Relaxation behavior of biodegradable aliphatic-aromatic block copolymers as revealed by dielectric spectroscopy

Thermoplastic elastomers are copolymers composed of a hard block, typically a polyester, and a soft block, typically a polyether. Most commercially available poly(ether-ester) thermoplastic elastomers are produced based on petrochemical monomers. The increasing necessity of eco-friendly polymers has driven the interest for the production of thermoplastic elastomers fully or partially based on monomers from renewable sources. Poly(lactic acid) (PLA) is a biodegradable aliphatic polymer which can be obtained from natural products.Here we present dielectric relaxation results of a series of thermoplastic elastomers based on poly(tetramethylene oxide), as soft segment, and on a a multiblock of poly(buthylene terephthalate) (PBT) and poly(lactic acid) (PLA) as hard segment. The results indicate the existence of a single alpha relaxation, associated to the segmental motions above the glass transition temperature, regardless of the PBT/PLA ratio of the hard segment pointing towards an absence of phase segregation between the two blocks within the hard segment. In addition, different local dynamic processes are revealed below the glass transition temperature contributing to a multimodal beta relaxation that can be assigned to different bonds of both hard and soft blocks.