Pei Jiwei, Wei Wenjing, Li Bian, Huang Jundan, Chen Xiao-Fang
Suzhou Key Laboratory of Macromolecular Design and Precision Synthesis, Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P. R. China.
Soft Matter. 2021 May 5;17(17):4594-4603. doi: 10.1039/d1sm00161b.
Copolymerization is an effective approach to tailor the thermal and structural properties of liquid crystalline polymer materials, which is essential for various applications. In this work, two series of polynorbornene copolymers, A-r-B and A-r-C, with the biphenyl mesogenic side group at different substituent positions were synthesized via ring-opening metathesis polymerization in various compositions. The corresponding homopolymers A and C are liquid crystalline polymers, exhibiting an oblique columnar structure (Colob/p2) and lamellar structure, respectively, while homopolymer B is amorphous. The composition-dependent phase behaviors of copolymers were systematically studied with the combination of SAXS, GISAXS, AFM, DSC and POM techniques. With increasing molar content of A (xA), the self-organzied structure of copolymer A-r-B follows the sequence from amorphous to lamellar, undulated lamellar, and Colob/p2 structures, and that of A-r-C follows the sequence of lamellar, undulated lamellar, and Colob/p2 structures. Then, copolymers with undulated lamellar or Colob/p2 structures tend to enter lamellar phase first at higher temperature and then change to the isotropic state during heating. The composition-induced transition from lamellar to supramolecular columnar organization is somewhat reminiscent of block copolymers and other soft matter systems that can form ordered structures. Furthermore, the subsitituent number and position of rigid mesogenic units in the side chain can further modify the morphologies of self-organized phases.
共聚是一种调整液晶聚合物材料热性能和结构性能的有效方法，这对于各种应用至关重要。在本工作中，通过开环易位聚合反应合成了两个系列的聚降冰片烯共聚物A-r-B和A-r-C，它们在不同取代位置带有联苯介晶侧基，且具有不同的组成。相应的均聚物A和C是液晶聚合物，分别呈现倾斜柱状结构（Colob/p2）和层状结构，而均聚物B是非晶态的。结合小角X射线散射（SAXS）、掠入射小角X射线散射（GISAXS）、原子力显微镜（AFM）、差示扫描量热法（DSC）和偏光显微镜（POM）技术，系统地研究了共聚物组成依赖的相行为。随着A的摩尔含量（xA）增加，共聚物A-r-B的自组装结构依次从非晶态转变为层状、波浪状层状和Colob/p2结构，而A-r-C的自组装结构依次为层状、波浪状层状和Colob/p2结构。然后，具有波浪状层状或Colob/p2结构的共聚物在加热过程中倾向于先在较高温度下进入层状相，然后转变为各向同性状态。组成诱导的从层状到超分子柱状结构的转变在某种程度上让人联想到可以形成有序结构的嵌段共聚物和其他软物质体系。此外，侧链中刚性介晶单元的取代数和位置可以进一步改变自组装相的形态。
