Thermoplastic polyurethanes (TPU) 屬於逐步聚合反應，分子量逐步增加，不易控制分子量。然而，TPU的力學強度隨著分子量增加而增加，伴隨而來的是TPU的加工性能(軟化點)隨分子量增加而增加。因此，TPU的分子量控制、力學性能和加工性能存在矛盾的問題。本研究藉由自製封端劑的濃度控制TPU的分子量以及設計封端劑的分子結構增強TPU的氫鍵網路。使TPU在低分子量時，具有低溫的加工性質以及良好的力學性能。首先合成4種N,N-Dimethyl acrylamide (DMAA)濃度的封端劑分別為D03 (DMAA 3.0 wt.%)、D05 (DMAA 5.0 wt.%)、D07 (DMAA 7.0 wt.%)以及D10 (DMAA 10 wt.%)。本研究以Polytetramethylene Ether Glycol (PTMG)與4,4-Methylene diphenyl diisocyanate (MDI)作為原料，分別加入封端劑D03、D05、D07以及D10，採用本體聚合法合成TPU。TPU在FT-IR光譜中分別顯示苯環、氨基甲酸酯以及DMAA的特徵峰；在2268 cm-1附近未顯示-N=C=O-的吸收峰，證明TPU的結構中含有封端劑、PTMG以及MDI的分子結構並且充分反應。在FT-IR光譜，-C=O吸收峰值往低波數移動並分裂為雙重峰。當封端劑的DMAA濃度由3.0 wt.%增加至10 wt.%，產生氫鍵的-C=O(H-bond)面積百分比由41.7 %增加至57.6 %。這個結果證明DMAA提升TPU分子結構的氫鍵數量。TPU的分子量隨著封端劑的DMAA濃度由3.0 wt.%增加至10 wt.%，TPU的分子量由35517 g/mole增加至56103 g/mole。這是因為來自於DMAA分子結構中的N(CH3)2產生的空間位阻效應，抑製封端劑-OH與異氰酸酯基團形成共價鍵。TPU的熔點指的是硬鏈段的熔點(Tmh)。封端劑分子結構中的DMAA濃度增加，TPU的Tmh與ΔH增加。這是因為硬鏈段間氫鍵作用力增強，增加TPU的Tmh與ΔH。當封端劑分子結構的DMAA濃度由3.0 wt.%增加至10 wt.%，拉伸強度由1.4 kg/cm2增加至1.7 kg/cm2，這表示DMAA濃度逐漸增多，氫鍵量逐漸增加，力學性能提高。封端劑分子結構的DMAA濃度由3.0 wt.%增加至10 wt.%；剝離強度由0.9 kg/cm增加至2.2 kg/cm，剪切強度從24 kg/cm2增加至30 kg/cm2。本研究合成的5D10、10D10以及15D10與市售商品Bemis 3405經過50次水洗後的機械性能如下所述。5D10、10D10以及15D10的軟化溫度為130℃至135℃優於Bemis 3405的軟化溫度150℃至170℃。5D10、10D10以及15D10，剝離強度分別為2.1 kg/cm、1.0 kg/cm以及0.5 kg/cm皆優於Bemis 3405的剝離強度0.3 kg/cm。在TPU的剪切強度方面，5D10、10D10以及15D10的剪切強度分別為26 kg/cm2、23 kg/cm2、21 kg/cm2皆優於Bemis 3405的剪切強度17 kg/cm2。本研究合成的TPU經過嚴苛的高溫儲存環境測試以及低溫儲存環境測試剝離強度以及剪切強度皆可與市售產品相提並論。

The thermoplastic polyurethanes (TPU) is synthesized by stepwise polymerization, during which the molecular weight increases stepwise. As a result, it is difficult to control the molecular weight. When the mechanical strength of TPU increases with molecular weight, the processability (softening point) of TPU increases as well. Therefore, the molecular weight control, mechanical properties and processability of TPU are considered contradictory issues. This study used the concentration of self-developed end-capping agent to control the molecular weight of TPU, and designed the molecular structure of end-capping agent to enhance the hydrogen bond network of TPU, so that the TPU at low molecular weight can have low temperature working properties and good mechanical properties. First, this study synthesized the copolymer of end-capping agents at four N,N-Dimethyl acrylamide (DMAA) concentrations, which are D03 (DMAA 3.0 wt.%), D05 (DMAA 5.0 wt.%), D07 (DMAA 7.0 wt.%) and D10 (DMAA 10 wt.%). The Polytetramethylene Ether Glycol (PTMG) and 4,4-Methylene diphenyl diisocyanate (MDI) were used as raw materials in this study, mixed with end-capping agents D03, D05, D07 and D10 respectively, the TPU was synthesized by using mass polymerization. The TPU showed the characteristic peaks of benzene ring, carbamate and DMAA respectively in the FT-IR spectrum. The absorption peak of -N=C=O- was not shown around 2268 cm-1, proving that the structure of TPU contains end-capping agent, and the molecular structures of PTMG and MDI fully react. The absorption peak of -C=O in the FT-IR spectrum moved towards low wave number and split into double peak. When the DMAA concentration of end-capping agent increased from 3.0 wt.% to 10 wt.%, the -C=O(H-bond) area percent of hydrogen bond increased from 41.7 % to 57.6 %. This result proves that the DMAA increases the number of hydrogen bonds of molecular structure of TPU. The molecular weight of TPU increased from 3.0 wt.% to 10 wt.% with the DMAA concentration of end-capping agent, the molecular weight of TPU increased from 35517 g/mole to 56103 g/mole. This is because the steric hindrance effect generated by the -N(CH3)2 in the molecular structure of DMAA inhibited the end-capping agent -OH and -NCO groups from forming covalent bond. The melting point of TPU refers to the melting point of hard segment (Tmh). As the DMAA concentration in the molecular structure of end-capping agent increased, the Tmh and ΔH of TPU also raised. This is because the increase of hydrogen bonding force between hard segments led to the increase of the Tmh and ΔH of TPU. When the DMAA concentration in the molecular structure of end-capping agent increased from 3.0 wt.% to 10 wt.%, the tensile strength increased from 1.4 kg/cm2 to 1.7 kg/cm2, meaning the DMAA concentration increased gradually, Moreover, as the number of hydrogen bonds increased, the mechanical properties were enhanced. When the DMAA concentration in the molecular structure of end-capping agent increased from 3.0 wt.% to 10 wt.%, the peel strength increased from 0.90 kg/cm to 2.2 kg/cm, and the shear strength increased from 24 kg/cm2 to 30 kg/cm2.
The mechanical properties of the synthetic 5D10, 10D10 and 15D10 of this study and commercially available goods Bemis 3405 after 50 times of water washing are described below. The softening temperature of 5D10, 10D10 and 15D10 was 130°C to 135°C, which are better than the softening temperature 150°C to 170°C of Bemis 3405. The peel strengths of 5D10, 10D10 and 15D10 were 2.1 kg/cm, 1.0 kg/cm and 0.5 kg/cm respectively, which are also better than the peel strength 0.3 kg/cm of Bemis 3405. In terms of the shear strength of TPU, the shear strengths of 5D10, 10D10 and 15D10 were 26 kg/cm2, 23 kg/cm2 and 21 kg/cm2 respectively, which are better than the shear strength 17 kg/ cm2 of Bemis 3405. This study also tested the peel strength and shear strength of the synthetic TPU in the harsh high temperature storage environment and the test in the low temperature storage environment. The results are comparable with the commercially available products.

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