Synthesis Of PCL Based And PCL/PEG Based Shape Memory Polyurethanes And Study On Its Structure And Properties

Recently, Shape-memory polyurethane has become the focus of academic research in intelligent materials because of its excellent smart character and more applications in spacious area. However, there are many undefined relations between its structure and property, so a series of shape-memory polyurethanes were prepared and their micro-structure, thermal properties, mechanical properties and water vapor permeability were investigated in order to characterize their relations in this paper.Linear and crosslinked shape-memory polyurethane solutions with about 25% solute were prepared from polycaprolactone diol (PCL3000), polyethylene glycol (PEG2000), 2,4-toluene diisocyanate (TDI), 1,4-butanediol (BDO) and glycerin (GA) through changing the soft segment component, hard segment content and chain extender type according to fixed synthesis technic. PCL or PCL/PEG mixture were the soft segment component, TDI was the hard segment component, BDO and GA were respectively used as the linear and crosslinked chain extender. The membranes were prepared with corresponding shape-memory polyurethane solution through coating and drying method. On this base, ionic shape-memory polyurethane solution and membrane were also prepared through adding DMPA in prepolymerizing and TEA in neutralizing after reaction of chain extending.Thermal properties, microstructure and tensile property of the membranes were characterized by using four testing methods such as differential scanning calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), wider-angle X-ray diffraction (WAXD) and omnipotence tensile tester. The result of DSC test indicated that i) soft segments of all the SMPU samples showed an obvious crystal melting behavior between 45℃and 55℃; ii) increasing of hard segment content led to lower crystallinity and higher crystal melting temperature; and iii) adding of PEG as soft segment component improved the crystallization of soft segment and also increased the crystallinity as well as the number of crystal peaks of soft segment. The FTIR analysis showed that i) increasing of hard segment content didn't influence the shape of infrared spectroscopy, but the changing of soft segment component did; ii) adding of PEG strengthened the hydrogen-bonded degree of C=O in hard segment; and iii) out-of-order hydrogen-bonded C=O peak and N-H bonds peak were presented in all the three series of linear, crosslinked and ionic SMPU. The WAXD analysis exhibited that the soft segment and hard segment of all the three series SMPU presented obvious diffraction peak respectively, and it's the important evidence of phase-separation between the soft segment and hard segment. The tensile test showed that the tensile property of linear and crosslinked SMPU membranes were more excellent than those of ionic SMPU membranes with corresponding hard segment content.The water vapor permeability of membranes was tested by fabric water vapor-permeating measurement instrument. The results indicated that all the membranes presented evident temperature-sensitivity and the corresponding water permeability improved greatly at the temperature between 35℃and 50℃. Comparing with other membranes, ionic membranes presented more excellent intelligent water vapor permeability, especially the water vapor permeability of some ionic ones around memory temperature increased more than twelve times as that of them at the original temperature.