Development and charactarization of thermoplastic polyurathane based thermo-responsive shape memory polymer blends

Shape memory polymers are materials that can respond to external stimuli and hold an important place in the category of smart polymers. These polymers can change their shape with the help of an external stimulus. Thermally responsive shape memory polymers use heat to transition between temporary and permanent shapes, and these types of polymers are the most common among shape memory polymers. Thermally responsive shape memory polymeric materials can be produced as polymer blends using an elastomer that enables the recovery of the permanent shape and a switch polymer that maintains the temporary shape. In this study, polymer blends with different compositions, where the elastomer phase is ester-based thermoplastic polyurethane (TPU) and the switch phase is poly(butyl-co-isobutyl methacrylate) (PBMA-co-PiBMA), were prepared using the melt blending method. In the blends with TPU/PBMA-co-PiBMA ratios of 90/10, 80/20, and 70/30 by weight, it was observed that the PBMA-co-PiBMA phase was dispersed in droplet form within the continuous TPU phase; whereas in the blends with ratios of 60/40 and 50/50, a co-continuous morphology was formed. Dynamic mechanical analyses (DMA) showed that the ester block of TPU and PBMA-co-PiBMA polymer were compatible, and in the polymer blends, the glass transition temperature (Tg) was found to lie between the Tg of the soft block of TPU and the Tg of PBMA-co-PiBMA, increasing proportionally with the amount of PBMA-co-PiBMA. The thermal transition properties of the neat polymer components and the produced polymer blends were examined with DSC analysis. It was observed that the glass transition temperature of the soft segment of TPU generally increased in the presence of PBMA-co-PiBMA. Additionally, due to the interactions between the two polymers, increases were observed in the melting temperature and crystallization temperature of the hard segment of TPU. In thermally responsive shape memory analyses, it was found that as the amount of PBMA-co-PiBMA increased, both the shape fixing (Rf) and shape recovery (Rr) ratios increased, and values above 98% were obtained for the composition with a 50/50 ratio. Thermogravimetric analyses (TGA) showed that in the presence of PBMA-co-PiBMA within the blend, the onset decomposition temperatures of TPU decreased, but the maximum decomposition temperature and the maximum decomposition rate of the ester block of TPU increased.