Structures and properties of side-chain liquid crystalline polynorbornenes containing an amide group: hydrogen bonding interactions and spacer length effects
Structures and properties of side-chain liquid crystalline polynorbornenes containing an amide group: hydrogen bonding interactions and spacer length effects
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DOI：
10.1039/d0py00586j
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发表时间：
2020-07
影响因子：
4.6
通讯作者：
Dong Shi;Wenying Chang;Xiang-Kui Ren;Shuang Yang;E. Chen
中科院分区：
文献类型：
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作者：
Dong Shi;Wenying Chang;Xiang-Kui Ren;Shuang Yang;E. Chen
为了研究具有特定相互作用的侧链液晶聚合物的结构与性能的关系，我们合成了一系列带有苯甲酰苯胺侧链的聚异戊二烯衍生物（记为P8-n，其中n表示间隔基中亚甲基单元的数目，数字8表示辛基的侧链尾部）。为了比较，还通过用酯基取代棒状介晶中的酰胺基来合成参考聚异戊二烯衍生物（表示为P8-6-E）。研究发现，与其它含苯甲酰苯胺的聚合物不同，主链为聚苯乙烯的聚合物具有丰富的液晶行为。P8-2和P8-4形成双层近晶C（SmC 2）相。另一方面，具有较长间隔基的P8-8和P8-10的分子可以包装成高度有序的结构（表示为X1）。X1相具有正交晶格，侧链和主链沿着c轴和b轴，其中侧链显示具有晶体E（CrE）结构的一些特征的叉指堆积。对于P8-6，一些双层CrE结构域可能与X1共存，导致X1/E2的混合相。结果表明，P8-ns分子中的酰胺基总是倾向于形成氢键，这导致了P8-ns独特的分子堆积，而这种堆积依赖于间隔基和尾部之间的尺寸匹配。此外，减弱P8-ns（n ≥ 8）中的氢键，可导致X1到X1/E2的相变。与具有近晶B相的相当柔软和延展性的P8-6-E相比，P8-ns由于侧向氢键的存在而显示出高得多的杨氏模量。虽然具有X1相的那些是脆性的，但具有SmC 2结构的P8-ns表现出更好的整体机械性能，使断裂应变达到450%。
To investigate the structure–property relationship of side-chain liquid crystalline (LC) polymers with specific interactions, we synthesized a series of polynorbornene derivatives bearing benzanilide side-chains (denoted as P8-n, where n represents the number of methylene units in the spacer, and the number 8 indicates the side-chain tail of the octyl group). For comparison, a reference polynorbornene derivative (denoted as P8-6-E) was also synthesized by replacing the amide group in the rod-like mesogen with an ester group. It is found that with the polynorbornene main-chain the samples can exhibit rich LC behaviors, different from other benzanilide-containing polymers. P8-2 and P8-4 form a bilayer smectic C (SmC2) phase. On the other hand, with longer spacers, the molecules of P8-8 and P8-10 can pack into a highly ordered structure (denoted as X1). The X1 phase has an orthorhombic lattice with the side- and main-chains along the c- and b-axes, wherein the side-chains show interdigitated packing with some features of a crystal E (CrE) structure. For P8-6, some bilayer CrE domains may coexist with X1, resulting in a mixed phase of X1/E2. It is unveiled that the amide group at the center of benzanilide always tends to form hydrogen bonds, leading to the unique molecular packing of P8-ns which is dependent on the size matching between the spacer and tail. Moreover, weakening the hydrogen bonds in P8-ns (n ≥ 8) could induce a phase transition from X1 to X1/E2. Compared with the rather soft and ductile P8-6-E with a smectic B phase, P8-ns show much higher Young's moduli because of the presence of lateral hydrogen bonds. While those with the X1 phase are brittle, the P8-ns with a SmC2 structure exhibit better overall mechanical properties, rendering a breaking strain of ∼450%.