侧链结构对聚合物以及嵌段共聚物有序组装行为的影响

Natural materials are able to exquisitely make use of self-assembly to get delicate hierarchical organizations and complex structures, in order to perfectly realize specific functionalities, which is still hard to replicate in today's synthetic materials. So learning from nature, current materials research now require us to increase ability not only to property synthesis, but also to control the self-organization and self-assembly behavior to realize designed smart and multifunctional characteristics. It is well known that in most cases, a functional polymer chain generally consists of a polymer backbone and side chains. The interaction between the polymer backbone and side chains should be considered, which can have a strong effect on the physical and chemical properties of the polymer. Inspired from all kinds of ordered soft matter structures formed by thermotropic or lyotropic liquid crystals, surfactants, amphotropic molecules, and block copolymers, in this proposal, we focus on the molecular design of side chains with different molecular shapes and polyphilicity properties. We'd like to investigate the side chain effect on the mesomorphic behavior of resulting polymers.By taking advantage of living/controlled polymerization techniques, we are able to synthesize block copolymers with different side chains. The micro-phase separation behavior must be different from traditional linear coil-coil block copolymers. Side chains will play an important role on the micro-phase separation, besides the volume fraction of different blocks. So the side chain effect on the microphase behavior and the formation of complex hierarchical ordered structures will be investigated as well. When both A and B blocks are dendronized polymers and have similar cross-sectional area, lamellar phase would be favorable and thermodynamically stable during a wide range of volume fractions. On the other side, when the A and B dendronized blocks containing different diameters, the interface curvature will be existed and columnar or cubic nanostructures could be formed to some extent. Furthermore, due to the polyphilicity of side chains, more delicate hierarchical self-assembled nanostructure will be formed and investigated in detail.

天然材料多通过复杂而精致的分级有序组装结构来实现功能性的精确表达，与之相比,人工合成材料在复杂有序组装体系构筑和功能表达方面还存在很大差距。主侧链型化学结构是聚合物体系常见的一种分子链构建方式，在本项目中我们将着重考察侧链结构对聚合物和嵌段共聚物多级有序组装结构的影响。从侧基的分子设计入手，通过设计侧基液晶基元从直棒形到树枝形的变化以及侧基尾链化学组成的变化，引入多组分的不相容性，结合多种物理研究手段系统研究所合成的聚合物组装结构的形成、受挫、共存、转变等过程，揭示出组装过程中聚合物主侧链之间的相互作用内在机制，并在此基础上合成梳形嵌段共聚物，研究侧链结构对嵌段共聚物微相分离结构的影响，利用侧链结构的多亲性，在嵌段共聚物体系中引入不同尺度的有序结构，研究其多层次分级有序组装行为，并探索其在本体以及薄膜状态下的功能性。

向自然界学习，如何在合成材料里实现多级有序组装结构，并进行调控以及功能性体现，从分子层次上理清结构与性能之间的关系，是很多领域科学家们致力解决的基本科学问题。该项目从主侧链型聚合物这个高分子科学领域重要的拓扑结构入手，通过一系列分子设计，合成了以聚降冰片烯为主链，烷基取代联苯、烷基取代氰基二苯乙烯为液晶基元为侧链构筑单元的聚合物。侧链结构以中心苯环为核心，将液晶基元接入苯环的不同取代位置，得到侧链结构精确控制的9大类联苯聚合物体系以及6种氰基二苯乙烯体系聚合物，详细研究了主侧链间柔性间隔基长度，烷基尾链长度，取代基位置、数量对聚合物液晶性能的影响，发现了双液晶取代聚合物体系具有特殊的超分子组装功能，根据取代基位置不同，可得到不同对称性的二维有序组装结构，该组装结构源于邻位取代的两个液晶基元无法完全平行排列，导致层状相结构的受挫，产生周期大于10 nm的波动。通过共聚合方法，可对这类二维有序组装结构进行进一步的调控。这类特殊组装结构的出现有助于我们深入了解高分子体系液晶态的形成。氰基二苯乙烯为液晶基元的聚合物体系随着柔性烷基尾链数量和位置的不同，出现了层状相和六方柱状相结构等液晶相态，该类聚合物在不同波长的紫外灯下能够发生可逆转变。在非共价键构筑的侧链聚合物体系，系统研究了氰基二苯乙烯结构的光致异构化引起的聚合物有序组装结构以及荧光颜色的可逆变化，并在嵌段共聚物薄膜表面构筑了多尺度有序结构互相匹配的复杂图案。