Preparation and Characterization of Shape Memory Polyurethanes Based on Adamantane-containing Dendrons
Date Issued
2016
Date
2016
Author(s)
Chen, Wei-Lun
Abstract
A series of poly(urea/malonamide) dendrons with peripheral adamantyl groups were incoporated into polyurethanes to investigate their shape memory behavior. The dual functional (4-isocyanato-4’(3,3-dimethyl-2,4-azetidino)diphenylmethan) (IDD) was used to synthesize a series of hydrogen bond-rich poly(urea/malonamide) dendrons via convergent route. With high reactivity of isocyanate and reaction selectivity of azetidine-2,4-dione, a sequential method to prepare dendrons without protection-deprotection process was developed under mild condition The dendrons were further introduced into polyurethanes, providing physical crosslinking interactions to polyurethanes. Well-defined poly(urea/malonamide) dendrons were successfully prepared as evidenced by analyses of IR, NMR, and Mass spectroscopy, and EA. GPC analysis showed that the molecular weights of dendrons in this study are mono-dispersed. Differential scanning calorimeter (DSC) revealed that with the increasing generation of dendritic poly (urea/malonamide), the glass transition temperature rose as a result of increasing hydrogen bonding interactions. Universal tensile machine (UTM) and dynamic mechanical analysis (DMA) were utilized for evaluating mechanical and shape memory properties of side-chain dendritic polyurethanes (SPUs) and end-capped polyurethanes (EPUs). A series of linear polyurethanes (LPUs) were prepared for comparison. All the EPUs were fragile under room temperature, which were not available for mechanical testing. UTM shows that SPUs are more rigid than LPUs under room temperature due to better crystallinity or stronger physical crosslinking interactions. DMA shows that SPUs exhibited higher storage modulus than did LPU at low temperatures owing to higher crystallinity. This would further enhance shape retention properties. On the other hand, the higher density of physical crosslinks in SPU-G2.5 than those in SPU-G1.5 and LPU would also enhance storage modulus of SPUs-G2.5 at high temperatures. This would improve shape recovery properties. The result of cyclic shape memory test shows that shape memory process of SPUs took less than 3 seconds. Furthermore, SPUs with high soft segment content exhibited excellent shape retention over 97%, and the SPU40-G2.5 sample exhibit shape recovery over 95% even after 3 rounds of cyclic shape memory test. It is concluded that the enhanced physical crosslinking interactions improved shape memory effect in polyurethanes, along with a proper tuning of hard segment content. A series of PUs with excellent shape-memory effect have been successfully developed in this work.
Subjects
physical crosslink
Shape Memory Polyurethane
Type
thesis
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