ABA型液晶三嵌段共聚物的合成、微结构及介电性能研究

采用原子转移自由基聚合（ATRP）制备了一系列ABA型液晶三嵌段共聚物P11CBMAm-b-PDMSn-b-P11CBMAm，并研究其微观形态和介电性能。首先分别合成液晶前驱体11CBMA和大分子引发剂Br-PDMS-Br，然后以甲苯为溶剂、CuBr/HMTETA为催化剂，由Br-PDMS-Br引发11CBMA进行ATRP聚合。通过控制投料比，制备出一系列具有相同长度PDMS段（n=356）和不同长度液晶P11CBMA段（m=49,79,115）的样品。通过1H-NMR、GPC和DSC对样品进行表征，并利用热退火的方法促进其微观结构的形成。TEM结果显示，样品在经过退火后PDMS段聚集成球状结构；随着液晶段含量的增加，PDMS球状相的尺寸逐渐减少。嵌段共聚物的微观形态对材料的介电性能有很大的影响。退火后样品的介电常数明显高于均聚物PDMS和P11CBMA，这说明控制材料的微结构是提高材料介电常数的有效途径。

Synthesis,microphase morphology and dielectric properties of ABA type liquid crystalline triblock copolymers

A series of ABA type liquid crystalline (LC) triblock copolymers P11CBMAm-b-PDMSn-b-P11CBMAm(P11CBMA = poly11-(4-cyano-4'-biphenoxy)undecyl methacrylate];PDMS=poly(dimethylsiloxane)) has been synthesized by atom transfer radical polymerization (ATRP). Firstly,the monomer 11CBMA and the macroinitiator Br-PDMS-Br were prepared. Then, by using Br-PDMS-Br,toluene, CuBr, and hexamethyltriethylenetetramine (HMTETA) as the macroinitiator, solvent,catalyst and ligand, respectively, P11CBMAm-b-PDMSn-b-P11CBMAm was synthesized through ATRP of 11CBMA. Three samples with the same PDMS block length (n=356) and different P11CBMA block lengths (m=49, 79, 115) were synthesized by controlling the molar feed ratio of the LC monomer to the difunctional macroinitiators. The characterization of the triblock copolymers was performed with 1H-NMR, GPC and DSC. Their microphase separation behavior and dielectric properties were carefully investigated. After thermal annealing, the particles adopt a spherical morphology. As the length of the 11CBMA block increases, the morphology of the PDMS phase becomes smaller. The dielectric properties of the block copolymers were strongly influenced by the microphase separated morphologies. After thermal annealing, the triblock copolymers show higher dielectric constants than homopolymers of PDMS and P11CBMA. These results show that the self-assembly method is an effective approach to improve the dielectric permittivity of materials. 