Widening the Application Range of PLA-Based Thermoplastic Materials through the Synthesis of PLA-Polyether Block Copolymers: Thermal, Tensile, and Rheological Properties

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 approximate to 24 degrees C) and the elastic modulus (E approximate to 500 MPa) are reduced, while the elongation at break (epsilon(b) approximate to 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.

Automated summary

In this study, PEG, PPG, and PEPG were used as macroinitiators in the ring-opening polymerization of l-lactide to synthesize PLLA-b-polyether-b-PLLA linear triblock and starblock copolymers. The results showed that PEG and PEPG blocks were miscible with PLLA blocks, leading to a plasticization effect. On the other hand, PPG-containing block copolymers exhibited phase separation, resulting in microstructures in the melt. Tensile tests indicated that phase-separated PPG-containing block copolymers were more ductile than PLA homopolymers but more brittle than PEG- or PEPG-plasticized block copolymers.