Role of Increased Crystallinity in Deformation-Induced Structure of Segmented Thermoplastic Polyurethane Elastomers with PEO and PEO-PPO-PEO Soft Segments and HDI Hard Segments
Role of Increased Crystallinity in Deformation-Induced Structure of Segmented Thermoplastic Polyurethane Elastomers with PEO and PEO-PPO-PEO Soft Segments and HDI Hard Segments
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DOI：
10.1021/ma8022052
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发表时间：
2009-03-24
期刊：
影响因子：
5.5
通讯作者：
hammond, Paula T.
中科院分区：
文献类型：
--
作者：
Waletzko, Ryan S.;Korley, LaShanda T. James;hammond, Paula T.
聚氨酯的相分离性质允许在形态和物理性质之间建立有意义的联系。我们利用这一行为，合成了一系列具有不同结晶度的聚氨酯，并研究了它们在无应变和变形状态下的形态，从完全无定形的软链段到具有类似化学性质的软链段，显示出高度的软域结晶，从而增强了相分离。与非结晶软链段聚氨酯相比，连续软域内分散的半结晶区域的存在已被证明可提供增强效果。事实证明，加入半结晶软链段（PEO，1000 g/mol）可以提高样品的整体韧性；然而，如果使用较高分子量的 PEO 软链段 (4600 g/mol)，由于连续域模量增加，延展性和韧性会受到不利影响。原位变形实验展示了两种截然不同的变形响应。在含共聚物的聚氨酯（PEO-PPO-PEO，1900 g/mol）中，硬域在应变高达 450% 时仍保持倾斜构型，只有一小部分硬域发生重新排列。另一方面，含有 PEO 1000 的聚氨酯在 200% 应变下开始表现出子午散射，在 300% 应变下成为主峰。这两种变形行为表示对变形的两种主要响应，分别是剪切和拉伸。通常，拉伸机制表明聚氨酯机械性能下降，尽管在感兴趣的系列中没有看到这种现象。
The phase-segregated nature of polyurethanes allows meaningful connections to be made between morphological and physical properties. We have taken advantage of this behavior by synthesizing a series of polyurethanes with varying extents of crystallinity and Studying their morphologies in both the unstrained and deformed states, going from a completely amorphous soft segment to one with similar chemistry that displays a high extent of soft domain crystallization, thus enhancing phase segregation. The presence of dispersed semicrystalline regions within the continuous soft domain has been shown to provide a reinforcing effect when compared to that of a non-crystalline soft segment polyurethane. Incorporating a semicrystalline soft segment (PEO, 1000 g/mol) has been shown to improve overall sample toughness; however, if higher molecular weight PEO soft segments are employed (4600 g/mol), extensibility and, Consequently, toughness are adversely affected due to an increased continuous domain modulus. In-situ deformation experiments demonstrate two very different deformation responses. In the copolymer-containing polyurethane (PEO-PPO-PEO, 1900 g/mol), the hard domains retain a tilted configuration up to strains of similar to 450%, with only a small fraction of the hard segments undergoing reshuffling. The PEO 1000-containing polyurethane, on the other hand, begins to demonstrate meridional scattering at strains of 200%, with it being the dominant peak by a strain of 300%. These two deformation behaviors are indicative of the two primary responses to deformation, which are shear and tensile, respectively. Frequently, a tensile mechanism points to decreased polyurethane mechanical properties, though this phenomenon is not seen in the series of interest.