Creep-resistant porous structures based on stereo-complex forming triblock copolymers of 1,3-trimethylene carbonate and lactides

Abstract

Stereo-complexes (poly(ST–TMC–ST)) of enantiomeric triblock copolymers based on 1,3-trimethylene carbonate (TMC) and L- or D-lactide (poly(LLA–TMC–LLA) and poly(DLA–TMC–DLA)) were prepared. Films of poly(ST–TMC–ST) could be prepared by solvent casting mixtures of equal amounts of poly(LLA–TMC–LLA) and poly(DLA–TMC–DLA) solutions and by compression moulding co-precipitates. Although compression moulding was performed at 191 °C, thermal degradation was not apparent and materials with good tensile properties could be obtained. For compression-moulded poly(ST–TMC–ST) specimens containing approximately 16 mol % lactide, the values for E-modulus, yield stress and elongation at break were respectively 17, 1.7 MPa and 90%. Also a very low long-term creep rate of 2.2×10⁻⁷ s⁻¹ was determined when specimens were loaded to 20% of the yield stress. When compared with compression-moulded poly(TMC), poly(ST–TMC–ST) specimens deform at a rate that is one to two orders of magnitude lower. Furthermore, poly(ST–TMC–ST) specimens showed complete dimensional recovery within 24 h after loading to 20% and 40% of the yield stress for 40 and 5.5 h, respectively. Highly porous poly(TMC) and poly(ST–TMC–ST) structures with interconnected pores were prepared by a method combining co-precipitation, compression moulding and salt leaching. After prolonged compressive deformation, solid and porous poly(ST–TMC–ST) discs showed significantly better recovery behaviour than poly(TMC) discs.