Mechanical properties of melt-fabricated, drawn films of A–B–A triblock copolymers of poly(l-lactide) (A) and two types of polyethers (B)

High-molecular-weight ABA triblock copolymers (PLA–PEs–PLA), consisting of poly-l-lactide (PLLA: A) and two types of polyethers (PEs: B), i.e., poly(oxyethylene) (PEG: polyethylene glycol) and Pluronic^® [PN: poly(oxyethylene)-b-poly(oxypropylene)-b-poly(oxyethylene)], were synthesized by ring-opening polymerization of l-lactide by using bis-hydroxyl-terminated PEs as macroinitiators. Polymer films of these block copolymers were fabricated by the conventional hot-pressing method and uniaxially cold drawn to five times at 80 °C. Evaluation of the mechanical properties of these films revealed that the drawn films can retain high strength (ca. 100 MPa) and improved flexibility (2 GPa in modulus). It was therefore evident that the drawn films of PLLA–PEs triblock copolymers are highly useful as flexible films that can be controlled by the PEs content.

The A–B–A triblock copolymers consisting of PLLA and polyethers (PE: PEG and PN) were synthesized by the ROP of l-lactide in the presence of telechelic PE as the macroinitiators. The drawn films of these block copolymers were found to compete with the conventional petroleum plastic films and exceed the current biobased and biodegradable polymer films in terms of toughness. Thus, the oriented copolymer films were shown to be highly useful for flexible PLLA-based films.