Widening the Application Range of PLA‐Based Thermoplastic Materials through the Synthesis of PLA‐Polyether Block Copolymers: Thermal, Tensile, and Rheological Properties
Benjamín Hernández, Antje Lieske
Abstract
Abstract Polyethylene glycol (PEG), polypropylene glycol (PPG), and poly(ethylene glycol‐ co ‐propylene glycol) (PEPG) of number average molar masses ( M n ) of 6–20 kDa are used as macroinitiators in the ring‐opening polymerization (ROP) of l ‐lactide to synthesize high molar mass (50 kDa < M nCopo < 120 kDa) PLLA ‐b‐ polyether ‐b‐ PLLA linear triblock and starblock copolymers. At the studied block lengths, PEG and PEPG blocks exhibit miscibility with the PLLA blocks in the amorphous domains leading to a plasticization effect. As the PEG or PEPG block content is increased to 18 %wt, the T g ( T g ≈ 24 °C) and the elastic modulus ( E ≈ 500 MPa) are reduced, while the elongation at break ( ε b ≈ 280%) and crystallization rate are increased. At the same time, small angle oscillatory shear (SAOS) rheometric measurements show that the plasticized copolymers have a reduced melt viscosity. In contrast, SAOS and DSC measurements of the PPG‐containing block copolymers reveal phase separation of the PPG and PLA blocks leading to microstructures in the melt. Tensile tests show that the phase‐separated PPG‐containing block copolymers are more ductile than PLA homopolymers, but more brittle than the PEG‐ or PEPG‐plasticized block copolymers.