Synthesis and characterizations of segmented thermoplastic polyurethanes with shape memory behaviours

A group of materials that have been in our lives in recent years have the ability to respond appropriately to a certain stimulus by changing certain chemical physical properties. These materials, technically called stimulus-reacting materials (Stimulus Responsive Materials, SRM), are stimulus-acting materials. They can be classified as stress and/or pressure-mechanical sensitive, heat-temperature sensitive, electric current or voltage sensitive and magnetic field sensitive according to their types [1-4]. In this thesis, shape memory thermoplastic polyurethane films were synthesized by using polyester polyols, methylene diphenyl diisocyanate (MDI), Dibutyltin dilaurate (DBTDL) as catalyst and N,N-Dimethylformamide (DMF) as solvent. 1,4-butanediol (BD) was used as a chain extender. Polymers were synthesized using three different polyols at different NCO:OH and polyol:chain extender ratios. The molecular weight (Mw, Mn) values of the synthesized films were examined by gel permeation chromatography (GPC), thermal characterization was examined using differential scanning calorimetry (DSC). Dynamic mechanical analysis (DMA) was used to determine the viscoelastic behavior of polymers. The rheological properties of the polymers were investigated using a dynamic rotational rheometer. Shape memory properties of polyurethanes were also investigated by using a rotational rheometer custom the shape memory test procedure. At the end of the test, the recovery rates were calculated by placing the samples in an oven at determined temperatures. Shape memory feature; It varies according to the ratio of soft and hard regions in the structure and the chain length of the soft region in the structure. In addition, the type and amount of chain extender used are also effective parameters on shape memory performance.