| Summary: | 碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 102 === With precise synthetic control of hydrogen bond-rich side chains, shape memory polyurethanes (PUs) were prepared. These PUs comprising dendritic (DG series) or linear (LG series) polyurea/malonamide hydrogen bond-rich side chains with uniform chain lengths, providing physical crosslinking interactions to PUs. With the reactive functional group, azetidine-2,4-dione as the side chain of SPU to be a crosslinking site, different grafting ratios with various chain lengths of poly(urea/malonamides) were incorporated onto SPU. Consequently the physical crosslinking density could be adjusted.
Via NMR, IR, EA, Mass and GPC analysis, we were able to confirm that the precise control of the poly (urea/malonamide) chain lengths were obtained. Differential scanning calorimeter (DSC) showed that, with the increasing chain length of the dendritic or linear poly (urea/malonamide), the glass transition temperature rose as a result of increasing hydrogen bonding interactions.
Cyclic thermal-mechanical tests were conducted for evaluating shape memory properties. A higher E''low value would make the movement of the polymer chains limited at low temperatures. Consequently the shape retention was enhanced. Moreover, a significant phase transition peak (tanδmax) and a broad rubbery plateau region would also help to improve shape recovery. Because of this, SPU-DG series exhibited excellent shape retention, but relatively poor shape recovery. On the other hand, the SPU-LG series with higher generation side chains exhibited excellent shape and shape retention. S45-DG2.5-50, S45-DG2.5-25, S35-LG2.5-50, S45-LG2.5-50, S45-LG2.5-25 and S45-LG3.5-50 exhibited excellent shape memory effect, with both shape recovery and shape retention higher than 90%. It is concluded that these well-defined PUs with excellent shape-memory effect have been successfully developed in this work.
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