bioinspired All-Polyester Diblock Copolymers Made from Poly(pentadecalactone) and Poly(3-hydroxycinnamate): Synthesis and Polymer Film Properties

A bioinspired diblock copolymer is synthesized from pentadecalactone and 3-hydroxy cinnamic acid. Poly(pentadecalactone) (PPDL) with a molar mass of up to 43 000 g mol(-1) is obtained by ring-opening polymerization initiated by propargyl alcohol. Poly(3-hydroxycinnamate) (P3HCA) is obtained by polycondensation and end-functionalized with 3-azido propanol. The two functionalized homopolymers are connected via 1,3-dipolar Huisgen addition to yield the block copolymer PPDL-triazole-P3HCA. The structure of the block copolymer is confirmed by proton NMR, FTIR spectroscopy and GPC. By analyzing the morphology of polymer films made from the homopolymers, from a 1:1 homopolymer blend, and from the PPDL-triazole-P3HCA block copolymer, clearly distinct micro- and nanostructures are revealed. Quantitative nanomechanical measurements reveal that the block copolymer PPDL-triazole-P3HCA has a DMT modulus of 22.3 +/- 2.7 MPa, which is lower than that of the PPDL homopolymer (801 +/- 42 MPa), yet significantly higher than that of the P3HCA homopolymer (1.77 +/- 0.63 MPa). Thermal analytics show that the melting point of PPDL-triazole-P3HCA is similar to PPDL (89-90 degrees C), while it has a glass transition temperature similar to P3HCA (123-124 degrees C). Thus, the semicrystalline, potentially degradable all-polyester block copolymer PPDL-triazole-P3HCA combines the thermal properties of either homopolymer, and has an intermediate elastic modulus.