Synthesis, nanostructures and dielectric properties of novel liquid crystalline block copolymers

Abstract

International audienceIn this work, a series of diblock copolymers with a defined length of a soft poly(dimethylsiloxane) (PDMS) segment and different lengths of liquid crystalline (LC) poly[11-(4-cyano-4'-biphenoxy)undecyl methacrylate] (P11CBMA) segments were synthesized by using the atom transfer radical polymerization (ATRP) method. Their microphase separation behavior and dielectric properties were carefully investigated. The well-defined diblock copolymers PDMSm-b-P11CBMA(n) possess three different soft/rigid ratios (m = 62, n = 15, 22, and 40) and narrow molecular distributions (PDI <= 1.25). Due to the supramolecular cooperative motion effect, the copolymers can form lamellar morphology (W-LC = 57.8%), predominant lamellar morphology with PDMS cylindrical defects (W-LC = 66.8%), and PDMS cylinders embedded in the LC matrix (W-LC = 78.3%) after annealing at 160 degrees C (above T-i) under N-2 for 24 h, respectively. The dielectric properties of the block copolymers were strongly influenced by the microphase separated morphologies and orientational directions of mesogens. Compared to homopolymer P11CBMA, PDMSm-b-P11CBMA(n) showed higher dielectric constants due to the confinement effect of microdomain dimensions. The dielectric constants of diblock copolymers could be further improved by aligning mesogens parallel to the electric field through substrate treatments. These findings will inspire researchers to design and develop novel LC block copolymers for dielectric elastomer actuator applications

Synthesis and dielectric properties of novel liquid crystalline triblock copolymers with cyanobiphenyl moieties and poly(n‐butyl acrylate) segments

“…As expected, triblock copolymers show higher dielectric constants than homopolymer PBA and P11CBMA. This is consistent with our previous research . After annealing, the dielectric constants of block copolymers increase dramatically, but their loss factors basically remain the same.…”

“…The LC precursor 11‐(4‐cyano‐4′‐biphenyloxy)undecyl methacrylate (11CBMA) and homopolymer poly[11‐(4‐cyano‐4′‐biphenyloxy)undecyl methacrylate] (P11CBMA) were synthesized as reported previously …”

Intrinsic Tuning of Poly(styrene–butadiene–styrene)-Based Self-Healing Dielectric Elastomer Actuators with Enhanced Electromechanical Properties

“…The deformable nature of the elastomers can also be maintained after modification. 1 Small polar groups including allyl cyanide, 14 3-mercaptopropionitrile [15][16] and 2-(methylsulfonyl)-ethanethiol, 17 and liquid crystal [18][19] have been grafted to various polymer structures resulting in an increase in their relative permittivity up to 22.7. 17 Grafting conducting poly(aniline) to poly(urethane) through a copper phthalocyanine ring resulted in a large increase in relative permittivity to 105.…”

Synthesis, liquid crystalline mesophases and morphologies of diblock copolymers composed of a poly(dimethylsiloxane) block and a nematic liquid crystalline block

“…PDMS has the extremely flexible Si-O backbone, which exhibit comparatively strong thermodynamic incompatibility when connect with conventional aliphatic polymers [19]. As a result, this block can easily separate from the other sub-phases to form a rich variety of nanostructures [8,10,20]. Owing to the strong segregation of the PS-PDMS system, Lo et al [8] obtained different microphase-separated morphologies, including double gyroid, hexagonally packed cylinders and randomly distributed spheres.…”

“…For liquid crystalline polymers with the 'end-on' structure, they usually tend to form smectic phases [27,28], while the nematic phase is usually obtained in 'side-on' liquid crystalline polymer [29,30]. In recent years, block copolymers composed of a smectic liquid crystalline block and a PDMS block have been widely investigated [10,18,20,31], while block copolymers containing both a PDMS block and a side-on nematic block is still lacking in the literature.…”