Synthesis and Properties of Functional Polyurethane-Acrylates Bearing Hindered Urea Bonds
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摘要: 以双（2,2,6,6-四甲基-4-哌啶基）癸二酸酯（TMPCA）为软段、1,3-双（1-异氰酸酯-1-甲基乙基）苯（TMXDI）为硬段、甲基丙烯酸异冰片酯（IBOMA）为反应性稀释单体，经甲基丙烯酸羟乙酯（HEMA）封端后得到含有大位阻脲键的聚氨酯丙烯酸酯预聚体；预聚体经紫外光固化，制备得到光敏树脂材料。随后，通过微量热和变温红外对体系中大位阻脲键的热解离机理进行探索，并对光敏树脂的修复性、形状记忆性和二次塑形能力进行了研究。结果表明：大位阻脲键在46～56 °C范围内存在吸热效应，预聚体和固化后树脂中均可以观察到异氰酸酯含量随温度改变发生动态变化；即体系具有动态共价高分子的特点。固化后的光敏树脂修复性能良好，修复后试样的拉伸强度由13.8 MPa恢复至18.4 MPa，且修复界面宽度小于50 μm。此外，含有大位阻脲键的光敏树脂展现出良好的形状记忆和二次塑形能力，并且二次塑形后材料仍能保持80%的弯曲强度。Abstract: Inspired by the dynamic properties of hindered urea bonds (HUBs), prepolymer of polyurethane-acrylate (PUA) with HUBs was designed and synthesized using 1,3-bis(2-isocyanato-2-propyl)benzene (TMXDI) as hard segment, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (TMPCA) as soft segment, isobornyl methacrylate (IBOMA) as reactive diluent, and 2-hydroxyethyl methacrylate (HEMA) as block agent. The prepolymer was subsequently UV-cured to obtain PUA photopolymer. The property and reaction mechanism of the incorporated dynamic HUBs were investigated via Differential Scanning Microcalorimetry (MicroDSC) and Fourier Transform Infrared (FT-IR) spectroscopy. And studies were carried out in terms of the repairability, shape memory and reshapability of the corresponding photopolymer. Results showed that the thermal effect of the HUB could be identified in MicroDSC analysis, as an endothermic peak appeared in the range of 46 °C to 56 °C. In addition, the dynamic content variation of the isocyanate group (NCO) could be observed via temperature-dependent FT-IR in both prepolymer and cured resins. In the in-situ FT-IR spectra of prepolymer with HUBs, the characteristic peak of NCO was observed to increase when heated from 30 °C to 80 °C, which later decreased when cooled down to 30 °C. Also, the peak area of NCO characteristic peak increased in cured resins with increased temperature. The dynamic nature of HUBs allowed the obtained photopolymer to be repaired with a demonstrated improvement in mechanical properties. By drilling a 1 mm hole in the center of a testing sample, refilling prepolymer, and treating with UV-cure and post-cure, the tensile strength of the material was observed to recover from 13.8 MPa to 18.4 MPa after repairing. Meanwhile, the repair interface width was less than 50 μm. Also, the incorporated HUBs provided the PUA resin with shape memory and reshaping capacities, and the testing sample was able to reserve a 45 MPa flexural strength after being reshaped.
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Key words:
- hindered urea bond /
- polyurethane /
- dynamic covalent polymer
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图 1 以TMPCA为软段、TMXDI为硬段的异氰酸酯齐聚物的合成路线示意图
Figure 1. Synthetic route of PU oligomer with TMPCA as soft segment and TMXDI as hard segment
图 2 含大位阻脲键的的光敏树脂的DMA分析
Figure 2. DMA analysis of photopolymers with hindered urea bonds
图 3 含大位阻脲键的预聚体的微量热表征
Figure 3. MicroDSC analysis of prepolymer with hindered urea bonds
图 4 含大位阻脲键的预聚体的变温红外表征
Figure 4. Temperature-dependent FT-IR spectra of prepolymer with hindered urea bonds
图 7 修复前后含大位阻脲键的光敏树脂的应力-应变曲线
Figure 7. Stress-stain curves of photopolymers with hindered urea bonds before and after the repair
图 8 修复试样拉伸断面的 (a) 形貌示意图与 (b) SEM照片
Figure 8. (a) Diagrammatic cross-section and (b) SEM image of cross-section of a repaired sample
图 9 含大位阻脲键的光敏树脂的形状记忆过程
Figure 9. Shape memory process of photopolymers with hindered urea bonds
图 10 含大位阻脲键的光敏树脂的二次塑形过程
Figure 10. Reshaping process of photopolymers with hindered urea bonds
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