Preparation, characterization, and thermo-mechanical properties of poly (ε-caprolactone)-piperazine-based polyurethane-urea shape memory polymers

Abstract

A series of segmented polyurethane-urea (PUU) shape memory polymers were synthesized from poly e-caprolactone (PCL)-diol, hexamethylene diisocyanate, and piperazine (PP) with different hard to soft segment ratios. Chemical structure of PUUs was characterized using hydrogen nuclear magnetic resonance and attenuated total reflective-Fourier transform infrared spectroscopy methods. The results confirmed the formation of urethane and urea groups as well as incorporation of PP ring into polymer chain. Differential scanning calorimetry and wide angle X-ray scattering analyses were conducted to study the thermal properties and crystalline morphology of PUUs. It was found that crystallization of PUUs originated from PCL crystals. The reduction in degree of crystallinity was also observed with increasing of hard segment content (HSC). Mechanical properties were examined by tensile test at two different temperatures; above and below the PCL melting temperature. It was revealed that the chemical composition and temperature greatly affect the mechanical behavior of PUUs. A correlation between mechanical properties and physical structure of PUUs was established. Shape memory properties of PUUs were studied at two different programming processes. All of the samples show shape recovery over 94 % with a broad recovery temperature ranging from 40 to 65 °C. However, the shape fixity showed a great dependence on both HSC and programming process. The reasons of this dependency were discussed.